applying epoxy to hull

[geconParticipant @gecon]

I have applied glass and cloth epoxy to the Fisher hull. The finish was not much to shout about….rather uneven with several run lines. Sanded it all well back and second application of epoxy -with added thickener- is much better.

Question is: do I need to sand at all, this second coat of epoxy before applying a third coat? I'm thinking of applying this 3rd coat brushing from keel to bulwarks, while previous was brushed on lengthwise. I expect that the 3rd coat will give me enough depth to sand down to a smooth surface to apply epoxy primer, enamel primer, then topcoat.

Any opinions ? suggestions?

George

[geconParticipant @gecon]

[Tim RoweParticipant @timrowe83142]

Hi George

If you leave coating too long the epoxy will have cured and it is better to rub down to provide a key. This only needs to roughen the surface and not change the profile.

The other thing to watch out for is "amine bloom". You will know if you have got it as the surface will feel slightly greasy and this will come off on your finger. This does not mean the epoxy hasn't cured but any bloom must be removed before re-coating. The bloom is water soluble so the prescribed way of removing it is with water with a little detergent. Some people use solvents but be careful.

If in doubt – sand lightly I would say because the best way to obtain thickness with epoxy (solventless varieties) is to apply wet on wet.

Tim R

[geconParticipant @gecon]

Many thanks Tim, I should perhaps have given the hull a new coat last night -while it was a little tacky. I'll give it a light sanding with fine grade and apply another layer. I'll look out for 'amine bloom', never heard of it but then that applies to a lot of things for me!

The epoxy primer I have is also 2-part. Does that mean I can apply that to 'tacky epoxy' and then leave sanding it all smooth until the epoxy primer has cured? Or do you think the epoxy primer should be applied after the last layer of epoxy has cured and has been sanded smooth? Come to think of it, the epoxy primer is meant to give water resistance to the epoxy so that should probably be applied to a cured and ready-sanded hull?

Off to google on 'amina bloom', many thanks,

George

[Colin BishopModerator @colinbishop34627]

Epoxy is waterproof in its own right. In a marine environment you might apply epoxy primer and paint to a GRP boat hull which is normally laid up with polyester resin and gel coat which can absorb water over a long period when immersed (incorrectly referred to as osmosis).

No reason why you can't use it over epoxy resin of course but it's quite expensive. Many modellers use automotive primers and top coats which are cheaper.

Colin

[geconParticipant @gecon]

Thanks Colin, I read the info on the webpages of a 'Halfords type' shop in Norway which sells car parts etc and a lot of cheapish maritime products. That's why I've ended up with treating the Fisher hull as though it was to live in a marina!

I've just added another layer of Epoxy -German made Epoxyhartz- from the nearest model shop 1hr drive each way. I'll consider over this evening what to apply next!

Many thanks.

George

[Tim RoweParticipant @timrowe83142]

Hi George

Your model like you said is not going to be sitting in a marina staying wet all the time so what we do is probably a huge overkill. Except perhaps for Bob who bravely is using hardboard in his latest build. In industrial use there are comprehensive data sheets that tell you exactly when and how extra coats can be applied and cure times etc. Advice for modellers products is sometimes a bit thin.

However because your epoxy primer probably has solvents, to be on the safe side I would apply it to cured sub-coats to avoid the risk of the solvents softening or spoiling the cure. The other thing is that if you apply the primer to a rough surface you are going to sand most of it off so personally I would try to put it onto a relatively smooth base.

I absolutely agree with Colin and there are some excellent high build primers (not epoxy as it is not necessary) that come in aerosols and are very easy to sand. That is what they are designed for. Depending on the colour you can then often go straight to a top coat(s).

The epoxy you are using is the dog's danglies. Used on competition model gliders and precision work. I use it for special jobs and it doesn't bloom. The stuff I am having trouble with is industrial and I am beginning to wonder if it is a faulty batch or been on the shelf too long or something because I have used huge amounts in former jobs.

Hope this helps.

Tim R

[geconParticipant @gecon]

Great help and many thanks to you both. I have just given the hull it's second application of epoxy for today. The previous coat having become 'tacky'.

In >24 hours. I will sand it as smooth as I can and apply the epoxy primer which is coloured white and according to the instructions will fill small flaws. When that's cured, it'll be sanded and that will show any 'valleys' as the white is sanded off the tops!

After that it'll be enamel -primer as often as necssary!- followed by enamel topcoat.

After all your kind efforts, I'll have to post a photo irrespective of the resulting finnish. I saw a matt black Porsche the other day -you couldn't see much detail on that! So there's always the possibility of a matt black 'stealth' hull!

Many thanks again, should have a result by early next week.

George

[geconParticipant @gecon]

Further to my last…I should of course have remembered that epoxy is inherently waterproof. During the build of my full size Fisher 34 in 1985/6 Northshore Yachtyards informed that they gave the hull a coat of EPOXY below the waterline before applying antifouling -to prevent water absorbsion!- into the the gelcoat and polyester laminates.

Anyway, I'll keep plodding along with my non-absorbing model until the fininsh is as good as I can get it.

That's enough 'soapboxing' on epoxy for me, thanks again for sharing your knowledge.

George

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