Osmosis DIY

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swanson37

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Probably a thread thats been done to death, but my searches didn't turn up that much.

My hull was diagnosed by a surveyor as having a slight trace of osmosis a couple of years back. At the time the boat was anti-fouled and bunged back in the water with the surveyor saying "she'll be right" (this is in Australia obviously) and the boatyard guy issuing dire warnings about the nightmare it will be if I don't fix it immediately (and that'll be 8000 dollars please). Needless to say I ignored the boatyard guy, used my crowbar to get his hand out of my wallet, and I find myself two years later needing a new antifoul and thinking that this time I'll do it all myself (normally too damm busy with work to a job this large). So I want to treat whatever blisters are there, IU'm not looking for a full strip job....I'm fairly handy when it comes to DIY, I have refurbished the interior of my boat, rebuuilt a couple of vintage cars and restored a few old houses and therefore am no stranger to hard work and power tools...

My plan is to get her out on the hard and get her power washed and dried. Then I'll grind out the blisters (must buy an angle grinder) while the missus and any other poor sod I can rope in sand down below the waterline to get rid of the old antifoul. Then I figured I'd wash out the blisters and leave the boat a couple of weeks in the warm Oz sunshine to dry out before filling with epoxy sanding/fairing and then finally a new coat of antifoul...

What I'm looking for is a bit of advice (or if you feel like popping down to Melbourne for a bit of hard labour that would be good too :-), I'll stand you a beer or three ) around the whole process, particularly around grinding out the blisters...

a) is an angle grinder the best thing for the job, is there a Fein multi tool attachment that may be better?
b) How do you know you have ground out enough, do you get down through the gelcoat to the matting, is it obvious? - my hull is very thick as the boat was laid up back in the 80s as a custom build to be able to go down the antarctic

Any advice you expert do it yourselfers can give will be greatfully received....

Cheers

Si
 
swanson37 said:
a) is an angle grinder the best thing for the job, is there a Fein multi tool attachment that may be better?
b) How do you know you have ground out enough, do you get down through the gelcoat to the matting, is it obvious? - my hull is very thick as the boat was laid up back in the 80s as a custom build to be able to go down the antarctic

Any advice you expert do it yourselfers can give will be greatfully received....

Cheers

Si
Click to expand...

I paid for a very light grit blasting of the entire underwater section of the hull.
The process automatically opened up the few blisters since the damage caused already offered an exploit to the blasting. The finish resulting from the process offered up an ideal key for the subsequent epoxy skin that I applied over the entire hull.
 
I used a Bosch power scraper to remove my old anti fouling, on my present, non osmosis affected, boat.
Some years ago on a previous boat that had osmosis blisters, after removing the AF,
I cut out the blisters with the same tool, less aggressive than an angle grinder, after drying out, [a bit longer than a couple of weeks here in UK] the holes were filled with epoxy and the hull sanded [make sure you use solvent free epoxy filler] then the whole under water area was coated with Blakes epoxy coating 4 coats, then a tie coat, then AF. Grit blasting as stated is a better and quicker operation, it depends on cost, I was quoted £450 for a 28ft boat last year, hence doing it my self with my Bosch scraper.
 
I think you're on the right lines with most of what you plan - if it's necessary to do anything at all! Surveyors will often say "some signs of osmosis" to cover their backs. It might well mean there is just slightly higher moisture levels below water than above which is hardly surprising in a 20+ year old boat!

Unless the boat is badly blistered I agree best to grind them out. It will be obvious when you get to the bottom of them and most will be at the interface of gelcoat and laminate anyway. Instead of just one wash, do it several times (with fresh water) and with a pressure washer.

If you have access to a moisture meter you can monitor change in level relative to the topsides as it dries out.

As already suggested fill the voids with a solvent free epoxy filler but I recommend coating the voids with a solvent free epoxy resin before filling - it's a much better sealer.

Only other comment I would make - unless there is a plan B with SWMBO - make sure they wet sand the bottom or, even better, use power chisels or blast to remove the old A/F. Lungfuls of poisonous dust are not to be recommended.
 
My 1974 Atlanta had loads of small blisters when I bought her 7 years ago... the usual dire warnings but I thought I'd wait a year.. then another... then another, 7 years later she still has a ( similar) lot of small blisters!
I did treat one square metre by removing all old antifoul, grinding out each blister with a small tool on my drill like a countersink tool, dried out, painted each hole with epoxy then epoxy filled then epoxy 'painted' the whole area. It seemed to work as the area has remained blister free.
So why not try a pilot scheme like this you may then move and do, say, a whole side at a time then rest for a year!!
 
Helped a buddy five years ago do this over a few weekends and he did it much as you've said so IMHO it seems you've hit the nail on the head. Slight difference to angle grinder we used one of the Black and Decker power files, but I guess an angle grinder would be just as good. Just be careful with an a/g that you don't get carried away and go right through the hull - now that would be embarassing.

He used normal slow setting Araldite and last time he checked the hull (2008), there was a few new signs of osmosis but no evidence that the original fix had failed in any way. And overall it cost him about 50 quid in Araldite so not an expensive fix.

You do have to build the epoxy up over three or four layers, cos it's a bit viscous and flows out of the dimples you've ground in the hull and then once you've got it about right, a bit proud, go over it with a sanding disc. We didn't bother with trying to get the finish perfect, the boat is a displacement cruiser used on the river so performance isn't an issue. Maybe with a fast planing hull or racing sail boat, you might want to spend more time getting the surface finish right.

But it is a bit time consuming. Still what else you got to do in the winter? Haven't even got any Ashes to look at.!!!!
 
It has been suggested that an orbital sander be used to show up the blisters, you may find more than you expected. I've been putting off this repair for 17 years, last survey said there's osmosis, so what. (given the heavy lay-up on the early Cygnus commercial boats).
 
Make sure that you remove all traces of the trapped catalyst from the voids with acetone:they'll start to bleed immediately you break the blisters.
I still have some osmosis on my boat but the blisters I've filled previously with epoxy have stayed sound,but still more to do this year.I've seen the results from sandblasting the complete underwater surfaces ,it does a pretty good job. A few members of my club got together and had 5 boats blasted at a knockdown rate of £s from the contractor.
 
swanson37 said:
My hull was diagnosed by a surveyor as having a slight trace of osmosis a couple of years back.

The boatyard guy issuing dire warnings about the nightmare it will be if I don't fix it immediately (and that'll be 8000 dollars please). Needless to say I ignored the boatyard guy,

I find myself two years later needing a new antifoul and thinking that this time I'll do it all myself. So I want to treat whatever blisters are there, not a full strip job.

My plan is to get her out and power washed and dried. Then I'll grind out the blisters sand of the old antifoul. Then wash out the blisters and leave the boat a couple of weeks to dry out before filling with epoxy sanding/fairing and then finally a new coat of antifoul...

Looking for is a bit of advice around the whole process, particularly around grinding out the blisters...

a) is an angle grinder the best thing for the job, is there a Fein multi tool attachment that may be better?

b) How do you know you have ground out enough, is it obvious?Si
Click to expand...

Nice boat,
From the information above I would say do nothing, have another look next time you take her out of the water, I suspect it will be much the same. There is no point in spending time and money as well as loosing sailing time for a problem you don't have.

Even is this was Osmosis a few spots is nothing on a Swanson that age and it certainly will not sink as a result of it.

If and when it gets bad enough and you see blisters the size of 50 cent coins, you can consider fixing it. Just make sure you do the full below water area rather than spots here and there.

Some tips:
Never sand antifoul paint at all if it can be avoided, high pressure water blasting or wet scraping, never a dry system antifoul is highly toxic.

Mark any blisters you see soon after washing, some will shrink overnight. A tortch held close to the hull at night will show even small blisters, you can mark them for grinding later.

Grinding, I only use an angle grinder 100 or 125 mm disc, I use a flexible concrete grinding disc, very aggressive and will not block up. If your back is good you should be able to strip all the gel coat off below the waterline in a day.

You will also need a Dremel rotary tool to get into tight spots and slots.

Grinding affected areas: Holding the grinder at about 12 to 15 degrees to the hull, remove the gel coat and look for a small brownish dot or streak, grind this out a little at a time till you find the hollow or very whitish (no resin) glass, grind till you have a solid clean area with no blemishes or discolouration.

I find it faster to grind out effected areas first then the rest of the gel coat after.

Moisture levels and Washing - drying:
It's very important that no moisture is sealed in the hull, it it is you have wasted time effort and considerable dollars for nothing.:eek:

Washing will remove the chemicals left behind but exposed, it will several washes over a few weeks, if the work is close to home a morning and evening was is good.

After washing has completed you must let it dry out, this can take a long time depending on moisture content and external conditions.

I'm a bit more than half way up the Queensland coast with about 300 days a year of sunshine and even here it has taken up to 14 months in extreme cases, thou 3 to 4 months is more common.

I hope this helps.

Avagoodweekend......:rolleyes:
 
There is a good article in this months PBO from somebody who has done exactly what you are proposing - in Greece so comments about drying will be relevant as well.
 
Do Nothing

Do Nothing go sailing is probably the best bet.

There is a system where you can blast the surface of GRP with dry ice. It bursts the bubbles as well as removes the anti fouling. It does not scour or score the original GRP in any way. The bubbles burst due to the dry ice freezing the liquid. Dry ice blasting is used on the likes of heat exchanger tubes, blades and other delicate items requiring industrial cleaning. My hull was blasted with fine grit but I am not sure that it was necessary.

If you just treat the blisters and do not dry out, just re-antifoul - do not epoxy coat the hull other wise you will lock in the moisture.

Wash frequently with fresh water after bursting to dry out the hull out as the fluid is a salt. The salts absorb moisture, hence the reason to wash frequently during the drying process.
 
Traces of osmosis...mmmmm.

As others have said this could mean anything. You may just have high moisture content or a slight rash rather than defined blisters. I would spend a fair amount of time just exploring exactly what you have before getting yourself ready for action. If you are happy to do this then great but you could try and find a decent hull surveyor who would tell you exactly waht is happening for not much money.

If you don't much then I would leave it be and find something else to do with the spare time (something more enjoyable won't be hard to find).

Good luck.
 
If blasting use the coarseset and heaviest grit possible and blow the hell out of the hull. Only way to pop all the blisters including the incipient ones.
 
BlowingOldBoots said:
Do Nothing go sailing is probably the best bet.

There is a system where you can blast the surface of GRP with dry ice. It bursts the bubbles as well as removes the anti fouling. It does not scour or score the original GRP in any way. The bubbles burst due to the dry ice freezing the liquid. Dry ice blasting is used on the likes of heat exchanger tubes, blades and other delicate items requiring industrial cleaning. My hull was blasted with fine grit but I am not sure that it was necessary.

If you just treat the blisters and do not dry out, just re-antifoul - do not epoxy coat the hull other wise you will lock in the moisture.

Wash frequently with fresh water after bursting to dry out the hull out as the fluid is a salt. The salts absorb moisture, hence the reason to wash frequently during the drying process.
Click to expand...

I have a nephew that has a dry ice blasting business, unfortunately he is in Perth but there is bound to be others in Melbourne. This is definitely the way to go. Clear off all the old antifouling and pop the blisters at the same time.
If it was my boat though I would probably just spot repair the obvious ones each time I slipped. Is it a Swanson 36 or a one off?
 
Thanks...

Wow, thanks for the responses very informative, particularly oldsaltoz (was kind of hoping you'd chip in, that's exactly what I was looking for, thanks for saying she's a nice boat as well!) , I'll definitely do something... :-)

I'll see how she looks when I slip her and make up my mind then. I like the idea about carrying on sailing and not doing anything about it, I guess I'm mainly concerned with resale as I may haveto sell up in a year or so....maybe I'll be just better off knocking off the price of the treatment

I asked my boatyard guy a while back for the price of a grit blast to strip the gel coat and he was asking for 2000 dollars (think he was miffed that I was contemplating doing any work myself), and there is some half baked club rule about external contractors doing certain jobs....fairly certain he is in cahoots with the club secretary..

fishermantwo, she is a true Swanson 37, fitted out at a queenscliff yard. If club bar information is anything to go by she was custom built for the CEO of Ford australia back in 1985. She has a bubble set aft of the mast (rather than a coach roof extending along) and has flush teak decks (proper teak about 3/4 inch thick), I'll try to work out how to post a picture of her.

Thanks again folks...appreciate it..
 
swanson37 said:
I'll see how she looks when I slip her and make up my mind then. I like the idea about carrying on sailing and not doing anything about it, I guess I'm mainly concerned with resale as I may haveto sell up in a year or so....maybe I'll be just better off knocking off the price of the treatment.
Click to expand...

I suspect it will look much the same, if you do decide to sell here there is a very good chance the surveyor will make the same comment re slight evidence of the the big 'O', this is common and is a band-aid for surveyors bot.:eek:

Avagoodweekend......:rolleyes:
 
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