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It sounds like it might be efflorescence.

Efflorescence is ugly white stains on masonry, brick and stone, and is the result of water getting in and pulling the water-soluble salt out. Masonry needs masonry sealers to stop efflorescence. The dirt around your retaining walls needs to be treated as well.

The first thing to realize is that these mineral deposits are just an aesthetic problem. They do not compromise the structural integrity of any of the masonry in and about your home.

These trapped salts are set into motion when water enters masonry. The water dissolves the salts and carries them through the masonry towards the surface. Sunlight and wind draw the water to the surface but as the water evaporates, the salts are left behind.

The salts contained in the brick, mortar, stone, concrete block eventually exhaust themselves and the white mineral deposits simply go away. But salts within soil can persist for decades. Each time you try to wash wall surfaces to remove the salts, you actually compound the problem. The water you use simply soaks into the masonry surfaces and dissolves the salts to create more problems days later. The surfaces typically look fantastic when wet, but the white powder appears again when the surfaces dry.

Hope this helps.

great scott has it right..... but also in older buildings leaving it alone is not an option because the walls are drawing damp from the ground continuously... and in general it will never go away.....

the first thing in a long term solution to try and alleviate if not eliminate is to make sure no outside surface is above the floor level internally....

then what you will find in general in these cases is that there have been cement based products to render the wall either internal/external or both...these will allow the water from the ground to rise through the walls and when they reach a certain level escape thru...thus giving you what great scott describes....

the next step is to remove all these cement renders and re do the walls using lime based products....this allows the natural breathing of the wall to take place.... in the case of the house having an earth bank...half way up the wall...quite common here where houses are often set into hills...the earth has to be dug out and either a holding wall put in to retain the earth away from the house...with drainage to take ground water away or you just have to keep repainting.....

its difficult... you could try in the first instance only doing one side of the wall with the lime based renders... say the internal side...because eventually if you knock the wall where the stains are you will start to hear a sort of hollow sound...this is where the water has broken the seal between plaster and stone/brickwork and eventually it will fall off ... try tapping different parts of the wall to see if there are differences in sound...

...but greatscott says.... your wall will not fall down ...its generally the appearance of a deeper problem.... am presuming you have an older property...and all building materails will have dispersed these salts long ago..... if its a new building ...get the builder in to fix the problem....

.... remember most house here were never intended to have human occupancy in the ground floors and the interanl walls were often not rendered at that level...this provided a sort of damp cours.... now people come along and want to inhabit or improve hence ...the problems

Glad we are not the only ones, buying an older property we have a single wall that has this problem, we are hoping that draining a very scary well will certainly help (and stop me having nightmares about the floor collapsing)! :mad:

... if you have the space a quick way of hiding nor solving the problem is to build an interior wall with a gap between the damp wall and the new wall.... if you use those light blocks...hey look a bit like cement blocks but are very light and are stuck together with a special cement... also come in different thickness ...so the thinest can be used for a jb like this... a decent bricklayer will put something up like this in less than half a day ...come back the next day and render it off.... make sure you put in a protective membrane to stop the damp rising.. other alternative line the wall with plaster boars .... dont use wooden battening use specific metal railing...leave a small gap at the bottom so the damp doesnt enter the board....

the well in general will not have an effect...i would say never fill in a well under a house ...the fillings will act like a syphon drawing the water up.... cap it yes.... but even then it might be necessary to have some sort of breather on it.... a bit like shutting off an old chimney....and leaving an airvent.... however if a geometra/geologist has told you its ok they will know best....

[QUOTE=greatscott]Masonry needs masonry sealers to stop efflorescence. [/QUOTE]

First off - Greatscott and John, thank you so much for your knowledge. I am now armed with so much more than just optimism and a scraper.

I am familiar with masonry/plaster sealers in the UK. Does anyone know what the right phrase for these in ½ûÂþÌìÌà might be?

Otherwise I can see another entertaining, yet fruitless, game of charades developing with my very nice local hardware store owner!

Thanks again

Mike

idrorepellant...or fixative... you can generally find them near the paint counter ...have checked and i have about five different ones from five different stores.... it will work higher up in an old building ....more as a selant and to allow paint to hold better... but if its an older building and its rising damp...it will be another waste of money im afraid....though it is cheap enough.... so it can never hurt to try