TREATING OSMOSiS

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killick

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The past couple of years have noticed small(fingernail size) osmosis blisters on the hull of my boat. Over time it did not become bigger but certainly more plentyfull.I have opened some and the vinegary smell leaves no doubt that it is osmosis.
On treating it I would like to know like to know if,after opening the blisters,I should just rinse it with fresh water or should I use a pressure washer to blast it out? Judging from the smell I persume that the liquid in the bubble should be acid.Would it thus be adviseable to neutrelize this by using an agent such as bicarbonate of soda?
I would also like to know how soon I can fill the cavities and seal the hull in our present hot wheather of up to 30 degrees centiigrade
All advice will be greatly appreciated
 
3 schools of thought.

1) Leave them alone. The boat won't sink.

2) Treat the worst

3) Do the lot in one hit. Full gel coat strip etc.

Depends on the value of the boat really. I've never done anything with small blisters.
 
I'm not at all convinced that surface treatment as you describe is any more than a temporary patch. If the GRP is absorbing water then it is doing it to some depth, surely, if not much/most/all of its thickness, not just the surface layer. Thus it seems logical that to effect a cure you need to remove that moisture and the only way I am aware of that achieves this is the hotvac process. Costly, sure, but when you see the amount of condensate that comes out of the hull you'll realise why I say it can't all be just in the surface layer. In Turkey, where my boat was , the surveyors said even if you peel the gelcoat and leave it to air for a season the moisture level won't change significantly - temps 30 - 35 for months. It is only the combination of heat (55/60deg perhaps?) and vacuum that pulls it out, and even then fairly slowly.

However...lakey is right, the boat won't sink. A cosmetic fix will cost far far less and will only affect you on resale value if when high readings are found. Depends on the value of the boat and how long you plan to keep it I suppose. Cheap repairs for a cheap'un, as Kipling said.
 
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The Hotvac system speeds up the process but the same end can be achieved by removing the Gelcoat and the outside layer of mat and allow to dry naturally.The hull should be rinsed dayly preferably with a pressure washer.All hulls are different because the laminates are not the same for all boats.If your boat has a properly laminated hull then it'll dry quickly in those temperatures especially if the relative humidity is low.If you have a bad laminate with voids and areas of low or no resin then the problem it's much greater.
It is a fact that a reasonably well built hull won't sink because of osmosis and generally the problem is more cosmetic than anything else but I've seen a Taiwan built hull that you could stick your finger through in places.
I keep my boat in the Algarve in Portugal.I have millions of tiny ,shallow blisters,most don't go through the gelcoat.After two weeks ashore in temperatures of 30/35ªC they disappear. I'll strip the gelcoat eventually but the blisters have been there since I bought the boat 12 years ago and haven't got worse.
It's up to you to repair or ignore and go sailing.But make sure the layup on your boat is a good one.
 
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If the boat is a Sadler 26 as shown in your profile a full gelcoat peel and epoxy recoat will be a very high percentage of the boat's value. Grind out the bigger ones (carefully) to slightly bigger circumference but not much deeper than the visible blister, hot water wash out a few times, leave to dry as long as possible and fill with epoxy paste.

I don't know what the glass/resin thickness of the outer skin of a Sadler 26 is, but it may be thinner than might be normal for a boat of this size as it is stiffened by the foam and inner skin. Perhaps someone who has cut a hole in a Sadler 26 hull might like to comment.
 
I have a friend who had an elderly 1/2 tonner.He noticed blisters,the area having gained a marina, the enemy of hulls!
He was fortunate in having loyal racing crew, many who volunteered time to poke open the blisters, leaving them open for a goodly time of months.
Then the entire affected areas only were filled with a good quality marine filler, not epoxy.
When the vessel was offered for sale, there was no demur on the part of the surveyor.
This lack of alarm is probably supported by the opinion that all boat of this vintage have some osmosis damage, which may or may not be apparent.
t'wont sink is the accepted widom,
One of mine has crossed the Atlantic,mind you the only blisters were under the pad areas where the cradle pads were in contact with the hull.so much for six months ashore each year!
 
The fix is to grind out the top layer and allow to dry. Just how dilligent the OP is, is a matter of his patience energy and time availbale. Certainly on an older boat a loss of season in doing it properly is just not worth doing. I think if it were me I would end up doing this sort of job in a day ie grind out the blister, hose off with fresh water wait for it to dry then fill with epoxy. Antifoul the next day.
Hopefully an adequate fix if not there is always next lift out. good luck olewill
 
If it is an old boat and the blisters are too many and very small; sand down, three coats of Jotun HP Penguard epoxy paint, followed by hard antifouling and then ordinary antifouling; ready in 3 days. Or carry on sailing it as it is, it will not go any slower, will not sink and will not get worse.
 
30boat said:
The Hotvac system speeds up the process but the same end can be achieved by removing the Gelcoat and the outside layer of mat and allow to dry naturally.The hull should be rinsed dayly preferably with a pressure washer.All hulls are different because the laminates are not the same for all boats.If your boat has a properly laminated hull then it'll dry quickly in those temperatures especially if the relative humidity is low.If you have a bad laminate with voids and areas of low or no resin then the problem it's much greater.
It is a fact that a reasonably well built hull won't sink because of osmosis and generally the problem is more cosmetic than anything else but I've seen a Taiwan built hull that you could stick your finger through in places.
I keep my boat in the Algarve in Portugal.I have millions of tiny ,shallow blisters,most don't go through the gelcoat.After two weeks ashore in temperatures of 30/35ªC they disappear. I'll strip the gelcoat eventually but the blisters have been there since I bought the boat 12 years ago and haven't got worse.
It's up to you to repair or ignore and go sailing.But make sure the layup on your boat is a good one.
Click to expand...

The snag is that it's scarcely ever dry in the UK (at least sufficiently to thoroughly dry a wicked laminate) - hence the horrific costs of having the job done professionally.
Probably there are many boats out there with osmosis but, fortunately, the habit of having the boat on a hardstanding for half the year prevents that becoming too much of a problem. The number of unsuccessful osmosis treatments reported, compared to costs make it at least as hazardous as "patching".
It's really only possible to take a view after someone who knows what they are doing does a meter survey on the boat after at least 2 months out of the water.
I had several 2-3mm blisters at the waterline, when checked the boat was completely osmosis free and the blisters were between 2 layers of gelcoat where they overlapped.
After mechanically removing all the old antifouling, I put 5 coats of GelShield on and have forgotten about osmosis.
 
charles_reed said:
The snag is that it's scarcely ever dry in the UK (at least sufficiently to thoroughly dry a wicked laminate) - hence the horrific costs of having the job done professionally.
Probably there are many boats out there with osmosis but, fortunately, the habit of having the boat on a hardstanding for half the year prevents that becoming too much of a problem. The number of unsuccessful osmosis treatments reported, compared to costs make it at least as hazardous as "patching".
It's really only possible to take a view after someone who knows what they are doing does a meter survey on the boat after at least 2 months out of the water.
I had several 2-3mm blisters at the waterline, when checked the boat was completely osmosis free and the blisters were between 2 layers of gelcoat where they overlapped.
After mechanically removing all the old antifouling, I put 5 coats of GelShield on and have forgotten about osmosis.
Click to expand...
The OP is in South Africa,It's a lot warmer down there.In the 30/35ºC temperatures there the hull shuld dry up allright.
 
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