I've got to renovate a house and the garage wall shows signs of humidity coming through the brickwork. It had been painted with appears to be acrylic.
I'd like to seal the brickwork so the humidity doesnt come through the fresh coat of paint I will apply afterwards.
The humidity will be able to escape from the other side of the wall.
Any idea what the best sealant/waterproofer would be given it's been painted already?
Welcome to the Bunnings Workshop community @PhilB. It's great to have you join us and many thanks for your question.
From my experience dealing with waterproofing membranes, they need to be applied to the exterior side of the wall. This stops the moisture entering the wall in the first place. Some types can be applied to the interior side, however, the moisture will constantly be trying to push them off the wall. They also need to be applied to the brick substrate and not a painted coating.
What is causing the issue? Is it damp soil piled up against the wall? No damp coarse layer in the brick wall? Any idea where this humidity is coming from? I'd hazard a guess that there is something more than the humidity in the air causing this moisture to migrate through the wall. I'd be interested to hear what's going on behind the wall. Some photos would also be of assistance if that was possible.
@PhilBMitchell has given you a couple of good tips. Before doing any sealing you need to carefully inspect the outer face of the Garage wall. Moisture penetration is often due to leakage through the mortar joints.. (missing mortar, mortar shrinkage or cracks). Repointing the damaged joints with fresh mortar needs to be done before any sealing is attempted.
There are waterproofing treatments you can apply to external walls that soak in to the bricks and mortar making them less porous. As the outer wall was previously painted I expect it will be largely ineffective. Instead, I suggest removing any loose and flaking paint and (following mortar repairs) giving it 2-3 coats of good quality exterior paint.
Update: I just came across this article which contains lots of good info. Hope this helps!
Hi all, thanks a lot for the replies.
The outer wall was in contact with damp soil with very poor drainage, thus the humidity in the wall. I have since taken the soil away from the wall and built a retaining wall about 2m away from the wall. So, there is now no soil against it and plenty of air flow. But the humidity that accumulated inside the brickwork is showing up on the inner side. I want to seal that side so the humidity can escape from the outer side and not leave stains on the inner side. I think 2-3 coats of outdoor paint may not be enough and was after a sealant/membrane of some sort.
Thanks for your help!
Just to clarify, the inside wall is painted and you want to put a sealant/water-proofing coating on that paint and then paint over the top?
After speaking to several of our water-proofing coating suppliers, non of their products are suitable for going over a painted surface. The best advice I could suggest would be to wait for the wall to completely dry out, apply Rust-Oleum B-I-N Primer Sealer Stain Killer and then apply a topcoat. This product is designed to stop staining penetrating through your paint layer.