Step 1
Sand the back of the chair shell with 100-grit sandpaper to roughen the surface.
Step 2
Wash the front and back of the chair shell with acetone and a rag.
Step 3
Apply masking tape over the crack on the front of the chair.
Step 4
Tear four pieces of fiberglass mat into pieces to cover the crack. The first piece should be one inch larger than the crack on all sides. The other three should each be slightly larger than the previous one.
Step 5
Put on rubber gloves.
Step 6
Mix a small batch of fiberglass resin with catalyst in a bucket, following the mixing ratio on the resin container.
Step 7
Brush resin onto the sanded portion of the chair's back.
Step 8
Place the smallest piece of fiberglass over the crack.
Step 9
Tap more resin into the fiberglass until it turns clear, indicating that it is saturated. Work out any trapped air bubbles with the bristles of the brush.
Step 10
Place the next larger piece of fiberglass over the first and saturate it with more resin. Add the third and fourth pieces of fiberglass in the same way.
Step 11
Allow the resin to harden for several hours.
Step 12
Remove the tape from the front of the chair.
Step 13
Mix a small batch of gelcoat and catalyst. The gelcoat color should match the chair.
Step 14
Scrape gelcoat across the crack with a putty knife, completely filling the crack.
Step 15
Allow the gelcoat to harden.
Step 16
Sand the repaired crack with 120-grit sandpaper to remove any marks left by the putty knife. Sand it again with 200-grit, 300-grit and so on until the repair is polished and blends into the surrounding surface.
Step 17
Apply a clear coat product to the chair if desired.
Step 18
Sand the back of the chair smooth if desired.