Hull blasted - what next?

[sirnippy]

Hi folks - got hull blasted. Goodbye loads of old antifoul. Do I put a coat of epoxy on before priming and painting? Thanks for your help.

 

[Caer Urfa]

I assume the hull is GRP, seeing that you have gone to the expense of having the hull sandblasted I would finish the job properly and now protect the hull.

I applied 5 coats ( different colours) to make sure of good covereage of International Paints Gelshield 200. BUT make sure you apply it at the right temperature and do NOT mix big batches
as it can go off quickly, I suggest mix all you can apply in say 20 minutes at a time.

Once the Gelshield has been applied then 1 x coat of primer then 2 coats of antifoul.

Job Done

 

[DipperToo]

Useful to make the primer a different colour to the Gelshield and antifoul - easy to see when the antifoul wears away then.

 

[Bobc]

Depends on the age of the boat, what it's made of, and how damp the hull is.

If you put epoxy on a hull with dampness in, you will simply be trapping the moisture inside, which at best is a waste of money on epoxy.

 

[PuffTheMagicDragon]

I agree 100%. Have the hull (underwater part) examined for moisture content and mark the readings with a felt pen. Repeat readings after a week and note the new figures. If they are high the way to reduce them, seemingly paradoxical, is to thoroughly wash with fresh water, preferably with a high pressure washer if you have access to one. You can do this twice a day if you wish. Do this washing-drying-reading until the moisture contact appears stable.
At that stage you can start to apply the epoxy; there are many brands, some use different colours (International) while others rely on the successive (transparent) coats giving a darker shade as more coats are applied (Veneziani). I have used and prefer the latter as it gives a better indication of dry paint thickness and which areas reguire more paint because the initial coat was absorbed too easily.
Not a cheap process, by any means, but an expense that is well worth it, IMHO, especially if you intend to keep the boat for at least five years.

 

[Nigelb]

If the hull is dry I would take the opportunity to apply 5 coats of Gelshield, alternative colours and the a coat of hard antifoul before the final coats of eroding antifoul in a contrasting colour.

 

[GrahamM376]

The beauty of gelshield is that coats can be applied over days or months, rather than following on immediately when the last one is tacky, as with some other products. No need for a primer coat if the first coat of antifoul is applied within a few hours.

 

[laika]

Stupid question if I may as I've been considering getting my hull blasted. What about hulls which were already epoxied? I believe my hull was epoxied many (20+?) years ago (before my ownership and before many of the layers of antifoul). As epoxy is harder than eroding antifoul I imagine it's perfectly possible to blast the antifoul and leave the epoxy but what is the normal procedure? Is it to re-epoxy after the blasting?

 

[sirnippy]

Thanks for the help people. The hull is GRP. Looks sound. Boat forty years old. Had chat with yard, and they are going to take moisture readings.

 

[ottow]

A tip to lessen the work involved:
After putting on the last layer of epoxy, wait no more than an hour or two (depends on temperature) and then apply a layer of antifouling.
This practice negates the need for sanding or any extra primer before antifoul, with the epoxy not fully hardened it sticks very well to the surface. Later you may apply a 2nd coat if needed.

I did this on my previous boat and was very happy with the result. Had it blasted in early fall and let it sit until late spring to dry out.

 

[Bobc]

If its 40 years old, I wouldn't waste your money. It will be made of orthophalic polyester resin and chopstrand and is bound to be holding moisture, and it it isn't wet after 40 years, it isn't likely to get wet in the next 40.

Paint it and go sailing (and spend the money you saved on beer).

 

[PuffTheMagicDragon]

Stupid question if I may as I've been considering getting my hull blasted. What about hulls which were already epoxied? I believe my hull was epoxied many (20+?) years ago (before my ownership and before many of the layers of antifoul). As epoxy is harder than eroding antifoul I imagine it's perfectly possible to blast the antifoul and leave the epoxy but what is the normal procedure? Is it to re-epoxy after the blasting?

Epoxy treatment does not last forever.
When I bought my present boat (commissioned in 1973) I proceeded to remove all the layers of old antifouling so as to get to the old epoxy. I noticed some minor 'bumps' (3 or 4mm diameter) and investigated further with a flapdisk on an angle grinder and, sure enough, there was the tell-tale star-burst of water (no smell at all) made very evident by the dust. Trying other areas that looked OK gave similar results. My conclusion was that, although the epoxy looked sound enough, the previous epoxy treatment had started to fail.
That is when I had the yard remove all the old epoxy so that I could apply a new treatment 'from scratch'. The epoxy was so hard that they had to blast it twice, the second time using dry grit. (This did not change the cost because the agreed quotation was to remove all the epoxy). I had calculated that to do it with an angle-grinder would have taken me three weeks.
Although I did not cost my time (being retired) I consider that it was money and effort that was well spent since the boat is a 'keeper'.

 

[sirnippy]

I probably should have put all the details of boat at beginning of thread - particularly that it is forty years old, and not worth a huge sum. Also, it spends six months on a swinging mooring, and six months on the hard.

Bobc - your point - a coat of primer, and two of antifoul? Me and my buddies do like beer.

 

[Bobc]

I probably should have put all the details of boat at beginning of thread - particularly that it is forty years old, and not worth a huge sum. Also, it spends six months on a swinging mooring, and six months on the hard.

Bobc - your point - a coat of primer, and two of antifoul? Me and my buddies do like beer.

Tis the way forward. Mine's a pint, thanks.

 

[EuanMcKenzie]

I've just (last year) had mine blasted then went for copper coat straight onto the bare fibreglass after prep with lots of wet and dry, filling chips etc.

its 1972 age. It has no osmosis so i reckoned it wasn't going to fail on me any time soon. Coppercoat is designed to go straight onto gel coat as long as its clean and dry.

The coppercoat is epoxy based and you put on four coats. I couldn't see the point of the base layer epoxy coat under the copper coat on what is an elderly cruising boat and now I have long term anti-fouling.

Four of us did the painting in a day.

You might find its a cheaper way to go in the longer term

Food for thought!

 

[Halo]

Having gone to the trouble and cost of blasting I would go the extra mile and apply epoxy and Coppercoat. Trouble is both these need warm conditions. If your yard can get her indoors with ample heating then do it. If not then it’s a long wait for warm days or you will do a half baked job.

 

[Neeves]

I could not understand the original post - after blasting, what else but Coppercoat.

I am concerned the yacht spends half the time on the hard and half on a swing mooring - does not leave much time to sail, unless my maths has become worse And as most people here will tell you - age does not come into it.