DIY Doctor

Breathable Masonry Primer for Exterior Walls

Postby saki » Wed Feb 20, 2019 12:34 pm

Going round in circles on this one but unable to find a clear answer so apologies if I have missed previous posts.

I want to paint an external fyfestone wall for decorative reasons. No problems with damp. I have read the DIY project on this site which recommends using a primer first before applying masonry paint. It emphasizes that both must be breathable but doesn't give an example just suggests asking local supplier. LOL. Not round here - they have not got a clue.

Could someone recommend a suitable primer. Thanks.
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Postby thedoctor » Thu Feb 21, 2019 9:46 am

Hi

Many thanks for noticing that we have not stated a suitable priming product, we have now updated the project page with info: https://www.diydoctor.org.uk/projects/e ... inting.htm

Just to confirm, if the surface you are painting on to is dusty, chalky, flakey or powdery then you should use a stabilising solution such as the Everbuild 406 stabilising solution mentioned in the project, but if they are otherwise solid and sound, then you should be fine.

If the walls are standard rendered or stonework walls then a stabilising solution is not the best primer choice. You should instead use a watered down coat of masonry paint (if the paint is water based, if not consult with etc manufacturer as to what you should use to thin it down).

If however the property is old and has no cavity wall, only a solid wall (or single skin) then you will need to ensure that its breathable (so that trapped moisture can escape), so a lime-based render should be used.

Hope this helps

Kind Regards
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Postby saki » Thu Feb 21, 2019 11:47 am

Thanks for that. The surface is fine and it is a cavity wall and paint is water based so will go with a dilution of that as first coat.
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Postby Dr. Strange » Thu Apr 04, 2019 8:08 am

We had a masonry retaining wall built around our patio and the finish isn't what we expected. We elected masonry over other materials because we thought it would complement the concrete foundation of our house better than brick or stone.

The wall is made of 12" concrete filled block with a two coat parge finish on both sides. It was installed about 3 months ago and the finish is still very blotchy and wet looking in areas. It never seems to dry out. There are white swirls from the troweling. In some spots you can see the blocks telescoping through. I was told it would "dry out" to a uniform gray. I don't mind waiting, but I don't want to wait too long and find out that's not the case. It looks fine when it's soaking wet.

We think the contractor did a good job. If we have to paint it we will, but we thought it would look a lot better.

Has anyone had experience with parge finishes like this?
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