Waxed polyester resin and Nidacore layup question

Hello Boat design community. I am planning for my upcoming rebuild project and have a question about polyester resins. I laid up a test panel of nidacore with waxed polyester resin yesterday to test bond strength and panel strength. panel was 1/2" Nidacore with to layers of 17oz biaxial. I wet one side with resin then proceeded to lay one layer of glass, wet it out. then second layer and wet it. then I flipped the panel and did the same on the other side. Then I placed it on a piece of melamine then put another piece of melamine on top and weighted it down. Once cured the panel was very stiff.

I commenced with destructive testing. Hitting it with a 2x4 to see if it would show signs of delamination at the point of impact. It faired well. Then i tried peeling it off the nidacore itself. I was able to peel it off only up to an inch from the saw cut edge. Failure was at the scrim to honeycomb section not the glass to scrim. I attribute this to the sawcut edge and the fact that this piece of nidacore has been sitting around my shop for a while being moved from here to there as it only failed up to an inch from the edge and the inner scrim was well bonded.

What confused me was that this layup was done all at once but I was able to peel the outer layer of one side of the biaxial clean off. I'm wondering if the fact that I used waxed resin and placed the melamine over it that this may have trapped the wax in between the glass layers and acted as a release agent from one layer of glass to the next. for this type of semi closed layup should I use unwaxed resin? could the wax have been the problem?

 

The wax wouldn't have much to do with the layers separating unless the resin was cured when the next layer is applied. Polyester resins don't do well at bonding woven or uni type products (Biax) without CSM between the layers, so being able to peel them apart isn't all that unusual.

There are very few occasions where you would use a waxed resin, as in almost never, so in the future only buy unwaxed resin.

 

Ok so mat acts as a binder? I figured since it was all laid up wet it would cure as one matrix. Most of my laminating experience is with epoxies and never came across this issue. I'm going to try another test with some CSM in between.

Thanks for your response!

 

Giving up on polyester for repair work. Even with mat my results are suspect. I've never had bonding issues with epoxy and not willing to gamble on a full rebuild.

 

You're probably having some degree of air entrapment, along with uneven bonding pressure. Both of which can cause issue. Most of which are solveable by going to vacuum bagging. Epoxies have a higher bonding strength, but can still suffer from the same issues, given the same construction methods. They're just less obviously evident is all. And due to the resin's higher bond strength, some other aspect of the panel/part may fail first, instead of the type of bond in question.

Think of the length of the gap which the resin has to span between the core & the laminate, & also between individual layers of the laminate as a lever. And obviously, the longer the lever, the weaker the bonds/part. Thus more pressure while things are being laid up, & or, curing results in a stronger finished part. This is true even if to the naked eye there aren't any gaps or air entrapment. But if viewed under magnification, the difference in layup styles is evident. And on layups with more layers, the differences in thickness between the 2 methods becomes obvious. With the thinner, more compacted laminate being stronger.

When building thicker parts with materials like pre-preg carbon, they'll use vacuum bagging at certain points during the layup phase to debulk things. Adding more reinforcements after this, but prior to the final vacuum bagging, & subsequent curing of the part, for the same reasons. When they do things this way vs. a hand layup, or without debulking, the finished part has better overall mechanical properties. Though sometimes it's less stiff due to being thinner.

This is also part of the reason that infusion is more popular now. Both for production boats, & DIY builds.