On 20 Jun 2004 01:05:33 GMT, (Andrew
Gabriel) wrote:

In article ,
Phil Addison writes:
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
warn her!!) who had done it up to re-sale. There was no sign of damp
then, it all being freshly decorated.

That would probably be about the time to inspect and possibly
replace the sealant around the window.

Certainly the frame seal was badly applied and next to useless, and I
re-did it a couple of weeks ago before applying the silicone to the
sill. I don't think that is the root cause though, largely because there
are two windows in identical situations both with equally poor seal and
only one has bad damp. The two sills are both poor but the one with the
bad damp also has hollows where water collects. At least the other
drains off, even though it may be porous to a degree.

The builder had replaced the original sash windows with uPVC, and the
sills are now concrete, and I suspect the sill heights have been
increased. These sills are not 'bought' concrete ones but appear to have
been cast locally, possibly in-situ. The finish is pretty poor and the
top surface seems to be hand trowelled and not very flat. In fact there
are some hollows that retain little puddles on the sill with the worst
damp problem.

These actually sound like original rendered brick window sills.
I have these too, and thought they were concrete until one was
removed by a bricky.

That is most interesting, Andrew. I have not heard of that construction
before. Do you mean original brickwork sills, rendered at a later date?
I didn't think sand/cement render was available that early (1890's) or
am I wrong there? If it is rendered brick, I may be able to remove and
replace the render with proper waterproofer additive and hopefully make
a better finish of the slope.

I'm going to have a good look at that and perhaps drill to see if I can
hit brick. My daughter would be relieved not to have the upheaval of new
sills. On the other hand, the sills do look like cast ones - there is
evidence of framework marks on the front, and there is a cast drip
channel underneath.

My money would be on water leaking in around the window or from the
window's drainage.

That was certainly possible. I have now made a good seal all around the
frame, and it definitely was leaking along the bottom edge - caulk
broken away and evidence of wet under it. The drainage channels look OK,
but I suppose the uPVC frame itself might have a cracked bottom corner
joint allowing water to egress directly to the brickwork, though I
imagine that an unlikely failure. Also the inside of the openers is
quite clean, so it seems that little if any water is passing the rubber
seals to the frame innards.

Assuming the sills are in fact concrete, my big question now is how do I
prove that it is (or is not) the sill before embarking on replacing
them. I suppose once the internal bricks have dried out I could rig up
some kind of water drip to keep the sills soaked, but how long would I
have to run that to be sure it is not soaking through? This assumes that
the internals will actually dry out before the next storm!

I was toying with the idea of over-painting the sills to waterproof them
with, for example, one of Max Bone's products at
http://www.decoratingdirect.co.uk/Co...onry_Coatings/,
but I'm not sure if that would seal the sill completely or how durable
it is. If it will last 2-3 years before repainting it would probably be
preferable to sill replacement because my daughter is expecting a baby
in 11 weeks and is anxious to get the nursery decorated, for that is
what this room is to be. I would have to 'get a builder in' (aaargh!!
the shame of it) to do that and that will take a while to sort out.

I am leaving it for a few days to see how this wet dries out, now that
it can via the exposed inner brick surface.

It takes weeks for wet walls to dry out. IIRC, it took about
6 weeks for the single brick front wall of my fireplace to
dry out after I reopened the fireplace (blocked up with no
ventilation for probably 20 years).

Hopefully not that long as there is only about a height of 2ft of bricks
below the sill to dry out. Your fireplace presumably had wet brickwork
to a much greater height replenishing the opening as it evaporated from
there?

What I need now is advice on is what to do to make good the inside wall.
I am not convinced that re-rendering it is a good idea - I want to stop
the damp at source, and the original render put on to contain it has not
worked very well. Is a 'waterproof' rendering really waterproof? I
suspect that under the pressure of a couple of feet of water inside the
brickwork wet will seep through; or could it be that the builder didn't
mix the render correctly?

Given that I have exposed a 4' x 2' patch of brickwork, what is the
appropriate materials to make this good? I was planning on a background
of Carlite Browning with a skim of finish or multi-finish. Any hints
anyone?

Phil
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