How to Block Sand Body Filler

Block sand your car's body filler.

Preparing a car body to be painted is one of the most tedious jobs of the entire process. Every low spot and dent must either be removed or filled evenly with body filler. If a body filler is used, it must be sanded with the aid of a plastic or wooden sanding block. The sanding block is, just as the name implies, a block that the sandpaper wraps around for support. The block is also used to ensure an even, smooth finish while sanding the body filler area.

Things You'll Need

• Sanding block
• 220-grit blocking sandpaper
• 400-grit blocking sandpaper
• Lint free rag
• Naphtha or paint thinner
• Paint primer

Instructions

1. Attach a piece of 220-grit blocking sandpaper to the sanding block. Body filler should be dry to the touch, not completely hardened. It should produce a powder when sanded if it is dry enough to be worked.

2. Hold the sanding block firmly and sand the body filled area in a criss-cross pattern. Extend the sanding strokes about two inches in each direction beyond the area containing the filler. This will help blend the repaired body section into the surrounding body and make for a seamless transition.

3. Wipe the excess dust away from the area being worked to help prevent the sandpaper from becoming loaded with filler. Continue sanding the area until it's smooth to the touch.

4. Remove the 220-grit sandpaper from the sanding block and install the 400-grit sandpaper onto the sanding block. Sand the body filled area using the same criss-cross pattern as before. Continue to keep the area clean of excess powder produced by the sanding action. Extend the strokes of the sanding block a couple of inches beyond the body filled area to blend the repaired section of the body into the surrounding body part. Once this area is smooth to the touch with no blemishes, stop sanding.

5. Wipe the repaired area clean with a lint free rag and naphtha or paint thinner to lift all powder and debris from the area to be primed.

6. Apply paint primer over the repaired body filled area and allow to dry.

Tips & Warnings

• Properly mixed body filler should have a solid color indicating it has been completely mixed.

• Do not mix more hardener into the body filler than is called for by the mixing instructions. Excessive hardener will not allow the body filler to properly cure and cause it to crack.

References

• Hot Rod: Block-Sanding Basics - 125 Steps To Perfect Paint