Absolutely! In fact, a good putty knife is perfect for wood filler-way better than those tiny plastic spreaders they give you with the filler. Let me tell you why: wood filler is thicker than drywall mud, so you need a blade that's sturdy enough to push it into cracks and holes, but not so stiff it scrapes the wood. High-quality putty knives have just the right balance-stiff blade to spread evenly, but a little flex to get into tight spots.
I refinished a wooden desk last year, and used my 2-inch Warner putty knife for the wood filler. The blade was thick enough to pack filler into the small cracks in the wood, and the sharp edge let me smooth it out perfectly. I tried a cheap plastic spreader first, and it bent under the filler-ended up with lumps everywhere. The good knife? Filler went on smooth, and I could sand it down to match the wood in minutes.
Just make sure you pick the right size. For small wood cracks or nail holes, a 1-2 inch blade is ideal-precision is key. For bigger gaps (like between floorboards) or covering large areas, a 3-4 inch blade works better. I fixed a big gap in my wooden bookshelf with a 3-inch Stanley knife, and the filler spread so evenly you can't even tell it was there.
One thing to note: clean the knife right after using wood filler! Wood filler dries hard, so if you leave it on the blade, it'll be a pain to scrape off. But since high-quality knives have smooth blades, a quick wipe with a damp cloth (or mineral spirits for oil-based filler) does the trick. I've used my knife for wood filler a dozen times, and it still looks brand new.
Don't waste money on special wood filler tools-your high-quality putty knife can do the job better. I've talked to carpenters who swear by using their putty knives for wood filler-they say it gives them more control than any other tool. Give it a try, and you'll see what I mean!
