By John Wilde - 9/3/2020 8:33:22 PM
Hi,
Very new here - so go easy on me; but help appreciated if possible.
I have a reasonably decent size GRP sailing yacht, which is quite old, and the gel coat is suffering a lot in discolouration. Most problematically there is a lot of fine crazing. This isnt structural stress related, but is rather fairly uniform across the decks and coachroof seemingly from uv deg or possibly the gel coat being laid up a bit thick back in the 80s. Any painting over the gel coat as is would likely just show through the crazing in time. The extent of crazing makes it impossible to feasibly open all the cracks and fill; while the boat value doesn’t make gel coat stripping viable at all.
I have had a few people recommend the gel coat can be skim coated with an epoxy resin (after a thorough clean and keying in parts) to form a new smooth base (possibly after some sanding) on to which a paint coat can be applied.
This seems like the way forward and a cost and effort I’m willing to take on, but I’m trying to decide on the best epoxy for the job. The variables I have to work to are:
* will need to skim coat both flat, vertical and angled surfaces, which I guess mean high viscosity?
* will be applying in the open air, or at best under a tent; so dust control will be challenging; but I also quite an area to cover;
* would like to try and do over the winter, while boat is out of water, but this mean I need something tolerant to lower temps or that can mixed to compensate for lower temps; or possibly wait for warmer days;
* needs to be paintable, if necessary after sanding;
* would like a strong hard surface, but likewise GRP does tend to flex somewhat, so a degree of flexibility might be necessary
I realise that some of these and at odds so compromise needed. However, I’m not chasing a 100% perfection.
any help appreciated?
John
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By explorecomposites - 9/8/2020 1:07:04 AM
Hi John,
Since it is your boat and you have time, you could try a small area during the warm months and see if it works. Normally the gelcoat would have to come off or the cracks ground out and filled with an epoxy filler and then primed and painted with a 2-part paint. This is tons of work!
You could take an area that is especially bad and try to grind out the cracks with a dremel or pencil grinder... make sure the cracks are in fact only gelcoat-deep! The grind-out doesn't have to be super fussy - you're just trying to prep a bonding surface inside the crack. If chunks of gelcoat pull off like it isn't stuck to the fiberglass you have other issues. Fill the cracks with an epoxy putty using a squeegee to press it in and skim off the excess. You want a putty that is hard enough to almost match the gelcoat - like silica or talc - not a light-weight fairing filler. The Aquastop Dentex suggests may be this. Come back and sand the fill and the gelcoat surface and then try an epoxy primer - with a foam roller is fine - and roll on a few coats. It can usually be recoated after half and hour. Sand this fair and try a topcoat 2-part with a roller, foam brush or spray (depending on the product and your fussyness) - if you have non-skid this can be done with a roller and skid particles too but spray looks better.
If you like the result then you could do some more filling with the epoxy over the warm months when adhesion and cure time is good. Make sure it is all clean (wash with soap and let dry before the repair) and then let the ground out gelcoat dry out too. Worst-case it is a ton of work and the cracks pop back through in a month and you have learned something! If the cracks are prepped/ground out ok the epoxy should stick - and if there is no underlying structural flexibility the propagates the cracking (like wet/delaminated core) you should have decent results.
Your picture didn't come through so we are all imagining - but gelcoat cracks are pretty common so that's ok. They would help though!
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