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How to repair external timber window sill?

Hi team,
I have an east-facing awning window and its sill needs a good level of attention. My goal is to restore it without having to replace it(full or partial)
Please review the photos.
I have reviewed previous articles in the forum and understand that the general approach is to:

remove as much rotten wood as possible
treat the surface with the wood hardener
fill any void/gap with external-grade wood filler
prep surface
undercoat
top coat with water enamel paint

I have previously tried to repair the same section using builders bog & low sheen Weathershield and ended up with paint chipping off (Some of the photos show this)
Do you think this happened because I skipped the process to remove rotten wood & harden its surface?

Secondly, is it still advisable to fill the groove with the bog only after hardening the surface? I think I have already sanded enough.
I realise that I may need to trim off the bottom of the jamb/sash using the multi-tool, chisel, etc and refill the space with filler, etc.

Thank you in advance.

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Comments

MitchellMc

Welcome to the Bunnings Workshop community @hmukai. It's brilliant to have you join us, and many thanks for your question about repairing a window.

It sounds like you have the method down pat. It's a bit hard to tell why you previous repair has failed. I suspect it was likely due to the window scrubbing on the repaired area when opening and closing. I can't see any other reason why the Builder's Bog would be chipped out like that. Ensure there is enough room, at least a few millimetres. Trimming/sanding the edge of the window frame might be needed to establish this room.

Weathershield is a softish paint whereas an enamel is much stronger.

I would suggest filling areas after you have hardened the timber.

Please let me know if you have any questions.

Mitchell

hmukai

https://www.workshop.bunnings.com.au/discussion/comment/46728#Comment_46728

Hi @Mithcel

Firstly, my hats off to you for such a quick turnaround.
I apologise for omitting the details. Those chipped-off bog patches (So it's not the entire sill surface) were forming a bubble (Before I scraped them off).
So, I think it is safe to assume they did not adhere to the surface due to poor surface prep. Hopefully, the extended sanding & wood hardening will overcome this issue.
Also, it's great to know that an enamel is stronger, so I am convinced the new approach will be worth the effort.

Thanks again!

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/85403#Comment_85403

No worries at all, @hmukai! Can't wait to see your results.

Mitchell

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