1. WATERFORD INSTITUTE OF TECHNOLOGY
Workshop Portfolio
Semester 2
Workshop
Marie Wilgaard Kelly, w20066429
7/5/2015
Lecturers:Ian O’Neill andTerryPrenderville Word count2,353
3. 2
Chapter 1: Introduction
This workshop portfolio is presented as a part of the BSc in Applied Conservation Skills
workshop module. This portfolio represents the practical assignments carried out in semester
two of the programme.
The content of the appendix are the demonstrations in stained glass, thatching, and the lecture
held by Peter Cox on cleaning. Also included in the appendix are the guided visits to the
Heritage Council in Kilkenny, the Bishop’s Palace in Waterford and the site visit to St.
Mary’s hall in Kilkenny.
This portfolio will be covering the following practical assignments:
- Plastering with lime externally and internally
- Natural slate roofing
- Construction of a model of a king post truss from drawing to finished model
- Drawings of a selection of arches
This portfolio will conclude with a brief summary, references and appendix.
4. 3
Fig 2. Direction of work for a right
handed plasterer.
Fig 3. Levelling with timber bead
Fig 1. Starting in top right corner
Chapter 2: Workshop Practical assignments
2.1. Lime plastering
2.1.1. External Lime Render Plasterwork
The lime mortar was mixed in a cement mixer. First mix the dry ingredients 3 x sand and 1 x
hydrated Lime. Then carefully add water a little at a time. Let the mixer run for a while to
ensure the mortar is well mixed. Hydrated lime is a high calcium lime, made by slaking the
quicklime by adding a precise amount of water to the quicklime. Hydrated lime is a powder
(McAfee, 2009). See appendix for more information on lime.
The sand is very important for the look of the finished
wall. The sand chosen will have a big impact on the
finished look of the wall. River sand can be more beige
and sand from in land can be much greyer in
appearance.
A small wall was used for the sample work of external
render plastering. When the mortar is mixed and ready
for use it is placed on a board and further mixed and
water may be added to achieve the correct soft texture.
The mortar is then placed on the hawk and the metal
plastering trowel is used to apply the mortar onto the
wall. For a right handed plasterer works from the top
right and down, see Fig 1 and Fig 2. Working like this minimizes the amount of mortar
dropped on the floor and it is easier to apply pressure in this direction. Corners and edges are
worked back in over and NOT out over, as this will round the edges and corners.
Fill up the wall with the lime plaster and use straight
edged length of timber to level the wall. See Fig 3.
The matt areas are full and the smooth areas need to
be filled up further. Keep filling until the whole wall
is all matt. Finish of this first coat with a scratch
brush finish or keyed finish, so that the next coat will
5. 4
Fig 5. Finished rendered wall with nap finish
Fig 4. Filling up of edge with
plastic float. Straight timber
bead used.
attach better. Leave this coat to dry. Depending on the thickness of the plaster required
another coat might be necessary before floating. Leave this coat to semi-dry.
The next coat is done with the plastic float instead of the
metal trowel. The little dips in the wall are filled with lime
plaster using the float. After filling, the float is used in
circular movements over the whole space of the wall. Use a
bead for the edges/ corners, see Fig 4 and fill into it. Tilt the
timber bead slightly forward and slide out to remove without
damaging the edge. Use the straightedge timber bead again
to see where further dips need filling and float the wall
again. Leave to semi-dry.
The wall was in this case finished off with napping. Napping
is done by using the plastic float again. The wall is
dampened with water and the wall is floated again and
finished off with rapping the float of the wall creating small
tops with the lime mortar. See Fig 5 for finished result.
6. 5
Fig 6. Laths soaking in water Fig 7. Laths beingnailedbackonthe wall
Fig 8. Horsehair added to mix Fig 9. Mortar with added horse hair.
Fig 10. Mortar mix
applied to laths
Fig11. Closerlookof mortar mix with
horse hair
2.1.2. Internal Lime Render Plasterwork
In this practical assignment a wall was clad with laths and the mortar was applied on top of
the laths. First the existing laths were carefully removed from the wall to avoid breakage. The
laths were then merged in water, see Fig 6 and then nailed back in position on the wall. See
Fig 7.
The mortar is then mixed and for the internal mix horsehair was added into the mortar for
extra strength. See Fig 8 and Fig 9 for the finished mixed mortar with horse hair.
The finished mix is then applied to the wall on top of the laths in the same way as the external
wall. See Fig 10 for application and Fig 11 for close up of the mortar with horse hair on the
laths.
7. 6
Fig 12. Fig 13.
Fig 14. The finished scratch coat.
The straight edged timber bead is then used to level out the wall. More filling is needed in the
smooth areas and the matt areas are already filled up. See Fig 12.
The wall is the scratch or keyed in preparation for the next coat. See Fig 13 for scratching and
Fig 14 for the wall with the finished scratch coat.
8. 7
Fig 15 Fig 16
Fig 17 Fig 18
Fig 19.
2.1.3. Lime Plaster Panels
The panels were created on top of the first scratch coat by creating a framework of timber
beading on top of the scratch coat. See Fig 15. The panels were then filled up, levelled and
floated. See Fig 15 and Fig 16.
The template for the panel was then screwed on to the beading and the template was filled up,
levelled and floated as above. See Fig 17, Fig 18 and Fig 19.
A satisfactory finished result was not achieved
with the panelling, because the template was left
too long to dry, before it was removed. This
resulted in the panels breaking. The lime mortar
sets so strongly and adheres so well to the timber
bead, that the template can only be removed by
breaking the panels. See finished result below on
Fig 20. It was therefore not possible to complete the plaster work with the last coat, the skim.
9. 8
Fig 20. Broken panels after template was removed.
Fig21. Sectionof a cornice showing
the base coat andthe white skimcoat
A skim consists of two by silica sand, one by NHL 5 and one by lime putty. This would have
given a smooth white finish to the wall and panel.
2.1.4. In situ Cornicing
In situ cornicing is constructed with a pair of mould
runners. They have the profile of the shape of the
cornice cut out. The wooden mould runner is for the
base coat and the runner with the metallic edge is
for the last coat, the skim. See Fig 21 for Cornice
section. The mould runner runs on a timber bead
along the bottom of the cornice.
10. 9
Fig 22. Scratch coat. Fig 23. Wooden mould runner
Fig 24. Gap by metal mould runner. Fig 25. Second coat mixed by hand.
Fig 26. Using small trowel and hawk. Fig 27. Second coat in pale grey
The base coat or scratch coat is a standard lime mortar made in the cement mixer. The ratio is
three sand to one lime. The mortar is applied with a small metal trowel, a little at a time and
the mould runner is then run repeatedly to remove excess mortar. The base coat is then gently
scratched and left to dry.
The second coat is mixed by hand See Fig 25. The metal runner is used for this coat; see Fig
24 for the gap between the metal runner and the profile left by the wooden mould runner. The
second coat is applied the same way as the first coat; a little at the time and the mould runner
used repeatedly to remove excess mortar, see Fig 26. Please note that it is very important to
wet the area to be plastered prior to work commencing and the mould runner must also be
kept clean and wet for use. The ratio used for the second coat is two parts silica sand, one part
11. 10
Fig 29. Skim coat result
Fig 28. Skim coat mix.
Fig 30. Drawing of king post truss on
board.
NHL 5 and one part lime putty. This mix makes it
possible to achieve really sharp edges and quite a
smooth finish, see Fig 27. Leave to dry.
Four different mixes was tried for the last coat and
it proved quite hard to get a workable mix. The
first mix was one part casting plaster to one part
lime putty, the mix itself was too dry and it set very quickly. The second mix was casting
plaster alone mixed with water, but that was even faster drying. The third mix was two part
casting plaster to one part lime putty that also dried to fast. Both the second and the third mix
dried on the mixing board and never made it to the cornice. The last and most successful mix
was one part casting plaster and one part lime putty, the same as the first mix, but more water
was added and the mix was much sloppier. This yielded the best result so far. See Fig 29.
The first two coats were very workable and easy
to apply and use the mould runners, the last coat,
the skim proved much more difficult to work with
and much harder to achieve a good result.
2.2 Carpentry: King Post Truss
As a part of the carpentry workshop assignments
a king post truss model was drawn on a board and
the model was then constructed using the drawing
as a template. See Fig 30. The king post truss was
constructed using mortise and tenon joints with
wooden dowels. See Fig 31 for other traditional
timber joints. Many of these traditional joints are
used for repair of older historic buildings, where
12. 11
Fig 31. Traditional timber
joints. (wisd, 2015)
Fig 32. Markings
Fig 33. Mortise cut out by machine
Fig 35. Sawing out tenon
Fig 34. Tenon clearly marked
Fig 36. Cut off removed
often a lot of timber was used (Jenkins, 2015).
The timber lengths were then cut and marked after the
template. The joints were then clearly marked and measured.
The angle double checked. The face and direction of each
length of timber was marked with a letter and an arrow. There
will always be small variations in timber and to ensure
consistency of measurements and angles a side of the lengths
of timber was chosen to be the true one and all measurements
and angles will be marked of that
side. This is marked with the shape of
a fish with the longer end touching
the side chosen.
The mortise is then cut out after the markings by machine. See Fig
33. The tenons are the cut out with a saw. See Fig 34, Fig 35 and fig
36.
13. 12
Fig 38. Angles cut with chiselFig 37. Tenon shaped with chisel
Fig 37. Joint closed Fig 38. Joint open
Fig 40. Truss ready to be glued and
dowelled
The chisel is then used to further shape and fit the tenon see Fig 37, but also the angles are
chiselled, see Fig 38.
When all six pieces of timber are fitted and ready, holes are drilled for the dowels. The
dowels were eight mm dowels and a five mm hole was drilled first in the closed joint, see Fig
37. See close up below of mortise and tenon joint, Fig 37 and Fig 38.
Then the joint was opened and the eight mm drill was used so that the two holes were a one
millimetre off. See Fig 39. This makes the joint close tighter, when dowelled.
Fig39. Slightlyoffsethole.
14. 13
Fig 41. The finished model of a king post truss
The facet on the centre post was cut with a chisel before assembly, then all the joints are
glued and dowelled together, see Fig 40. When the glue has dried, the dowels are cut of and
the whole truss is sanded. See Fig 41 for finished model of a king post truss. Please note the
timber model fitted perfectly on top of drawing, thus highlighting the benefit of a detailed
drawing and template.
15. 14
Fig 42. First course tegral slates
Fig 43. Start at the corners
Fig 44. Second course
Fig 45. Third course underway.
2.3. Natural Slate Roofing
Natural slate tiles for roofing are a very common
roof covering on period houses and as a part of
gaining practical experience with natural slate
tiles, a brief workshop was completed using
reclaimed natural slates.
For this assignment the tiles where screwed on
with galvanised screw simply because it would
facilitate removing them again without causing
damage to the slate tile.
Firstly timber was screwed in under the eaves to
facilitate a line for the first course. The first
course was half tegral slates. See Fig 42. The
tegral slates are used as the first half course to
save on the reclaimed natural slate tiles.
Second course was the reclaimed natural slate and
the course was started at the corner. See Fig 43.
See Fig 44 for completed second course.
On Fig 45 the third course was underway and so
the courses are continued till the roof was fully
covered.
See Appendix for more information on natural
slate and natural slate roofing.
16. 15
Fig 46. Different types of arches (Murdock, 2012)
Fig 47. Four centred arch
2.4. Drawings of Arches
An arch is a curved structure of any material. There are many different types of arches and
according to Murdock (2012) there is also endless variations, but they have a strong design
impact and are worth the extra time and effort (Murdock, 2012). For the purpose of this
assignment the type of arch has been put into a category depending on the number of centres.
See examples of the different arches in Fig 46. They all have to be constructed with great
accuracy to achieve the desired effect. In Fig 47 is an example of how to construct a four
centred arch,
which was
particularly
favoured by the
Tudors and
Victorians,
(Murdock,
2012). ,
Fig 48, Fig 49 and Fig 50 shows a further three arches drawings by author. Fig 48 shows a
semi-circular arch which is a one centred arch. Fig 49 shows a gothic arch, which is a two
centred arch and lastly Fig 50 shows a three centred arch, an elliptical arch.
17. 16
Fig 48. Semi-circular arch
Fig 49. Gothic two centred arch,
equilateral arch
Arch terminology:
Intrados (Inner circle)
Extrados (Outer circle)
Face depth (Width of arch)
Soffit (Underneath the arch)
Major axis (Outer span)
Minor axis (Inner span)
Striking point (Where the lines are drawn
from)
Crown (top of arch or keystone)
Springing point (where that arch starts)
Cord (goes across the circle and helps locate
the major and minor axis
Fig50. Semi elliptical archthree centred
18. 17
Chapter 3: Summary
This portfolio has described and documented the practical assignments and experiences in
Semester 2 of BSc in Applied Conservation Skills at Waterford institute of Technology.
It has covered the following:
- External lime plastering
- Internal lime plastering
- Panels in lime plaster
- In situ cornice in lime plaster
- Carpentry: drawing and making a king post truss model
- Natural slate roofing
- Drawing of arches
I have thoroughly enjoyed Semester 2 and especially the practical assignments, which I feel
have been very informative and give a better understanding of conservation techniques.
Yours,
Marie Wilgaard Kelly
19. 18
References
Advice Series. (2010). Roofs – A Guide to the Repair of Historic Roofs. Department of the
Environment, Heritage and Local Government. Dublin. All.
Cadw. (2010). Natural Slate. Available:
http://cadw.wales.gov.uk/docs/cadw/publications/Maintenance_Matters_Natural_Slate_EN.p
df. 2010. Last accessed 2nd May 2015.
Cadw. (2010). Patching Lime Render. Available:
http://cadw.wales.gov.uk/docs/cadw/publications/Maintenance_Matters_Patching_Lime_Ren
der_EN.pdf. 2010. Last accessed 2nd May 2015.
Jenkins, M. (2015). Timber in traditional buildings. Available: http://conservation.historic-
scotland.gov.uk/summer-school-timber.pdf. Last accessed 2nd May 2015.
McAfee, P (2009). Lime Works. Dublin: The Building Limes Forum of Ireland. All.
Murdock, T. (2012). Circular-Based Arches – Part 1: One-Centred and Two-Centred Arches.
Available: http://www.thisiscarpentry.com/2012/01/06/circular-based-arches-part-1/. Last
accessed 2nd May 2015.
Murdock, T. (2012). Circular-Based Arches – Part 3: Four centred Arches. Available:
http://www.thisiscarpentry.com/2012/03/02/circular-based-arches-part-3/#more-11795. Last
accessed 2nd May 2015.
wisd. (2015). Wood joints. Available:
http://www2.wisd.net/archive/industrialtech/WOODS/PHOTOS/WoodJoints.gif. Last
accessed 2nd May 2015.
20. 19
Appendix
Table of Content
Chapter 1: Guided Visits and tours Page 20
1.1. Visit to the heritage Council in Kilkenny City Page 20
1.2. Tour of the Bishop’s Palace in Waterford City Page 21
1.3. Site visit to St. Mary’s Hall in Kilkenny City Page 23
Chapter 2: Lectures and Demonstration Page 26
2.1. Peter Cox on cleaning Page 26
2.2. Stained glass demonstration by Sean Corcoran Page 28
2.3. Thatching demonstration by Jimmy Lenehan Page 29
Chapter 3: Materials Page 32
3.1. Natural Slate Tiles for Roofing Page 32
3.2. Lime Page 40
3.3. How to order stained glass; handout by Sean Corcoran Page 42
21. 20
Fig 51. Staircase with
Venetian windows
Fig 52. Window detail
Fig 53. Ceiling rose
Chapter 1: Guided Visits and Tours
1.1. Visit to the Heritage Council in Kilkenny City
The guided visit took place on the 14th of January 2015 at the
Heritage Council’s premises in Kilkenny City. The visit
commenced with a talk by Colm Murray about the history and
role of the Heritage Council (An Chomhairle Oidhreachta). The
visit concluded with a guided tour around the building.
The Heritage Council is almost 20 years old and was set up by
the then Minister of Heritage, Michael D. Higgins, as an
advisory body on all types of Heritage and good practice when
working on heritage projects. Colm Murray views heritage as
in-heritage and as a non-renewable
source. Once it is gone it cannot be
brought back.
The role of The Heritage Council is; to propose policy about
heritage, support public and local authorities, administer grants,
advisory body on planning applications, encourage and carry out
research. The heritage council supports a network of heritage
Officers & consultants, which meet up 3 – 4 times a year. The
Heritage Council also aims to make heritage values more
accessible to the public and thereby making the public more
aware about their Heritage.
The Heritage Councils work includes; grants, advice to the
public, promotion of traditional building skills, urban
policy, advocacy for certain buildings and conservation
planning. Conservation plans are being developed by the
Heritage Council and includes: statement of significance,
documentation, risk assessment, policy for protection and
22. 21
Fig 54. New glass and steel extension
Fig 55. Front façade
input from stake holders (See the Burra Charter). Another important aspect is to raise
awareness about the built heritage and sustainable environment; this involves providing
information that will help owners to go ahead with restoration projects instead of knocking
and building a new building. “The most environmentally benign building is the one that does
not have to be built, because it already exist”, Colm Murray, 2015. Research has shown that
a restoration project, because of its complexity uses more labour and thus gives rise to local
employment. Furthermore restoration projects are about 10% higher in costs, but because of
the values imbedded in the structure retain the craftsmanship and energy invested over the
years in a building will give the structure a value and identity that a new building cannot.
There is also great sustainability in re-using a structure.
The Heritage council is located in the old
Bishop’s Palace, built around the 1340’s.
The structure was renovated in 2007- 2008.
A new extension in glass and steel was built
on to the palace on top of what once was the
palace kitchen. See Fig 54.
1.2. Tour of the Bishop’s Palace in Waterford city
The guided visit took place on the 22nd of January 2015 and the
tour guide was Terry Prenderville. Terry Prenderville gave an
external and internal tour of the building explaining the
buildings history and the process of conservation that took place
a few years earlier.
The current structure was built in the 1740’s by Charles Este
(1696 – 1745), as he was not content with the previous building
that stood on the site. Este died before the completion of the
build and the new bishop Robert Cashel took over and
completed the build. It is a Georgian style palace and it has had
many uses until the present day, when it after a comprehensive
23. 22
Fig 56. Harled South facade
Fig 57. Rear façade with main entrance
Fig 58. Window arch detail
Fig 59. Staircase
renovation opened as a museum. It has
been first and foremost a bishop’s palace
then a boarding school, then derelict, then
county council offices until today a
museum. It has a very colourful and
interesting past with many well-known
persons connected to it from the Wyse
family to Brigadier Thomas Francis
Meagher (1823 – 1867).
Externally it is a stone building with the south
façade harled, because the condition of the
stones on that façade was too poor to re-point
with lime mortar, see Fig 56. Internally it has
been painted with calcium carbonated paint
(lime wash) to let the walls breathe and to
avoid locking in moisture. Inside it has the reception area, café and entrance lobby on the first
floor, magnificent furnishings in original style on the second floor and on the top floor is an
exhibition dedicated to the history of
Waterford.
24. 23
Fig 60. A Stone Mason’s maker mark
Fig 62. See cracks by Clerestory Window
Fig 61. Pot log hole
1.3. Site visit to St. Mary’s Hall in Kilkenny City
On the 14th of April 2015 Evelyn Graham invited us back on site to see the progress after
work had commenced on St. Mary’s Hall. It was very exciting to come back and see all the
changes and the site being a hive of activity. The tour was conducted by Evelyn Graham, the
foreman, Paddy Byrne and the Clerk of Works, Francis Coady with an added in talk by Coilin
O’Driscoil and Joe Kelly.
The tour started off with a climb up the
scaffolding to meet Joe Kelly, who gave a talk
on raking out the cementations mortar. The
cementitious mortar has to be removed all the
way in to the original healthy lime bedding
mortar. Although some joints are too tight to
rake out without risking subsidence and some
are left in place, while others are being raked out by a stone mason.
When raking out it is important to be aware of a few
different points:
- Pinching, which is where stone touches stone
- Holes that go all the way into the wall
- Window surrounds / subsidence / stability
- Ashlar stone
- Pot log holes
- Wobbly walls / subsidence
On some of the stones are left makers marks,
which were created by the stone mason
cutting and laying the stone. See Fig for
example of makers mark
25. 24
Fig 67. Table Tomb Foundation
Fig 63. Mortar test panel with local sand
Fig 64. Internal Plaster
panel sample
The clerestory windows, which are high on each side of the central aisle, are causing a bit of
trouble, because the arch is poorly made
and the window is actually holding up the
arch. The arch was constructed after the
window was put in and the Key stone is
too small and weak. The window will
have to come out fully and the whole
surround has to be replaced by a new one.
A relieving arch will have to be
constructed with bricks above the window opening inside the wall.
Two test panels of mortar were made one with local sand and one with beach sand. The local
has been chosen to be the closest in likeness to original mortar. See Fig .
Some of the ashlar stones will not be raked out, because the removal of the cementitious
mortar can cause subsidence, while others have been washed out over time and will be re-
pointed. The re-pointing will be very time consuming,
because the mortar will have be packed tightly all the way
into the wall as deep as possible.
Around the site many ornaments and effigies have been
boxed in or moved for protection. The internal plaster panel
sample is located inside the building and consists of hemp
plaster with a lime putty skim. The hemp has insulating
properties. The base coat is: 30% hemp to 70 % 3.5 NHL
lime mortar mix, scratch
coat is the same. The skim
is; 98 % lime putty with 2
% casting plaster. The base
coat was left seven days
before applying the scratch coat. The skim was applied one
day after the scratch coat to avoid it drying out too fast and
cracking. The panel has performed very well.
26. 25
Fig 66. Burial vault in transept floor
Fig 68. Opened original archways in nave. Location of Fresco.
Kilkenny Archaeology has been
excavating the crossing and
transept inside St. Mary’s Hall.
Coilin O’Drisceoil gave a talk on
their findings. They have found
many human remains in the form
of bones and skulls. They have
also located 8 vaults and a
foundation for a table tomb. They
had hoped to find more from the original 12th century structure, but have so far only located
two lancet windows. Based on their findings, they have formed a new theory as to what could
have happened with the original church building and why so little evidence remains. The
nave of the church is built on solid bedrock and the chancel, crossing and transept were built
on the river bank. The river bank would have been a much less solid foundation than the
bedrock. This could have caused subsidence and might have broken the church in half, which
would explain the lack of evidence and the reference to the church being in ruins in the early
17th century. This could also explain why the chancel was shortened and why the whole roof
was replaced. At the time of Coilin O’Drisceoil’s talk they were at the Georgian floor level
and they hoped to dig down further to the medieval floor level.
The plaster on the walls of the nave has been removed and it has revealed the original
archways. The archways have been opened up on one side of the nave. The opening up of the
archways revealed a small patch of what appears to be a fresco.
27. 26
Chapter 2: Lectures and Demonstrations
2.1. Peter Cox on cleaning
Peter Cox from Carrig Conservation held a lecture on the 27th of January 2015 in the council
chamber in the Tholsel in Kilkenny. The topic was how to clean stone, terracotta, concrete
and masonry. The following is a summary:
There are three different methods for cleaning:
- Abrasive – media blasting
- Nebulous spray – water spray
- Poultice – chemicals
Firstly is has to be established exactly what material that need to be cleaned; analyse the
material. Secondly what condition is it in; stable or un-stable? Lastly it must be analysed
what caused the staining; pollution, paint, cars etc.
The abrasive method involves blasting the material with a media. The media can vary
depending on what is specified and can be anything from talcum powder, glass beads, lime
dust to metals. Please note that sandblasting is illegal, because it is cancerous.
The nebulous spray method uses a copper pipe with pin holes every 50mm, which is tied to
the scaffolding. Water is pumped through the pipe and these results in continuous water
running down the material for a period a few hours. This is especially good for cleaning
heavily built up bearded carbon layers.
The poultice method applies chemicals to clean the material. There are two options; alkali
and acid both must be neutralised after use. Alkali is good for heavy soiling and looks a bit
like wall paper paste. It can be sodium hydroxide or potassium hydroxide. It is suitable for all
masonry and must be neutralise with an acid after use.
Acid poultice can be hydrofluoric acid, hydrochloric acid, phosphoric acid or acetic acid
(vinegar). Hydrofluoric acid is suitable for granite, sandstone and brick. Hydrochloric acid is
good with limestone and concrete. Phosphoric acid is effective on glazed brick and acetic
acid can be used on any stone, is good to remove efflorescence and is often used as a
neutraliser after the use of an alkali poultice.
28. 27
How to clean granite with an alkaline poultice; wet the stone to block the pores further in the
stone, apply the alkaline poultice and leave for 15 – 90 minutes, rinse thoroughly (600 psi),
neutralise and wash again.
How to clean sandstone and brick with an alkaline poultice; wet the stone, apply the alkaline
poultice, leave for 15 – 90 minutes, rinse thoroughly (600 psi), neutralise with hydrofluoric
acid and wash again.
There is a great difference in the porosity of stone and the more porous it is the more
susceptible and vulnerable to decay, damage and chemicals it will be. Therefore it is
important to test any method used on the material. Use the finger test first; apply four strips
of duct tape to the material crossing mortar points. Apply the method, remove the duct tape
and see the difference between treated and un-treated material.
Interior cleaning is different, because it is necessary to protect the interior finishes; plaster
work, carpentry, floor finishes, etc. detergents are used internally and can be mildly acidic or
a poultice that can be left in situ for a while without leaking. Tensid is a good chemical
cleaning system.
Paint removal can be required both externally and internally. Alkali based paint removers are
for lead based paint and solvent based paint removers are for oil paints.
For the use of all chemicals it is essential to know your substrate, know your products and do
your research.
Water repellents can be useful and it is best to use water based products that are reversible.
Chemical consolidation will freeze a material in its present condition. It is very costly, but
can be necessary in some circumstance to preserve a significant material. SL 100 works well
on brick and sandstone. SLX 100 works for limestone. It is important to know the decay
mechanism of the material to be treated, because salts will stop the penetration of the
consolidation material. This can cause the face of the material to break of after treatment, so
it is essential to do a thorough analysis at depth and check for salts.
29. 28
Fig 69. Cutting the
glass
Fig 70. Tools
Fig 71. Soldering the
joints.
Fig 72. Colour panel
2.2. Stained glass lecture by Sean Corcoran
This lecture was held on the 11th of February in Sean Corcoran’s
workshop on the coast near Tramore. The lecture was mainly an
informative talk on the different methods used to produce stained
glass and the process behind it.
First the design of the
stained glass must be drawn to scale and the glass it
cut after the drawing leaving space for the lead, see
Fig 1. When all the glass is cut, the lead is shaped
and cut, see Fig 2 for tools. Then the glass and the
lead are assembled and the joints are soldered, see Fig 3. Sean uses
an H-profiled lead strip. To make the joint, he widens out one side
of the lead, so the other lead strip end can slide in. This is called the
German method. Then it is soldered with a gas torch, see Fig 3.
Lastly the gap between the lead profiled and the glass pane are filled
with cement.
There are many colours, see Fig 4. The colours are created by
mixing metals in with the glass; gold makes
red, copper makes green, brass makes blue
etc. There is textured glass as well, see Fig
5. Another way to create effects is to matt
the back of the glass, see Fig 6 or to paint the glass, see Fig. 7.
Painting is done with enamel powder and then the panel goes in to
the kiln where the paint fuses with the glass.
Sean Corcoran further explained the process for working with
historic windows: it is more of a re-construction process, because the
glass is in a liquid state and is affected by gravity and therefore
slowly over time the glass will move towards the bottom of the pane,
leaving the top thinner and thinner till it breaks. That is why historic glass is not re-used in
repairs, only newly produced glass. Even the lead will weather and perish, so what is left to
30. 29
Fig 73 textures Fig 74. Matt lines Fig 75. Painted glass
Fig 76. Laying bundles of reed on the roof.
preserve is the design and layout. So a replacement stained glass window would very likely
be all new, but made as a copy of the old window. See chapter 3/ 3.2. On how to order
stained glass windows. According to Sean Corcoran any design and colour can be ordered to
ensure a correct match with the original window. Some glass are in stock and available
readily, as the sample panel on Fig. 4, but glass can also be ordered in according to specific
requirements and it would be a produced especially for a bespoke order/client. Repairs to
historic glass windows can be done in situ in order to protect the window and surround, but it
is much more difficult and very time consuming.
2.3. Thatching demonstration by Jimmy Lenehan
This demonstration took place in the
workshop on WIT on the 12th of
February 2015. First Jimmy Lenehan
showed a power point presentation of
thatch and its history, including
different types of materials and
techniques. After the power point
Jimmy Lenehan used reed to thatch a
sample roof in the workshop.
In the power point presentation Jimmy Lenehan spoke about the practical aspects of thatch.
The optimal pitch of a thatch roof is between 45 – 55 %, 5 % either way reduces the lifespan
of the roof by 5 years.
31. 30
Fig 77. Shaping the eaves.
Fig 78. Shaping the roof as the layers
of reed goes on
Thaec means any type of roof in anglo saxon and clearly
it was an easy and readily available roofing material for
the commoner and the knowledge of laying, repairing
and maintenance of the roof was used in every family
and passed on.
The types of thatch used in Ireland are:
- Straw ( hippie look with mixed heads and butts,
eaves rod, cross rod)
- Reed ( only butt end exposed, very straight lines
and neat looking)
- Combed straw ( cleaned straw, flag leaf
removed, no cross rod)
- Flax ( brown hue, round soft feel, eave rod wire,
no heads, mainly north Ireland)
The materials used can be straw, water reed, flax,
rushes, moor grass, heather. Lifespan is
approximately 30 years for reed and 14 – 20 years
for straw, depending of the skills of the thatcher.In
order to survey a thatched roof historic research
into the building itself may be required. Also a
general description of the structure itself; roof
shape, roof frame, style. Generally it would be a
vernacular house design with either a lobby
entrance or a gabled chimney. Also determine the
materials and technique used. Check under the
eaves to see if there is decay or damage and clarify
if there any historic thatch remaining. The roof
timber structure also needs to be examined; is it
sawn or un-sawn, smoke blackened (built during
penal times), couples and runners and the load
32. 31
Fig 79. Temporarily securing the reeds.
Fig 80. Making hazel rod
scallops
Fig81. Example of thatchedroof
with cross bars and hazel rod
scallops.
bearing capacity. The ridges can be
flush, block cut, butt up, wrapped
over, bobbin twist used or tin/zinc
tile. Scallops are normally made of
hazel or willows and must have a
slight downward tilt or they will let
in water.
When employing a thatcher it is
important to see examples of previous work that is at least 5 – 7 years old. Well trained
thatchers are rare in Ireland and seem to be better trained and regulated in the UK at the
moment.
If a roof needs to be re-coated there is a DOE grant
available of almost €4000. The house must be at least 10
years old, and the grant can be applied for every 7 years
regardless of income, but double the amount if owner is on
a medical card.
33. 32
Fig 82. Quarry in Roshine, County Donegal. (Advice
Series, 2010)
Chapter 3: Materials
3.1. Natural Slate Tiles for Roofing
Extract from Advice Series. (2010). Roofs – A Guide to the Repair of Historic Roofs.
Department of the Environment, Heritage and Local Government.
Slate
THE FORMATION OF SLATE
The word ‘slate’ comes from the Middle English ‘slat’ or ‘slate.’ It is related to the French
word‘esclater’, which means to break into pieces and refers to the cleaving characteristics of
the rock.
Slate is a naturally formed metamorphic rock extracted or mined from discovered seams
within the ground. These seams were formed millions of years ago by great pressure exerted
on mud layers, containing key clay minerals, lying on the base of shallow seas. During
massive earth movements, areas of the sea bed were uplifted into mountains and the mud,
now covered by sedimentary shale, was subjected to tremendous heat and directional
pressures causing the minerals present in the mud layers to crystallise into rock layers. The
re-orientation of clay minerals in parallel planes to the forces of greatest pressure is described
as ‘fissility’, and the ability to split along these planes is called ‘cleavage’. It is this particular
formation process that gives slate its chief characteristics and differentiates the material from
the thicker sandstone flags also used in Ireland as a roof covering.
SOURCES OF IRISH SLATE
‘……. slates are to be got in most places, on reasonable terms; all along the eastern sea coast,
slate from Wales can be procured – and in the interior, both north and south, valuable
quarries are accessible. All along the line of the Shannon, and the channels connected with it,
the Killaloe slates are procurable – and perhaps, not even Wales itself can produce a more
lasting, or manageable slate than the Killaloe quarries can produce…’ The Dublin Penny
Journal (1833)
Regional Irish slate possesses a wide range of colours and textures, from the coarse and
heavy Clare slate to the smooth and light appearance of Valentia Island purple slate from
County Kerry. Because of these characteristics, as well as its rarity, Irish slate is particularly
Worthy of identification, protection, and retention.
Reports and published descriptions dating from the nineteenth century identify the location,
operation and output of Irish slate quarries. The survey work of the Geological Survey of
Ireland (GSI), compiled just after the first Ordnance Survey, is an important archive. To date,
217 references to slate locations in 19 counties have been established by the GSI. Samuel
Lewis’s Topographical Dictionary of
Ireland (1837) identified and described
the quality and location of at least 122
sites for quarrying slate. County Cork
was considered to be the most
significant producer of slate, followed
by counties Kerry, Tipperary, Clare,
Wexford, Waterford, Kilkenny and
Wicklow, with small pockets identified
in counties Mayo and Donegal.
35. 34
Fig 84. Irish slate quarries
THE IRISH SLATE INDUSTRY
Slate, both local and imported, was used as a roof covering in Ireland from the thirteenth
century onwards. Ireland had its own native slate industry, and Irish slate was readily
available as a quality roofing material in areas adjacent to the productive quarries.
There is evidence that many Irish quarries were worked as small-scale concerns, supplying
only local demand. Irish slates were noted to be heavier than available British ones due to the
shallow seams that were extracted, but this does not hold for all slate types, as some
producers did excavate deep, higher quality, seams.
Historically, there were few large scale quarries operating in Ireland. Those at Benduff,
County Cork, Valentia, County Kerry, Broadford and Killaloe, County Clare and Ahenny,
County Kilkenny were the exceptions, producing the greatest quantity of native slate within
the country. The quarry at Valentia was worked from 1816, when it was opened by the
Knight of Kerry, and expanded greatly in the early nineteenth century; it was the second-
36. 35
largest ever quarried in these islands. Although Valentia slate was used mainly as flagstone,
there are examples of surviving roofs to be found in the Listowel area, and Valentia slate was
used to roof the Houses of Parliament in Westminster. It is a very durable slate of dark grey
with a purplish hue in the hand, whilst appearing black when on a roof. The Ormond and
Victoria Quarries, located on either side of the Lingaun River on the Kilkenny/Tipperary
border near Ahenny, supplied approximately 10 per cent of the Irish market before the Great
Famine. Samuel Lewis described Ormond Quarry as ‘an extensive quarry of slate of superior
quality … in which about 150 persons are generally employed, the slates have an extensive
sale in this and adjoining counties, being considered nearly equal to the Welsh slates in
colour and lightness; the quantity annually raised is considerable, and the works have been
extended to a depth of 120 feet’.
The same geological vein produced Killaloe, Broadford and Portroe slate. Records from these
quarries indicate that they employed Scottish and Welsh slate workers, who brought their
slate-handling techniques with them. Broadford had been quarried for slate since medieval
times for its use on castles as well as large country houses in the area. However, access to
transport was crucial and the use of Broadford slate declined in the 1800s when the Portroe
and Killaloe seams began to exploit their proximity to the River Shannon. These quarries
were able to use the Shannon waterway for distribution and for this reason became significant
providers of slate, at one time supplying 65 per cent of the Irish market. Moher/Liscannor
slate came from a number of quarries sited between Doolin and Liscannor, and was
generically named after the port from which it was exported. This area also produced stone
flags for roofing.
30
A series of quarries on the Tipperary/Kilkenny border made this one of the more prolific
areas of slate production in Ireland in the nineteenth century Convoy slate from County
Donegal is a grey/black slate; its small size and appearance make it almost similar in
appearance to a tile. It was widely used in Dublin during the housing boom in the early part
of the twentieth century and can be seen on local authority housing projects, such as buildings
in the suburb of Crumlin. Benduff slate from County Cork was also used in some housing
schemes of the time
IMPORTED SLATE
The development of canal and railway networks across the country from the late eighteenth
century onwards ensured not only the widespread use of native slate, but also facilitated the
increased use of imported slate. Shipping records indicate that substantial quantities of slate
were imported into Ireland during the eighteenth and nineteenth centuries, mainly from
Wales. During the nineteenth century, the intensification of slate production from the Welsh
quarries finally drove many Irish slate quarries, which were less mechanised than their Welsh
counterparts, out of business. There is also evidence that Irish builders bought Welsh slate for
use on roofs, even in towns such as Nenagh and Ennistymon, both of which were close to
several local quarries. Slate was also imported from America and Italy.
Slates from Wales vary from reddish and bluish purple to black to light green. Penrhyn slate
(Blue Bangor), the most commonly found Welsh slate, is heather in colour. Some Penrhyn
slate has a green olive mark in the heather rock, which is considered its distinguishing feature
or characteristic. Caernarfon slates are usually a deeper shade of heather than the Blue
Bangors, and vary in intensity to a deep heather colour known as ‘plum reds’. A paler heather
slate from Cardigan in South Wales was used in Cork and Waterford. Ballachulish slate was
imported from the Highlands of Scotland. It is dark or silver-grey in colour and usually only
available in small sizes. Westmorland slate, which is quarried in the Lake District in England,
is a thick green or grey slate with a rough surface that shows no grain. Westmorland Greens
37. 36
Fig 85. Welsh quarries
were used in several restorations of the roof at Christchurch Cathedral, Dublin. Welsh slate
was generally named after the ports from which the slate was exported: Bangor, Dinorwic
and Caernarfon. Many Welsh slates come from the same Cambrian stone vein, resulting in
slates of a similar colour. The slate from Porthmadog, by contrast, is blue-black
Some of the more than twenty sizes and standards of slate used up until 1933, when the use
of names was dropped:
Kings 36 x 20 inches
Queens 34 x 20 inches
Princesses 24 x 14 inches
Duchesses 24 x 12 inches
Marchionesses 22 x 11 inches
Countesses 20 x 10 inches
Viscountesses 18 x 9 inches
Ladies 16 x 8 inches
Doubles 12 x 10 inches
Slating methods
FIXING OF SLATES
The small, irregular, hand-shaped slates used in the eighteenth century were generally fixed
in place using wooden (often oak) pegs fixed through the heads of the slate (using single or
double holes) and fixed over the top of the timber batten. Battens are lengths of timber, small
in section, placed horizontally on top of the rafters and nailed to them. Wooden pegs were
38. 37
Thoroughly dried out before use and then re-hydrated so that they would swell in the slate
and add greater security to the fixing. The fixed slating was finished with a layer of lime
plaster, or parging, applied to the underside.
The fixing of slate with handmade wrought-iron nails became common in the eighteenth
century. Copper nails were subsequently used, as iron was prone to corrosion, which could
lead to premature failure of the roof covering. Larger slates were nailed in place on battens
set at intervals that related to the desired overlap between slates. A greater lap was possible
with larger slates than with smaller dimensions. The slate was often fixed in diminishing
courses ranging from large slates at the eaves to smaller slates at ridge level, as it was an
economical way of using slates of varying sizes. The band detail created by the large slate at
eaves level is one of the quintessential characteristics of a historic roof. It is a particular
characteristic of Irish roofs and it should be preserved where possible in subsequent re-
roofing projects.
PARGING AND DECKING
Traditionally, the underside of slates was coated with lime mortar to the interior of the roof
space, a form of weathering called lime parging. It was done to counteract wind suction and
to give additional security against driving rain, as only a small area of overlap could be
achieved between adjoining rows of small, shaped slates or tiles. It also consolidated the
slates or tiles and prevented them rattling. Lime parging preceded the technology of roofing
membranes to combat draughts and water ingress into the roof space. Remnants of parging to
the underside of slates. A method of slating sometimes referred to as ‘open slating’, ‘hit-and-
miss slating’ or ‘Scottish cant’. This slating pattern economised on the number of slates used
and was primarily used for outbuildings. It is difficult to repair without face-fixing and the
amount of exposure of slate surface can make the slates brittle for reuse.
33
The use of timber sarking or decking (jointed sheeting fixed directly to rafters) was used in
some high-quality nineteenth-century work. This system of boarding out, occasionally with
battening on top, was considered a superior construction detail in areas of severe exposure
and where high snow loads were an issue. It is still a traditional form of construction to be
found in the north of the country, but was less commonly used in the south. Decking is also
found below complex roof forms, such as curved bays, where the roof pitch is minimal and
slates were fixed directly to the boarding.
The boarding on the curved sections of roofs was fixed diagonally so that the joints did not
run parallel to the slate joints. This ensured a greater radius to curve the boarding as well as
better protection from water ingress. The setting of slate onto a bed of lime supported by
closely spaced riven laths fixed to the upper face of the rafters was a very early eighteenth
century detail known as a ‘wet roof’ construction. The bed of lime was used to accommodate
the handcut, irregular, uneven slates generally available from local quarries. There are very
few surviving examples of this type, as most roofs on historic buildings tend to be replaced
several times over the life of the structure. Occasionally, areas retaining mortar remnants with
riven laths and perhaps a few irregularly pegged slates may survive from when the roof was
modified or overroofed. This type of discovery can be a good indicator of the age and
development of the building, and evidence of this nature discovered within a roof should be
recorded. A full wet roof existed on Buncrana Castle, County Donegal (1718-19) and this
technique was replicated during re-roofing works in the 1990s. Remnants of this type of
roofing have also been found on the larger eighteenth-century buildings such as Castletown
House, County Kildare.
39. 38
VERTICAL SLATE HANGING
Vertically hung slate is a weathering detail found in exposed elevations. It was frequently
used in towns throughout Munster, particularly in coastal areas, but examples can be found
countrywide. Vertical slate cladding was often used to cover sandstone rubble masonry where
it was difficult to achieve a watertight external render. On some buildings, patterns in clipped
slates or contrasting colours were used. Vertical slate hanging was used to protect those parts
of buildings that are inaccessible and hard to maintain or are particularly exposed to weather,
such as parapets, chimneys and gable walls. Frequently, slate hanging was used to clad the
full internal face of parapet wallsinstead of lead.
The recent discovery, within a later roof space of part of the former medieval friary in Ennis,
of closely spaced riven laths fixed onto covered-over rafters substantiated the presence of an
earlier structure within the historic fabric The best surviving examples of native Irish slate are
most often found in vertical slate hanging, as it requires less frequent replacement than
roofing slate. It is thought that this example of a slated gable is covered in Ahenny slate from
the nearby Ormond quarries in the Carrick-on-Suir area
34
Vertical slate hanging was carried out in a similar manner to wet roofing (see above). The
wall was plastered with a lime mortar, which was allowed a few days to set. Lime mortar was
then applied to the underside of the slates, which were placed in position like wall tiles. The
slates were fixed at the head using wrought-iron nails with a thin shank. This fixing curled
on fitting, forming a secure fix into the lime mortar. The mortar bedding delayed corrosion of
the iron nails. Vertical slate hanging to parapet walls was generally carried out with the face
of the slate set into a wet lime mortar plastered onto the wall. This was also a technique used
in small roof areas and projections where a rough surfaced slate was used to provide more
purchase to the lime. Vertical slate hanging ensured a good run-off of rainwater. This meant
that the headlap may have been as little as 50mm. Sometimes shouldered slate (slates with the
top corners cut off ) were used, as were off-cuts or less expensive slate.
In some instances, vertical slate hanging is found covered with a coarse lime dashed render to
provide a waterproofing layer. This detail was used both internally and externally, for
example at parapet level. The existence of the vertical slate detail typically does not come to
light until the covering plaster fails, revealing the unusual construction underneath.
Stone slab
HISTORICAL CONTEXT
Sandstone slabs or flags were historically used as a roofing material, principally in west
County Clare where suitable stone was locally available. These loadbearing flags, sometimes
referred to as stone ‘slates’, are laid in a different manner to traditional slate roofs and
possess particular characteristics. Stone slabs were used on roofs in other areas of the country
where similar geological formations occur, such as in the north Kerry/west Limerick area,
and in areas of counties Carlow, Kilkenny, Laois, Leitrim and Tipperary. While the largest
number of stone roofs exist in County Clare, a small number of stone slab roofs, mostly on
outbuildings, survive in counties Leitrim, Donegal and north Roscommon.
STONE CHARACTERISTICS
The term ‘Liscannor stone’ is used generically to describe any fissile sandstone that displays
the fossilised tracks of marine life (molluscs, arthropods and worms) that existed 320 million
years ago, such as that quarried at Moher and Miltown Malbay. Doonagore stone flags are
40. 39
distinguishable by a dimpled or rippled texture. Luogh slabs are smooth, with ingrained
colours ranging from blue/black and grey/brown to russet. Quarries are still worked at
Luogh and Moher, providing slab sizes ranging from 1150 x 880mm to 450 x 450mm, with
thickness varying between 13mm and 25mm.
SETTING STONE SLABS
The limitations of the material did not allow for details such as hipped roofs, valleys or
dormer windows, and so stone slabs are generally found on simple gable ended roofs. Due to
the heavy weight of the slabs, the roof structures that support them tend to incorporate large,
closely spaced timbers. Stone slabs are generally used on roofs with a pitch of no steeper than
40 degrees. A rare surviving example of a stone slab roof in County Donegal showing a
building covered with flags of a local stone
35
The size of available slabs appears to have dictated where the batten was placed so as to
provide an adequate lap. Each successive course of stone slabs (known locally as ‘flags’ due
to their large weight and size) were chosen to provide adequate headlap over the course
below. Luogh flag, due to its smoother nature, requires a lesser lap. The flags were laid with
the heavier and larger ones at the eaves, diminishing in size towards the ridge, where the
smallest flags were placed. Stone flags were traditionally attached by iron nails through a
double set of holes located near the head of the slab, or via side notches. Alternatively, flags
could be pegged and hooked over the battens.
The heavier and thicker flags were often simply hung from nails, which rested in notches
picked out from the underside of the stone. These flags could be up to approximately 2 inches
(55mm) thick. The immense size and weight of these stones meant that as a rule they stayed
in place without need for fixings.
41. 40
Fig 86. The lime cycle
3.2. Lime
Lime
Lime is produced by burning limestone in a kiln, turning the limestone into quicklime. The
quicklime is then by slaking (adding precise amounts of water) turned into either lime putty,
which has a soft cream cheese texture or hydrated lime, which is a powder.
Quick lime, sand and water make a hot lime mortar. Lime putty or hydrated lime mixed with
sand and water makes a lime mortar.
The watery substance left behind from the slaking, can be used as a lime wash.
Lime sets and hardens by being exposed to and absorbing CO2. The absorption of CO2
slowly turns the lime back into stone. See the Lime Cycle below (McAfee, ).
Natural hydraulic lime, also called NHL is in theory not a lime product, because it can set in
water and is not purely dependant on the chemical reaction with CO2. Natural hydrated lime
is also made from burning limestone, but is a less pure product containing clay or silica
42. 41
(McAfee, P). Natural hydraulic lime is natural, because no pozzolans, cement or other setting
agents have been added to it. Pozzolans are materials added to lime to speed up the setting of
the lime mortar, examples can be brick dust, ashes or tile dust. Natural hydrated lime comes
in different classifications based on their ability to set in water and strength: NHL 2, NHL
3.5, NHL 5. NHL 2 is the feeblest one and NHL 5 is the strongest one. (McAfee, 2009)
The reason why lime is so important in conservation projects is because it was often
originally used and should therefore be used for conservation and repairs. Mortar is sacrificial
and must be weaker than the stone or brick. This is not the case with cement or concrete,
which is stronger and can therefore damage the stone or brick. An example of this is St.
Mary’s Church in Kilkenny, where the cement used for re-pointing is so strong it causes
damage and decay to the stone and the building.
43. 42
Fig 87. Stained glass order information form
3.3. How to Order stained Glass.
