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Fixing exterior woodwork silll

Hope this helps with this sill,i can only show two pictures before and one when finished,the rot was so bad,i had to cut back half off window sill,even then there was still rot,got a piece off wood same size that matched nicely,glued wood to sill used grips to keep in place overnight while glue hardened,then screwed.Used Bonda wood hardener,then Bonda two part filler,but in my opinion plastic padding marine filler would have been a better choice,
then filled,two coats off primer,undercoat,then two coats off gloss job done.

Darlic See my reply on other post

Hi Guys,

Despite some great efforts, there are a few classic mistakes I can see as to why your systems are failing, which is mainly in the prep!

1). DONT use polyester fillers (2pk) fillers externally, they will IMO fail!

Why? Despite manufacturers claims of “For Interior or Exterior use” a polyester 2pk filler will basically act like a sponge over time, absorbing moisture and eventually causing the paint system to fail.

As with Darlic’s repair, I can see what your trying to achieve but in all honesty, that repair, depite your great effort will most likely fail by this time next year, if not sooner. You basically have 3 different substrates all attached to each other, the hard wood (original sill) will expand and contract naturally at a different rate to your softwood (repair), this will over a short period of time cause a hairline crack that will intern allow the ingress of moisture. The 2pk polyester will not expand and contract but take on moisture. If your going to do ‘splice in’ repairs such as this, use like for like substrates. Better still, I would have removed that sill completely and put in new or use the repair-care system.

Similar thing has happened with Markyb, the black sills that have failed most will most likley be on the south facing elevation, where it gets the most sun. Dark colours (Black especially) absorb the heat and will cause the wood to move at a much greater rate than the 2pk polyester. Moisture is then allowed to ingress under the paint layers, causing de-lamination.

BIN is only recommended for spot priming externally as it becomes to brittle due to its shellac base. Coverstain could be an option or aluminum wood primer.

Markyb, get that 5" disc on your new Deros and get blasting those sills down with some 80g abranet.

Please guys no more 2pk on exteriors

Good luck and press on!


Have interior window with rot ,the repair care system I am aware off but its expensive if you only do the odd window I have gouged out the rot will use wood harder any ideas on good filler if 2pk isn’t up for the job,this is on the inside this time not outside?

Hi folks since this post was written touprett have brought out a two pack filler extreme wood anyone used it?