Minwax® Wood Putty® is a non-hardening, pre-mixed putty that repairs small holes and covers other minor imperfections in bare, painted, stained, and finished wood. They will not move with the wood, and the bond between wood fibers treated with them and any subsequent filler will be very poor compared to that between CPES and Epoxy fillers, either Fill-It or our Epoxy Adhesives such as Layup and Laminating adhesive If you want long lasting repairs you must use two part epoxy products, and of all of those available on the market, these are the best.
I just finished doing a large job with this, the roof inspector told me I should put a coat of paint on the chimney siding this year, I went up and the west facing (lots of sun) side was really bad, the wood was getting soft, groovy and crackley and the paint was peeling and cracking, I thought it was a waste of time to put paint on this failing paint, I removed most of the bad paint with an angle grinder.
The damaged area must first be treated with a penetrating epoxy (CPES), to harden the wood and encapsulate any bacteria or fungi, and then either a flowable thick epoxy (Layup & Laminating Resin) added to penetrate the insect tunnels or, if access is clear, an epoxy filler (Fill-It Epoxy Filler) applied to build back bulk and bond with the CPES treated wood.
When repairing wood that has mild dry rot, the CPES will travel through capillary action along the abnormal porosity which dry rot fungus creates within the wood, as long as it continues to be fed in. Impregnation of wood with CPES changes the cellulose of wood (which fungi and bacteria find tasty and easily digestible) into epoxy-impregnated cellulose which resists further attack by fungi and bacteria while reinforcing the wood, accomplishing restoration.
On old, weathered or soft wood the coverage will depend entirely on the absorbency of the wood, and usually varies between 100 and 175 sq. ft. per gallon. Read and follow the instructions and cautions on the container before using any product for repairing rotted wood. The wood is strengthened while allowing normal expansion and contraction with changes in temperature and humidity. I have to say when I was working the chisel, I noticed that the wood filler acted almost just like wood. You have to somehow get the rotted wood out and repaired and then re lad which is almost impossible. But after reading this you still want to try to patch the wood without replacing it, I will continue.