Exterior breathable paint on top of old non breathable? Front of victorian house

[jen18]

Hi all,
This is probably a stupid question but is there any point in using breathable exterior paint when painting over the existing paint( which was probably cheap) on a victorian house? I don't have any damp on the wall but it is a cheap victorian with a single skinned front wall. Many thanks guys

 

[Cubist]

Hi There,

Frankly put, no! A breathable paint over a none breathable earlier paint will contribute nothing by way of benefit to the house. To do that you would need to strip off the old paint back to the brick surface. Its possible too that moisture penetrating the new breathable paint may become trapped and cause the new paint to fail.

 

[Toby Newell]

Lol. And no.

Wrap yourself in clingfilm then pop on a Goretex gillet.

Still quite clammy.

 

[jamest]

I must confess to committing a sin of the sort you're wondering about. I painted over existing layer(s) of standard (i.e, plastic) masonry paint with a breathable paint (specifically, some stuff from Earles). The thing was that the original paint was/is strongly adhered to the brick surfaces and extremely difficult to remove. However, it was blowing off the mortar beds and in many places moss was growing under it. It was very easy to remove from the beds (which are mostly lime) and I scraped it all off, repointed (in lime) where needed and then painted over the whole thing with the Earles paint as per their instructions so as to get a uniform finish. No moss or paint loss problems since. Obviously, I couldn't possibly recommend this approach, but since there was little to no paint flaking/blowing off from the brick surfaces (where it was strongly adhered), I figured that moisture was evaporating (or trying to) almost entirely from the mortar beds, so doing what I did could improve things significantly. It seems to have worked, so far anyway. Under other circumstances, I would not have taken this approach!

 

[Toby Newell]

There is nothing technically wrong with applying a microporous coating over a non breathable coating if it is compatible and you obtain good adhesion, it's just that you will not be getting any specific benefit from the breathable top coat.

 

[88v8]

I figured that moisture was evaporating (or trying to) almost entirely from the mortar beds, so doing what I did could improve things significantly. It seems to have worked, so far anyway. Under other circumstances, I would not have taken this approach!

A good illustration of the fact that a stone or brick wall breathes through its joints.