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How to repair rotting timber window sill?

Hi,

I have an old house with wooden exterior window frames/window sills.
A few of these are in pretty bad shape, how can I go about restoring or repairing these?

In the photo attached you can see the paint has started to peel away. The wood is brittle in areas and soft in others.

I would appreciate any help!

Thanks

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DIYGnome

Hello @lilh

There are a few different schools of thought (and approaches) so I will simply detail the process I use and other members will hopefully chip in with their suggestions 😉

@Dave-1

Essentially it depends on the degree of wood rot, if severe I strip down the frame (or cut out bad sections) and replace the wood as required but if only partial damage has occurred I prefer to dig out the nasty soft rot until I locate some "good wood" applying wood stabilizer helps prevent moisture seepage and shores up the remaining timber, for this I use PVA wood glue but specific products are available.

Builders bog or automotive body filler is my filler of choice, sand and paint 👍

JacobZ

https://www.workshop.bunnings.com.au/discussion/comment/37408#Comment_37408

Hi @lilh,

Thank you for your question and welcome to the Bunnings Workshop community, it is great to have you with us.

It's great to see you've already received some advice from @DIYGnome which I completely agree with.

I'd advise you pick up a Turbo 500ml Timber Rot Repair Kit, which includes a wood hardener, builders bog, putty knife and sanding block.

Like DIYGnome has said, dig out the soft stuff until you hit decent timber, clean the area up sufficiently then apply the wood hardener following manufacturer's instructions. Once dry, apply your builders bog with the putty knife, once again following the manufacturers instructions, then sand back to a smooth surface. Once done, paint over the top.

Let me know how you go and if you need any further assistance.

Jacob

Dave-1

Afternoon @lilh

Depending on how bad the timber has rotted (If its rotted my first thought is to replace the timber) you can repair it as @DIYGnome has mentioned. I have seen some very nice wood restorers and if the timber isnt to bad (push a flat blade small screwdriver into various sections of the frame and see how bas it is) then the easist way would be the Builders Bog.

If the timber is spongy along the length of it or even spongy all the way through then I would replace the bottom sill. I cant tell from the photo if the window is sitting on it or if its just a fron face type piece. If its a front faceing piece then you could remove and replace. You could use a Ozito 300W Multi Function Tool MFR-2200 to cut it out easier.

Dave

lilh

Hi @DIYGnome @JacobZ @Dave-1 ,

thank you all for the advice. It seems like the length of it is pretty soft so it seems like it will need to be a replacement job 🙁
Is it possible to DIY replace the timber sill? Would love to get some advice about the process and the type of wood I would need to replace the sill.
thanks!

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/37800#Comment_37800

Hi @lilh,

The window sill travels partially under the window, so you might need to remove the window to replace it. I'm not sure of your D.I.Y. ability, but this is a job I would consider leaving to the professionals. There is a possibility of cutting the exposed deteriorated sill away and replacing just that portion.

When you say it is soft, how soft is it? Can you push a screwdriver straight through it or just chip off rotted sections?

Please let me know if you have any questions.

Mitchell

lilh

@MitchellMc I can’t push a screwdriver all the way through it, but it definitely has rotten sections.
I’ve used Earl’s wood hardener and then their multi fill product on other water damaged wooden things before - would that be a suitable alternative to the Turbo Rot Repair Kit suggested?

Otherwise any suggestions for partial replacement of the bad sections?

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/37806#Comment_37806

That would be a suitable alternative, @lilh. You'd just want to ensure you adequately paint it afterwards to prevent water seeping into the timber.

For replacement, you'd need to cut out the damaged portions and a multi-tool will come in handy for that. Once removed you'd need to purchase some timber in a suitable size. You'd likely have to cut down the timber to suit, as chances of something matching off the shelf would be slim. You'd then glue and screw the pieces into position, fill seams and joins with putty, sand them smooth and then undercoat and paint.

Mitchell

DIYGnome

https://www.workshop.bunnings.com.au/discussion/comment/37806#Comment_37806

Hello @lilh any hardener / 2 part filler solution will suffice, the greatest challenge is removing the rotten wood and having the weather stay "favourable" long enough to get the job done, replacement wood will have to be hardwood as pine just doesn't hold up well for exposed surfaces in my experience, if in doubt speak to a Bunnings Member and tell them your intended application 👍

Multi-tools are a wonderful product and make life easier but a wood chisel and mallet would also be effective in removing the effected section of wood (unless it's a full timber shelf on which the aluminium window frame is installed).

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