Do you like frosting?

Actually I'm still using imperials with timber, nails and boat lengths.. and for a quick calcs footlibs is quite handy... But weight of fabrics and engine volumes

 

Am I right that such a layer is not neccesary with infusion or bagging?

 

I would imagine it's not necessary for infusion, but my designer suggests it for bagging.

 

Years ago, most members of the forum agreed that Diab do absorb a lot of resin. It was our practice then, and as the diab rep reccomends, to give the foam a coat of resin slurry.

Corecell do not absorb as much. My collegue, is resin infusing formula 1 boats at nearly 100% vacuum and says they do not pre coat corecell. So there is a difference between the type of core.

Class societies (lr, DNV) requires an interface or tie coats between foam and fiber. They recommend a light CSM in between. Obviously there is a concern for skin to substrate adhesion.

Microbaloon is weak. Cab o sil or cotton flox is stronger. Plain epoxy is an adhesive. You might want to experiment.

ASTM d1781 climbing drum method is the accepted method for peel strength but it is not suitable for you as your laminate has a thick skin.

You might want to make home test samples with the resin slurry mentioned above and try pulling the cured laminate (by vice grip) away from the foam. You will be looking for separation if it is breaking at the fibers, in the resin, or in the foam. Fiber or foam is good.

 

You can soak the corecell in dye, there is no penetration other than the cut surface cells ,I would figure about 1 1/2 ounce per square foot to coat the surface ,this outside of what the laminate requires,some foams need a primer/hot coat but with epoxies that is a mute point since there is no chemical action and you are looking for the mechanical side,I would squeegee just a little on the wetout to fill the cells and avoid the resin "bridging" a trapped air bubble.

 

Corecell and PVC foam do not absorb resin.
My experience is that 80kg divinycell has a better surface finish than 90kg corecell.
It takes 200g/m2 to coat divinycell, 250 - 300g for corecell and 160g for plywood, you need to add these amounts to the cloth weights when calculating your resin requirements.
I find that the surface finish of divinycell is smoother and much more consistent and as it is cheaper and has slightly better properties other than elongation it is my choice for all areas other than below the waterline.

Maybe this pre coating is a regional practice I also assumed you are sgueegeeing on the slurry just before laminating, ie wet on wet. I can not see how this improves adhesion in fact one time I had a very rough surface finish on a sheet of corecell and I did not want to sand it down so I did fill this with a qcell slurry to save some weight. I found it harder to see if there were any trapped air bubbles under the laminate in this region compared to the rest.

If you want to save a slight amount of weight then do the pre coating otherwise its a waste of time in my opinion.
Transverse planking will produce a very smooth and fair (if your stations and battens are true) surface. So pre coating and letting this go off and then having to sand as also suggested, this I definitely dont recommend. It wastes time and introduces a secondary bond.

The best thing you can do to maximise the quality of your laminates is not to laminate in the night when the humidity is high as you have previously indicated.

One way to look at this is that practices that have made their way into boat building standards and classification codes are based on scientific evidence.
In these humidity level is a requirement, pre coating foam with a slurry of silica and microbaloons is not.

 

Hmmm... could it be that the precoating is very important for the 34oz (1150g) fabric to be completely filled in where it meets the foam?

Might you get a "waffle" effect if you don't give the heavy triaxial something to sink down into?

Andrew, yes... it is best to do the bogging seconds before the layup, so it's wet on wet.
I will watch humidity closely. I am in good shape for many moths from now. Humidity seems to be the worst in the summer, or "rainy season" here.


War Whoop: I didn't quite get that last sentence. When you say "squeegee just a little on the wetout", do you mean squeegee just a little on the foam ahead of the wetout, or only use my squeeegee a little bit on the laminate, leaving it resin rich?

I know... dumb newbie!

 

LOL I never had a problem with the corecell surface and found it superior to anything else I have used and second the Factory is new and very sophisticated.

 

No I was talking about the foam only as that is the recommended Hot coating procedure for some foam systems ,however a short nap roller should do the job, You need to do a test, chances are the epoxy will pull some foam off, I can't imagine the epoxy just releasing unless something is VERY Wrong,Myself I would keep the bondline resin neat as possible.

No a squeegee in the right hands will not leave the laminate resin rich.

 

Let the games begin!

Here we have a sample of "frosting" on some Corecell and a sample of "no frosting."

Both use Silvertip laminating epoxy from System Three. The frosting is done with System Three General purpose epoxy and phenolic microbaloons. (you can't mix anything with the laminating epoxy - it's against the rules)

I used a hot coat of neat epoxy on the "no frosting" test panel.

I must say, the 34oz triaxial wet out was a lot easier without the frosting. It used less epoxy over all, too... although I can't really say that with 100% accuracy because the frosting used a lot of microbaloons. So, while the frosting used more "goo", the overall amount of epoxy may or may not have been less. I wasn't paying attention to that.

Destructive testing to follow!

 

Seems a little bit odd that War Whoop was the only one to include the word "bond line" in this discussion. Bond Line is indeed the most important factor here, no matter what method you choose, if the resin /glass ratio is perfect but the bond line is resin starved, well...you've got problems. Lay up some test coupons and do some destructive testing. You might be surprised at how much BS is floating around out there. The method you choose has to work for YOU.

 

I think, if I'm understanding what the bond line is, this is exactly what I'm testing. I'm assuming the bond line is the epoxy that is connecting the foam and the fiberglass, correct?

If so, the whole "chocolate frosting" debate is all about the bond line.

My designer and many others suggest using a bog as the bond line. At the same time, plenty of other people (nearly half) suggest using neat epoxy as the bond line.

The test I'm doing here is one sample of each. They were laid up today and will be destructively tested on Monday afternoon. There certainly does seem to be a log of BS out there. It's hard to sort through it when you are new to this stuff.

Doing these layups for the test coupons today, it seemed natural to put a thin coat of neat epoxy on the foam first, then wet out the 34oz triaxial from the top. It worked very well.

 

Exactly right. No matter what the laminate or core, if they are not still connected 5 years from now, you're in trouble. I've never felt a need to thicken the epoxy "prime" coat, except at joints or other irregularities, but I can tell you with some certainty that wherever a density change occurs, a stress riser also occurs. As a fiberglass repair tech for the last 45 years, i can tell you that these stress risers have contributed substantially to my financial well being.

 

I got a good laugh out of that last line. The rest of the post makes perfect sense.

Can I ask you a quick question unrelated to the topic of the thread?

What do you think about FL humidity? I'm building in FL. It's often 90%+ humidity and you still have to do fiberglass and epoxy work. How do you handle it?

 

CatBuilder; how are you performing the destructive test?

I did a comparative test to see if humidity levels effects the laminate my self. Without any test equipment the only simple test I could think of was to laminate a narrow strip of glass back to back on a base laminate. The test was a peel strength, to get the peel started I covered one end of the base laminate with packaging tape before doing the lamination. This allowed me to put my thumbs under each laminate and simply pull apart against each other. In this way I hope the force on each laminate was equal and gave me a qualitative result.

Something like this would also be appropriate for you, but what you should find with your 90kg corecell is that the foam will fail and not either of the bond limes.
I think you would need to go to a 200kg + density foam to start testing the bond line differences.