External wooden joint

[scudo12]

I am replacing a small section of a wooden window frame (about 10 inches) I have copied the part quite accurately but wondering about the left and right sides should I pack the sides with 2 part filler then insert the `new part` to get a good seal before painting.
As it stands the gap would be approx 1 mm either side but I could widen that if better for the filler to adhere.
I also read sawdust & wood glue as an alternative.

Suggestions?

 

[Notch7]

If you want a long term joint, I’d use MS polymer or polyurethane mastic.

sikaflex is one brand, sold in screwfix.

it won’t sand flat like 2 pack, but it’s flexible so will last a long time and it’s paintable unlike silicone.

2 pack will give you a perfect invisible joint, but will crack eventually

 

[opps]

MS polymers are a good shout. A better (sandable) option would be epoxy resin filler. They aren't cheap though and most require a special skeleton gun to dispense them before you mix them. RepairCare however do sell one that will work in a regular gun.

https://www.brewers.co.uk/product/NC940512

40 quid though

As Notch7 says, regular 2 pack is likely to crack and let water in. Epoxy is slightly flexible and designed specifically for the task.

Personally, I normally use the TimbaBuild epoxy resins. I have used RepairCare in the past but TimbaBuild is about 30% cheaper. Both are good brands though.

If cost is a factor, polyurethane glue (Gorilla, etc) should provide a decent seal (provided that your joints are pretty tight). It expands as it cures but is easy to sand back. The MS polymers recommended by Notch7 have far better gap filling properties and if the joins are not load bearing, will be fine. The downside is that you will see the glue line. Oh, and if you do use them, paint them with water based primer first. Oil based paints remain tacky when painted straight over them.