Effect of Moisture & Temperature on the bonding of Adhesives & Sealants

3 Main Types of Curing Systems

Curing System	Types of Products
Moisture Cure (or Condensation Cure)	MS Polymers Polyurethanes Silicones
Moisture Loss	PVA’s Acrylic Wallboard Adhesives Acrylic Gap Fillers
Solvent Loss	Synthetic Rubber/Resins

Clause E2 External Moisture E2/AS1 at time of completion

NZBC	%	Lining System Suppliers	%
For timber framing at the time of installing interior linings	20%	GIB Aqualine Wet Area Systems	18%
For timber weatherboards and exterior joinery at the time of installation	18% or less	Kopine Ultralock	18%
For reconstituted wood products	18%	Seratone	18%
H1.1 and H1.2 treated framing	20% max	HardiGlaze	18%
Kiln-dried untreated timber	18% max	Hydrapanel	18%
		Window Sill Tapes (Traditional)	12-14%

What is “ Wet vs. Damp”?

Wet	Damp
Means you can even strain water from the item/object. ie: if you can ring water from a hat it is wet	Means that you can smell the presence of water in the object. ie: if the hat feels “clammy” it is likely to be damp.

What does this mean?

Too much moisture	Too little moisture
The GRAB not being made to the substrate	The bond does not set, as not enough of a curing reaction has taken place

What does this mean?

Too much moisture	Too little moisture
Possible diluted strength at the adhesive bond line between the substrate and the adhesive/sealant.	Generally not a bad thing as moisture is absorbed into the substrate/air.

What does this mean?

Too much moisture

Too little moisture

The GRAB not being made to the substrate

The adhesive may skin before adhesion takes place

Not such a bad thing

More solvent is absorbed back into the timber initially

In discussing curing rates and ambient temperature the process is logarithmic NOT linier
Therefore: The rate at which curing takes place could very well be MUCH longer than your would normally expect

Not only is the ambient air temperature important, BUT
You also need to manage both the substrate (substrate surface & substrate internal) temperature.
Many adhesives and sealants require a minimum substrate surface temperature of not less than 5˚C (also depending on local conditions, you can get “micro-frosts” which will prevent bonding at lower temperatures).

What does this mean?

At low temperatures

The adhesive takes much longer to set, or does not set at all. Where items have been clamped they may come apart once the clamps have been removed
More chance of dirt sticking to sealant joints as it doesn’t skin off
The bond does not set, as not enough of a curing reaction has taken place

What does this mean?

At low temperatures

The adhesive takes much longer to set, or does not set at all, until temperatures increase

What does this mean?

At low temperatures

The GRAB not being made to the substrate
The adhesive may skin before adhesion takes place
If ambient temperature increases but the substrate temperature does not then there is a possibility of the adhesive skinning before a full bond is created

Effected by changing temperatures

Published curing/skinning times change with variances in temperature & moisture.
Curing is logarithmic over time.
While curing/skinning times are given based on 20°C, 65%R.H., the reality is that in a 24 hour period temperatures constantly change, which can result in apparent longer cure times.
As temperatures approach 10°C and go below this, the curing process goes into a state of stasis (hibernation). As temperatures increase, so the curing process continues.

Moisture & temperature

Temperature & moisture can effect the bonding of many window/sill tapes.
When sealing against timber, you should always consider the moisture content of the timber and the temperature at the surface of the substrate
Sealing against the building wrap and or the window sill tapes can be impaired
Plastizor Migration changes, especially in warm conditions
Good practice (in residential fitting) is to seal directly between the “scriber” and the exterior cladding where possibly with a MS based polymer, to create a seal.
In cold conditions do not trim back PU based expanding foam before it is fully cured
When sealing against timber, you should always consider the moisture content of the timber and the temperature at the surface of the substrate

Both moisture in the substrate and temperature have a big impact on the success of bonding systems
Curing rates are logarithmic when taking into account against moisture and temperature
The success of the use of adhesive and sealants to get the best out of them requires awareness and planning
An increase in the use of adhesive and sealant bonding systems are coming to a construction site near you

Want to save this guide? Download the PDF version here