Advice please on 'patching' rotting window frame

1 Feb 2006
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United Kingdom

I've recently moved into a house which had been lying empty for about 7 years.

Surprisingly it is in very good condition considering it's lengthy vacation.

One of the external window sills has some rotting wood in the centre of it - caused by a broken gutter that had been dripping water directly onto the area that is rotten. The wood is very soft in this part, going down to a depth of about 25mm, and extending for about 350mm (using a pointed knife to test it). The remainder of the wood on the sill seems fine.

Having mended the guttering a few weeks back, the wood now seems dry, as the window is quite sheltered - unless there is horizontal rain :cool:

I would prefer to 'patch up' the existing wood, rather than cut a bit out and replace it, and I think it would be quite awkward to replace just the sill, as it seems to be recessed into the wall.

I had thought about using putty - do you think this would work? At some point I will probably put in double glazing, so I would appreciate any advice on a repair that is likely to last for a couple of years.

Many thanks,

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I have seen a product in my local shops I think it was "wilkinsons" that you apply to the affected area and it hardens the softened wood you can then sand, fill or paint to your hearts content

Get Google to search for two words which I think you might want to add to your vocabulary; Borocol and Impel.

Borocol is a liquid borate based wood preservative that comes in a can. Two versions are available; one is for painting onto new wood that is to be protected and one for appling to wood that has already begun to rot to stop the rot and prevent further rotting.

Impel rods are solid borate based rods that you implant into wood to protect it from rot. If the wood gets wet, then the rod dissolves and releases a borate based wood preservative into the wood. They come in different sizes from 6mm in diameter and 55 mm long, 12 mm in diameter and 100 mm long and other sizes as well.

The advantage of borate based wood preservatives is that unlike topically applied oil based wood preservatives, borates will penetrate THROUGH the entire cross section of the wood, including even heartwood, to leave the entire cross section rot resistant, not just the surface. Consequently, you can implant Impel rods in pressure treated wood to get something that's both rot resistant on the outside (and which won't wash off) and rot resistant on the inside, too! (cuz if the wood gets wet, the Impel rod inside the wood dissolves, releasing borates into the wood).

The reason you probably haven't heard of these wood preservatives is that they're not suitable for all applications. Specifically, borates are soluble in water, so they will wash off of wood easily, thereby leaving the surface of the wood unprotected.

What you can do, however, is:
1. Go to any place that sells epoxy products for repairing rot in wooden boats, and buy some epoxy repair compound

2. Remove any weak wood and fill with epoxy.

3. Drill some holes into what's left of the sill and stick in some Impel rods and plug the hole behind them with anything (a soft latex caulk for easy removal, maybe).

4. Have a piece of metal bent to fit over your sill and screw it to the front of the sill.

Now, the metal keeps the rain water off the sill, and even if any does get in and the water content of the wood increases, then the borates released into the wood will prevent the wood from rotting. The only time you'd lose any borate is when the borate had penetrated all the way to the surface of the wood and the metal wasn't in place to prevent rain water from washing it off. However, by that time all the wood under the surface has a higher saturation of borates in it, and is completely protected from rot no matter how wet it gets and for how long it stays wet.

And, periodically (say every several years) you can take the metal sill cover off and check the condition of the Impel rods. Replace as necessary.

Borate based wood preservatives are used all over the world, and when used in conjunction with pressure treated wood allows you to have wood that has both rot resistance on it's surface that won't wash off and rot resistance on the inside that responds to the wetness of the wood. If the wood doesn't get wet, the Impel rods will remain undissolved for years. If the wood is always wet, then you'll have to replace the rod periodically (even though the residual high borate saturation in the wood from the last rod will protect the wood for many years, it will still leach out of the wood at the surface if water is washing over the surface of the wood).

Borates are very popular with builders of log homes here in North America because not only do they penetrate through the entire cross section of the log, they protect the wood from BOTH rot and insect attack. And, borates are extremely environmentally friendly to people. We mammals can almost eat the stuff. But they're very poisonous to fungii and insects don't like wood with borates in it. They are also used to protect telephone poles here in North America because of this characterists, and the fact that they're very environmentally friendly.

Here's the web site of the Canadian distributor of these products. You might want to find out from them who the UK distributor is.
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You don't need to add poison - the rot won't grow if the wood is dry.
Yes putty will do te job for a while so if you are replacing the window in a couple of years that would be the cheapest solution. A more permanent solution would be to use one of the resin products. Rather like car-body filler but there are some specifically formulated for timber treatment. Paint it over and your sill will be fine for a long time, so long as you keep that gutter fixed :)

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