Paint System For Epoxy Hull

[VIKING]

I Have A Female 47ft Hull Mould And Would Like To Know If It Is Ever Possible To Layup An Epoxy Hull With The Whole Paint System / Fish As In Polyester Layups So The Demoulded Product Is The Finished Item.

This Would Depend On How Perfectly Fair I Can Get My Mould Surface. Aree Any Other Factors. Awlgrip Seem To Do A Good Range Of Paints. Any Ideas/advice From Previous Experience. We Currently Demould , Fair And Then Spray (very Time Consuming)

[Herman]

I ThinK It WoUlD Be MoRe HelpFulL To UsE LeSS UppErCase.

Now your question:

There are several epoxy compatible polyester gelcoats in the market. However, I have not experienced very good results.

This is what we recommend untill so far:

High quality polyester gelcoat (ISO-NPG)
225 grams mat with ISO-NPG or vinylester
cure
sand
do an epoxy layup to your liking

or
home made epoxy gelcoat (epoxy with a little bit silica)
epoxy layup to your liking
demould
sand and paint with a 2K polyurethane system (awlgrip and friends)

[Raggi_Thor]

"Home made epoxy gelcoat" sounds very interesting.
Will that work in a female mould with a lamination if glass+epooxy+divinycell+glass+epoxy?

[Herman]

Yes, depending on circumstances, it would.

Select an epoxy with a large "overcoat window" and thicken this slightly to increase viscosity. Apply this to the mold with a brush or roller. Thickness of the layer should be in the region of 400-800 mu (0,4-0,8mm).

Do some testing before doing the real thing. Experiment with the amount of silica (sold as aerosil, cabosil, coloidal silica, etc).
The thickness of the epoxy should be such that a layer of 0,8mm can be applied without problems. But it should not be so thick that air cannot escape.

Once you have reached a system which works to your likings, write down the mixing ratio with silica, and mix a batch large enough to cover your mold. Let this rest a day, and mix again. Reason is that tiny bubbles of silica can exist, and these only dissolve after a couple of hours.
Of course, mix in the hardener just before you apply the system.

Please remember your boat will need to be painted afterwards. Epoxy is not UV stable. Even epoxy with UV stabilisers will yellow significantly over time.

The only goal is to provide your boat with a layer, which can be sanded without getting fibres on the surface.

Please be very carefull with the following things:
-humidity. Can affect adhesion of the following layers.
-sun (outside or through windows). This can fully cure, affecting adhesion.
-amine carbonate. Sometimes forms on epoxy, depending on formulation, temperature and humidity. If this occurs, wash of the amine layer with a 10:1 mixture of water and ammonia, and a scotchbrite.

[Herman]

Forgot something:

Do test your setup, every time. Never trust assumptions or recommendations from anyone, no matter how experienced. What works for one, might not work for someone else.

[Raggi_Thor]

Thanks, very interesting, we'll try it :-)