Posted on the Fibreglass Portal on Thursday September 3rd 2009

Fibreglass is easily repaired with fresh fibreglass but there are two types of finishing. Either you can have a gel coated finish like the original fibreglass would have had, or a polyester filler finish which is then painted. If you want a gel coated finish then get the correct coloured gel coat before you start old gel coat fades so if you want the finish to blend in send a sample of the gel to us and we will do our best to match it.

First we will look at a repair with a gel coated finish

• Cut the damaged area away, if the old fibreglass has been holed, then cut a round hole at least 2 inches around the damaged area completely removing all the damaged fibreglass. This may leave a circle about 3 or 4 inches in diameter, which is fine. The damaged fibreglass should be ideally cut, using a gig saw or a fine saw blade.
• File the edge of the hole you have made at around 45 degrees, this will enable the new fibreglass to bond to the old
• Clean the area of dust and grease with acetone
• Now you will need to cover the entire hole from the original gel coated surface with a ridged board, waxed card, melamine or plastic sheet. This must be held firmly in place, screw from the out side or if possible wedge the ridged face against the hole.
• This board must not move as it needs to be waxed and polished so the new gel will not stick permanently to it or all you will be doing is sticking a piece of plastic over your hole with fibreglass.
• Once your board is fixed securely and will not move then you can start gelcoating. You will need to use 2% catalyst (2ml per 100ml of gelcoat) do not “whisk” the catalyst into the gelcoat, instead gently mix and stir slowly, this will avoid adding air into the gelcoat and causing pin holing.
• Apply the mixture at least 4mm thick and wait for it to cure, then apply another 4mm and again wait to cure. A cured gelcoat will be tacky to the touch, 2-3 hours will give it ample time to cure.
• Cut your chopped strand mat to fit the area you have cut out, you may need 4 or 5 pieces. If you are going to be needing more 6-7 pieces for example then you will need to do this in 2 sessions, no more than 4 layers of fibreglass should be laid in each session, the heat will generate too much heat during curing and will cause excessive shrinkage.
• Mix sufficient resin to wet out the glass you have cut, the amount of resin you will need os 2.5 times the weight of the glass you have cut,  2% catalyst again and then you can start to laminate the glass with a Laminating brush, stipple the resin into the glass rather than the brush and make sure that all the air has been removed out of each layer before proceeding to the next layer. If you have a laminating roller then use this to get out the air but for small 3-4 inch holes it is not necessary to use a roller.
• Finally cut some glass overlapping your repaired hole by at least 3 inches, two layers should be enough. Abrade the existing fibreglass around the repair with wet and dry which will rough up the surface, clean with acetone then laminate these last 2 layers and allow to cure.
• Remove the board from the front face and with working through the grades of wet and dry 240 grit, 600 then 800, rub down carefully to match the original profile. Do not rub in one direction only, use a circular motion with a rubbing block. If you had screwed the board to the surface then these holes will need to be filled with catalysed gel before rubbing back. When filling the holes leave a slight raised meniscus on top to allow for shrinkage.
• Buff and polish to a desired finish using a polishing compound.

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.