Do you like frosting?

I am performing the destructive test like Rxcomposite said somewhere along the way... with Vise Grips. I'll tear the triaxial off the Corecell and see what breaks.

If the foam breaks, I'm in good shape, since these are the materials my hull is made from. If a bond line breaks, I am in trouble.

I did the lamination in 65F (18.3C) weather with 90% humidity. We will see...

I'm giving it until Monday afternoon so it's somewhat well cured. It went down toward freezing temperatures last night and 100% humidity, so the cure was slowed down a bit.

 

Catbuilder, I wish i had some definitive data for you concerning laminating in high humidity. With the small amount of testing we've done, the results were all over the map. Lots of variation between different epoxies and different temperatures. But one thing is certain - all fiberglass products (dry) will wick moisture from the atmosphere. So it MUST be stored in dry containers, or well wrapped when not in use. If it's been stored in high humidity for a month, it will be way worse than the couple of hours it's in place before getting wet out.

 

Try to search this. They have some literature regarding epoxy blushing and blooming and cure

http--msdsearch.dow.com-PublishedLiteratureDOW.COM

 

Thanks, rx. My epoxy is non blushing down to 35f with any humidity. It's more the moisture on the core surface before bonding that I'm concerned with at this point. My glass will be dry in q hot box before laminating.

 

At those temperatures it will take weeks to get a reasonable cure, put the samples in your car and park it out in the sun.

 

Ripped Off The Laminate From the Core

The test is complete. It is also somewhat inconclusive.

I waited about 10 days in 60-70F (15.5C-21C) daily heat, with night time temperatures going down to around 45-50F (7-10C). The epoxy cured, but not all that stiffly. It would have probably needed some post curing to attain absolute full rated strength. It was more flexible than expected, but not at all "green."

Here are the results:

Frosting:



The frosting side peeled off with the same approximate force as the neat epoxy side. There were slightly less voids in the frosting side. I had some voids running along the warp of the 34oz (1150g) triaxial. These didn't appear to be from the foam absorbing resin, but rather from a "waffle" effect. Does this mean not enough resin?

The texture of the foam below the frosting pull was more "smooth" than the texture of the foam under the neat epoxy pull. Neither really tore up the foam at all and mostly separated along the first layer of foam bubbles... the open cells. It didn't appear to dig deeply into the foam, which makes sense in retrospect, because the foam is close cell. It can't get down into the foam to tear it up anyway. It *has* to be only in the open cells of the top layer. Because the cells are so tiny in Corecell, it was next to impossible to tell where it failed.

Neat Epoxy:



The neat epoxy pulled off with nearly the same force as the microballoon frosting, possibly with ever so slightly more force to pull it off. It created a rougher texture on the foam where it was pulled from. The cells there felt "sharp", while the cells on the frosting side felt much like the cells on virgin, unbonded foam. Does the sharp feeling to the cells indicate cell rupture? If so, this means the neat epoxy ripped the foam. Still, Corecell cells are so tiny, it's impossible to really know where it failed.

The neat epoxy had a few extra voids along the warp of the triaxial. Why did I get these voids? How do I get rid of them?

Overall:



Overall, I'm not sure how to interpret the findings. They are quite vague.

You can see the tiny bits of foam on the microballoon frosting piece just because of the color difference. It would appear the same amount of them are on the neat epoxy piece, but they are nearly impossible to see.

One thing that is disturbing are the voids along the warp of the triaxial. These voids are long and can be seen as horizontal lines in the first two pictures above and as vertical lines in the last picture above this section. These are not large "neverbond" areas, but very small, about the width of a single "yarn" of the triaxial fabric. However, added up over a large area, they might represent a 10% loss of bonding strength and create small pathways for water to migrate along if the skin is compromised. What do I do with these? Both methods (frosting and neat epoxy) resulted in the small voids. Frosting created just slightly less of them. (probably a 10% difference in total void area)

As to adhesion, they both tore off with a similar force, with neat epoxy being slightly more difficult to pull... ever so slightly. The neat epoxy left a more "keyed" or rough surface on the foam it was pulled from. The microballoon frosting left a foam behind that felt like the virgin foam before applying anything. What does this mean? How would you interpret this result? I had not expected the texture difference.

Peel force: Vice grips were not required. I used normal pliers to peel these off the foam. It took a very firm grip and a hard pull, but they weren't as strong as I expected. Thoughts?

 

I interpret the results as the frosting does not improve the bond strength for the 80- 90 kg foam.
But the test could not pick the differences as the foam is weaker than the neat epoxy or the frosting. You need to do the test with high density foam or the balsa to start seeing the difference. But I guarantee you that neat epoxy is stronger, think about it how can the addition of hollow micro spheres designed to make the resin easy to sand improve the strength. If you used silica only then it would be different.

The voids you had is very common with triaxial, especially on a vertical surface.
You have to expel the air with the squeegee or roller, using peel ply also helps.

The relative ease that you were able to delaminate the glass is normal, only with stronger cores will you see interlamina sheer.

So in conclusion you can save your self work and money by sticking to neat epoxy!!!!

 

I guess this means I can just go right ahead, since my entire hull is made from this density.

I got a good deal on the more dense foam - Corecell A600, which has a density of 116.5 kg per cubic meter (or 7.3lbs per cubic foot). This was originally to be the foam for the keel area, but I am using it on the entire hull at a small weight penalty. The price was just too good to resist.

I will go with the neat epoxy, since this also makes more sense to me.

It is good that I did a test run of the triaxial without any special rolling or heavy squeegeeing. If I did squeegee these small patches, they slid around on the foam too much (not full sheets). It's a relief to know that the voids are common and are worked out with rolling and squeegeeing.

Thanks for the input as always, Andrew.

I will be kind of quiet here for a bit, heating Corecell and putting it on the mold for the next couple weeks. I'll probably report back when I have a set of hulls out of the molds and ready to join together. Should be several weeks, but I will report back with progress.

Looks like all systems go for a "no frosting", neat epoxy lamination.

One more question: Later, when I am done with this laminate for inside the hull and want to have a smooth surface, I use microbaloons to fill in the weave, of the triaxial, correct? Is this nice and waterproof? Do people ever add neat to fill in the weave, or is that just too expensive, difficult to sand and time consuming? Do people usually finish off the interior surface, or just leave it be? Is one layer of 34oz triaxial just "wet out" with epoxy waterproof without doing anything else to it? Or.. are there many little pin holes and places where standing bilge water will make its way into the laminate?

 

I concur with Andrew. Seems the neat epoxy is the way to go.

Just one observation about the voids. When I was in California, whenever the temperature drops to less than 15 degree, the guys would leave the portable heaters on when an overnight job is to cure.

We were doing secondary bond with Epon 828 and when it is cold. the resin runs down before it cures. In the morning, we could see some resin run offs and small white patches on the 90 degree inside corners. Not voids but white streaks. More like resin starvation. For their quality, they don't like it so we have to strip it whenever they see something like that.

Your void on the fibers could be something like that. Resin run off.

 

Whenever you add filler or solids to a resin, you make it less waterproof. In the bilge areas, a coat of resin will suffice. Some class rules requires a layer of resin rich mat, same treatment as the outside skin in contact with water.

On the dry interior part of the boat, if you have some ugly laminate showing, micobaloons mixed with epoxy is easy to sand. I use it as a fairing compound.

As a general rule, you don't finish the surface where it cannot be seen.

 

Thanks for the input, guys. It's unanimous (and much easier!), I will use neat epoxy.

I guess I'll just fair whatever needs to be faired for looks in the hull. Maybe the bilge, so that it's easier to clean up if something spills.

Time to get to work laying up hulls. Thanks.

 

Pictures!

 

OK
define frosting please

 

It's in the first post.

 

oh I read it but how is less absorbed simply because it is applied separately from the fabric

I can understand how it might help prevent starvation but I'm a bit baffled about two things
one would be the color differences I see in some of the pictures and the other is what dynamic is involved in less being absorbed

the actual frosting is a coating you put on the core before you apply the cloth seems easy but I'm embarrassed to say I'm not getting the mechanical properties that make this so

sorry to interrupt a fine thread but as I read along I cant help but feel like I"m missing something

ps
I've exactly no experience with composites so gimme a break on what must seem like a dumb question