I have been on my window repair project for a while now. I would suggest Abatron Liquidwood and Wood Epox.

For the exterior trim, some I repaired with Abatron, some I had replaced with Azek trim (back of house), and some with wood (front of house).

Here is a link that might be useful: Abatron

Good stuff, I have used it for my exterior wood shutters with very good results( over 5 years now and still holding up)

There are many threads and videos about wooden window repair in John Leeke's forums. You should also consider the elastomeric epoxy repair system from www.advancedrepair.com.

Here is a link that might be useful: John Leeke's Historic Homeworks

I have both products - Abatron and Advanced Repair's Flexible Wood Epoxy Repair System. I like them both, but I believe the Abatron is less expensive.

I'm working on a set of 6 round-topped double-hung windows right now (at work). They seem to be getting water coming from outside and inside (via condensation) so I'm removing the glass, making new check rails, dipping the weak areas in Abatron, and filling gaps with ART Gel Epoxy before reglazing, painting and reinstalling. The gel epoxy's only flaw is that you cannot really feather it out as you can the Abatron filler. It turned out that the painters 10 years ago had scraped the glass right down to the putty instead of leaving a small margin of paint onto the glass (as one must to ensure that rain is excluded). Hopefully this won't happen again.
Casey

John,

You are welcome.

When I tell people about your forum in person, I tell them it's the place with the eleven-page thread about putty, lest they think the coverage might be superficial. I have gotten some pretty astonished looks in reply.

OMG thank you. I have a bunch of repairs and windows to do and had gotten the Compendium book, I wasn't away there was a forum!

Just wanted to reiterate what others said about getting a GOOD product - Abatron was my choice. As opposed to one that sorta works but not really. I wasted a lot of time and money trying Minwax wood hardener and putty - it is next to useless for anything exterior - hardly made it through one winter. The good stuff is a bit extra cost, but you more than make up for it by saving time & expense not having to deal with it again.

Abatron does not appear to specify the filler used in the paste.

Abatron is so very lightweight I always assumed it was glass micro balloons.
Casey

I bought some glass micro balloons intending to mix them in paint until I saw some posts that the benefits might be over rated. Are they good filler?