It looks like damp. How far up the wall is it? Does the wall have a
damp-proof course? It looks as though the damp is rising and bringing salts
with it which remain when the water evaporates (rather like the way a
stalagtite forms) and cause the plaster to come off. I imagine that you
could scrape it off with a scraper and that you'd be left with bricks with a
slightly crumbly surface. If my reasoning is correct you'd need to get a DPC
in somehow. This could be injected by either yourself or a professional
It may be, or it may be some other reaction.
What is on the other side of the wall, and what is the wall construction?
When did this first appear?
Does its appearance coincide with any rain?
What is the room used for?
The dampness appears to be forming along a horizontal plane, and if this is
at ground level, then it is possible that moisture is creeping along
horizontally. Cracked mortar joint is a common facilitator of this.
Another possibility is that this is a form of condensation dampness, where
warm air has been condensing on a cooler wall - this is common during dry
spells, and especially at the junction of a cold basement and warmer room
If there are no other possible ways for moisture to have reached this spot
by travelling down the wall (such as a leaking pipe or roof), then DPC
failure or bridging is the most probable cause.
For a proper diagnosis, a surveyor or rep from a damp treatment company may
have to have a look.
If you want to DIY, then do a search for injected damp proof course or
Bear in mind though, that you may need a vertical and horizontal barrier,
and if there is excess moisture in the ground around the wall, then this may
have to be addressed too.
We have patches like this on the 4th floor here, from roof and air con. leaks
tracking down inside a wall to a solid floor then going sideways to a wall that
effectivily doesn't terminate on a floor slab, I.E. the stairwell, the plaster
at the point it crosses the slab is worst affected due to concentration.
Look for the ingress point, it might be external, or it could be a small leak
tracking, before getting the big guns out.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.