K-Rend damp patches after rain


New Member
Hi there,

I'm just after some help/advice please.
We have had a rear ground and first floor extension which has been fully rendered in K-Rend. When we get a lot of rain i'm seeing damp looking patches on the first floor external walls, at first i was thinking it was the window sill, but can see the patches higher up on the wall. The inside of that room is fine, no dampness. But we have had a small leak when we have had hard driving rain in the room below from where the steel would sit supporting the wall you see.

I can't work out where its getting in as window is fully sealed (window company and builder have checked), window sill and window header above are in a different coloured K-rend to the wall so wondering if its where they meet the wall as have beading around them but can't see any hairline cracks.

Is it the window or the sill or the header above?

Rest of the walls have no damp patches, even the other one facing the same direction.

Any pointers appreciated,


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New Member
Thanks, are there any comments to help point me in which direction to with this. patches only appear in hard driving rain and only on this wall, other walls facing same direction are all ok.

I'm just a customer with no experience of rendering, but would say the rest of the house looks great including this wall when dry.

Just looking for some guidance really.

Many thanks


New Member
Not many people know about that k rend but my cousin did my auntie's shop and it looks banging I'll ask him for you.

Steve Brown

Well-Known Member
If the water is coming inside via the lintel/steels that means that a cavity tray wasn’t installed which should have been under today’s regs.
Having said that a rendered wall would have prevented the driving rain from penetrating into the cavity.
Without an inspection from a competent person you’ll not get a diagnosis of what’s at fault.