On 27/09/2020 08:51, Martin Brown wrote:
On 26/09/2020 19:10, John Rumm wrote:
On 26/09/2020 18:11, Peter wrote:
Bay window has rot in the bottom of the 6 boards which form the
boxes. Going to cut away and piece in new timber lower 6-12" or so
each one. Could cut 90deg and put a couple of dowels in, or scarf to
increase the connecting end grain area. Or something else?

I quite like doing a scarf joint since you can then use screws into
the face to bring the joint together. You can use a two part resin
filler in the joint as well to form the glue and exclude any voids in
the process, and fill the screw head holes (if countersunk a little).

+1

But I prefer the space filling high strength high tack PU glues for
sealing the joint since the foam is somewhat more flexible to allow for
the wood dimensions varying with humidity. Two part resin filler looks
neater at first but invariably cracks after a year or two.

Two part is fine over the screw heads but I have always found that it
cracks sooner or later if used in a joint.

In reality any glue can fail if there is differential movement between
the parts. The foam of a PU glue does not have much strength though.
Something like gripfil may retain some flexibility for longer.
Ultimately trying to use a similar wood that will expand and contract at
a similar rate, and also painting everything really well to keep the
water out for as long as possible. (and ensuring things like drips,
seals, and flashings are in place and working)


--
Cheers,

John.

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