How-to repair damaged fibreglass part 2

Last month we looked at repairing damaged fibreglass with a gel coated finish, this month we take a look at a repair from the back where the surface finish is simply rubbed down and painted, this is when you cannot get to the back of the fibreglass and have to repair from the front surface;

• Cut out the damaged fibreglass area with a gig saw or fine saw blade leaving a rectangular hole not circular. The reason here is that you are going to make an “oversize” patch which will have to be manoeuvred into the back of the repair hole at an angle then straightened into position and pulled against the back with wire or string. You cannot get an oversize circle into a smaller circle
• Once the rectangular hole has been cut file at a rough angle of 45 degrees to allow new fibreglass to bond to the old fibreglass
• Cut a piece of thin 2 or 3 ply plywood about 1-2 inches bigger than your hole. Cut 2 holes in it 2 inches apart in the centre of the plywood and run some string through the two holes so that when you place the wood through the repair hole it will straighten the wood up and pull on the string you can then tie the string around a piece of wood in front of the repair hole with the plywood firmly held at the back.
• Abrade the fibreglass at the back of the hole with wet and dry to rough up the surface then clean with acetone.
• Cut 2 pieces of fibreglass mat the same size of the wood, make 2 small holes to thread the string through on both pieces of glass fibre mat.
• Catalyse the resin at 2 % (2 ml per 100 ml resin ). Wet the wood with a brush then lay a piece of glass on the wet wood. Stipple the glass mat with resin holding the string well away.
• Place the other chopped strand mat through the string and with more resin wet this out on to the first piece of glassfibre again stippling to get the air out. You should have a piece of wood with two wet layers of fibreglass adhered to it with two pieces of string coming up the centre area.
• Manoeuvre the wood through the repair hole and straighten into position so the wet resin and glass are pressed to the rear of the hole. Place an other  piece of wood in the front and tie the string loosely around the wood in front, then twist the wood around tightening the string and thus Appling pressure to the plywood holding the wet laminate to the rear of the repair hole. Only apply enough pressure to hold the plywood and resin  to be held with a very slight bow inward.
• Allow to cure
• Cut the string, now either add layers of resin and glass to go close to the surface, and let it cure, then fill with body filler, or if it the repair is to a thin laminate then just fill the hole with a good body repair mixture. Leave slightly proud.
• Rub down the repair with various grades of wet and dry 240 600, and 800 grit, then paint to match.

PLEASE NOTE: This advice is given in good faith for guidance only, and is given without guarantee, or warranty, and users should use there own judgement on the suitability of there specific project.