Damp patch in the corner of pvc window

3 Jan 2021
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Hi I have recently had a room drylined I have noticed a damp patch on the bottom right hand side of the window, there is also a tiny spot at the top of the window any ideas what's causing this there are no leaks in the roof and I have applied concrete water sealer outside as I thought it might be dur to porous plaster. Thanks Harry


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Harry1, good evening.

Looks as if there is no external mastic between the cement and the window?

Suggect you consider application of a bead of mastic? a worth while [cheap] non-invasive option??

Thanks for the advice unfortunately after following advice on the previous post the problem still exists any further advice would be apricated.

Although it has the potential to create further damp/wet spots inside, I'd recreate rain on the outside of the window e.g. medium sprinkler sprayed around the outer edges of the window (top, bottom, sides) from a couple of feet away then see if this translates to damp/wet inside. If it does, then you know the issue relates to water ingress in this area. Temporarily block the bottom weep/drain slots whilst doing this, remember to unblock them after.
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Thanks for your reply I have tried doing this but there is no immediate damp patch and it does not necessarily happen when it rains, for example we have had cold frosty weather over the last couple of days and the damp patch had just about disappeared but increased in size today despite there being no rain.
If you're absolutely confident there are no leaks from outside and no leaking pipes inside, could it be condensation on the window causing the damp? What room is it, what's it used for, is it well vented etc. If there are no leaks and you're sure it's not condensation then tbh I'm not sure.
its an upstairs bedroom with a vent in the room, there is condensation on the window but also a tiny damp spot on the top of the window which leads me to believe its getting in around the frame of the window could it be down to a poorly installed window I have recently had the room drylined, the builder replaced the plaster board around the window with dryboard this brought the problem to my attention.
If the window was already installed for a while before the most recent works, and if damp was never noticed before, it's unlikely to be the issue. I'm wondering if it could be condensation? Wouldn't take much to create what looks like small damp patches. Are you 100% confident it can't be coming from outside? It's maybe just the pictures, however the cement work that's been done looks as though it could be a source for water to be absorbed, perhaps creating the interior damp issue?

I suspect that moisture is creeping past the frame at the head and sides?

The external metal angle beads are rusting and the render is degrading so:
What you are going to have to do is to hack off about 150mm back from the angle beads - both jambs and head.
remove the jambs and head angle beads
and knock off the render from the external reveal jambs and head reveals.

Seal the exposed frame with a recom sealant.
Replace the a/beads with plastic beads and re-render and paint to match when dry.

You replaced the old plasterboard interior reveals with drywall aka plasterboard or do you mean something else?
There appears to be nothing to encourage rain to run off the top of the windows reveal and using a sealer will have trapped any moisture already in the brickwork, you are looking at summer at the earliest for that to dry out.
Thanks for the advice yeah I had the old plasterboard interior reveals replaced with insulated plasterboard.

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