A waterproofing system can look perfect from the outside and still be failing underneath.
One of the biggest hidden risks is trapped moisture.
Moisture may already be present within the substrate, insulation or existing roof build-up before the new waterproofing system is installed.
It can come from:
- A damp concrete substrate
- Rain during installation
- Wet or damaged insulation
- Residual moisture in screeds
- Condensation within the build-up
- An existing leak that was never fully investigated
Once the new membrane or liquid waterproofing system is installed, that moisture may have nowhere to escape.
As temperatures rise, trapped moisture can turn into vapour and create pressure beneath the waterproofing layer.
The defect appears above. The cause may sit much deeper.
The result can be:
- Blistering
- Delamination
- Loss of adhesion
- Corrosion of metal components
- Deterioration of timber or insulation
- Reduced thermal performance
- Premature system failure
The visible defect may appear on the surface, but the real cause can be hidden much deeper within the roof build-up.
This is why moisture assessment should happen before the waterproofing system is selected and installed.
Before work begins, we should ask:
- Is the substrate dry enough?
- Has moisture testing been carried out?
- Is the existing insulation wet?
- Where is the moisture coming from?
- Can the build-up dry safely?
- Is a vapour control layer required?
- Is the proposed system suitable for the existing conditions?
Applying a new membrane over a wet build-up does not remove the moisture.
It may simply seal the problem inside.
Trapped moisture does not always remain hidden.
Eventually, it can destroy the waterproofing system from inside.