Damp windows reveals

[mark2256]

Hi All. I am a new member to this site and ahve read lots of interesting topics. I am looking for some advice on how to fix a problem with damp window reveals in my home, it causes the paint to crack and flake with black mould now forming around the windows and doors the problem has gotten worce since we had new double glazing fitted "bodge job". The plasterboard has now come away from the dab and dorbe fitting so needs new plasterboard?.

The house was built "thrown up" in 1983 and is brick built with polystyrene filled cavity wall with gaps between outer brick wall polystyrene, gaps between polystyrene and inner breeze block wall then dab and dorbe fitted polystyrene backed plasterboard again with gaps. The window reveal this just plain plasterboard with no anti-moisture membrain.

Any advice on how to cure this please?

Thank you in advance.

 

[RobinBHM]

It could be a number of causes, but the obvious starting place would be to see if the detailing at the window reveals is correct or not.

Modern house construction has open cavities at window reveals, ie where the walls stop at window openings the cavity is open. A cavity closer is then pushed in place and the window is then fitted between the ribbed plastic faces of the closer.

Older houses hed the cavity closed of by returning the bricks or blocks linking the 2 walls. This construction has the disadvantage that there is a thermal bridge. To prevent lateral travel of damp, there needs to be a vertical dpc in the reveal. Quite often it is fitted in line with the inner face of the window frame and should still stick out a bit after plastering when it can be trimmed off. Quite often this dpc ends getting fixed in the wrong place or is loose and gets pushed back when plastering. If the bonding plaster or plasterboard edge touches the external damp side damp patches will appear.

Incorrect detailing at lintels can also cause damp issues. Not usually an issue with modern catnic types as they have insulation and a cavity tray with external weep holes built in.

If you have thermal bridging issues then the mould may be due to condensation

To stop it happening you need to find the cause of the incorrect detailing and repair before making good the plaster. Its a pain but not a massive job.

If you had new windows fitted can you contact the company and get them to investigate?

 

[Random Orbital Bob]

What an excellent quality response Robin....thanks for being so comprehensive.

 

[CHJ]

As the window reveals are going to be the coldest spot if any of the thermal breaks between outer and inner walls are compromised and even with best practice are still likely to be the coldest spot, the fact that you now have PVC sealed windows fitted means that you probably have a much higher humidity level within the whole property due to less drafts and air exchanges than previously.

This will inevitably condense out on the cold spots, you may find that running a small dehumidifier in the rooms where this is most prominent draws several litres a day out of the internal atmosphere.

This time of year we run one sometimes two and it's not unusual to remove 4 litres of water in twenty four hours despite having kitchen steam extractors etc.

If you use a steam iron, or bring damp clothing indoors this can increase the level considerably this time of year when windows and vents are left closed.

 

[Paul200]

+1 for RobinBHM's excellent response. We've just had a new kitchen extension built and our bodging builders returned the internal wall straight into the external - I assume they thought I wouldn't notice! I'm no builder but even I knew it was wrong. My subsequent research online showed them the error of their ways and it was corrected. But I also got them to install a thin vertical insulation strip as well as the DPC. Like this -

I hope the resolution to your problem isn't too intrusive mark.

Slainte Mhath!

Paul

 

[mark2256]

Thank You for the replies I found the information very helpfull and will keep you posted as I continue to resolve the problems.

Happy New Year to you all

 

[Jacob]

Not read the above (just back from the pub) - insulation keeps the reveals warmer - behind plaster board? and reduces condensation. Ventilation also reduces condensation. You may need both.
Basically the U value of the reveal close to the window needs to be lower than the U value of the window itself. Or condensation takes place on the reveal instead of on the window.
Condensation on the window is good - as long as it is collected and drained off to the outside.