April 2003 Telltale page 7-8 - by Tom Winlow and Marcel Laroche.
Last month, we replaced the wet core in the cockpit seat by removing the inside skin of the laminate. If the exterior skin does not need any repairs, it is simply a matter of drilling the holes for the hinges and reinstalling the seat. Voila, you are finished. If the seat's outside skin laminate is cracked right through, it will have to be repaired, otherwise the core will rapidly get wet again. Begin by grinding the gelcoat and laminate until the core is reached. Feather the edges of the laminate on each side of the crack to a slope of 1 in 12. For a 1/8inch thick top skin laminate, that's 12/8 or 1-1/2inch on each side of the crack. Fill the repair area with glass cloth and polyester resin, not epoxy resin. The reason for not using epoxy resin to repair the top part of the seat, is that gelcoat will not harden properly when applied over epoxy resin. Sand the repair area and the rest of the non-skid surface of the gelcoat, until it is smooth. There is no need to remove all the gelcoat. Then sand the repair area until about 1/16inch below the surrounding gelcoat. This will allow for sufficient gelcoat thickness to hide the repair area. Gelcoat is not nearly as opaque as paint; therefore more thickness is required to hide the darker colour of the laminate. Open up isolated gelcoat cracks to the "V" groove shape with a sharp knife. If there are many gelcoat cracks close together, sand gelcoat off to the laminate in that area. In order not to damage the smooth part of the gelcoat surrounding the non-skid, cover it with two layers of masking tape before sanding the non-skid off.
The two main problems encountered when doing gelcoat repairs
A) Matching the colour of 10-20year old gelcoat
B) Matching the non-skid pattern.
This can be quite a problem if the repair area is in the middle of the deck, but is much less so if the whole seat hatch is being resurfaced. A slight colour mismatch, or a small difference in the non-skid pattern, will not be so evident due to the gap around the cockpit seat edges.
Buy a litre of white gelcoat with air dry already mixed in it. The air dry seals the gelcoat from the air and allows it to cure tack free. Also, buy a colour kit with mixing instructions, explaining which colours to use to make different colours. A kit usually contains six basic colours (black, white, red, green, yellow and blue). Matching the colour of new gelcoat to 20-year-old gelcoat is more an art than a science. A near match is about the best that most of us can achieve.
Begin by washing the seat surface thoroughly, to see what is the real colour of the old gelcoat. Since most deck colours are white or nearly so, pour about one ounce of white gelcoat in a small dixie cup, then put a drop of that gelcoat on the old gelcoat. You will be surprised at how white the new gelcoat is compared to the old gelcoat. That is due in part, to the sun yellowing the gelcoat through the years and also because builders often used a bit of beige, yellow or gray, to obtain an off-white colour. Add colourant to an ounce of gelcoat only and not to a whole litre, until you are satisfied that you have the proper proportions.
When adding colour to white gelcoat, add only a speck of colourant at a time, mix well and put a drop of this new mixture next to the previous one, to see how you are progressing. Keep on adding a speck at a time and check again. If you overshoot slightly with the colour, add 1/2ounce of white gelcoat and check again. If it is still too yellow, put that mixture aside and begin anew. You may have to add a bit of beige or gray to your mixture. You may have to start over many times before you obtain a near match. The old adage; "If at first" Is quite applicable here. Sometimes it pays off to put the whole thing aside and try again later. If all else fails, get a woman. (Not for that, silly.) It is a medical fact that women are five times less likely than a man to be partly colourblind. Once you are satisfied that the one ounce mixture is close enough, mix twice as much gelcoat needed to regel the cockpit seat surface. Proceed as with the small sample mixture, by adding the required colours in small amounts and checking the colour match frequently against the old gelcoat, until you are satisfied of the colour match.
If the repair area extends into the smooth part of the gelcoat around the seat, this will have to be repaired first. Clean that area with acetone, and apply two layers of masking tape about ½inch outside the repair area. Apply the gelcoat with a brush so that it is proud of the masking tape. Level the gelcoat with a wide putty knife flush with the masking tape. The gelcoat will feel hard in 2-3 hours, but wait 12 hours before sanding for a smoother finish. Rough sand with 320 or 400grit wet and dry sandpaper, then finish sanding with 600 grit paper using lots of water and polish with rubbing compound. Use a wood block behind the sandpaper for a smooth and level finish. Tape the smooth area of the seat with two layers of masking tape and apply gelcoat to the repair areas of the non-skid portion of the seat, until it is slightly higher than the rest of the seat surface. After it has hardened, sand flush with medium grit dry sandpaper backed by a wood block. Use a metal ruler to verify that the repair area is level with the rest of the seat. You are now ready to apply the final coat of gelcoat and at the same time, trying to duplicate the non-skid pattern of the rest of the cockpit.
Pour one ounce of gelcoat without catalyst onto the seat and using mall paint rollers with different hair lengths, try to duplicate the existing non-skid finish. This should give you a finish similar to older C&C, and Ontarios. For other non-skids that look and feel like sandpaper, use a foam roller for a flatter finish and add fine or medium grit to the gelcoat and mix well before applying. Once you are satisfied of the non-skid finish, wipe off the uncatalysted gelcoat. You are now ready for the real thing.
Pour enough coloured gelcoat into a container to cover the whole seat, add the grit, if that is the case, and the catalyst (about one drop per tablespoon) stir well. Put some gelcoat onto the middle of the seat surface and start rolling in all directions. Add some more as required. The gelcoat should start to harden between one to two hours. If it is slow to harden because of a cold seat surface, apply heat with an electrical heater. Let it harden for about 24 hours before stepping on it.
If the seat surface has a geometric pattern, like Tanzers or Catalinas, do not sand the whole non-skid surface but only the area to be repaired. Apply coloured gelcoat to the repair area until it is higher than the surrounding area. After it has hardened, protect the surrounding area with two wide layers of masking tape. Using a body file, (see your local body shop) carefully file the surface until flush with the two layers of masking tape. Fill in any depressions with gelcoat, let harden and file again. Once all depressions have been filled, remove the masking tape and file the repair area until flush with the geometric pattern. Let the gelcoat harden for 12 hours. Now is the time to do some sculpting. It is not very difficult and it is fun.
Line up a steel ruler that overlaps the repair area by at least six inches on each side, with the grooves in the geometric pattern. Once satisfied that the groove on one side lines up with the grooves on the other side, use a very sharp utility knife to cut a 1/16inch deep groove in the repair area. Begin in the middle and work outward, being careful to maintain an even spacing between the grooves. Once you have cut all the grooves in one direction, cut all the grooves in the other direction. Are you having fun yet? Using a new (SHARP) square file and the steel ruler as a guide, carefully file the grooves progressively deeper until they match the depth of the grooves in the old pattern. Be careful not to go too deep, because the darker glass laminate will show through. This can be rectified with a bit of gelcoat and a toothpick.
If you have done a careful job, the repairs will stand out a little, but people will be amused and amazed at your sculpting skills. Gelcoat work is similar to brain surgery, but when working on an old boat that looks like FRANKENSTEIN'S, don't be afraid, it's bound to be an improvement.