On Jan 30, 6:42 pm, "Arthur" wrote:

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.