Damp under upstairs window. Porous sill?

It rather sounds like there is the problem right there, Phil.

I had exactly the same situation in the first house that we bought, except it was the ground floor windows. The walls had been rendered following an injection damp treatment.

I also did the soaking in silicone fluid thing. It did have some effect but water would still find its way past.

In the end, the cills were taken out and replaced with proper ones and the problem stopped.

On ours there was render instead of the special plaster normally recommended after a damp treatment. I ripped it all off.

The bricks being damp isn't that surprising. They could also be porous. If the dampness is in a patch below the cill then the implication is of water soaking down rather than through the bricks.

Certainly trapping any water behind any making good is asking for trouble.

I remember testing mine with a hose played on it for about half an hour. Even after the siliconing (which did help a bit), water continued to seep through.

To be honest, I didn't do it, a builder who was doing other work did.

Basically though, it wasn't that difficult. He removed the window frame and then carefully chopped out the mortar from around the cill and removed and replaced it with a "new" one - actually a stone one from a reclamation place. No further trouble after that.

.andy

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

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.

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

It takes weeks for wet walls to dry out. IIRC, it took about

Sounds like you have lousy sills which you should ideally replace (particularly if they don't have a drip groove on the underside). If you prefer to modify the existing, you need to get a flat surface, preferably sloping away a fraction. Polyfilla Exterior filler is fairly easy to use as a skim although I would use car body filler if you can face the extra work. Then you need to get something genuinely waterproof on there. Pliolite paint is good but any solvent based paint will be better than conventional masonry paint, which is not at all waterproof IME.

Thanks Andy, that's encouraging to know I'm on the right track.

I haven't heard of that 'special plaster'. Is it water resistant in case the damp treatment didn't work, or just tolerant to being applied to still-wet brickwork?

I thought these were the reasons for rendering, though I really can't see why one should render if the source damp is eliminated.

I wasn't surprised that they got damp, just that they were STILL wet after the long dry spell we have had, interspersed with some baking sun on the wall. I'm presuming it is the render both sides that trapped the water and prevented it drying out over this period.

Yes, I aim to cure it at source. The problem is being sure of what the source is.

You mean it penetrated from the sill to the inside in 1/2hr? I am looking for a test method to prove it is the sill, as opposed to say leakage around the window frame, which I have recently re-sealed with a decent bead. I thought that it would take many hours or a few days to penetrate through.

These sills seem to butt up against the frame edge rather than go under the frame, and in one of the pair the sill is very high, nearly up to the uPVC drain outlet (about 1/4" clearance). I wonder if this could be a cement render on top of the actual sill - as per Andrew's post. I'll need to investigate that possibility next.

Phil

Phil The uk.d-i-y FAQ is at

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.

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.

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

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?

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 The uk.d-i-y FAQ is at

On Sun, 20 Jun 2004 13:23:57 +0100, "stuart noble" If you prefer to modify the existing, you need to get a flat surface,

The 'concrete' they are made of does seem to be fairly soft, and no obvious concrete-type gravel visible at the surface. I did wonder if I might be able to grind them down in-situ to get a decent run-off slope. We had our limestone frontage restored last year and the stonemasons used an air chisel to rough it back and a stone rasp to smooth it. I wonder if I might achieve similar on these sills with my small SDS chisel and/or an angle grinder if its not too hard. Don't know where to get hold of a stone rasp though.

By 'extra work' do you mean sanding it smooth after it has gone off? I had the impression that Polyfilla Exterior was not particularly durable or perhaps I'm biased by the interior stuff.

I'm not clear why you suggest both a skim and a waterproof paint.

That was my other question (see my reply above), so thanks - I will avoid conventional masonry paint. I'm not familiar with Pliolite though

- what is it? By 'any solvent based paint' is that as in ordinary gloss woodwork paint?

Phil The uk.d-i-y FAQ is at

I've been trying to find what the reason for the special plaster (although I don't think it's very special) is. THe standard procedure with injected dampcourses has been to rip off plaster to a height of about 1 metre, treat and then replaster with this stuff. It may have something to do with preventing migration of salts, but I can't remember now - I don't think it was to stop damp though. Even then I don't think that this would apply to an upstairs situation.

Sounds like it, so it seems to me that the important thing is to identify and fix and test that the damp through the bricks really is eliminated and then replaster. Trapping water in the brick seems like a bad idea to me.

It was in a few minutes, it was so bad. In this particular situation, the house faced a park and the wind would drive the rain at the front of the house. Once it started raining and the wind was blowing a bit, even in quite light rain the wall would become wet.

Could be - i.e. a poor repair to an old cill.

.andy

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"stuart noble" If you prefer to modify the existing, you need to get a flat surface,

Just to offer an alternative based on my own experience.

I was suffering something similar with 3 windows built in an extension and went through some of the steps mentioned. It was only in some weather circumstances that there was leakage.

What I did notice is that the window cills didn't have a drip - they were sealed with silicon or something to the concrete cill but the actual drip part of the wooden cill appeared to have been removed when the windows were installed; the only reason I can think of for this is to make it easier for applying the external render. I re-created the drip with an add-on to the wooden cill and the problem has never reappeared after 10 years.

Rob

I found this

Also this helpful chart about which plaster to use on which surface

buildingpreservation explains, I think, what you are getting at regarding "migration of salts" at

I read somewhere that the background to use is Bonding, not Browning as Bonding is lightweight with vermiculite bits in it, whereas Browning is sand based, and now obsolete. Don't know how that squares with the Thistle chart which does call it browning.

Answering myself, the buildingpreservation paper explains this, and as I say, I Don't think it necessary for my problem. Anyone diss/agree?

I certainly don't plan to trap water!

Surely that must have been a direct leak through a crack or something. This damp took a long to appear and equally long to fade back when the warmer weather came. My worry is what is the upper limit of time it might take to get through rather less porous material. In other words how long do I have to soak the outside and wait inside for signs before I decide that is NOT the source? OK, I know there can be no definitive answer to that one - finger in the wind territory!

I'll be trying to determine if its just a render, or concrete throughout, in the next couple of days.

Thanks again everyone for thought provoking inputs. I'll let you know any developments.

By the way, should it come to sill replacement, is it essential to remove the frame or is that just to improve access, i.e. allow access from inside the room as well.

Phil The uk.d-i-y FAQ is at

Thanks Rob, but mine do have drip channels already.

Phil The uk.d-i-y FAQ is at

Hi,

If you want a good sealer for the concrete sill have a look at Bondaglass G4 eg:

Worth trying a sample area though to see what it looks like.

cheers, Pete.

That's an interesting one - a pond sealer. Should be waterproof then! Not sure about the colour though, Browny translucent, Mid Green, or Black. Could over paint it I suppose. Thanks for the pointer.

Phil The uk.d-i-y FAQ is at

Rendered when built. All the houses in the terrace have the same sills (1895). The render is very hard -- I was bashing away with a scraper on it to get 100 years of paint off, and it doesn't damage or even mark it. It is vulnerable if the render cracks though -- water can get in and then freeze in the brickwork, causing large chunks of the brickwork to fall off, which had happened on one of mine.

Cement goes back to roman times. However, prior to Portland cement, it was more expensive, so it wasn't used for everything like it is today.

I think the only way the sill will be letting water in is if there are cracks in the render.

Mine also has a drip channel. It's a bit far back for my liking though.

It was about a 2' square (plus much of the bricked up area which was removed). It was quite waterlogged though.

If you stop the water entry and let it all dry out, you can use pretty much anything (personally, I use bonding coat as the scratch coat). However, none of the gypsom-based plasters are suitable if it's damp.

I have done a scratch (base) coat of cement (and lime if you like it) and sand in a 1:1:6 ratio, with waterproofer added. Follow up 24 hours later with regular plaster finish coat (no PVA required unless you leave it much longer and the scratch coat has dried). The sand and cement is very effective at keeping the water away from the plaster finish coat. However, you'll probably need to let the wall dry out first, at least so it doesn't feel and look wet.

That and polyester being generally sticky and difficult to work with.

As a skim, more durable than any cement based mix

Skim to get it smooth/flat and provide a better base for the paint.

A type of synthetic rubber I believe. Macphersons, Johnstones, and most of the other trade outlets do it. Based on solvent naptha so not too environmentally friendly.

Yep, although a matt might look better on sills. Mine are coated in red oxide primer which is quite a good match for adjacent brickwork.

I think a fibreglass resin would be better. G4 cures on contact with moisture which may not be a good thing if the concrete is damp close to the surface. Foul stuff to work with too.

Hi,

I think the tranlucent is more like a varnish colour. Another possibility is a UV stabilised clear expoxy.

cheers, Pete.

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.

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.

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. Is there a good seal to it, is there a dpc beneath it, are you sure the drip mould works?

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. 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

Regards

Patrick

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.

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

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.

There is a good seal all round now.

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?

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.

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.

Err, yes :-)

Thanks again for the ideas Patrick.

Phil The uk.d-i-y FAQ is at

Is that 'paint-on' or spread as a skim?

Phil The uk.d-i-y FAQ is at