What is it?
This is an issue known as “Osmotic Blistering”, often identified by pockets of swelling in the coat of resin paint.
this can occur in an epoxy coating due to moisture, either from rising damp or moisture contamination.
Common Causes:
Lack of preparation - A poorly prepared concrete surface is the main cause of epoxy blistering, the number one problem associated with this is a bad surface profile. Surface profile is the roughness and porosity of the substrate that allows for a mechanical bond of the epoxy. With all coatings, we would recommend ensuring a Damp Proof Membrane is installed. If you do not have one, you run the risk of rising damp.
Moisture - Osmotic blistering occurs after the coating has cured, water is pushed up through the substrate but cannot pass through the coating as pressure builds up forming fluid filled blisters.
So, how would I resolve this?
- It is recommended that you to sand the coating back, ensuring all blisters are popped to release any water/moisture and rectifying the underlying cause of the damp before recoating.
- Applying a damp tolerant primer where there is any residual moisture present is then recommended, the primer will form a bonded layer with the substrate prior to applying the topcoat.
- If there is excessive moisture rising from the surface, you may have to consider applying a damp proof membrane, which is a physical sheeting to prevent moisture.
- Once the damp-proof membrane is installed and the primer has cured, you will be able to apply the new topcoat.