gelcoat V's painted finish

In my opinion the gel has more protection because of material thickness

 

How much is the difference actually? Gelcoat is something like 1 kg/m2 for boats (how much for dinghies?). What is the weight of the needed filler + paint to get a smooth surface and enough protection?

 

Here you are worried about the weight of paint on a small boat ! the percentage differance is about half a hamburger so next time you dont eat and dont forget to drop a few grams of brown in the loo and a good long pee and you save a lot more than the weight differance between paint and gelcoat !! could even just drop your undies andleave you sunnies and tee shirt on the beach then get a close shave hair cut and a wax job on the sort and curles hell you could really lose that half a hamburger and you save all that weight .you think this is stupid !! Its about as clever as what i been reading .

 

solid GRP density is ~1500kg/m3.
for 25-30 ft boat skin thickness could be 4-5mm, lets say 4.
than 1 m2 weight will be:
1500*0.004=6kg/m2.
+1kg/m2 of gelcoat is 1/6=17% - huge addition.
even 0.5kg/m2 is 8% - still very much extra weight.
0.25kg/m2 =4% - still something to think about.
For small dinghies thickness will be even less, I don't recall now skin thickness of an Optimist, something ~2-3mm come to mind.
And we do not even mention modern sandwich panels, let alone high-tech fibres in them, allowing much less structural weight.

According to those weight calculations, it turns out that main reason for universal use of gelcoat is low cost in production.

 

My question was not how much of the laminate weight is gelcoat. I asked how much less would a filler + paint weight. E.g. Hempel suggests over 1 kg/m2 of epoxy when gelcoat is removed during osmosis reparation: http://www.hempel.com/Internet/IneG...7277854BCF224AC1256CC6004FCE23?OpenDocument&1

 

I do not talk about repairs here, but about new-buildings.
When working from good female moulds, skipping the gelcoat will mean significant weight saving at cost of painting it (labor + materials).
Apparently, not many clients ever ask for this option today .

 

Yes, I know you talk about new boats, but I didn't find any specs for new boat paintings. So how much filler + paint is needed? And why would you need less than for a repair?

 

As new boats are normally built in female moulds, the surface is already smooth.
If gelcoat is skipped, only paint needs to be added.
_________________________

As to osmosis repairs, before adding 1kg/m2 of material, quite a thickness of old, waterlogged, damaged material is removed, so weight wise it could break even.

 

I see no reason that highbuild/primer can't be the first coat in the mould, wait until green and then lay up over it.

I have done this on smaller components that I have moulds for with great success, see no reason why it wouldn't work on larger components.

 

You only need high build if you have to sand and fair etc ! If you have a mould and have to high build theres something wrong . !! Spray a coat of resin on the mould and when it hard lay your glass over it comes out beautiful and oh so thin, backed up with 225 gram csm P matt and then your cloths from there You can colour all the resins using neo zappon dyes !, resin can be 1000 w/d sanded
I used to do this a lot a long time ago !! Its the thinnest coat you can possibly get to keep the glass away from the moulds surface !!

 

Gelcoat on dinghies: ca 300 g/m2
4-5 mm is extremely thick and I would only recommend it in combination with chopper spray method: because the result will be **** in any case.

 

Like I said, highbuild/primer, the product I use is one and the same.
You do prime before topcoat don't you?

Sounds heavy to me, at least 450g/sm heavy and CSM, really?
I thought that stuff had gone the way of the

 

You do use primer, but you do not use high build. We here may have different understandings of terminology.

CSM in UP building is still an option. Especially as first layer after gelcoat it helps to prevent print-through due to curing shrinkage. There is also 30 or 60 g/m2 on the market.

 

I use CC24, it is both
http://www.ppgpmc.com.au/docs/0024 Amercoat CC24 PDS May 08.pdf

Epoxy Primers and topcoats with oilrigs and aeroplanes on the the tin are far more affordable that the ones with shiny yachts on them.

 

From what I have understood, finish type do affect overall weight, and so performances.

Assuming high performance, you are building with vinylester or epoxy resin.

1) Epoxy resin. You will have bonding problems with polyester based gel coat and epoxy. So, you will need a vinylester skin coat , hand wetted, between gel coat and epoxy for resin compatibility and bonding.

So you will have to compare gelcoat weight + skin coat weight (hand wetted CSM is something rather heavy) vs paint + minimal finish on epoxy. Epoxy does not retract on curing, so finish from the mold may be pretty good and need very little fairing.

2)Vinylester resin. Gelcoat has a good bonding with vinylester. The problem of is that vinylester will retract curing, giving print thru aspect. You will also need a skin coat between gelcoat and structural layer, to avoid this print thru effect.

So , in this case, you will have to compare gelcoat + skin coat weight against paint + some finish to fill the print thru aspect (more than with epoxy).

NB the skin coat is something between 2 * 225gr/m² or 225gr/m² + 450 gr/m² CSM hand wetted (not infused). That can be catastrophically heavy when compared to 600 or 800 gr/m² infused biaxial of a sandwich skin.

gelcoat + 225gr CSM + 450 gr CSM is around 3kg/m². Something not to forget.