Osmosis Blisters between waterline and deck (topsides)

C

crown22

Well-Known Member
Joined
19 Jul 2004
Messages
292
Location
Manchester
Visit site
Hello Everybody,
On a low budget I have looked at a project boat-a late seventies Westerly. Possibly because of the use of a plastic sheet being left covering the boat for a long time there are a large number of small blisters on the topsides covering an area of about a quarter of each side of the hull.Have read about DIY blister removal but was wondering if there were any issues with this part of the hull? is relative thinner layup above the waterline likely to cause too big a problem?Planning on handpainting the hull afterwards.Thanks in advance.
 
crown22 said:
Hello Everybody,
On a low budget I have looked at a project boat-a late seventies Westerly. Possibly because of the use of a plastic sheet being left covering the boat for a long time there are a large number of small blisters on the topsides covering an area of about a quarter of each side of the hull.Have read about DIY blister removal but was wondering if there were any issues with this part of the hull? is relative thinner layup above the waterline likely to cause too big a problem?Planning on handpainting the hull afterwards.Thanks in advance.
Click to expand...

has it been painted, there was an issue with international 2 pack paints 25 yrs ( ish ) ago
 
Thanks for the quick replies.Maybe the broker is just trying to cover himself.I had a Jaguar 23 many years ago which had blisters on
the water line which is where I thought was a common place for osmosis to develop,The boat has supposed to have had successful treatment below the water-line previously.I couldn't see any evidence of recent painwork. It's good news if it is just a paint reaction.Maybe I should have tried to burst a blister to see what came out?There was a lot to take in.May need to go back and investigate further.Excuse my ignorance is two pack for brush or spray application?
 
Two pack can be either brush or spray. Gives a superior finish to single pack if done properly, but more difficult to actually do properly. So, perhaps most people with older boats that don't justify the cost use a single pack such as Toplac. This gives a very good durable finish and much easier to apply plus more tolerant of less than perfect conditions.

So, suggest you find out a bit more about how it is currently finished and what is inside the blisters. If you do repaint single pack will go on top of two pack but not the other way round. If it is still gel coat you can use either, but remember the quality of the final finish is perhaps more dependent on the quality of the preparation than the type of paint. Plenty of information on using paints on the manufacturers' websites.
 
crown22 said:
In a low budget I have looked at a project boat-a late seventies Westerly. Possibly because of the use of a plastic sheet being left covering the boat for a long time there are a large number of small blisters on the topsides covering an area of about a quarter of each side of the hull.
Click to expand...

What are the blisters like? Westerly at that time were a but cavalier in how they mixed their gel coats, and it's very common to a have areas where numerous small dish-shaped pieces, 2 - 5mm in diameter, spall off, leaving corresponding craters behind. No structural implications that I'm aware off. You just ping out all the wee pieces - in its own way as satisfying as squeezing blackheads - before filling and painting.

If it has already been painted, you may have a reaction between paint and lower layers or gelcoat. I had to strip the hull of my Hunter 490 because of this.

I'd be quite surprised if there were real osmotic blisters in a part which hadn't been immersed.
 
Two pack can be put on by spray, brush or roller. But be very careful as some of the two packs are quite toxic.

Thirty years ago they didn't use epoxy barrier coats so the f/g hulls were prone to osmosis. You certainly need to establish whether it is osmosis or just bubbles.

Maybe it wood be worthwhile reading about the West System for osmosis repair to see if you could manage it yourself.
https://www.westsystem.com/wp-content/uploads/British.pdf
 
Small blisters are almost never the huge problem sellers of "osmosis" treatments would have you believe. On the topsides, I'd go along with the others that paint is far more likely to be a culprit than the layup, but even if not, it wouldn't put me off buying an otherwise ideal boat. It would, however severely influence my initial offer.

Just a little word of warning about project boats in general. If you've reckoned 3 month's work and £1000 to bring it up to scratch, if it only takes 6 months (not allowing for bad weather) and £2000, break out a large bottle of champagne - you've done a hellava lot better than most people.
 
Gelcoat blisters on the topsides are not that uncommon: not pretty but almost always no structural loss of strength. Usually occur where covers or pads trap rain water against the hull sides, then sun warms the water - perfect conditions for "osmosis" blisters to develop.

If you are painting afterwards you may as well make the boat prettier by grinding out and filling before painting.
 
I have just done a repair to my own boat (Sabre 27) like this. Built in 71 she had been stripped & epoxied below the waterline in 82. At the same time the topsides were sprayed with 2 pack polyurethane. No issues until i bought the old boat 8 years ago.
Over the winter a fender squashed up against the hull by the trolley arm caused a fender shaped patch of heavy blisters right down to the laminate. I ground out & re gelled it before repainting again with 2 pack poly.
Last year it had happened again but worse, a strip of blisters under the trolley fenderboard a foot deep & four feet long. Again it was gelcoat that had failed not the paint.
I ground the gelcoat away & have just epoxied the area & faired it. Another paint job!
On my boat it only occurs on the stb side, the port side which is against the jetty when afloat with a damp fender board has no problems. As to what causes it, I have heard of poor quality gel, Gel with too much glycol in it. Gel that has been contaminated with dirty acetone at lay up time, take your pick!
Its only going to be cosmetic.
 
Last edited:
My Westerly Fulmar has areas in the underwater area covered with micro bubbles of 2 to 3 mm diameter. These can appear on the topsides if left in constant contact with moisture. What has occurred is small air bubbles were left in the gel coat when first applied to the mould, as there was inadequate brushing out of the gel coat to brush them out. Over time moisture cause them to swell slightly, hence the bubbled look.

If you decide to proceed with this boat, then you will need to sand the topsides to open every bubble and then fill them all before painting. The original gel coat was in fact a double coat and will measure about 2 to 3 mm thick. The long term problem will be that once repainted, some more bubbles might appear.

My advice would be to look for another boat unless it was cheap as chips. There are so many boats of that age on the market that are project boats, you can choose the best one to start work on. The age old advice is always to buy the one in the best condition as all repairs/improvements on any project boat will cost you more than the most expensive example available today. You will also save yourself a lot of hard work and can go sailing as soon as you buy a boat.

My Fulmar has undergone extensive renovations and has cost £10,000 more than my original renovation budget of £12,000 - and I am still not quite finished. You can read and learn from my renovation of what I have done at https://www.westerly-owners.co.uk/woaforum/viewtopic.php?f=1&t=2748 and view the changes in photos starting at what she looked like when I bought her http://s1294.photobucket.com/user/ConcertoFulmar32/library/?sort=3&page=8.
 
I had a few blister like projections on my Westerly's waterline, but when I opened them they turned out to be lumps. No cavity or liquid in them. It was a very simple job to fill and sand them.
 
You must log in or register to reply here.

Share this page

Top