Repairing auto body using bondo body filler

Bondo body filler is that body filler that fills in dents, used for sculpting curved areas. It’s extremely important to prepare the area properly before applying the bondo, so that it can properly adhere. Find bellow some tips for a successful application.

What to use: 60 and 120 grit sandpaper, square or rectangular shaped power sander, hand held sanding blocks, plastic filler spreaders, bondo, (long hair, short hair, premium or regular), cream hardener in a tube, pallet or mixing tray with a smooth plastic surface, 2-inch putty knife, WD-40 for cleaning, Bondo scraper molding tool, flat edge ruler, level or straight stick, glazing spot putty compound, auto primer spray.

  • Use a 120 grit paper to remove the waxes and paint from the surface where you want the bondo to be applied. You need a dull and dry surface in order for the bondo to stick. Make sure you remove rust from the surface also.
  • Take the mixing pallet, bondo, cream hardener, putty knife and the plastic spreader. Consider the amount of bondo that you need before hand, because you need to work really quick once the bondo is mixed. You can also mix in small quantities and fill areas at a time.
  • Use the putty knife to take the bondo from the can and place it in the middle of the mixing tray. Decide which is the amount that you will be needing.
  • Take the hardener and squeeze it onto the bondo. Use the putty knife to mix the two. This operation takes 1-2 minutes.Clean the blade on the side of the tray once in a while. The long hair bondo has a thick texture, while the premium hairless bondo is thinner.
  • Take some bondo on the edge of the plastic spreader and apply it.Leave the mixing tray bellow the working area in order to catch the drips. Use long single strokes to cover the area from one side to another. It’s important to obtain a smooth finish, sags free. the moment the bondo stats to get stiff stop spreading it. It’s OK if it’s not smooth enough because you will be able to remove the excess when it’s dried hard. In case the deep is too deep, you can come back later and build with new application.
  • According to its thickness, to the temperature and humidity, it may need a few hours to dry.To check if it’s hard enough, stick your fingernail into a corner. If you can do this, it means it’s not dry enough.
  • Take the scraper forming tool and scrape down the edges that are in excess. Move the scraper up and down, from one side to another in angular directions. Maintain the the scraper flush to the surface until the hard edges are smoothed enough.
  • Use 60 grit paper and sand over the area back and forth, from one side to another in order for the bondo area to be as flush as possible.
  • In case there are still rough edges remained, take the 60 grit on a hand block sander and smooth out. Then take the 120 grit paper to sand down and remove all remaining edges.
  • Take the flat edge ruler and verify if the filled area is properly flush. Place the edge across the area at different angels and seek for low and high spots.Take a pencil and mark the areas where more filler is needed or where the sanding needs to be more down.
  • After smoothing the bondo, spray prime the whole area in order to see if there are any flaws remained.
  • Take 120-220 grit paper and hand block sand. Take spot putty glazing compound and fill in the pinholes, smooth the feather edging and create height if needed. The height should not be greater than 1/16-1/8 inch at a time. More bondo might be needed in this case.
  • This operation can be compared with sculpting, so you need a steady hand. Use WD-40 to clean the mixing tray, putty knife and the plastic applicators.
bondo body filler, cream hardener, filling the dents, flat edge ruler, mixing tray, power sander, putty knife, removing the paint, sand block, sandpaper, WD-40