I Had A Go At Repairing My Sash Windows

I’ve had a look at the outside wooden sills on my sash windows and I really think that it might be a job for a DIY enthusiast. Sash window repair doesn’t seem all that complicated, to my understanding we simply cut out all rotten section of timber, treat it, splice the timber back as neatly as possible, and then fill joints with a two part filler designated for external repairs. This is within range for a DIY effort I think. Here’s a look at the problem, I’ve marked in pen around where I intend to cut:


I would then sand the two part polyester based filler, prime, undercoat, and top coat with a high quality paint. So with my window looking a bit rough as pictures below I am going to prepare myself with a list of tools and materials:

  • Hammer – this is to remove the rotten section of timber in conjunction with the sharp chisel.
  • Sharp Chisel – this is required to cut straight clean lines making it possible to keep the joins neat and tidy.
  • Pliers – we might come across unwanted nails from the original construction of the frame.
  • Saw – this is to cut the piece of wood I will block splice back into place.
  • Filling Knife – to apply the filler as evenly as possible to reduce the amount of prep work.
  • Sand Paper – to smooth off the timber and filler after the repair is complete and to provide tack for the paint to bond properly.
  • Necessary paints – for finishing
  • Timber for the splicing, I intend to buy as closer match to the section I cut out as possible.
  • Filler, the two part resin I have already mentioned
  • Wood screws and glue to fix the timber.

So the process is pretty simple I start my sash window repair:

I start by cutting out the rotten section of timber. It’s helpful to place a dust sheet under the window to catch most of the mess. My main aim is to keep the cuts straight by using a chisel that’s as sharp as possible. I cut nice and square to try to leave the finish as easy as possible after. I used this sash window repair page for reference because it clearly shows how to splice timber. It’s so comprehensive wouldn’t even realise the sash window had been repaired. It gave me the inspiration to really give this a go knowing windows can be literally rebuilt without a trace after.

Once I removed the timber and treated carefully I then began to use my saw to cut the section of timber back into place. I’ll be honest, I needed to use more filler than I had hoped. Here’s a look at that repair put back together:


Please note, I have glued and screwed it so it won’t be going anywhere soon. Screwing alone is probably enough to hold it there but the way I see it is that the glue will bind the timbers nicely and stop the moisture and water getting between the joints if the two opposing timbers moved at different temperatures.

I was actually struggling with the selection of paint. I decided to be a bit cheeky and call up a window company to find out what paint was best to use. Many didn’t answer but a kind chap from South London Sash Windows recommended Dulux Weathershield so I thought I would give him a mention. I then found out that Dulux themselves recommended this paint externally which was handy to reaffirm what the window chap had said. It seems that if all rot is removed correctly then I should be good to go! DIY sash window repair ticked off the list.

This is a collaborative post.

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