Paint bubbling on exterior retaining wall. What can be done?

[andyfr]

Hi

We have a blockwork retaining wall which was smooth rendered then left for a year before painting with Sandtex smooth masonry paint. This was done last summer but a few weeks ago I noticed that it is bubbling in places, so I will be removing the bubbling paint before repainting. Is there anything I can do to prevent this happening again?

Thanks in advance for any advice.

 

[wwwebber]

Did you paint it with a watered down coat first ? if not you should. The last time I used exterior paint (Dulux Weathershield) this is what it suggested for new / unpainted surfaces.

Plus, this should really be in the painting and decorating section.

 

[andyfr]

Thanks for your reply.

No I didn't water it down. I will try that.

I wasn't sure if that was just for interior painting. Do you know if it's possible to get a thread moved?

 

[andyfr]

Hi

We have a blockwork retaining wall which was smooth rendered then left for a year before painting with Sandtex smooth masonry paint. This was done last summer but a few weeks ago I noticed that it is bubbling in places, so I will be removing the bubbling paint before repainting. Is there anything I can do to prevent this happening again?

Thanks in advance for any advice.

 

[JohnD]

puncture the bubbles. Are they full of water?

 

[andyfr]

No they are just lifting off the wall. Some are bigger than others.

 

[23vc]

Scrape off bubbles, allow to dry properly, repaint bare areas including mist coat (ie watered down). Issue you’ll have is you’ll still see the edges where the paint thickness is different where the patches were. Being render you can’t sand them away.

 

[andyfr]

Thanks for your reply. I will do that. Would there be any advantage in using PVA diluted to help adhesion?

 

[JohnD]

Absolutely not.

PVA is water soluble, so when it gets damp or wet, it will turn to slime and fall off.

 

[andyfr]

Okay, thank for that. Really appreciate all the advice. Will be getting the scraper out!

Cheers

 

[andyfr]

I am reviving my thread as an update to what has happened and hopefully find a resolution to the situation.

After the helpful advice I scraped off all the loose paint, gave it a good scrub with a hard brush and went over it with a softer brush to remove any dust. I did a mist coat then waited for it to fully dry before going over it with a top coat, this was fine until 2019 winter when it started to bubble again.

In spring 2020 I scraped off all the bubbled and flaked Sandtex and this time I used a water based white masonry primer & undercoat before two coats of Sandtex. It looked fine for several months until late autumn and winter when it has started to completely flake off. I will try to post some photos to show the extent of the problem.

I’m not hopeful that anything can be done as it’s obviously the fact that the concrete blocks and render are allowing the water to penetrate the retaining wall and then get behind the paint, but I would be grateful for any suggestions.

 

[freddiemercurystwin]

If the retaining wall has been I'll thought out it will just permanently allow moisture to seep through and will fail with respect to this time and time again.

 

[andyfr]

I thought that may be the case.