Flowcoat -GRP only or is there an epoxy too?

[ianat182]

When I last had repairs done to my boat they used Flowcoat to finish and match the existing white GRP. Is there a source that describes fully how to make up the flowcoat for DIY application. I understand that it is resin or gelcoat mixed with a wax (What wax?) to obtain the paint-like finish. How much wax etc.?
Is there also an epoxy resin version of the same.
The finish they achieved was very good, as if the repair had been moulded and very smooth.
Does it have to be made up and used immediately or does it have a longer 'life' ?


ianat182

[Avocet]

Flowcoat (sometimes called topcoat, I think) is just gelcoat with pigment and a tiny bit of wax disolved in styrene. Polyester gelcoat won't go off properly if its in contact with air. That doesn't matter when it's a gelcoat because one side of it will be up against the inside of the mould and the other will be covered by the laminate. If you want to paint it on top of something and set properly, you need to exclude the air from the surface. That's usually done by buying "wax in styrene" (I know Glasplies sell it) and adding 2% (by weight) to the gelcoat resin. You then paint it on as normal and leave it. The wax migrates to the surface and excludes the air, so it sets properly. It keeps for ages (a year or two in reasonable conditions).

I don't think there's an epoxy version of the same. Epoxy will set whether air is present or not, so there's no need. I'm sure you could thicken (and maybe pigment) epoxy resin with something to make it a bit like flowcoat, but I've never tried it. Epoxy is a damned site harder than polyester to sand. You can thicken it with microballoons (brown) or colloidal silica (white) but using the silica makes it very hard to sand! Microballoons are a lot easier.

[Norman_E]

I think that there may be an issue with using epoxy in places exposed to strong sunlight. The grp expert who has done gelcoat repairs on my boat did tell me that the epoxy putty I used on the rudder was fine there but should not be used for deck repairs because it was not very UV proof.

[Boreades]

I think that there may be an issue with using epoxy in places exposed to strong sunlight. The grp expert who has done gelcoat repairs on my boat did tell me that the epoxy putty I used on the rudder was fine there but should not be used for deck repairs because it was not very UV proof.

I've been waiting for my neurons to bump into each other, to tell me what it is I remember, but they're slow tonight. It's something like the same reason nylon mooring lines are carp, because UV exposure hardens them. In epoxy that would mean becoming brittle and more vulnerable to shock fracturing etc. Or something like that.

[oldsaltoz]

Just pop into a chandler and pick up a small bottle of wax, instructions come with it.

Do not use epoxy, UV light will cause to degrade and change colour, going brownish after some time.

Wax comes to the surface and prevents air contacting the resin/catalyst so it cures without the need to apply a thin film of plastic.

Good luck and fair winds.

[ianat182]

Thank you Avocet,Boreades,NormanE, and OldsaltOz. Seems the glass resin rather than an epoxy is the way to go.
Just one question more; is the Styrene/wax additional to the catalyst for the resin,or does it replace it?
I guess cure time depends on temperature as usual and mix proportions.


ianat182

[Norman_E]

You will still need the catalyst, nothing will set without it. The wax should have instructions on how much to add and when. If it says nothing it about when to mix it in it may be easier to get it mixed into the resin before adding the catalyst. I have seen deck repairs done with a plastic tape put over the setting mixture. Whether wax was also added I don't know.

[ianat182]

NormanE . Thanks again for that.


ianat182

[oldsaltoz]

The plastic covering is only required if no wax has been added, or, to get a smooth finish and reduce sanding.

Catalyst should only be added after mixing, because of the higher than normal ratio of solids in the mix you will need less catalyst than for a simple resin mix.

Good luck and fair winds.

[VicS]

I've never used the wax but I've often used sticky tape on small repairs.
However if you will be sanding back etc ITYWF that neither are necessary