Strange growth on external walls

Today I noticed a lot of what looks like white, fibrous growth on some of my external walls. It seems to have appeared after the recent wet weather. It looks a bit like cotton wool strands, and crumbles to powder when disturbed.

I'm not overly concerned as it appears to be easy to remove(at least superficially), it is not rooted in the mortar.


I'm more curious as to what it is, and is it a problem, i.e health hazard. I'm guessing it's some kind of fungus or algae. Any ideas?

It looks like efflorescence which is caused by moisture drying out and the salts crystallising into the white powder. The moisture will have come from the ground as we don’t have damp proof membrane in Spain. The salts themselves are hygroscopic so they will attract moisture anyway. Is there a pile of soil up against the other side. If it’s your house wall below the ground floor workman in Spain knock a hole in the floor and shovel all the rubbish down underneath and this can pile up against a wall and let the damp in.

Thanks Niktam, I have no access to the other side so can't confirm there is a build-up of material. We are on high ground so water table should be low. I'm guessing the ground is saturated from the recent heavy rains.

Have it as well, kt comes and goes depending on the humidity. No worry's

It's efflorescence.
gerry

It's only salt

it should just brush of when dry! If the ground is higher at the back you may never get rid of it but it will not cause a problem.