Should I use undercoat on relatively good surface?

slawosz

slawosz

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I think its time to paint my boat. My choice is Toplac, and I wonder if I should use undercoat (probably Precote) - the current surface is looking quite good, but here and there the old paint is showing - mostly due to mooring incidents or dinghy parked alongside without fenders. I think when I will sand everything down the surface will be even.
 
Yes. It underpins the depth of colour of the top coat plus ot gives a good key and enables you to see any lumps and bumps you might need to deal with before you apply the top coat. Quality of finish is largely determined by the quality of preparation, not the application of the top coat!
 
john_morris_uk said:
It’ll get filled and sanded but I know I won’t truly see the imperfections until it gets undercoat on it.
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That was my experience, too. It looked great, then it got some primer on it, and all the bits I'd missed screamed out! Fill and sand, fill and sand, then prime again. I still hadn't got 'em all perfect, so repeat until I had.

The roll and tip result justified all the hard work and was getting to where, if I were that fussy, it's be time to do it again 15 years later, but I'm not. From 20m away, it was still fine.
 
Right. So thining, where do you stand on thining, then? Should I thin Toplac or it will be ok as it is?
I am starting having second thoughts about painting, as most of the time I don't get to look and topsides anyway and being relatively new to boating I will ruin my topsides by dinghy or mooring anyway.
 
Not going to answer your question directly, nor dismiss forum wisdom at all, but one of the things I have found on any boat project is it is amazing how helpful the technical departments can be, in my case International paints, Planar heaters, Photonic Universe and Beta marine and the producers of arboseal have all been brilliant. Forums are great but a quick or definitive answer can be obtained by phone or e mail. You might get a little delay in response at antifouling time though if the sun comes out:)
 
slawosz said:
Right. So thining, where do you stand on thining, then? Should I thin Toplac or it will be ok as it is?
I am starting having second thoughts about painting, as most of the time I don't get to look and topsides anyway and being relatively new to boating I will ruin my topsides by dinghy or mooring anyway.
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Thinning depends on conditions when applying the paint - see International's application instructions.

Painting a GRP hull is a last resort activity. It serves no practical purpose - that is does not provide any extra protection. It is a one way street as once you have done it you are stuck with it and if you cock up it can look awful. On the other hand it is cheap on materials but long on time to do properly so the sort of job you undertake when you have run out of more important things to do on the boat - or you want to escape from other things in your life for a couple of weeks in the summer. "Just off to apply another coat of paint, darling - has to be done today to bond properly"
 
Tranona said:
Thinning depends on conditions when applying the paint - see International's application instructions.

Painting a GRP hull is a last resort activity. It serves no practical purpose - that is does not provide any extra protection. It is a one way street as once you have done it you are stuck with it and if you cock up it can look awful. On the other hand it is cheap on materials but long on time to do properly so the sort of job you undertake when you have run out of more important things to do on the boat - or you want to escape from other things in your life for a couple of weeks in the summer. "Just off to apply another coat of paint, darling - has to be done today to bond properly"
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Not disagreeing with Tranona but there is a lot to be said with prioritising bonding with your wife rather than worrying about the top coat. You might actually find your wife it better at tipping off than you - and she will develop ownership. :)

Jonathan
 
So I've ran my own painting and decorating business for 30 plus years and whether it's a boat or not, the core of my job is and always is about the preparation.
Im about to paint my hull for the new season, I painted it last year as well but fancy a different colour just.. Well.. I just do and I have all the kit etc to do it quickly and easily.
That said I'll be sanding it back, cleaning down and undercoating prior to the finish coats of gloss.
If you fancy thinning things down I would advise doing so for maybe a little pot of say 200ml or so (depending on condition and amount of filler etc, it may well be a full litre! ) and once prepped, use this thinned down amount to roll over (foam roller /brush)and seal the bare filler and or imperfections and let dry before full coat of all surfaces with the rest of the undercoat. Then a light rub in between gloss coats with some 240 ish grade paper will give a good finish.
Thinning can be a useful tool but I'd say in UK conditions this time of year to make sure drying time is more than sufficient as well as the temp when applying! Very few paints will enjoy being applied in cold conditions onto a potentially colder substrate and then not given time to "go off".
Other than that if its a colour change like mine will be make sure its a suitable colour UC to make sure the finish looks solid
 
FairweatherDave said:
Not going to answer your question directly, nor dismiss forum wisdom at all, but one of the things I have found on any boat project is it is amazing how helpful the technical departments can be, in my case International paints, Planar heaters, Photonic Universe and Beta marine and the producers of arboseal have all been brilliant. Forums are great but a quick or definitive answer can be obtained by phone or e mail. You might get a little delay in response at antifouling time though if the sun comes out:)
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There is also excellent advice on International's website and on the technical data sheets for each product. I was very pleased with the result of following those directions when using Precote
(necessary over an epoxy repair job) under single-part polyurethane Brightside, which I applied using the roll-and-tip method.
 
Thanks. Just for the record, current paint is really well laid. I should mention that in the first post. It’s sprayed, and finish is very very good. Only got scrubbed by dinghy in few places and peeled off near AF during using club powerful power wash.
Now as I think about it, I indeed newer see topsides during sailing and have plenty other jobs to do, including painting cockpit area and refreshing Interdeck.
 
Two words: Two Pot!
Toplac is a good paint and i have used it myself, but Perfection or opposition company equivalent two pot polyurethane is more than twice as good in terms of finish and durability.
Of course you need the appropriate two pot undercoat.
Yes its a bit more difficult to mix up and you need exactly the right thinners and brush cleaners, but its not that difficult for someone of average intelligence and literacy(i.e read the instructions!) The roll on tip off method can produce results indistinguishable from sprayed on.
 
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