It’s best not to use screwdrivers or dirty tools for mixing because they are much harder to clean and could add grease or oil into the mixture.
Finding the right ratio takes experience, but you can get close by estimating that each inch of raw filler diameter requires an inch-length of hardener. For example, if you use an amount of Bondo with a 3 inches (7. 6 cm) diameter, you would mix it with a 3 inches (7. 6 cm) line of hardener. If you’re struggling with finding the right ratio, look at the product instructions or ask a professional for assistance. [4] X Research source
Make sure to apply the mixture within 3 minutes of combining. If you wait longer, the mixture will turn into a gel and won’t stick to anything.
Never use Bondo for any imperfections deeper than 1⁄4 inch (0. 64 cm). Using the product on a ding deeper than 1⁄4 inch (0. 64 cm) will likely not adhere or hold up well, and the Bondo will eventually shrink and either crack or fall off. [7] X Research source If you applied masking tape beforehand, let the filler sit for several minutes before gently removing the tape. [8] X Research source
To avoid scratching the surrounding area, keep the sandpaper on the filler only and don’t let it slide onto the painted surface. Sanding in straight lines creates waves in the filler, so always sand in a criss-cross pattern.
This can be a long and tedious process, but all of your sanding will soon pay off with a smooth, even application!
