Sandblasted GRP hull and preparation - Gelshield

[iainmillett]

During the winter, my Hunter 23' had her hull sandblasted to take off years of antifoul. I am now faced with a bare hull and subject to filling in any pinholes with Interfill 400 would expect to prime with 5 coats of Gelshield epoxy (by roller?) before 2 coats of antifoul, usually Init Micron Extra.

Are there any snags in any of this - for instance, should I check that the hull is dry enough before I seal in any moisture? The boat has been ashore since last September and appears not to have any osmosis as yet.

I am also not sure whether I will need to mix all the Gelshield in one go or whether I can measure it out as I go along. /forums/images/graemlins/blush.gif

 

[boatbuilder]

Gelshield comes in two colours so that you can see complete coverage of the previos coat. So only mix as muchas you can put on in about 30mins.

 

[wotayottie]

would be sense to check moisture levels first - I did.

you need to thoroughly wash the underside before epoxy coating and if you use normal household detergents, rinse very well.

then it depends on the epoxy you use. the solvent based ones are easier to apply, but need more coats. the solvent free are harder to apply but only need 2. if you chose the latter, dont do what I did and diy with a roller and no one to flat off. I now have a hull with a lovely dimpled finish. /forums/images/graemlins/frown.gif

do it on a nice dry day. have the primer handy so you can apply before the epoxy had completely gone off.

 

[swampthing]

I stripped my Hunter back to gell. It looked immaculate. I got in a surveyor to document this in case I ever want to sell her . He said there was moisture in there and Id be wasting time/money sealing moisture in with gelshield. There was not the tiniest hint of a blister anywhere. Then I see in this months PBO, theyre popping big blisters and sealing a hull? Whats the deal?

 

[oldsaltoz]

G'day Iain,

Check surface key by sanding a small area with a 200 grit paper, if the hull feels smoother than the sanded area, sand the rest.

Run a batten over the hull and check for low spots, you will need to fill them or have a very odd looking finish with smooth edged craters; make sure you only use 'closed cell' balloons or fillers and epoxy resin below the water line.

Essential that a moisture reading is done and confirmed as within required limits prior to any coating.

After sanding, wipe down with plenty of Acetone and use white rags only and plenty of them, leave for 20 minutes to dry just before applying protective coating.

If on a stand, consider treating small areas that the boat can rest on with a small move, or move first and treat areas under contact points. Moving after a full coat to treat small areas can result in damage.

Hope this helps.

Avagoodweekend......

 

[30boat]

The problem with moisture and gelcoat is that if you have the former and the latter is permeable blisters may not develop at all.

 

[paul]

I applied 5 coats to my boat last year. The hull was tested for moisture and found to be dry. It is recoomended that the hull is not treated of the moisture level is high (that means above 15 on a Tramex meter). You can apply wet on dry with Gelshield, so you don't have to do it all in one day. It's the easiest coating I've ever put on a boat (much easier to do than normal antifoul). I put coppercoat on afterwards and have been delighted with the result after one year in warm Med waters.

Paul

 

[iainmillett]

My boatyard has advised me to apply 2 coats at the start and end of each day to make 6 coats in all over 3 dry days. With Gelshied will there be any problem if one coat dries out before a further coat is applied? Also I am told by the boatyard to apply the initial antifoul when the epoxy is still 'tacky'.

The surveyor is lined up this week - and I am advised that for a 7 metre boat that each coat will take 2.5 litres. - seems a lot for a small boat!

 

[Pete7]

Just wonder if there is an advantage in using a hard scrubable antifoul for the first layer then an erroding one on top. That way if the top layers wears away you still have a hard layer of antifouling underneath, worth a thought, just don't use VC Offshore as nothing sticks to it, found that out the hard way.

Pete

 

[iainmillett]

Well - it's all done 5 coats of Gelshield 200 plus 2 coats of Micron Extra - total cost some £500 applied over 5 sunny days. With hindsight my 7M boat took about 1.8 litres of geshield per coat and I would have saved a lot if i back mixed each additional coat into the previous tin! Damn the colours!

Still, we are ashore at present and waiting for the coats to harden up prior to launching around about the 18th July.