Bumps on hull

[rajhnsn]

@rajhnsn , you are spot on with the majority of what you said, but I have never heard that uncured resin is part of the equation. I am not saying you are wrong by any means, I just haven't read that from any source. It is a likely explanation if PE resin wasn't fully and thoroughly mixed with catalyst. My understanding is that PE resin is not totally waterproof at a microscopic level, it allows water molecules to work into the laminate and this is more typical in 'loose' layups where chopper guns were used, higher content of air bubbles, and poor quality resins that were used during the fuel crisis in the late 70's that also persisted into the 80's. I dunno... but what you said seems to make sense, what else would cause the chemical reaction with the water when the resin (if it were properly cured) should basically be inert plastic? Food for thought.
I think your recommendation for a full gelcoat peel makes sense for larger yachts that show signs of significant osmosis in the laminate rather than between the gelcoat/laminate. At the end of the day it is probably LESS labor to do the full peel than it would be to just spot grind all the blisters. The key is the drying time and verifying a fully dry laminate with a moisture reader, a full peel makes this process more comprehensive. Using VE resin is a good choice, but the best choice would have been epoxy resin. VE is much more 'waterproof' than PE resin, but only epoxy is completely waterproof. I know all the major manufacturers are now using VE resins in the first layers of the mold and have no issues with it, so I doubt you will ever have any issues. I would lean toward epoxy whenever possible because of its superior secondary bond. for my blister job I applied a 'soak coat' of epoxy to the laminate, sanded, and then an 8.9 oz layer of cloth and floated fairing compound while it was tacky. This method wasn't to increase the strength of hull but to replace some of the mils thickness of the removed gelcoat. Labor wise I think I saved time rather than rolling multiple layers of epoxy, but my boat is also much smaller (22 feet).

I'm not sure if I still have the research that I based the statement about the resin not being activated that was the root cause of blisters but I will try to search it out again when I get the chance. I recall seeing research about the chemical property difference between PE, VE and epoxy. It was clear that epoxy was the most waterproof out of the three by a large margin. The drawback of epoxy was the cost. VE is the second most waterproof but the cost is significantly lower. I think I recall that there is a brittleness issue with epoxy but I'm not sure. I did not put a layer of cloth on mine but I had considered it. Since the gelcoat is not structural, I did not feel as though I needed a structural layer. The 11 coats provided the thickness.

 

[BobbyFunn]

@BobbyFunn , good points but that is epoxy resin/hardener... we were talking about un-cured polyester resin in the laminate causing osmosis.

Thats why i also looked up the safety data sheet for the hardener 3m uses for poly resin. I didnt have a link for it though. You just read the post too quickly. Both hardeners appear to be water clean up.

Sailnet has a fierce religious battle about this topic based on the research of a 1987 University of Rhode Island study by Thomas Rocket and Vincent Rose, The Causes of Boat Hull Blisters.

Since the centerboard of my trailer sailer was covered with blisters and was filled with about 2 cups of water im gonna argue that the water had easy access to the layup and ruined the gelcoat from the inside, by dissolving the water soluable portions of cheap layup. For some, the scenerio might be similar to condensation on the inside of the hull touching the layup side.

Ive already rubbed out the tip of the repaired paint job by shallow river sailing, so im monitoring to seeing if they come back.

 

[Joe]

Has anyone considered this rash to be from "bubbling", rather than osmotic blisters... google it.

 

[Hayden Watson]

Has anyone considered this rash to be from "bubbling", rather than osmotic blisters... google it.

Why don't you just provide a link? googling "bubbling" will return millions of hits most of which will have nothing to do with fiberglass boats.

 

[Joe]

Why don't you just provide a link? googling "bubbling" will return millions of hits most of which will have nothing to do with fiberglass boats.

Sorry friend... let me try to be more helpful...

First, let me off this excellent link where a surveyor clarifies his view on buying a boat with blisters. Of special interest is his comment on new versus older boats and their potential for further problems.

Regarding my previous post, I intended to simply suggest that osmotic blistering is not always the culprit.. it can be an application problem that shows up in the form of bubbling.
Here's an excerpt and link (understand that this is not limited to boats) regarding bubbling.

Non-Osmotic Blistering: Bubbles
Even though many blistering problems are commonly associated with coatings in immersion service and high continuous moisture exposures, blisters can and do form by other mechanisms. These non-osmotic blisters, which we call bubbles, are often associated with characteristics of the substrate or environmental conditions during coating application.

Coating Application During High and Low Temperatures
In many locations, the coating application season is limited to a time when environmental conditions are favorable (i.e., typically in late spring, summer and early fall). Those “blue sky” days must be productive. The environmental conditions that give us these kinds of days are usually advantageous; however, they also have their pitfalls. For example, applying a coating to a surface in direct sunlight exposure or applying the coating thicker than recommended can result in bubble formation. Bubbles typically form because the heat from the sun causes the surface of the applied coating to dry more rapidly than the body of the coating film. This rapid surface drying process creates a rigid, “skinned over” surface layer that prevents solvent within lower levels of the film from escaping. As the solvent in the lower layers heats, it volatilizes and expands and creates vapor pressure within the coating film. It is the vapor pressure that causes bubbles to form.

In other instances, bubbles can form in coatings due to cooler temperatures or high relative humidity during application. When application occurs during cooler temperatures or elevated humidity, the drying and curing of the coating film is slowed considerably. As a result, the proper release of solvents from the film does not occur. Consequently, if the next coating layer is applied too soon, the solvent in the underlying film becomes trapped and bubble formation can occur. However, the bubbles may not occur immediately, and their appearance can be delayed until the environmental conditions become warm enough to cause the entrapped solvents to volatilize.

 

[Hayden Watson]

Good explanation. In my case none of the tiny bumps extended through the gelcoat. Pimples is a good name for them although Goosebumps would be more to the fact of size and quantity. When I was looking for a solution I found that others had experienced this same failure of the factory barrier coat which did not penetrate the gelcoat.
I am just happy that after 12 years no more have surfaced. Problem solved.

 

[Joe]

I'm not quite clear on your comment. The factory applied epoxy barrier coat is supposed to penetrate the underlying gel coat? Or do your tiny bumps show through the bottom paint... which lays over the barrier coat? The article I submitted, and other similar pieces, about air bubbling in epoxy coatings would make a lot of sense then... the barrier coat was improperly applied and a phenomenon called "out gassing" occurred. That's not difficult to correct.. because we're talking about air trapped in the epoxy covering...so applying a few layers of new barrier coat should solve the problem. If you search related subjects, such as "repairing air bubbles in epoxy coverings" you'll find plenty of info. It's pretty common with projects like covering bars and tables, or garage floors.

As a side comment... I always thught that applying barrier coats and bottom paint to a new boat was a dealer prep thing.... of course I've NEVER purchased a boat new so I'm coming from limited experience.

 

[Hayden Watson]

I'm not quite clear on your comment. The factory applied epoxy barrier coat is supposed to penetrate the underlying gel coat? Or do your tiny bumps show through the bottom paint... which lays over the barrier coat? The article I submitted, and other similar pieces, about air bubbling in epoxy coatings would make a lot of sense then... the barrier coat was improperly applied and a phenomenon called "out gassing" occurred. That's not difficult to correct.. because we're talking about air trapped in the epoxy covering...so applying a few layers of new barrier coat should solve the problem. If you search related subjects, such as "repairing air bubbles in epoxy coverings" you'll find plenty of info. It's pretty common with projects like covering bars and tables, or garage floors.

As a side comment... I always thught that applying barrier coats and bottom paint to a new boat was a dealer prep thing.... of course I've NEVER purchased a boat new so I'm coming from limited experience.

My goosebumps were in the barrier coat and did not affect the gelcoat. I did not recoat the whole below water surface with a new epoxy barrier. What I did was mechanically scrape the bumps with a two-hand paint scraper which affectively popped the deboned tops of the bumps off. I then filled the resulting holes in the barrier coat with Interlux Watertite Epoxy Filler. I sanded this flush and pained the bottom with bottom paint.

That was in 2005 and there have been no more bumps found when the boat was pulled for bottom painting. If I ever get any more I will spot treat.

I am not sure who applied the barrier paint but it showed up in the original invoice which was with the boat docs.

 

[wing15601]

Just came across this post and thought I would comment. When Pacemaker Yachts went out of business (1980 I think) I bought an unassembled 26 foot boat at the factory auction. Took me 3 years and a broken ankle to get it into the water. Anyway, after 3 years the brand new hull which had never been in water but had factory applied antifouling paint below the water line, had hundreds of those pencil eraser sized 1/16” high bumps all over on the part of the hull painted with antifouling. They weren’t there when I bought the hull home (Philadelphia) and I don’t know at what point in time they appeared. Used the boat for about five years before selling. No more bumps appeared and none ever grew larger. Last I heard the boat was somewhere in New Jersey.