Pimples, Not Blisters

[Guest]

My GRP boat has got a a few hundred pimples which are spreading each year. It started 2 years ago with a few here and there, spread to more areas last year, and is pretty generally all over the undersides now.
I've been and read the articles on the famous American serveyors web site (can't remeber the name) and firmly get the impression that DIY fixes are mostly disasterous and professional jobs not much better but a lot more expensive.
It's a well known saying that no boat has ever sunk because of osmosis but this is really starting to play on my mind. I keep thinking of a DIY job, I saw someone in the yard do one last year and he said it is quite straightforward, get the gel coat sludge blasted off then coat with epoxy. However, this is exactly what the American feller seems to be warning against. A professional job would cost almost half the value of the boat which I don't think is cost effective.
What are peolpes' views?

Cheers

 

[Trevor_swfyc]

When you burst one of these pimples is it wet underneath or dry also is there any odour on bursting a pimple?
The answer will point to what the problem possibly is.

Trevor

 

[Guest]

My boat had mild osmosis - just a few blisters - which I ignored because 'no boat has ever sank etc etc' I ignored it for several years until one day I noticed it down by the head. Removed from water and poked screwdriver through hull in several places. Left alone it would certainly have sunk...

With hindsight, whatever your pimples are, I don't think ignoring them, but very tempting of course.

 

[gtmoore]

There's quite an interesting article I found a while ago at
http://jwmarine.bizland.com/Surveying plastic hulls.htm

Some of it's a bit over my head but under the heading Blisters, it lists the 4 types that the surveyor says can occur. There are two types that apparently need no remedial action so if you can identify which ones you have (if it is osmosis) then it might ease your fears!

Cheers

Gavin

 

[trev]

I gather that these pimples are of little fingernail size, or less.
I had an old boat (1970's) which was like this just after removing from the water for winter lay-up. After a few months ashore the pimples would largely disappear.
Anyway, after a couple of years I took her out of the water and allowed the hull to completely dry out (moisture readings taken by surveyor) and again the pimples largely disappeared. Then it was off with the old antifoul and a good coat of epoxy.


Trev

 

[romany123]

had the same problem a few years agoit seems a if it was salt water gerring under layers of old antifoulcleaned of all the layers and bingo gone..what realy upset me was when i asked a guy in the marina that treated osmosis,he took one look and said i had RAMPANT osmosis and should let him quote, I told him to forget it but it was a worry.
Hope all turns out well for you.
Dave



Dave

 

[Guest]

Thanks all of you for the above. I'll poke a few of the pimples to see what occurs.

 

[Nigel_Ward]

A few years ago I had a small sailing cruiser which was covered in small pimples. In some places there were hundreds together, so I sanded all the gel off in the worst area to inspect the laminate behind. It was obvious what had caused the problem which was tiny hollows or cavities in the laminate next to the gel coat. The laminate was perfectly OK. Eventually I decided to remove the gelcoat myself (the boat was only small) which took several days and a lot of dust. I used West System filler and barrier coat to complete the job following their excellent book of instructions. Ans as they say "it does exactly what it says on the can".
I would remove a small patch of gel around a pimple or pimples, just to see what the laminate is like. If it is OK you could get someone to strip the gel and then treat it youself after it has dried out. Do not try doing what I did which is to remove the gel youself unless you have an open space with no-one near as it is very messy!

 

[stretch33]

Had the same trouble on Moody29 surveyor picked it up on pre purchase survey his advice was to strip antifoul and give gel coat good sand. This we did, its messy, time consuming and bloody uncomfortable. But it saved £3500. This removed all the pimples (none had styrene in em) Boat was then coated with 6 coats VC Tar. Two years later boat sold after full survey 'no trace of boat pox or pimples' on report. Good Luck!