Vinylester reacting with ISO/NPG gelcoat

Was in westport Thursday, circum navigated the facility going to and from the harbor...man that's a big yard.

Had alligator cracking on one of my builds, we were new and doing it outside under a shelter. Got complacent on first two as the temp and humidity were alright. Third was a big old alligator. Much more mindful of temp and haven't repeated that mess...

 

And the one in Westport is just one of their facilities, there's a more modern one in Port Angeles.

I used to do a lot with Delta Marine until they went to mostly steel hulls, plus Christensen Yatchs until they went away then resurfaced in Tennessee.

I supplied Ocean Alexander with gel coat and other materials for quite a while, tech service for them was a bit more difficult due to the distance, and it was prior to easy Zoom calls. We supplied gel coat and other products to various yatch builders in China and that general region. Several friends had moved to China to run these operations during certain periods of time, most have retired or died by now though.

I don't do as much international travel anymore, we try to handle most international training stuff with Zoom calls. I have a large shop at my home with cameras set up to demonstrate products and techniques.

We have one customer that has production in China, The Philippines, Turkey and Columbia. I may go to one plant to dial in the product and techniques, then do the training for the other plants live in my shop on Zoom, plus record the session so each plant can review it when needed.

 

Thank you. this is exactly what I was struggling with: as you can see from the video, the gelcoat is dry but slightly tacky to touch. But then in "dissolves" when applying vinylester over it.

 

mvoltin- This is not the first time. We have encountered the same problem.

We were laminating Derakane 411 over polyester gel coat and it is alligatoring. The tech rep was there and adjusted the mixture of the derakane. It was made manageable but remained. Our laminator used a heat gun to "cure" or form a barrier on the sanding gel coat. Whatever works.

Later, I was working in a boat factory and it was the practice to layup the first layer with Derakane Vynil Ester over ISO finish gel coat following the "tacky dry" rule. There was no problem at all.

Looking back, Derakane is more aggressive than poly and will attack the preceding layer (will not bore you with the chemical process). The resin will attack a thin layer of gelcoat OR an uncured gelcoat. The first example example are Aircraft Parts so the sanding gelcoat is applied thin. We were using just a gelcoat gun and we thin the gelcoat to make it sprayable. This could lead to a delay in curing. Further, a thin layer of gel coat will cause it to "flash dry", The evaporation was faster than the polymerization process leaving an uncured gelcoat.

On the other hand, the gelcoat in the Boat Part is laid on thick using commercial pump type gelcoat spray gun. This allowed partial to complete polymerization process and was impervious to the succeeding layer. No problem at all.

Notice that I said the technician/laminator was using a heatgun to cure the gelcoat before the next layer. He was probably initiating a thin film of barrier to minimize the incompatability.

This rule of thumb is not gospel truth (It is the correct way and all others are false) and can be approached several ways. We always test everytime the process or material type was changed.

Today, with the advent of good poly resin, we are no longer using VE over poly. Good ISO poly resin will provide a good hydrostatic barrier for a long time.

 

Now you are very much back on track like normal.

Thin gel coat, and gel coat that has been reduced with a solvent won't cure nearly as good as properly used gel coat. All resins will work fine over properly applied and cured gel coat. VE may possibly attack under cured gel coat more often because the styrene content is frequently higher. This depends a bit on where you're located in the world though, polyester resins are frequently limited in styrene content, so they may be blended with DCPD because DCPD requires less styrene to create a usable viscosity. If you live in a location where there is no limitation on styrene content the two resins will perform more alike.

Some parts of the world don't require the lower styrene levels, and closed molding resins are typically exempt, so what is normal in one area of the world is very different from another. VEs are typically categorized as specialty resins, so they are commonly not restricted on Styrene content. And they tend to be almost unusable at lower styrene levels, so DCPD may added, and many marine and tooling resins go that route. DCPD likes to cure, VE is a bit more sluggish, so you get a better cure by adding DCPD, and DCPD tends to shrink less, so cosmetics may be better.

For weight sensitive parts I developed both VE and polyester in mold coatings that can be applied at 6-8 mils and they are also epoxy compatible. These are used a great deal in high end items where light weight and high performance are required. These come in both clear and pigmented versions.

There were excellent ISO resins that worked great below the waterline close to 50 years ago, I used them extensively at that time, we used 20 drums per week for years. It wasn't every ISO resin, you needed to know what you were buying. We had a long list of VE resins in the shop that were chosen for use on each job depending on their exact chemistry.

 

Thank you. To clarify couple things and a follow up question:

I am in Atlanta, GA.
VE used is from Fiberglass Supply Depot
Gelcoat from TotalBoat Marine Gelcoat
I also use PE from TotalBoat Polyester Laminating Resin

I am actually making a composite bucket seat, so, water resistance is not an issue. The primary reason for using VE over PE was because it's supposed to be stronger and less brittle (closer to epoxy in characteristics). I end up paying twice the price over PE, almost as much as epoxy.

Question: is VE really that much superior over PE in terms of strength and flexibility?

P.S. I ideally I would have used epoxy but having hard time transitioning from gelcoat to epoxy. It seems impossible to source epoxy based gelcoat. There is an epoxy-compatible gelcoat from easy composites but it's $200 gallon. I have to make about 50 of these bucket seats and any advice will be appreciated.

 

You can buy epoxy compatible gel coat right of the shelf near you. Try Revchem or Composites One.

VE is more durable than polyester, but knowing whether it's adequate for what you are doing requires some known stress requirements. But would probably work. But if you want to combine light weight and strength it will cost you more.