Rotted house windows

I have some wood windows that, in some cases, are rotted practically all the way through the slider. After I gouge all the rot out what should I use to fill the hole?

Some of the suggestions I’ve received are Bondo, plastic wood, sandable epoxy and wood dough. Also, is there a difference between Bondo and plastic wood?

I always associate Bondo with sheet metal repair but maybe someone knows something that I don’t. I am a big fan of Plastic Wood. I bought a couple of small cans just this week to replace parts of a door frame. It is easy to worth with, fairly inexpensive, and you can’t tell it is there when you are finished.

I don’t think Bondo has the needed density or strength. AFAIK, it is a filler only and cannot bear any structural loads.

I would recommend replacing the wooden parts entirely. There is no doubt rot, fungus, etc. that is not visible on the surface. To not replace the affected piece is akin to bondo-ing over rust pits on a car. This is especially true in cases of extensive rot such as you describe, where the objects are:
“in some cases, are rotted practically all the way through…”.

I agree with JCHeckler. Wood filler is not intended to be used for filling large holes. It’s best used for small cracks, knotholes and nail holes. Getting out ALL of the ritted material and moisture is going to be very difficult. If you don’t get it all out, the wood will keep rotting, but this time it’ll be hidden by the wood filler.

Bondo should not be used. It’s not as flexible as materials made for filling wood, so it will crack. It also may not adhere very well to wood.

If the rot is as extensive as you say, replacement is the way to go.

Plastic Wood is wonderful stuff, but for larger repairs a two part wood filler like this is easier to use, tougher and more economical. Of course YMMV.

Just rip the wood down to whats not rotted & put in fresh wood, thats the way to do it. Also,
find out how water got in to rot it in the first place, if it did. Redwood is great for window
frames, don’t you guys think? Pine tends to rot.