Do you like frosting?

My designer suggests putting a thickened epoxy frostong on the Core Cell foam as a priming coat before laminating the single layer of 34oz (1150g) triaxial.

I have heard this is not necessary.

He seems to think it is, as do the Gougeons when you look at their book. They show a thickened epoxy layer over the foam.

The idea of the frosting is to fill every little nook of the foam with epoxy, but not allow it to soak into the core cell foam. Supposedly, this reduced weight since less epoxy is absorbed and also creates a better bond with heavy, course fibers like 34oz (1150g) triaxial.

The alternative is to just wet out the foam and glass and stick them together.

So which is right? Which will have less chance of debonding or forming a neverbond?

Also, can just a single layer of triaxial be 100% waterproof?

 

Do you know how the 34 oz glass will wet out? Will you have to wet the back, put it on and then wet the front? If you do, and the foam absorbs any from the glass, you'll have a problem with air on the backside and no way to get more resin to it without lifting up the wet glass. That's no fun.

 

No, I don't know how it will wet out. I assume I'll have to wet the foam (or frosting layer) out well, then pour though the triaxial from the front side (benefit of a female mold). I'd then use my roller to work the epoxy into the triaxial, squeegee off excess and hope for the best.

That was how I figured it would go.

But yes... you're hitting on the key point the Gougeons make about putting a layer of "frosting" bog on the foam before doing the lamination. They say the foam might absorb too much resin from your glass and create dry spots and "neverbonds."

Delamination is my greatest fear... I've seen more production foam boats on the used market that were delaminating than not. Scary stuff. I want to get this right.

 

With the glass that thick, you might have to actually roll and wet out the backside of the glass itself, aside from wetting the foam. If that is the case, you'll have to plan how to do that. Long lengths of glass will be difficult to do by yourself and getting resin through the glass to take care of air bubbles on the backside will not be possible. Whenever I've covered wood or foam, if it wasn't primed and allowed to at least partially set, resin usually gets sucked out of the laminate. Even on a thin laminate such as 10 oz glass, which can easily be wet out from just the front, there can be problems as resin starvation can appear after the resin in the glass has set thick enough to block penetration from the front.

Try some practice layups for sure.

 

Will definitely do some practice layups. Thanks.

Maybe I can make myself a pre-preg tray ahead of the glass during layup that I can drag the triaxial through before it comes in contact with the foam (or the bog/frosting). That's probably the easiest way to wet the backside out, since I have to layup a continuous 45' x 50" strip. Thankfully, it's just one layer!

 

In such case thickened epoxy (with silica) on the base works well, as it doesn't run when aplied generously and still wets heavy fabrics. Best when working overhead..

 

I question the need for a continuous 45' strip and also for a continuous wet layup from one end to the other. It would seem to point to a structure where failure at any one point means failure of the whole structure. Laps and overnight delays in layup are common. If you don't have to do it all at once, your task will become exponentially easier and less stressful with a much better chance of success.

 

I may have not said it clearly...

I don't have to do the whole boat in one layup. I just have to do the longitudinal, full length (45' x 50 inch) strip all at once. I can then peel ply my overlap to the next strip, key it in and do the next 50" x 45' long piece some days later.

So, I'm only forced to lay up a single layer of triax 45' long by 50" wide in a single go.

My designer disagrees on the weakness of having vertical overlaps all along the hull. He feels it is stronger to have your overlaps running horizontally. I have no choice but to follow his design... he did the stress modeling for the boat. It's a high performance catamaran capable of hitting 18 knots if it's in some strong wind. I can't get anything wrong, structurally, as it's a highly stressed, light weight hull design.

 

Yes, Teddy. This is what the designer suggests... using a coat of epoxy thickened with colloidal silica (and microbaloons) to create a better adhesion between the core and the heavy triax.

 

Cat,

For what its worth I have doubts about most foams "absorbing" epoxy. I guess it is possible, but most foams used in boat construction are closed cells types that if they really absorb a significant amount of epoxy probably points to a failure in the substrate anyway.

That being said, I still think that this coat is a good idea for a whole host of other reasons.

1) This is the first time that you will have control over the final hull shape, and in many ways the only one until you begin the final fairing of the hull. The more imperfections in hull shape and fairing you can do here, the fewer problems you will have when you begin the fairing process.

2) Imperfections in each layer are COMPOUNDED and expanded as each additional layer of class is applied. Slight imperfections grow as additional layers are applied, and getting rid of them now will reduce the overall amount of work you need to do on the hull.

3) Given the above, and that you can't really sand or shape the underlying foam, this coat gives you a layer that can be filled, faired, sanded, and finished.


My advice is that this bonding layer should be finished to the same level of fairing you would apply to the finished hull. Perhaps not to the same grit sandpaper (since you will have to rough it up for the next application) you will finish with, but with the same attention to detail. This prevents minor imperfections from growing as additional layers are applied, and becoming larger issues down the road. So by doing the mass of the fairing now you actually save the weight of having to do it later.

 

Wow, good thinking, Stumble. Thanks.

Kurt alludes to this as well, in his document on foam/glass construction.

I don't see any reason *not* to do it, so I might as well.

 

4' x 45' = 180 sq ft. 180 x 34 oz = 6120 oz. 6120 / 16 = 382.5 lbs. 382.5 / 9 (?) = 42.5 gallons of resin for a 50/50 layup. That seems like a lot to do in one hand layup.

I don't think there's a weakness in overlaps, but maybe discontinuity of the even spread of forces can concentrate around them and overload the adjacent areas of single laminate. On the other hand, any future repairs would seem to do the same thing unless you resort to aircraft repair specs which go to extreme measures like 30 to 1 scarf slopes.

In the end I don't really know and am just making suggestions that might make it go smoother or to put things in perspective. I don't want to complicate anything.

 

??? a bit confusing with imperical.. but with metric 1.2m x 15m ~ 20sqm, 20sqm x 1kg = 20kg.. Anyway I understood it's only one length..

 

No, Sam... I'm here for input. I'm a beginner. By all means, please do comment however you see fit. I'm definitely interested in making things go more smoothly for the build. That's why I'm here... to learn from people who have experience.

The math was off though. I'll do it again....

4.166' x 45' = 187.5 sqft of cloth to lay. 187.5 sqft /9 gets us 20.8 square yards. I have fabric that is 34oz per square yard, so 20.8 x 34oz= 708.33 ounces total layup. Convert this to pounds by dividing 708.33 by 16oz in a pound and you have a total of 44.27lbs of triaxial to lay in one strip.

A 50/50% resin ratio (best you could ever hope for) would mean you are mixing 44.27lbs of mixed resin and hardener for the job.

Since epoxy weights approximately 10lbs per gallon, this means you'd be mixing 4.4 gallons epoxy for that layup, but we can call it 5 gallons because I'm hand laminating.

Seems doable, but a very full day for one guy with a lot of pre-layup prep work.

Is your brain exploding from this yet, Teddy? Imperial is fun! ha ha ha

I have at least some training in metric from my years working in science. We used MKS, which is all metric. I remember it being difficult at first though, until you were show it was all based on 10's.

 

That's right, that's right. Cloth and woven is weight per square yard, mat is per square foot. I was just testing you. Carry on.