Results 1 to 8 of 8
  1. #1
    Join Date
    Aug 2006

    Default How to treat Osmosis blisters on ahull that has had Osmosis treatment?


    My boat had Osmosis treatment in summer 2001 before I bought her. I believe it was the full strip and epoxy applied using the Blakes system. I have an invoice for £2,400 showing work carried out. It is a 25 foot boat. It is now kept in freshwater.

    The antifoul has been slowly coming off when the new yearly coat was applied so I decided to remove it this year. As I have done this with a chisel I have knocked the heads off a few lumps in the epoxy layer that I can only assume is limited Osmosis as it contained liquid and had that smell about it.

    I have read much on how to treat Osmosis but nothing on how to treat a boat that has has already been epoxyed. How should I treat the affected areas? There are probably only about 20 small blisters. But as the heads have been knocked off I need to do something.

    Also just a question on the epoxy already applied. I hadn't noticed when the antifoul was present but now that it is back to the epoxy layer it is very rough - orange peel effect. Is this normal? Would I be OK to try to sand it smoother or does this risk sanding away the protection?

    Finally I was going to apply a coat of International Primocon to help the antifoull to stick to the hull after the Osmosis treatment. Is this the best way to get the antifoul to stick?

    Many thanks

  2. #2
    Join Date
    Oct 2003

    Default Re: How to treat Osmosis blisters on ahull that has had Osmosis treatment?

    I cannot comment on how to treat the blisters but I'm sure others will do that shortly.

    However, I'm pretty sure that the "orange peel" effect is pretty normal for a boat that has been re-gelcoated. Remember, the original came out of a mirror smooth mould but after stripping, the recoating is done by hand presumably with a roller or spray so there is no way it can be as smooth.

    As for applying the antifoul, yes you will definitely need an anitfoul primer - and Int Primacon is as good as any - as if antifoul is put directly onto an epoxy coating it will just fall off!!

    Hope this helps

  3. #3
    Join Date
    Aug 2003
    Walton on the Naze

    Default Re: How to treat Osmosis blisters on ahull that has had Osmosis treatment?

    LIGHTLY grind out any blisters (a countersunk drill bit is good). Wash thoroughly with fresh water and leave to dry out for as long as possible (over winter is good). Fill with below the waterline marine filler and apply two coats of Primacon.

    Look out for any one epoxy painting their boat and ask to "borrow" a couple of dabs before priming.

  4. #4
    Join Date
    Feb 2003

    Default Re: How to treat Osmosis blisters on ahull that has had Osmosis treatment?

    Am I right in thinking that Blakes give a ten year gurantee?
    I would contact them and wave the invoice at them and ask what are they going to do about it?

  5. #5
    Join Date
    Sep 2008

    Default Re: How to treat Osmosis blisters on ahull that has had Osmosis treatment?

    no - dont think you are.

    the orange peel is common. ,managed to do it to my own boat by epoxy coating when there was just one of me to roller it on and no one to flatten with a brush.

    two types of blister under the epoxy - trad osmosis blister which will smell of vinegar, and blister dues to amine blush inter layerof the epoxy which gives an alkaline blister. check with some litmus paper.

    the amine blisters can simply be ground out and repaced with more epoxy. osmosis blisters are a bit more of a problem

  6. #6
    Join Date
    Apr 2002
    Norfolk UK

    Default Re: How to treat Osmosis blisters on ahull that has had Osmosis treatment?

    Probably caused by original blisters not being dry before epoxy being applied.

    I suggest cutting out blisters with a dremel and seeing whats behind. Often its just solid resin as its an air bubble in the original layup thats filled with water. Cut away till you get to dry grp. Then fill with epoxy filler and glass if the holes are big enough.
    Sand down the whole hull to get rid of the orange peel and recoat with 3 or 4 coats of epoxy such as Gelshield 200

  7. #7
    Join Date
    Feb 2005
    Hamble-le-Rice, Hants

    Default Re: How to treat Osmosis blisters on ahull that has had Osmosis treatment?

    I dont think that anybody offered anything like 10 years warranty on epoxy treatments by 2001 - mine was done in 1998 with Gelshield and the warranty ran out in 2001 !

    I have found one small bubble since which was in a water-filled skeg which I repaired with Araldite .....

  8. #8
    Join Date
    Apr 2011

    Default Also have a query about how to treat osmotic blisters on a hull that has been epoxied

    Apologies for resurrecting an old thread - searched the forum rules, but couldn't find anything which said I shouldn't - new here...

    I have a Westerly Renown which was refurbished in 1997 - the lower hull was treated for osmosis (I do not know if there were blisters or signs then or if it was done as a safeguard/over cautiously etc...) - the survey from then says that the treatment involved stripping the Gelcoat, allowing the hull to dry before being epoxied and a white anti-fouling primer applied. During the overhaul the cast iron fin keel was also removed and shot blasted and treated with epoxy before being refitted. The 1997 survey says that the moisture readings were low and that there was no indication of any major damage, etc...

    I had the boat surveyed a week or so ago, before purchase. The hull then had not been anti-fouled or lifted from the water in 4 years. So it was, as you can imagine, quite fouled!! This was scraped back and it was jet-washed for the survey. Some minor blistering liberally spread across the hull, below the waterline, has been found - which the surveyor has said appears to be osmotic (it smells a bit like gherkins, capers, etc...). The blisters are soft, easy to scrap back to get to the fluid and smaller than a penny or a jellytot.

    Will figure out how to post some pictures - though you can't really see much except the barnacle remains!

    Oddly the skeg was coated in something - not sure what (neither was the surveyor) - which appears to have some larger blisters within it - peeling it back the same blisters do not appear on the material under, they are just in the layer covering the skeg - perhaps 0.05mm thick.

    Anyway - I am wondering what the best approach is to deal with this. I am considering simply getting the antifoul removed by soda or similar blasting and then treating the blisters individually, filling where necessary and then adding a couple of coats of west epoxy before priming and anti-fouling and monitoring the problem going forward.

    My main concerns are:
    - I'm not sure its worth the effort of stripping back the 1997 epoxy coats and re-doing the whole job, the blisters don't look bad enough to warrant it.
    - Ideally I need to have the boat back in the water by mid-October as it's a liveaboard
    - I'm looking for a realistic solution - perhaps not the perfect one!

    Any advice or guidance appreciated. I've read a lot on the subject and stripping back the gelcoat etc, etc, but again - not much about what to do if the hull has already been epoxied?

    Additionally I planned to take the keel back to metal and re-do so that's its done - is this a good idea, or should I again just take off the antifoul - rather than take back the epoxy?

    Thanks in advance, Claire


Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts

Find Boats For Sale