Fiberglass quality

Ross · Mar 17, 2009

These folk seem to be knowledgable about fiberglass cloth. http://thayercraft.com/index.htm

Napa Ed · Mar 17, 2009

make sure you get materials meant for frp layup. unfinished fiberglass cloth or roving is very hard to wet out. there is a price difference. been there...

Ross · Mar 17, 2009

Their listings and pricing seems to be about right. They couldn't stay in business if their quality6 was misrepresented.

sailaway78 · Mar 17, 2009

Price difference

Franklin, the price difference between standard retail and some discount on line suppliers can be amazing. For the exact same product. Before I retired, when I lived in Dallas, I had a friend who worked at a place that built swimming pools, and bought resin by the tank car load.
A high quality poly resin, and I could buy it from them for about 1/10 of retail Course I had to take my own containers. Not sure about the mat and roving, but I know there is an insane markup in the resins.

sailingdog · Mar 17, 2009

I hope you're using EPOXY resin, not Polyester or Vinylester resin. Repairs, especially structural ones, are generally better done with EPOXY as it has far better secondary bonding (Adhesive) characteristics than do either Polyester or Vinylester resins.

Unless you're familiar with polyester/vinylester resins, getting them to bond well to previously laid up work is more difficult and less forgiving than doing the same with epoxy.

Ross · Mar 17, 2009

I am inclined to believe that people who have very high opinions of epoxy and very low opinions of ester resins haven't made very many fiberglass repairs. There is a practical limit to how strong the bond between old work and repairs need to be. This is why the very large bonding area specified for fiberglass repairs.

Maine Sail · Mar 17, 2009

Ross said:
I am inclined to believe that people who have very high opinions of epoxy and very low opinions of ester resins haven't made very many fiberglass repairs. There is a practical limit to how strong the bond between old work and repairs need to be. This is why the very large bonding area specified for fiberglass repairs.

Ross,

At least in my case you're wrong and before you spout Viatses, yes I have the book...

I do have a very high opinion of epoxy and have done fiberglass repairs since I was a kid, mostly with polyester resin both waxed and unwaxed..

I have also been on, seen and owned boats where secondary bonds (tabbing applied after the hull had cured) had failed and pulled free from the hull. Yes you can repair a boat with polyester but with limited skills the ease and open time of epoxy makes it nearly fool proof. It also wets out cloth and mat better & faster. Do I still use PE &VE? Yes for certain tasks just not generally structural ones.

If you are going to use PE resins make sure your scarfs are large enough to get good solid bonding.

I'll make a comment like yours....

I think people who have high opinions of polyester are just too cheap to spend the money on a better product.

Ross · Mar 17, 2009

Mainesail, I can't argue with you on that. However good engineering balances cost against need. Make it as strong as it should be made but don't gild the lily. I use epoxy where it is called for and that may be why my engine beds will be in place long after the engine is worn out.

Maine Sail · Mar 17, 2009

Ross said:
Mainesail, I use epoxy where it is called for and that may be why my engine beds will be in place long after the engine is worn out.

My one gripe about epoxy is that it eats sanding discs for lunch... The stuff is tough!

Steve Dion · Mar 17, 2009

Franklin:

Thinking forward, I hope you think you can make your boat repairs with the quality that will be made to make your boat seaworth and cosmetically sound. I would suggest that you "shop" around for some "qualified" fiberglass repair persons to do this job for you.

I recently had a repair done on my Hunter 36. It was repair by a fellow in the SF bay area and no one that knew where the damage was, can even spot it now. He charged me $45/hr plus materials and I will tell you that it looks better than new.

If you do this repair and it shows, you will take one hell of a hit on resale. While I reaslize that you got a boat that you know for a great price, I would at least consider what it is going to look like 2-3 years down the road and you may want to really trade up.

Good luck!

Maine Sail · Mar 18, 2009

Franklin said:
I had thought about doing that with epoxy because it's on the inside but figured polyester resin would bind with polyester resin better.

Franklin,

There are two types of bonds.

Primary Bond: This is a chemical reaction that occurs during laminating. The polyester resin actually cross links to itself and forms a very strong bond.

Secondary Bond: This is the bond you will get after the original fiberglass has cured. This bond of old to new is not a cross linking when done after cure and is nothing more than a glue or adhesive bond. PE is not a good glue/adhesive when compared to epoxy. Epoxies adhere at upwards of 2000 psi in a secondary bond/glue situation.

The myth that gelcoat does not adhere to epoxy is just that a myth. Gelcoat work over large areas is very difficult and should be left to an expert IMHO.

sailingdog · Mar 18, 2009

Franklin—

Gelcoat can be used on epoxy... see this article on West's website.

Franklin said:
Was planning on using Polyester resin because jelcoat sticks to polyester and not epoxy. I have done a few small jobs with polyester without much trouble and have been amazed at the strength of just 3 sheets of cloth and polyester resin.

There is only one area that I'm concerned about it holding and that's the "knee" between the chainplate and the backing plate. On the 376 they do something kind of different. They Build up a thick 1/2" of solid glass on the inside of the hull and extend that to 6 inches above the hull-deck joint. Then they mount the chainplate on the side of the hull and through bolt it with two 1 1/8 inch bolts through that backing (somebody told me it's called a "knee"). I'm not sure how much of the hull this knee is glassed two yet because it's covered by thin plywood that I haven't taken off yet...I'm still taking the inside apart.

I will be totally replacing that knee as I can see that the edge of it has seperated from the hull. I had thought about doing that with epoxy because it's on the inside but figured polyester resin would bind with polyester resin better.

sailingdog · Mar 18, 2009

Ross—

Please note, that I did say:

Unless you're familiar with polyester/vinylester resins, getting them to bond well to previously laid up work is more difficult and less forgiving than doing the same with epoxy.

Most people do not have the skill and expertise with polyester/vinylester resins to do a proper job with it. Doing so with epoxy is far simpler and much harder to screw up. Also, the greater strength of epoxy can help compensate for the damaged area's inherent weakness.

I've been working on boats for over 25 years, and have helped build a half-dozen as well as modified and repaired many. I stand by my previous statement.

Ross said:
I am inclined to believe that people who have very high opinions of epoxy and very low opinions of ester resins haven't made very many fiberglass repairs. There is a practical limit to how strong the bond between old work and repairs need to be. This is why the very large bonding area specified for fiberglass repairs.

Ross · Mar 18, 2009

sailingdog said:
Ross—

Please note, that I did say:

Most people do not have the skill and expertise with polyester/vinylester resins to do a proper job with it. Doing so with epoxy is far simpler and much harder to screw up. Also, the greater strength of epoxy can help compensate for the damaged area's inherent weakness.

I've been working on boats for over 25 years, and have helped build a half-dozen as well as modified and repaired many. I stand by my previous statement.

Then it become more a matter of the quality of the workmanship than the quality of the materials that determines the strength of the repairs? Epoxy simply compensates better for poor workmanship?

sailingdog · Mar 18, 2009

No. Someone may have excellent craftsmanship but not understand how to get polyester/vinlyester resin to bond well due to a lack of understanding of how the primary and secondary bonds form. The repair may look beautiful and be well crafted, but it doesn't mean that it will be a strong repair. There is a good reason most places I know of use epoxy resins for structural repairs.

Yes, epoxy can compensate somewhat for poor craftsmanship. However, it is far simpler to use than polyester/vinylester resins generally are, and far more forgiving of mistakes. Unless you do a lot of fiberglass work, you're generally far better off using epoxy than you are polyester/vinylester resins, especially for structural repairs.

Ross said:
Then it become more a matter of the quality of the workmanship than the quality of the materials that determines the strength of the repairs? Epoxy simply compensates better for poor workmanship?