salt walls

[poppie]

problem with the spanish paint work again is it possible for salt to be in the walls and causing the paint to react because pva has been used

[brachiopod]

The leaching out of salts (a chemical term - it does not just mean sodium chloride as in table salt) is common - especially in new plaster and brickwork. As the plaster or mortar dries and water evaporates, soluble salts are drawn out to the surface and appear as anything from a dusty bloom to a patches of white powder or crystals - known as effluorescence.
This is largely why it is recommended that newly plastered walls are left for around 3-6 months before decorating.
Although not 100% effective, the use of diluted PVA on bare plaster helps to seal the surface before painting - assuming you have left sufficient time for the plaster to properly dry out. (It also reduces the rate at which the paint is absorbed - meaning your tin will go further!) So using PVA in itself won't be the cause of the problem.

If, however, you have a damp problem - water will be continually drawn through the brickwork / plaster in a wick effect (capillary action) causing continuous effluorescence, and making your paint blister and peel. No amount of PVA will stop this until you address the root cause.

There's a regular here on AB who should be able to give you a better answer. So if buildersmate sees this, hopefully he can you offer some advice. Good luck !

[buildersmate]

After such an intro, I can hardly decline! However I'm not sure that I can add much to what's been said. The above explanation is spot on and leaching of salts is an effect, not a root cause. Having followed the thread back to its source (old stone walls, problem occurs close to the ground, no DPC in Spain) I reckon the comments to date are also good practice. Ideally you have to treat the root cause, which means creating an impervious layer that water can't penetrate but I appreciate that this isn't likely to be possible. There are damp-proofing liquids that can be coated on the inside (stronger than PVA) but these are really only a temporary solution. Eventually the water will find a way through. You can probably seal it with something like this product, but I suspect that paint won't stick to it. http://www.ruberoid.co.uk/index.php?page=83

Sorry I can't help further.