White Powdery Patch

[dennisb66]

There is a white powdery patch about 12 inch in diameter on the wallpaper just below the window in the spare bedroom.What has caused this and how do I remedy it?

[boxtops]

Sounds like mould, check you don't have a leak or crack under the window where damp's getting in.

[Mosaic]

How is the room heated?
It sounds to me like the typical 'coldest spot' you get in most houses. The coldness leads to condensation on which mould forms. If the windows get wet with condensation this might trickle off the windowsill and add to the problem.

You can also get crystals forming from slats in the plaster and bricks that have been drawn to the surface of the wallcovering by the evaporation of the condensate.

Try 24/7 gente warmth first of all, and use the time to look for any water-based leaks such as a faulty downspout.

[The Builder]

Yes, it does sound like mould or salt crystals. Several types of fungus can be white. Probably condensation.
Cavity wall, or an older house?

Key word here is "spare" bedroom. Most likely windows closed tight, and radiator turned off or too low to prevent vapour from condensing on the coldest spot.

[dennisb66]

Thanks everyone,Yes the heating has been turned off for a while as I had a leaking valve,the valve has been replaced and the heating is back on.I will monitor the problem,thanks again for your replies.