On 21 Jun 2004 09:05:57 -0700, (Meoww) wrote:

Phil Addison wrote in message . ..
My daughter's house has had a patch of damp appearing under the upstairs
windows since she bought the house 5 years ago from a builder (I did


big snip

I think you might be barking up the wrong tree here Phil.

It's almost certain that your problems are due to the outside
rendering and the poor detailing/workmanship of the window.

Must admit I tended to discount the external render because on the whole
face of the house there is damp coming through only under the sills of 3
windows (sorry, didn't mention the downstairs one before - that is only
a minor patch similar to the 2nd upstairs one). I imagine if the render
was duff it would come through in arbitrary places. But what you say is
quite possible, and I have rectified the useless seal between frame and
reveal and sill. The problem is finding out which of the possible entry
points is the cause.

Although there is a hairline vertical crack under the worst window, now
that I have exposed the brickwork inside it is clear that the wettest
course is the one right under the sill, getting progressively less wet
until it is dry at skirting level. That seems to point the finger at
either the sill itself or the sill/frame interface where I did find wet
behind the old sealant as I removed it.

If you have a strong mix on the external wall (3:1) or in that region,
then it's virtually waterproof. (BRE say mix strength this will hold
back hydrostatic pressure). Any water that gets behind it has
nowhere to go to get out but through your internal walls.

I understand that, but I have no idea what the external mix was. Is it
possible to test it somehow?

You say that you have hairline cracks and also that the wall is on an
exposed elevation. Put these two together and add it to the poor
detailing of the cill –

has he for instance just plonked it between
the reveals or is it inset.

I don't know quite what you mean. The frame is set about 3" in from the
inner wall surface with a narrow (about 3") inner wood sill. The
external reveal is about 6" deep.

Is there a good seal to it,

There is a good seal all round now.

is there a dpc beneath it,

Where should this dpc be? Directly under the sill I suppose. I don't
know if there is one. How can I find out? Good point though - if there
was a dpc it wouldn't matter if the sill was porous, right?

are you sure the drip mould works?

Well, I'm not SURE the drip channel works but it looks OK and is not
obstructed. I could run a hose over the sill to check.

The question of the internal rendering is a red herring. It could be
plaster or render, as long as it isn't repeat isn't waterproof then
it's probably doing its job. If it were waterproof, the water would
slowly but surely go further and further down your wall until a big
rust red mushroom popped up between the floor joists.

It was rendered internally, as I say, and clearly WAS trapping water. I
have hacked it off under the window now. It was pretty hard stuff, and I
guess waterproof (ish!) as it was dry on the surface and the bricks
behind were damp. Also the render I hacked off didn't appear obviously
damp - I'm pretty sure it was dry. I say "ish" because some damp did
penetrate and showed on the decoration.

Check the render, check the detail, keep the water out and you'll be
OK.
Easy when it's said like that in't it

Err, yes :-)

Thanks again for the ideas Patrick.

Phil
The uk.d-i-y FAQ is at http://www.diyfaq.org.uk/
Remove NOSPAM from address to email me