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Gel coat repair


jocave

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A few months back I had a slow speed collision with a bridge that jumped out on me , apart from losing a fender I didn't really pay much attention to it, just visited the boat to winterize it and now that its gone a bit green and mouldy I can see that the gel coat has cracked and has crazing around the impact area, what is the best way to repair this?? Not the best pic but if you zoom in you can see the damage just below the cleat and above the ball fender

IMG-20171202-WA0006-1.jpg

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Don't even think about doing it until the temperature is back over 15 deg C. You will be using polyester resin/ gel coat which will not cure properly below this temp. You can force it with extra catalyst and cobalt promoter so it goes off quicker but it will not get to full cure. Wait until April unless you have a heated dock.

Edited by Dr Bob
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9 hours ago, jocave said:

OK thanks ,anything I can do as a temporary measure over the winter or am I worrying about nothing, worried about moisture getting in and freezing and making the damage worse..

It be reat ;)

Dont worry about it until next year.

This way you have time to research what needs to be done and prep yourself for the job at hand. It will feel daunting to grind away you boat but by time you are ready it feel easier ;)

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If the surface is not painted and you want the repair to match the existing white GRP its best to have gel coat repairs done professionally. The experts can colour match to your gel coat and make an invisible repair. 

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I'm on a keyboard now so can give a bit more info.

As I said before polyester needs at least 15deg C to cure and preferably 20degC. Leave it 'till April earliest.

Your photo doesnt show enough detail. Can you do a much closer up one? A repair will be aiming to do 2 things, 1) repairing any structural damage 2) making it look good again. Most people can achieve (1). Very few can achieve (2) hence MartnG comments above. The biggest issue with (2) is being able to match the colour. It is not white. It will have a yellow/grey/blue element in the shade and colour matching that will be very difficult. If it is (2) you are after it is unlikely you will get it right first time. If you do it, watch as many Youtube video as you can or better still get someone who knows what they are doing to show you. Be aware that the colour of the gel coat before curing will not be the same as the finally cured product.

The repair will include:

-grinding back the damaged area to get rid of the cracked gel coat and to grind out any of the laminate that has been damaged (need to see the picture to assess this). I doubt however much laminate will be damaged. Also on these older boats, the laminate thickness was 'thick' so a small impact is going to do not real damage and the strength of the 'damaged' laminate will be fine for the duty it needs to perform.

- Repairing the laminate with chopstrand mat and polyester resin, worked in with a brush and roller, if bad laminate damage, or just apply some body filler (ie car repair body filler) if no real damage to the laminate. These body fillers are designed to cure very fast and then be sandable within minutes (and much easier to sand within a few hours of application - much harder the following day)

- Apply a gel coat over the top of the sanded repair. Easier said than done. Polyester cures to a 'tacky' finish if done in air. When you hand laminate a boat, the gel coat goes on first and so the outside face (on the finished boat) is not in contact with air on curing. The back of the laminate is and this will be slightly tacky - or more usually the resin is formulated with a bit of wax in it so this comes to the surface and takes away the tack. Gel coats dont have wax. The way we did it was to apply the gel coat to a piece of melanex film at the right thickness and then put that on the repair surface (like you would a plaster) and smooth any air bubbles under the gel coat. Once the gel coat has gone off then peel off the film. The skill is in getting this perfect and why you really need an expert doing it. Get it wrong and you have a lot of sanding, Tcut'ing etc to get a perfect finish. It is easy to get a good repair that will stop moisture getting into the laminate - but not easy to get it looking pretty.

Matching the colour will be very difficult there are at least 256 shades of white. Actually 10 to the power 256 shades of white.

Use a hair drier to get the temp up to 25C ish for the first hour of cure and if a cold night is due, cover it with a blanket to try and keep some heat in. Dont go over 40C.

Post a close up and we may be able to see how big a job this is. Water could get in and freeze and make it worse but that will only affect the laminate and I think you have so much 'in hand' that this is not a problem till next summer. Smear some vaseline/grease over any breaks in the gel coat as a temp measure but probably not needed on a vertical surface. You will be removing all the grease during the repair.

 

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