Using Thompson's Water Seal

[Arthur]

Instructions say, 'apply when surface is dry only' Do they mean bone dry? It hasn't rained for 3 days here and the hollow blovk wall is still damp in places?

Thnaks.

Arhtur

[The Natural Philosopher]

They do mean bone dry. The point is that the stuff sits in the pores where the water gets in. If its in already then then it can't get out, and the stiff can't get in

Wait till summer.

[Merryterry]

If the wall is even slightly damp dont apply it. The material is meant to be sucked into the pores of the substrate. It cannot be sucked in if the pores are full of water.

[John]

Yes, if it's even slightly damp, don't do it. And if you haven't already bought the Thompsons stuff, I'd personally go for Liquid Plastics K501 - once described by a builder friend of mine as Thompsons Waterseal on steroids :o)

[Aidan]

Using Thompson's Water Seal

But, more to the point, why would you want to?

Brick walls are porous and airborne water vapour migrates through the walls in winter, evaporating from/through the outside surface in dry weather. If you seal the outside face, it condenses (interstitial condensation) and can cause huge problems with damp and frost damage to the brick faces.

It's similar to putting on a waterproof jacket. OK in wet weather, you get less soaked. In dry weather you get soaked by water vapour from sweat that would otherwise evaporate harmlessly & unnoticeably.

Those plastic coating paint systems can cause the same problems. You'll never have to paint the walls again!!!! (You may have to rebuild them, though).

Brick walls had been around for a long time before Thompson's water seal and their chavvy builder geezer adverts.

[Stuart Noble]

But 100 year old brick walls are excessively porous, allowing more than just vapour to pass through them