Osmosis

[ireaney]

Someone told me that to check if a boat had Osmosis feel with your hand (if the boat is in the water) for blisters as it is more prevalent around the waterline and up to 3 inches below, is this true??

If so, why there??

[Cheechako]

It does seem to appear often near the water line, not sure why though. On t he other hand I have seen many boats that have a tendency to get it most everywhere. Maybe boats that have a marginal inclination toward blister get it near the water line....

[feelsgood]

No its not true. You have to get the boat out of the water and check for blisters. If you find any cut into them and smell. If you can smell something like vinager you have osmosis. It isnt as bad a job to cure if you go about it the right way if I can help just ask on my e-mail address

[ireaney]

Originally Posted by feelsgood

No its not true. You have to get the boat out of the water and check for blisters. If you find any cut into them and smell. If you can smell something like vinager you have osmosis. It isnt as bad a job to cure if you go about it the right way if I can help just ask on my e-mail address

Hi Feelsgood,
Thanks for the info, I should have added that this was said to me because the boat has been left in freshwater for 3 years and if I couold not feel blisters around the waterline then there was a greater chance it did not have osmosis, is that a possiblility?
Thanks
Ian

[feelsgood]

yes that is true if the boat has been in fresh water it is less likley to have osmosis but an underwater check is still worth it

[DeepFrz]

Fresh water where? That is the question. Fresh water in the tropics and it is very likely to have blisters. There is an article in Feb. 2009 Blue Water Sailing about boats that have been left in the Rio Dulce over the hurricane season and the acceleration of blisters.

The first blisters may form near the waterline because of the heat from the sun accelerating their formations.

[ireaney]

Originally Posted by DeepFrz

Fresh water where? That is the question. Fresh water in the tropics and it is very likely to have blisters. There is an article in Feb. 2009 Blue Water Sailing about boats that have been left in the Rio Dulce over the hurricane season and the acceleration of blisters.

The first blisters may form near the waterline because of the heat from the sun accelerating their formations.

Not in the tropics here in the UK, 50degree north, cold water, probably not higher than 16 degrees C.

[Cheechako]

I Imagine that the heat or warmer water may accelerate a blister problem in a boat that already has too much moisture in the glass. However, rest assured, we have many blister problems up here in the cold north. I've seen boats with ground out blisters as big as your hand...and the whole bottom covered with those or smaller. I had one boat years ago that developed blisters inside the bilge, in an area where the glass was 1 to 1.25 thick! Makes you wonder if they can develop from the inside also... just from the general moisture in the air. It would be interesting if someone (how about a college engineering student?) would do a survey and see if vacuum molded boats show a lower inclination for blisters...

[Camelot]

Hi Ireaney,

The osmosis process was very much connected to the boats produced in the eighties and early nineties. However, it seems that this chemical challenge starts at the same moment the boat is on water. Boats from late the late nineties reports of osmosis-like problems.
The blisters are surface symptoms on the process and very seldom critical – at that stage. What is much more dangerous is if the problem gets structural. If the chemical process expands the middle layers between the laminates in the bearing structure, it could be very serious for your boat. You have to examine the boat on land, and within two or three days after – before the underwater hull dries up. The blisters is pretty easy to identify, and they are often located around the areas that is most exposed toe the flowing water – the bow, in front of the keel. The reason is that these areas experience the toughest strains. The more serious and dangerous “stage II”, lies inside the laminates. You have to examine the underwater hull centimetre by centimetre. Do simply take a ball hammer and knock you from the bow to the stern. Healthy “concrete” sound gives you a good night, but hollow sound is an indicator of structural weakness. Epoxying this could increase the problem by locking the osmosis fluid inside the laminates to make the problem worse. Seek expert advises if the structural problems may be the issue.

Good luck!

[sabray]

Osmosis on a boat
water fresh or salt moves through a semi permeable membrane (the gelcoat). mixes with (dissolves) polyester resin. The gel coat acts as a screen semi permeable if the screen is big enough the energy or expanded molecules pass through . Large screen bad old gelcoat you may not see blisters.
If the screen is tighter the energy cant be released it wont pass through presses against the membrane wall forming a blister. so a blister is just a symtom of the problem.
Before the day of reduced saturation rates and cored hulls this wasn't such a big deal. Builders over saturated the fabrics and layed up thick solid hulls. The gelcoat was porous. So older boats didn't always get blisters the resin in which there was an abundance just rinsed through. THe quality of the resin plays a part the quality of the build plays a part. simply put if you took a blob of polyester resin and stuck it in a tank of water and wait long enough it will slowly dissolve. Takes a long time. Its probably worth having a surveyor check the condition of your boat. Used to be done by grinding a spot into the gelcoat and maybe into the finishing layer. Then a density meter and moisture meter are used to determine the characteristics present. simetimes you can see how far the ingress has gone.

[fstbttms]

You people use the term "osmosis" as if it were a disease a boat could catch. Osmosis is simply the process by which blistering occurs, it's not the symptom. A boat might have blisters but it doesn't "have" osmosis.

[sabray]

i thought it was the other way around a boat might have osmosis issues and no blisters.
i guess splitting hairs if a boat has a blister without osmosis its just plain delaminating.

[Daedalusk]

I have repaired literally thousand's of blisters while working in a boatyard in the Florida (USA) panhandle, and what follows will probably be much more than you want to know.

Small blisters the size of a dime are mostly cosmetic and produce no structural damage. Many times I repaired them because the owner was concerned with the cosmetic aspects, but one boat had over 300 the size of an orange, standing up almost 1/4". Some produced delamination within the hull for a foot or more around them. So, blisters can be destructive to the integrity of the hull laminate, so much so that in extreme cases it is necessary to peel the outer layers of glass from the entire hull, and replace them with epoxy laid-up new glass cloth. The issue is to stop blister growth, and to do that you need to know the mechanics of blister generation.

The following applies to polyester resin impregnated fiberglass hulls, since the new vinylester and epoxy resin/gel coats are themselves highly impervious to water.

Blisters are caused by inperfections within the hull lamination - either improperly cured resin, voids within the layup of the laminations, and even the use of certain kinds of resin (fire-retardant resin is notorious, hence the 80's problem) Since it is virtually impossible to lay up a hull without imperfections, it is absolutely essential to maintain an epoxy barrier coat between the hull and the anti-fouling paint. This, in itself, is the most effective preventative measure to avoid blisters.

The imperfections within the hull laminate create a chemical attraction to water. The water, at a molecular level, penetrates the gell coat (hence the Osmosis designation), and forms a new molecule with the resin. This new molecule (which smells like vinegar) is larger than the original water molecule, and thus is trapped within the laminate. As more water molecules are attracted through the gelcoat membrane, the pressure builds inside the laminate until the telltale blister appears.

First of all, blisters are evidence that the intergity of the barrier coat material has been compromised. The remedy for multiple small blisters is simply to remove the anti-fouling paint, and apply a good epoxy barrier coat to the entire subsurface area. Absolutely follow the directions about the barrier coat thickness. Here is a place where more is better than less. Also follow the directions about drying time before the application of anti-fouling paint.

If there are a few isolated larger blisters, use a grinder and remove the blister until there is clean un-delaminated glass all around it. Be sure to grind deeply enough to remove all damaged fiberglass. If the depth is significantly a part of the hull thickness, cut multiple pieces of glass cloth, first small in diameter, and increasing until they are the diameter of the section ground away. Four or five pieces should be sufficient. Remove all paint (barrier coat and anti-fouling) from a small area around the blister repair. Clean the area with acetone, paint the area with epoxy resin. When the epoxy has become tacky, begin to lay in the glass pieces you cut, starting with the smallest. Be certain the each piece is saturated with epoxy resin and that there are no air pockets. Continue until the glass patch is at, or slightly above, the surrounding hull surface. Let the patch cure overnight, sand it smooth with the hull surface. If necessary use a mix of epoxy resin and colloidal silica to fair the repair with the hull surface. Let it cure overnight. Then apply sufficient thickness of barrier coat and anti-fouling paint.
On small blisters, up to about the size of a quarter, you can uses a router set to 1/8" depth, and probably remove all damaged glass. Then simply fill the repair area with the above mixture (epoxy/collodial silica), fair, and paint as above.

I have only anecdotal experience with boats kept in fresh water, but that evidence seems to indicate that fresh/salt has little to do with blister formation. Again, the best guard against blisters is a properly applied barrier coat of proper thickness.

[Alejo]

The best product for blisters i made by Interlux, epoxy resin, primers, no other manufactured has this technology. go to yachtpaint.com - the official site of International and Interlux paints
boat painters guide.

Dont waste your time in other products, read and you will find out the difference.