This document summarizes research on controlling construction moisture in cross-laminated timber (CLT) used in tall wood buildings. Small-scale and full-scale CLT samples were exposed to moisture and different protective coatings were tested. Hygrothermal modeling was calibrated and used to project moisture levels over time under different coatings. Coatings like polyurethane and silicone sealers were found to reduce moisture levels compared to uncoated CLT. Left unprotected, CLT can absorb over 25% moisture content which can lead to mold or structural damage over time. Recommendations include protecting CLT from moisture during construction and using moisture management strategies like sealants and non-moisture producing heaters.

1. 1
Controlling Construction Moisture in
CLT in Tall Wood Buildings
CCBST XV
PAPER 15
2017/11/06
ROBERT LEPAGE, M.A.SC, P.ENG.

2. 2
 Intro and Concerns
 Experimental Set-up
 Experimental Results
 WUFI Calibration
 WUFI Projections
 Recommendations
Outline

3. 3
Risks and Challenges with Mass Timber Building

4. 4
Structural System

5. 5
Research Prior to Tall Wood & Key Lessons to Date
 Uncoated CLT panels should not be
exposed to rain during construction for
more than a few weeks
 When exposed to rain, CLT will quickly
wet up through end grain, and gaps
between boards of panels
 CLT can also dry quickly under
favourable conditions
 Prolonged cyclical wetting & drying can
cause structural damage to CLT
 North American and European CLT
behave differently. Both require
protection

6. 6
Concerns
 How to protect mass timber during rain
 Giant tarps?
 Temporary roof lifted by crane?
 Waterproof the floors?
 Enclose as fast a possible?
 Can enclosure keep up with pace of
structure erection?
 How long can mass timber get wet for?
Do we need to protect it?
 How do we enclose the walls quickly
and not be affected by inclement
weather?
 How could a flood in-service affect the
wood-structure?

7. 7
Experimental Protocols
 Phase 1 –Sample Testing
 (1) 400x400mm small sections
 (2) 1.2x4.5m floor mock-up
 Phase 2 – Hygrothermal Calibration
 Calibrate to (1) & (2)
 Phase 3 – Fungal Contamination
 VTT Improved Model to Predict
Mold Growth (Viitanen, 2007)
 Dose-Response Relationship for
Fungal decay (Brischke and Rapp,
2008)

8. 8
Phase 1 (1) – Small Scale Testing
Wood preservative Polyurethane primer
Silicone wood coating Porous substrate primer
Urethane resin wood sealer No coating (baseline)
Impermeable self-adhered
membrane (SAM)
No coating / no screed topping
(Baseline)
Acrylic latex primer
 9 different CLT samples with
different treatments
 Instrumented with MC pins

9. 9
Phase 1 – 1 Results
0
2
4
6
8
10
12
14
16
18
0
5
10
15
20
25
30
35
40
45
Jan 20 Feb 20 Mar 20 Apr 20 May 20
HourlyRainfall(mm)
WoodMoistureContent(%)
SILICONE TOP PLY MC POLYURETHANE TOP PLY MC ACRYLIC TOP PLY MC
POROUS TOP PLY MC URETHANE TOP PLY MC NO COAT TOP PLY MC
Hourly Rainfall (mm)

10. 10
Dye Testing

11. 11
Phase 1 (2) – Floor Mock-up Testing
 1.2x4.5m CLT floor mock-up
 Treatments installed in grid
 Each grid instrumented with
MC pins in centre and edge

12. 12
Phase 1 – 2 Results
0
5
10
15
20
25
30
35
40
45
Dec 17 Dec 25 Jan 02 Jan 10 Jan 18 Jan 26 Feb 03 Feb 11 Feb 19
WoodMoistureContent(%)
PRESERVATIVE TOP PLY CENTRE MC SILICONE TOP PLY CENTRE MC
URETHANE TOP PLY CENTRE MC ACRYLIC TOP PLY CENTRE MC
POLYURETHANE TOP PLY CENTRE MC POROUS TOP PLY CENTRE MC
SAM TOP PLY CENTRE MC NO COAT TOP PLY EDGE MC
NO SCREED TOP PLY CENTRE MC
TOP COAT EDGE COAT SCREED PLACED
PRE-SCREED WETTING
0
5
10
15
20
25
30
35
40
45
Dec 31 Jan 31 Feb 29 Mar 31 Apr 30 May 31 Jun 30 Jul 31 Aug 31
WoodMoistureContent(%)
PRESERVATIVE TOP PLY CENTRE MC SILICONE TOP PLY CENTRE MC
URETHANE TOP PLY CENTRE MC ACRYLIC TOP PLY CENTRE MC
POLYURETHANE TOP PLY CENTRE MC POROUS TOP PLY CENTRE MC
SAM TOP PLY CENTRE MC NO COAT TOP PLY EDGE MC
NO SCREED TOP PLY CENTRE MC
SCREED PLACED WETTING TEST

13. 13
Key Findings
 Exposed CLT can experience MC >25%
 Screed to uncoated CLT panels increases
the surface moisture content by 5-10%.
 Specific coatings can reduce this, others
have no benefit
 Wetted CLT at greater risk
 CLT with screed still at risk of
precipitation

14. 14
Hygrothermal Analysis
 Calibrate to untreated samples (Phase 1 – 1)
 Calibrate treated samples (Phase 1 – 1)
 Vapour permeable hydrophobic sealer (i.e. silicone),
 Low-permeable hydrophilic sealer (i.e. urethane)
 Impermeable, waterproof membrane (i.e. self-adhered membrane,
SAM)
 Calibrate with screed, with different treatments

15. 15
Hygrothermal Calibration
10
12
14
16
18
20
22
24
26
28
30
Jan 07 Jan 14 Jan 21 Jan 28 Feb 04 Feb 11 Feb 18
WoodMoistureContent(%)
Top Ply Centre 2nd Ply Edge Mid Ply Centre Bottom Ply Centre
SCREED PLACED
Measured Simulated
10
12
14
16
18
20
22
24
26
28
30
Jan 07 Jan 14 Jan 21 Jan 28 Feb 04 Feb 11 Feb 18
WoodMoistureContent(%)
Top Ply Centre 2nd Ply Mid Ply Centre Bottom Ply Centre
Measured Simulated
SCREED PLACED
10
12
14
16
18
20
22
24
26
28
30
Jan 07 Jan 14 Jan 21 Jan 28 Feb 04 Feb 11 Feb 18
WoodMoistureContent(%)
Top Ply Centre 2nd Ply Centre Mid Ply Centre Bottom Ply Centre
SCREED PLACED
Measured Simulated

16. 16
Projections – 15% MC
0
5
10
15
20
25
30
Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
WoodMoistureContent
SURFACE TOP 2nd PLY MID BOTTOM
NO COAT
0
5
10
15
20
25
30
Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
WoodMC(%)
SURFACE TOP 2nd PLY MID BOTTOM
POLYURETHANE
0
5
10
15
20
25
30
Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
WoodMoistureContent(%)
SURFACE TOP 2nd PLY MID BOTTOM
SILICONE

17. 17
Projections – 25% MC
0
5
10
15
20
25
30
Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
Title
SURFACE TOP 2nd PLY MID BOTTOM
NO COAT
0
5
10
15
20
25
30
Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
WoodMC(%)
SURFACE TOP 2nd PLY MID BOTTOM
POLYURETHANE
0
5
10
15
20
25
30
Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
Title
SURFACE TOP 2nd PLY MID BOTTOM
SILICONE
0
5
10
15
20
25
30
Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun
WoodMC(%)
SURFACE TOP 2nd PLY MID BOTTOM
SAM

18. 18
Fungal Predictions
 Rule of Thumb
 Less than 80% Okay!
 More Refined:
 Mould: VTT Model (Viitanen, 2010)
 Decay: Dose-Response (Brsichke, 2008)
Index Growth Rate Description
0 No growth Spores not activated
1 Small amounts of mold on surface
(microscopic)
Initial stages of growth
2 <10% coverage of mold on surface
(microscopic)
–
3 10%-30% coverage (visual) New spores produced
4 30%-70% coverage (visual) Moderate growth
5 >70% coverage (visual) Plenty of growth
6 Very heavy and tight growth. Coverage around 100%
Decay Rating Rating of Decay Dose Units
0 Sound-no decay 0-150
1 Slight decay 150-500
2 Moderate decay 250-600
3 Severe decay 350-800
4 Very severe decay
(stake fails during mechanical bending)
500+

19. 19
 Dose-Response
 Decay and rot
 Reduction in structural
capacity
 Dose-response in field
experiments
Fungal Models
 VTT Mould Growth
 Surface mould
 Aesthetic and health effects
 Laboratory regressions

20. 20
Fungal Assessment Results
0
1
2
3
4
5
6
20
22
24
26
28
30
32
34
36
Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May
MouldIndex
MoistureContent(%)
Uncoated Polyurethane Primer
Silicone Sealer Self-Adhering Membrane
0
2
4
6
8
10
12
14
16
20
22
24
26
28
30
32
34
36
Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May
DecayDose
MoistureContent(%)
Uncoated Polyurethane Primer
Silicone Sealer Self-Adhering Membrane

21. 21
Recommendations
 Protect the CLT from external moisture during transport and
handling
 Use active moisture management.
 Passive moisture management strategies are insufficient (e.g.
sealing surface). Moisture will find joints/cracks/checks
 Consider using preservatives for non-CLT elements.
 Install the screed topping on dry CLT panels
 Use non-moisture producing heaters (e.g. electric)
 Ventilate screed after placement to promote drying.

22. 22
Discussion + Questions
FOR FURTHER INFORMATION PLEASE VISIT
 www.rdh.com
 www.buildingsciencelabs.com
OR CONTACT US AT
 RLEPAGE@rdh.com
RLEPAGE@RDH.COM