Use a polyester filler to rebuild rotted or damaged wood. You can mold and shape it to match the original wood profile. It takes paint well and won't rot.
Remove rotted wood with a 5-in-1 or other sharp tool. Then coat the area with wood hardener as shown. Mix polyester wood filler and press it into the recess with a putty knife.
Carve the partially hardened sagging wood filler with a putty knife or chisel. Add another layer of filler if necessary.
If you've done any auto body repair, you've probably worked with two-part polyester filler. Minwax High Performance Wood Filler is one brand formulated for wood repair, but a gallon container of Bondo or some other brand of two-part auto body polyester will also work and may be less expensive for larger fixes.
The process for repairing wood is much the same whether you're using polyester filler or epoxy. Instead of epoxy consolidant, you'll use High Performance Wood Hardener to solidify and strengthen the wood fibers (Photo 1). Polyester begins hardening faster than Abatron WoodEpox. Depending on the temperature, you'll have about 10 to 15 minutes to work before the filler starts to harden.
Also, unlike WoodEpox, polyester tends to sag when you're doing vertical repairs. One trick is to build a form and line it with plastic sheeting. Press the form against the filler and attach it with screws. Then pull it off after the filler hardens. Or you can wait until the sagging filler reaches the hardness of soap and carve it off with a putty knife or chisel or shape it with a Surform plane or rasp (Photo 2). Most medium to large repairs will require at least two layers of filler. Complete the repair by sanding and priming the filled area and then painting.
Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.
Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.