mastic or mortar on window frames?

[Nathan Thompson]

I live in a barn that was converted eleven years ago. Since I've been here (two years) water has been coming in above the kitchen window. Vrtually all the windows have patches of mould at the bottom corners, closest the frame.

The walls are mostly cavity stone and the frames are wooden with double-glazed sealed units.

Looking outside, I see that the frames are all a little too small for their openings. The gap is around 5mm - 1cm at most.

To get around this, it looks like mastic has been used to fill in the gap. And I suspect this mastic is what's letting the water in - it's cracked and broken with age (the windows were fitted around ten years ago). The pointing is mostly okay throughout, by the way.

Here's the queston - what's the best plan? To scrape out the mastic and remastic everything, or can I use something much more sensible like mortar? Will mortar bind properly to the wooden window frame?

[BigWallop]

Mastics which stays flexible is the usually used on window frames. The flexibility allows the frame to move inside the opening without cracking the walls or the frame itself. It's amazing how much a window can expand and contract in different weather conditions.

[Nathan Thompson]

Hate to reply to my own initial posting but I've just been outside to have another look at the frames. It's not mastic they've used. It's putty. They've painted it brown which is why I thought it was mastic. I prodded it and was shocked to find it was soft. I scraped some away with my fingernail and, sure enough, it's putty. Just to confirm, this is on the OUTSIDE of the window and on all the windows.

Presumably the frames are held in place by fixings and they've simply filled in the gap with putty.

I think the original builders did this to avoid problems with the frames expanding and contracting. Or the might just have been half-arsed idiots.

I need to know what the best plan is. Mortar is obviously best but will this cause my sealed units to start separating because the frames won't be able to expand?

[BigWallop]

It's more likely to be Mastics that stays flexible and never hardens. To set frames which expand and contract so much in the open would cause cracking in both the frame and the brickwork.

[Michael Mcneil]

I live in a barn that was converted eleven years ago. Since I've been here (two years) water has been coming in above the kitchen window. Vrtually all the windows have patches of mould at the bottom corners, closest the frame.

The walls are mostly cavity stone and the frames are wooden with double-glazed sealed units.

Looking outside, I see that the frames are all a little too small for their openings. The gap is around 5mm - 1cm at most.

To get around this, it looks like mastic has been used to fill in the gap. And I suspect this mastic is what's letting the water in - it's cracked and broken with age (the windows were fitted around ten years ago). The pointing is mostly okay throughout, by the way.

You are not confusing the term frame and the term pane are you?

Putty would have hardened after a few weeks. A window is normally fit into a space with a 1/2" gap in height and width. This is ordinarily filled with mastic or cement pointing.

The main problem is that there is too much damp remaining too long upon the windows. Is the roof or whatever in need of repair. Clean the gutters especially around this time of year.

Check wherelse the damp may be coming from.

[Nathan Thompson]

Hmmm... my guess would be that such a thing would be akin to silicon used in bathrooms.

By contrast, the stuff surrounding my windows is actuall soft - push with the finger and you leave an indentation. Scrape lightly with your fingernail and it comes away in large chunks. If this IS mastic then I suspect it'll be called something like "Putty Mastic" because it is, to all intents and purposes, putty.

Your theory is supported, however, by the fact that aruond the house, other frames seem have a harder version of the putty on them. The bathroom window is a good example - on one side it's a hard-ish mastic, whilst on the other side it's more putty like and soft (although not as utterly putty-like as the bedorom window, where it came away as described above).

Question remains, however - what's to be done? Remastic it?

[Nathan Thompson]

Oh Usenet, I love you. Where else in the entire world would I get asked a question like that?

Frame = wooden thing which glass sits in. Pane = glass thing that sits in frame. Think I've got that straight. Just check my dictionary... yes. I'm correct. The putty in my case is surrounding the FRAME - the WOOD. The putty is inbetween the wood and the stone wall. It doesn't touch the glass.

IIRC putty doesn't go completely hard. It just gets a hard outer surface. Push and prod hard enough and you'll get through to the soft stuff underneath. Once again, this pretty much describes the stuff surrounding my frame (ie the WOOD).

[Dave Plowman]

Clean it all thoroughly and use silicone sealer.

[The Natural Philosopher]

Expanding foam IMHO.

[Dave Plowman]

The stuff I've used says don't leave exposed to sunlight.

[BigWallop]

[BillR]

It shouldn't have been putty around the frame and it should not be replaced with mortar. Mastic for the job should be used i.e. frame sealant. Silicone is the best imho.

[BillR]

Thats true. It can be used to fill the gap around the frame if its excessive, or even these days to hold the frame in, but silicone frame sealant should be used on the outside.

[BillR]

......

I think the other poster was asking this because he, like me, is very puzzled by putty apparently being used between the frame and the wall. I've never heard of this. The original fitters can't have known what they were doing. I wonder what other shortcuts they made ... e.g. is there a vertical damp proof membrane, or have they bridged the cavity in some way? If you watch proper window fitters they take great care with these points which may not be obvious to amateurs.

[Dave Plowman]

I had a new large wood window put in years ago. The builders used ordinary mortar round it and some fell out. They probably ran out of cement. I dug it out and remade it using mortar, but recessed, and finished with silicone. When I came to remove the window through rot ;-) this year, the silicone was still so firmly attached it would take the weight of the window at the top when 'hinged' out.

The rot BTW was in the exposed parts - top and bottom sills - the frame within the walls was fine.

[N. Thornton]

Silicone sealant. There are different versions of it, pick the most suitable one.

Regards, NT

[Michael Mcneil]

Bloody cheeky people who ask total strangers they never hope to meet, how to sort out problems with the most expensive piece of equiptment they will ever own in their whole lives; then slanging off the professionals on an amateur site who take the trouble to verify the OP is not a total wally! Then he turns out to be a total wanker.

(Not that I care if the house fall down now.) He can rake the pointing out and check on the fixings. Then I imagine that wedges and foam will solve the fitting/dampcourse problem. That still leaves the problem of where the damp is coming from.

I suspect the gutters -probably got the felt inside the fasia too. I bet its pooling in a spot at the top of the wall diagonally above the window about 45 degrees to the ends of the lintles. Or however the wall has failed after the windows were installed. (The prick!)

[stuart noble]

Whatever they've used I think I'd rake it out and replace it with a ready mixed gen purpose mortar, using 4 water:1PVA. Ideally you should leave a 3mm or so gap next to the wood for a flexible seal to be gunned in. It may be that the general area around the windows is absorbing water in which case the edges will be a red herring.

[stuart noble]

Some of these gaps are 10mm. To do the job properly IMO, set greased strips of hardboard against the frames and let the mortar set. Whip the hardboard out and gun in a mastic. Aesthetically, 3mm is about all the mastic I want to see round a window.

[Nathan Thompson]

It's definitely putty. The builders who did the barn up didn't know what they were doing. They also ran out of money half way through. Since moving in, I've effectively re-renovated the house. The most serious problem was an inadequate damp proof tanking but - argh - don't get me started.

THanks for all the advice. I'm going to have to assess whether the gaps in each of the frames is too large to take mastic. If it is, I'll try and follow the advice of one of teh posters above - mortar in some greased pieces of plywood and then mastic in the gap left behind when they're removed.