PLASTER FINISHES AND EXTERNAL RENDERING FOR BUILDING

1. COURSE CODE: ARC 491 MATTHEW MOSES
UJ/2018/EV/0532
400L BSC, 1ST SEM
DEPARTMENT OF ARCHITECTURE
DEPARTMENT OF ARCHITECTURE
UNIVERSITY OF JOS
FACULTY OF ENVIRONMENTAL SCIENCES
COURSE LECTURER: Dr. SHEM RIPNUNG LEKJEP
COURSE TITLE: BUILDING MATERIALS IV
PLASTER FINISHES IN
BUILDING CONSTRUCTION

2. PLASTERING is a process by which coarse surfaces of wall or ceiling roofs are changed or turned or rendered to provide
smoothness. At the beginning, wet materials are spread over the block or brick works and then suitable equipment is used to make
the surface smooth level. The prime purpose of plastering is to obtain hard and smooth surface that could be painted and provide
nice aesthetic appearances.
PLASTER FINISHES AND EXTERNAL RENDERING FOR
BUILDING
Recently, wall surfaces in modern houses are finished with bricks or
blocks or aesthetically pleasing stones to show beautiful appearances.
Wet materials that spread over wall or roof surfaces should not be more
than 0.3 cm. However, there are surfaces that irregularities are more
than 3cm. In this case under coat which is low cost coarse grain
material is used to render the surface followed by finish coat that is thin
layer of fine grain materials. Moreover, walls constructed from irregular
and different size stones might require three coating. This is because
thick under coat tend to sag due to weight of thick wet plaster. That is
why spreading thin layer and permitting to harden followed by
employing second under coat is the best practice as shown in Figure 1.
Finally, finish coat is applied for the surface.

3. TYPES OF PLASTER BASED ON MATERIAL USED
LIME PLASTER
Lime mixture consists of sand and line that are mixed by 1 sand to 3 of lime by volume. Not only this mixture is used for under
coat but also used as finish coat. Lime plaster might be shrink after drying so animal hair of about 5 Kg is used for 1 m2 to
avoid lime plaster cracking and shrinking. Lime plaster could be used for ancient structure restoration and rehabilitation.
CEMENT PLASTER
Grey powder Portland cement is mixed with water by the ratio of 1cement to 3 or 4 clean washed sand by volume as an under
coat for hard background for example brick block walls and partitions. Mixture of sand and cement might be plastic and require
experienced and skill labor therefore plasticizer or lime is added to the mixture usually by volume ratio of 1cement:0.25 lime: 3
sand or 1 cement to 4 sand with plasticizer. Plasticizer is a liquid that added to the mixture to ease plaster spreading over the
surface.
GYPSUM PLASTER
Gypsum plaster is widely used plaster materials that could be mined naturally or produced as a by-product. So, important
gypsum plaster that is employed as under coat, finish coat, and replaced lime and cement broadly. Moreover, small expansion
of gypsum is considered significant propertied that prevent shrinkages and cracks. There are various types of gypsum plaster
that are produced by heating gypsum to a specific degree for example anhydrous gypsum manufactured by heating gypsum up
to 170 Co, hemihydrates gypsum produced by heating gypsum more than 170 Co. Furthermore, depending on applications for
walls or ceilings gypsum plasters can be categorized such as casting, undercoat, finish, one coat and machine applied plaster.

4. TYPES OF PLASTER FINISHES USED IN BUILDING CONSTRUCTION
Different types of plaster finishes with different appearances are available as follows
•Smooth cast finish
•Rough cast finish
•Sand faced finish
•Pebble dash finish
•Scrapped finish
•Depeter finish
•Textured finish
SMOOTH CAST PLASTER FINISH
To obtain smooth cast finish, mortar used should be in the ratio 1: 3 [cement: sand]. Fine
Sand should be taken to prepare the mortar. For spreading the mortar, skimming float or
wood float is best suitable tool. Hence, smooth and levelled surface is obtained finally.
ROUGH CAST PLASTER FINISH
Rough cast finish is also called as spatter dash finish. Mortar used to get rough cast
finish consist coarse aggregate along with cement and sand. Their ratio is about 1:
1.5: 3. The size of coarse aggregate used is 3mm to 12mm. Large quantity of mortar
is taken by trowel and it is dashed into the surface and levelled using wooden float.
Usually this type of plaster finish is preferred for external renderings.
SAND FACED PLASTER FINISH
To get sand faced finish two coats of plastering is required. For first coat, 12mm thick layer of cement
sand mortar in 1: 4 ratio is preferred. The first coat should be provided in zigzag lines. And then it is
allowed for curing for 7days. After that 8mm thick layer of second coat with cement and sand in 1:1
ratio is applied. Level the surface using sponge. Finally take some sand and screened it to obtain
uniform grain size. The screened sand is applied on the second coat using skimming float or wooden
float. Finally, sand faced finish with uniform grain size of sand is obtained.

5. PEBBLE DASH PLASTER FINISH
Pebble dash finish requires mortar layer of 12mm thickness with
cement and sand in the ratio of 1: 3. After plastering pebbles of size
10mm to 20mm are dashed on to the plastered surface. Then press
them into the plastered surface using wooden float slowly. After
hardening they provide aesthetic appearance to the structure.
SCRAPPED PLASTER FINISH
To obtain scrapped finish, apply final coat of 6 to 12 mm thickness and allowed it
to dry. After some time using steel blade or plate scrap the plastered layer up to
3mm depth. Scrapped finish is less liable to cracks.
DEPETER PLASTER FINISH
This is also similar to pebble dash finish. But in this case pieces of gravel or flints are used in place
of pebbles.
TEXTURED PLASTER FINISH
Textured finish is obtained from the stucco plastering in which different textures or shapes
are made on the final coat using suitable tools.
EXTERNAL RENDERING OF BUILDINGS
Generally, external face of buildings constructed from concrete or clay blocks are not assumed to be pleasing aesthetically and do
not provide attractive appearances. That is why the external faces are changed and rendered by two or three coats of lime or
cement mixed with natural aggregate and finished textured or smooth. Moreover, rendering improves and increases wall resistant to
penetration of rain fall. Furthermore, external rendering is based on strong bond to the background, utilized mixtures, and surface
finish.

6. SPECIAL PLASTERING MATERIALS FOR DIFFERENT
PURPOSES USED IN BUILDING CONSTRUCTION
Different types of special plastering materials are used in building construction for various purposes to provide aesthetic
appearances to walls, columns and ceilings. Plastering is the formation of smooth / rough durable surface over the rough surfaces
of walls, columns, ceilings etc. The layer or coat is termed as Plaster. Plastering protects the structure from weathering actions,
dust, vermin etc. it also gives beautiful appearance to the structure.
Apart from the common mortar materials like
cement, aggregate, lime etc. some special materials
are available for plastering in building construction
works. These special plastering materials enhance
several properties of plaster such as, durability, fire
resistance, weather resistance, sound proof etc.
1.Asbestos marble plaster
2.Acoustic plaster
3.Granite silicon plaster
4.Gypsum plaster
5.Martin’s cement plaster
6.Barium cement plaster
7.Kenee’s plaster
8.Scagliola plaster
9.Snow Crete and colourcrete cement plaster
10.Sirapite plaster
11.Parian cement plaster
12.Thistle hard wall plaster

7. 1. ASBESTOS MARBLE PLASTER
Asbestos marble plaster provides marble like finish to the plastered surface. It is obtained by adding asbestos, finely powdered
marbles to the cement.
2. ACOUSTIC PLASTER
Acoustics plaster is obtained by adding gypsum to the cement mortar. This is applied in two coats with 6mm thickness of each coat.
Gypsum undergoes chemical reaction and form bubbles in the plaster which absorbs sound. Thus, it is called as acoustics plaster.
Acoustic plastering material is generally used in cinema halls, auditoriums etc.
3. GRANITE SILICON PLASTER
Granite silicon plastering material is made from granite and silicon mix which has high elastic properties. This plaster does
not crack due to the action of weathering. It sets quickly and used for superior works.
4. GYPSUM PLASTER
When the gypsum is heated at 160 to 170oC, plaster of Paris is obtained which hardens quickly when water is added. Generally,
Plaster of Paris with lime combination is used for plastering or repair works. It has many advantages like fire resistance, sound
proof, light weight etc.
5. BARIUM CEMENT PLASTER
Barium cement plaster is obtained by adding barium sulphate to the cement and sand mix. It is used for X-ray room finishing. It
absorbs radiations from X-ray machines without effecting the people.
6. KEENE’S CEMENT PLASTER
Plaster of Paris is calcined with alum to get Keene’s cement plaster. It is white in color and takes few days to set. It provides glass
like finish to the surface.

8. 9. SNOW CRETE AND COLOURCRETE CEMENT PLASTER
Snow Crete means white colored plaster and colourcrete implies colored cement plaster. These special plastering materials are
made by adding different color pigments with cement. These are used for exterior surfaces.
10. SIRAPITE PLASTER
Plaster of Paris is slaked with petroleum to get sirapite plaster. It provides white surface finish after hardening. It also sets quickly
and has good resistance against fire.
11. PARIAN CEMENT PLASTER
When Borax is calcined with plaster of Paris Parian cement plaster is obtained. It is similar to Kenee’s cement plaster but it is
cheaper than that.
12. THISTLE HARDWALL PLASTER
Thistle is nothing but high-grade gypsum. It is quick setting and sound proof. It provides good finishing to the surface and generally
preferred for interior works.
8. MARTIN’S CEMENT PLASTER
When Plaster of Paris and pearl ash are calcined together Martin’s cement plaster is obtained. It also sets quickly and gives white
hard finish after drying.
7. SCAGLIOLA PLASTER
When Kenee’s cement and color pigments are dissolved in glue, the obtained plastering material is called as Scagliola plaster. It
produces marble like finishing. This plastering material is used for column finishes, panel finishes etc.

9. REFERENCES:
 Building Construction : Dr B.C. Punmia
 Civil Engineering Material : Prof. Singh
 Internet Web Sites
 https://en.wikipedia.org/wiki/Sustainable_architecture
 http://www.slideshare.net/Dingus009/sustainable-architecture-ppt
http://www.slideshare.net/deepthi12345/green-buildings
 http://www.greenhomebuilding.com/articles/susarch.htm
 http://www.doiserbia.nb.rs/img/doi/1450-569X/2004/1450-
569X0411091M.pdf