Masonry Paint Problem

[RealPolitik]

I've just painted a brick outhouse with B&Q white masonry paint.

The outhouse hadn't been painted for about twenty years and was about half bare brick. I removed all the loose old paint with a stiff broom and have given it two decent coats of the masonry paint a day apart.

In some areas the new paint has already cracked and come unstuck to reveal the old paint and brick underneath - it looks almost like a crackle-finish paint which has crackled too much.

Any ideas as to what the problem is? Could algae or fungal growth be to blame? There was a hint of some sort of light orange-brown dusting on some of the old paint.

 

[Robbie uk]

Outhouses years ago were coated with Lime wash to deter against the amonia smell. This could have reacted with the emulsion. Might have been an idea to thoroughly scrape the walls and apply a coat of stabilsing solution to fasten back the powdery surface.

 

[ifatfirst]

Think Robbie is spot on. I repointed some of this outhouse but some still had the lime mortar. Only parts of the paint bubbled up - took a few years, but it's exactly over the old mortar joints.

I put stabiliser on all the exposed parts and then did a few coats of Wickes masonry paint. No problems since.

Untitled

• ifatfirst
• 6 Mar 2009
• 1

Untitled

• ifatfirst
• 6 Mar 2009
• 1

 

[RealPolitik]

Thanks - it's splitting on the brick, not the mortar. I'll try to get a picture.

I imagine I'll be doing it all over again with fungicide and stabiliser ...

 

[ifatfirst]

This outhouse had never had lime wash, only lime mortar. Yes, now your remind me. I had part where there were some strange fungus type growths, and bubbling, blistering all over the brick but not on the wall shown. Possibly where the lime had sort of dribbled out of the mortar. I scraped them off and put neat bleach all over the affected place (can't remember if I rinsed it off - probably not), left to dry, did it again, left to dry. Then I put the stabiliser on before the paint. Fine now.

Sorry to say, but think you will have to start again!

 

[Driff]

Using B&Q what do you expect?

 

[RealPolitik]

Using B&Q what do you expect?

Well, I expected it to work - it is, after all, thick white paint and not magic dust.

 

[Robbie uk]

To be fair i tend not to use own brand masonry paint because it usually doesnt cover very well. The lower price usually means some of the more expensive ingredients are missing.

 

[RealPolitik]

Quite possibly - it looks even worse today. I'l leave it a week and start again.