Bay window cill repair

[jsmac]

Hello all,

We have two first floor bay window cills that need sections replacing as the repairs over the decades have allowed for serious rot to set in. We have had matching cill profiles machined by a local timber yard so I am hoping that the perished sections can be cut out and replaced with new timber.

We are having a nightmare finding someone to undertake this work for us so I am now contemplating doing the work myself. I would really prefer to have someone experienced doing this part of the renovation of the bay but the weather is getting cooler and we would like to get the bay painted and the sashes refitted before winter.

I have attached a couple of photos of one of the bays showing part of the rotten section of the cills. You can see where someone in their wisdom previously used cement as filler!

I am thinking of starting by cutting out the rotten section back to good timber on a 45° angle and splicing in the new cill. A reassuringly expensive amount of two-part resin wood filler can then be used to tidy up the areas that need it. My experience with this long suffering house tells me that it will likely not be as straightforward as that so any advice would be most appreciated.

Many thanks.

 

[fernicarry]

As you've gone to the trouble of getting matching profiles made, and if you have enough of it, then it might be best to just replace the whole lot. It'll be faster than mucking about cutting matching profiles and then filling and you won't have the joint as an ongoing weak spot. My thinking is to fill small areas to life-extend but once that stops being viable then do the whole thing, but then none of mine are original having been replaced several times over so I'm not particularly attached to them.

The pulley stiles are rebated into the cill so you would have to cut back some amount of those to get the new piece in. They do look a bit suspect at the bottom so this is a good idea anyway. Drop the new cill into position, pack it up to the correct height so that your meetings rails are lined up and then slot the pulley repair sections into it. Attach to existing pulley stile with a rebate/rabbet joint. A foaming glue is useful if your joinery isn't completely perfect (mine isn't). A little palm router with a trimming bit is good for making the rebate in situ on the existing stile.

You may need to support the window case whilst the pulley stiles are cut away. Mine miraculously defied gravity, except for the one that didn't, depositing a massive birds nest into the room...

Doing a partial replacement would be the same work albeit only at one end but with the added hassle of getting the new sill piece to sit nicely in line with the existing piece. So the swings and roundabouts would be a) whole new sill and two pulley stile repairs, or b) one pulley stile repair and splice a piece into the sill. I'd offer up a guess that the rot is going to turn out to be worse than expected pushing you towards option a).

Are the outer parts of the sills separate or is it one piece across the whole width? If its one piece you have the extra challenge that you need to stay level across all three openings plus get the mitred corners spot on and pulled tight against each other!

 

[LeonUk]

The way forward is to cut out all of the rotten timber until you’re back to something that’s properly solid. Doing that on a 45° angle or a shallow scarf works well because it gives the splice more surface area and helps the joint shed water rather than letting it creep in. Once you’ve opened it up, splice in your new piece of cill. Use a strong glue like epoxy or polyurethane and fix it in place securely, then deal with any small gaps or awkward corners with a two-part resin filler. The filler is there to tidy and seal, not to act as structure.
It helps a lot if your new timber is close to the original in density, and if you can prime every face of it before it goes in, even the hidden ones. When it’s fitted, make sure the outer face has a slight fall so rain runs off cleanly rather than sitting. Once everything is joined and filled, sand it smooth, then get primer, undercoat and topcoats on as soon as possible.

 

[mardinor]

Just make sure to use Timbabuild or RepairCare or similar two-part epoxy. Car body filler or Ronseal is too inflexible and cracks after 2 years. Ask me how I know. (RepairCare still perfect after much bigger repair than yours 10 years later, in direct sun)