Teardrops n Tiny Travel Trailers

ghcoe wrote:
I did sand and wipe off with alcohol before doing the test.

That was my thoughts that it did not need air to cure. The next day it was a sold piece. I even cut it to see how the cure was in the middle. It was cured. I tried to pull the two pieces apart and the foam broke before the glue line. I think I am satisfied with the results of bonding. I did not use a trowel to apply the glue, but I think that if applying to larger pieces I would apply with a trowel.

Curious. How much of a change in deflection? Probably too small a piece to tell.. What what kind of strength would be added if you glued up, say 3 layers of 1"? I'm looking at replacing my lift roof next year to another design and don't wish to frame it (add spars). Hmm..

RJ Howell wrote:Curious. How much of a change in deflection? :

Not sure what you are asking here.

I don't think it would give the foam any more support over a span. The dried glue has a rubbery texture to it when it dries.

TCJ wrote:

QueticoBill wrote:3M 100NF contact adhesive is what I've seen used.

yup, works great . . . once pressed together you'll never get them apart.

Very good shear strength which is exactly what's needed at the center of a panel.

ghcoe wrote:

msaxton63 wrote:

ghcoe wrote:
I did sand and wipe off with alcohol before doing the test.

That was my thoughts that it did not need air to cure. The next day it was a sold piece. I even cut it to see how the cure was in the middle. It was cured. I tried to pull the two pieces apart and the foam broke before the glue line. I think I am satisfied with the results of bonding. I did not use a trowel to apply the glue, but I think that if applying to larger pieces I would apply with a trowel.

Excellent, thank you, I'm picking up one sheet of 1" foam today to do some experiments myself, I'm also thinking that I will try using it in pmf on the samples. I figure at $15 per gallon its worth doing some trials

tony.latham wrote:

I have some epoxy on hand, tried it, somewhat melted the foam and left voids, not an option at all, maybe just wrong epoxy, I don't know, just tried what I had on hand.

That's exactly what polyester resin does. It has styrene in it. You add a few drops or a squirt of catalyst to get it to go off. Does that sound right?



Epoxy is mixed 1:1 or 2:1. It doesn't dissolve foam board.

Tony

this was not polyester resin, its a 1:1 mix, but, its also sat in my hot shed for about 4 years, so maybe some chemical breakdown occurred? When mixed it was no longer clear but kind of yellowish. It does still harden fine and I've been using it with coloring in epoxy art and it turns out fine when colored.

and I've been using it with coloring in epoxy art and it turns out fine when colored.

What brand is it, and what's the intended purpose? Epoxies –-used for glassing--have been used in moldless aircraft construction (foam core) for at least thirty years.

http://www.captoscana.com/captoscana/Documenti_Materiali_Compositi_files/MCHSAC-1%20composite%20construction.pdf

Tony

If the epoxy kicks off hard due to mixing a large batch and not getting it spread quickly, I suppose the heat could have caused something similar to what you described. Were there any visible fumes?

I guess that is unlikely because it would likely be gelling pretty hard by then, too, and wouldn't have spread easily.

Epoxy isn't supposed to eat the foams we typically use.

tony.latham wrote:

and I've been using it with coloring in epoxy art and it turns out fine when colored.

What brand is it, and what's the intended purpose? Epoxies –-used for glassing--have been used in moldless aircraft construction (foam core) for at least thirty years.

http://www.captoscana.com/captoscana/Documenti_Materiali_Compositi_files/MCHSAC-1%20composite%20construction.pdf

Tony

Honestly, I don't remember the brand, the poorly attached labels fell off the jugs long ago.

KCStudly wrote:If the epoxy kicks off hard due to mixing a large batch and not getting it spread quickly, I suppose the heat could have caused something similar to what you described. Were there any visible fumes?

I guess that is unlikely because it would likely be gelling pretty hard by then, too, and wouldn't have spread easily.



Epoxy isn't supposed to eat the foams we typically use.

Yes, I have noticed it tends to get hot in bigger batches and has less working time than it used to. I need to order more epoxy soon, I'm just trying to make use of whats left in small art projects.

Epoxy is the best option. A boat grade. Like WEST, RAKA, System3, MAS. The stuff is actually a lot cheaper than it was when I got into boat building around 1980. Will not melt foam. And it has the perfect consistency for lamination as it comes from the bottle.

Here is famous yacht designer Kurt Hughes, talking about the material he used in his tiny house, which is made of pink foam vac bagged to plywood, in the form of a lunar lander. He used fairly heavy ply, but I have used even 1/8" doorskins and the end result is massively strong.

https://youtu.be/PCoymiQ13s8?t=235

Using a really thick material like pink foam you are not going to get all that much strength in rugged abusive situations, like boat building. He would use a structural foam in a boat hull. However, in materials where defining a space, stiffness, and in this case, insulation are at a premium, it is good enough.

I think someone asked what the increase in strength would be with 3 layers vs 1. Strength is squared. So 3 squared in 9, and 1 squared, is one. So your strength increases 9 fold. Stiffness is a third order thing, the cube of 3 vs the cube of 1, so 27-1. From an engineering by the seat of the pants perspective, you can get deceived by materials of this type, as the stiffness rises faster than the strength, from the math. But with a foam one can really pile on the thickness. If it is overloaded (not too likely in the case of a teardrop shell, it will fail catastrophically. It seems fantastic because it is unreal in stiffness. Foam is an incredible material, but blue/pink foam is relatively weak. Stuff is so cheap in the US, it might be worth considering what some cheap structural foam like Carbon Foam might cost.

A problem people have with epoxy is that it can take a long time to dry, and you need even pressure to hold it until that happens. Vac bagging is the best method, and all one needs when working with smooth level materials is a shop vac. One runs the hose to the bag, but there has to be 4 x 1/4" holes to provide the air required to cool the motor. At least with the small shop vacs I use.

One can stack layer after layer so that one bagging will get all the flat parts in one shot, however they need to organize so that the layers are like a wedding cake, getting smaller as one goes up, or all the same.