CAUTION - Wear a respirator, have good ventilation, especially when sanding. Don't touch the putty with your hands (wear gloves) for both parts of the two part mixture can be dangerous to your health.

TIPS: If you run out of the tube of hardener, you can buy more. Before adding the hardener, kneed it in the tube to make sure it's mixed up well. Be sure the temp is above 65 and below 80 before using it. The mixing ratio is a golf ball size of putty to an inch of hardener. After mixing, you'll have to work quickly because it hardens within a few minutes. 

Excellent Bondo video by Craig Shotwell  >>>  https://youtu.be/zXEsvErcvFY

Durhams Rock Hard Putty - This is an inexpensive wood filler that has high recommendations from furniture flippers. Durhams can be used in molds.

Mix the powder with water and use a metal scraper to apply it. It doesn't shrink much if at all, so put it on, let it dry and sand off any extra. See video below.

TIPS: Make sure your piece is clean and not too shallow, though filling scratches is possible, depending on how deep the scratch goes. If it is very shallow, you may be able to just sand it out.

Some reviewers say to expect some shrinkage with wood putty so compensate by overfilling just a bit and then sand it down. The only caution I have with that advice is the fact that Durhams dries ROCK HARD and will be hard to sand down. Practice a bit if using that product till you get the hang of it.

If you prefer working with a liquidy type of filler, consider Retique It's Mud Filler. It's easy to work with. We use either product depending on the piece we are working on and our preferences at the time.

Add very little water to start with if using Durhams. It dries quickly and hard, but you can sand it easily and it sticks well. If you keep the canister top on tight, the putty powder will last a long time.