Sandtex woes

kitty08

We have recently repainted our house using Sandtex masonry paint. The house is rendered, and was previously painted using Sandtex, and was in good sound condition. It's all fine, except a small area of wall, about 30 cm by 15 cm where the paint refuses to stay on. For the first attempt, there was over a week of warm dry weather before it rained, which was when the problem started. I noticed this area was covered in tiny bubbles, each no more than about 1 mm, and when I gently prodded it, it was clear the paint had let go.
To try and fix it, I scraped off all the loose paint, washed and wiped away any debris and left it to dry overnight. The following day was dry and around 21C. I waited until the wall was in the shade before repainting the patch, as I had read that it's not good to paint with the sun on the wall. This time there were 7 days before it rained, and the temperature did not drop below 10C. Once again the same thing happened.
So ... yesterday I scraped all the loose paint off yet again and repeated the process. This time the tiny bubbles appeared as I was painting, even though I was using a brand new brush. I just brushed it out as well as I could and good for the best. I left it over night and checked again this morning, and sure enough, the paint was once again loose. It doesn't look "right" and even a finger nail is enough to move it.
How can I get the paint to stay on? I can't believe that a week wasn't long enough for it to dry, especially as the temperature remained above 10C. The instructions said between 3 - 5 hours drying time. There's nothing obviously wrong or different about this small area of wall, a that would cause problems with paint. I also forgot to mention that the paint was new, not something that had been lying around in the garage.

I have thought of two possible things I could do to solve this, and would value people's opinions as to whether either or both would help:

(1) Apply a stabiliser to this patch before trying to paint again - Sandtex do one which is supposed to be "quick drying" and suitable for use under Sandtex masonry paint.

(2) mixing some PVA with the Sandtex and painting that on - I have seen this tip online, but I'm a bit confused as I thought PVA was children's glue and water soluble? Also I'm unsure of the proportions to use?

Please does anyone have any ideas how to solve this problem, as I've really had enough of scraping and repainting!

Lorian

Is it the smooth version or the version with Sand?

Stirring it properly? IE electric stir for several minutes?

But given its just one patch, I'd anticipate the wall being damp from the inside.

Can you post a photo?

I have to declare I'm not a great fan of sandtex, having had to previously repair someone else's walls that their builders had put this on.

Also are you still seeing the old paint on this patch, or are you down to the render?

No sign of green algae anywhere near the patch?

[Deleted User]

Hi,


oh well after all your attempts you might as try PVA,


PVA is a multi-purpose agent, primer sealer, cement filler and plaster admixture that adheres to most common building and DIY materials except PVC and rubber. Ideal for priming unsound surfaces prior to plastering or painting, as an adhesive on wood, cork, textiles and most applications where at least one surface is porous, for general dust sealing on flaking paintwork/walls etc. and as a cement admixture.





Just an example, other brands are available, you should be able to get a small bottle in your local diy.


You should get a small bottle in your local diy store.

Lorian

If it's damp PVA wont help.

kitty08

Thank you for your replies. I'll try and get a photo when it stops raining. It's the smooth version of Sandtex, being applied over the smooth version of Sandtex. I did stir it, but just manually, so not sure if this could be the problem?
The strange thing is that although the new paint won't stick and is peeling off, the old paint surface underneath is completely sound. There's no sign of any algae or anything else growing, and no sign of any damp indoors.