Composite fiberglass/foam panel build question

[IdaSHO]

Cool stuff.

On the good side, that urethane is a chemical cure. So a vacuum table should work well, depending upon the viscosity of the mix.

On the other hand, with such a low shore hardness (compared to actual bonding adhesives and epoxy) Id be concerned about panel rigidity.
With the stuff basically being as flexible as a stiff rubber, it will have a reduced panel rigidity.

But don't confuse rigidity with strength. Adding a bit of give would likely increase the actual panel strength


Interesting stuff.

Id be interested in comparing your urethane with an actual panel adhesive that Epic Resins carries.

Ad also be interested in their explanation as to why they suggested this potting urethane instead of an actual panel adhesive, that they also carry.


BTW, I've done quite a bit of work using "casting" urethanes that are probably very similar to the potting urethane you are working with.
One specific use Ive used the urethane for was a series (100 or so) of custom motor mounts. :ylsmoke:

 

[rruff]

On the other hand, with such a low shore hardness (compared to actual bonding adhesives and epoxy) Id be concerned about panel rigidity.
With the stuff basically being as flexible as a stiff rubber, it will have a reduced panel rigidity.

It'll be much harder and stronger than the foam it's bonding to. I don't think it will be a problem.

Adhesion is to the foam is probably the highest priority. One nice thing about the epoxy is that you can score the foam with a dog brush, making many thin shallow grooves, and the epoxy is thin enough to penetrate. Other adhesives may adhere better to the foam though and not require scoring.

 

[IdaSHO]

Problem? Probably not. But my point still stands.
Regardless of core material, a softer adhesive will have a low modulus, which will reduce rigidity.

As mentioned though, reduced rigidity does not mean reduced strength, unless the urethane lacks sufficient adhesion. Which may very well be the case.
I've worked with plenty of different types of pour-able 2-part urethanes over the years, and none of them had great adhesion properties, at least when compared to epoxy, or even that of a moisture cure PU.

As for foam prep... No need for a silly dog brush.
60 grit on a DA is plenty, much faster, easier to be consistent, and is more than enough for epoxy to grab well.

Adding "grooves" doesn't do much for bonding, assuming you are using a proper adhesive.
Sanding off any residual film/residue and scuffing the surface sure, but by no means do you need to gouge the panel.

And yes, binding to the foam is critical, but to imply that it is more important than bonding to the skin is just ignorant.
You are bonding two materials together. Bonding to both materials is EQUALLY as critical.

Which begs even more scrutiny... as every material is different. EPS vs XPS, FRP vs ABS vs FILON

What may work for one particular pairing may not work for another.


But for XPS and FRP, Ill always suggest epoxy over anything else.

Just make certain BOTH surfaces are prepped well (60 grit on a DA)

 

[stomperxj]

...unless the urethane lacks sufficient adhesion. Which may very well be the case.

This stuff is nearly impossible to get off of the Filon. Using a sharp utility knife blade you can sort of scrape it off but it's not that easy and you usually take some gel coat with you. That is with zero prep done to the Filon. Glossy finish. So with prep on both materials I would imagine my panels will last a long time.

 

[IdaSHO]

Good to know, and if you think it is sufficient, by all means go for it.

But realize that its all relative. So unless you have done comparative tests with actual panel adhesives, you really have no way to determine just how good it is.


Similar to materials, all adhesives are different. This one might be very good.

 

[stomperxj]

For reference I also tried Loctite UK 3173/3182 2 part and it was pretty good but way too thick and was over $300/gallon. The stuff Styromax uses isn't available in anything less than a 55gal drum in the US which was well over $5k. I don't need 55 gallons

 

[rruff]

As for foam prep... No need for a silly dog brush.
60 grit on a DA is plenty, much faster, easier to be consistent, and is more than enough for epoxy to grab well.

Try it and see!

There was a lot of discussion of this regarding surfboards (I'll see if I can find links), and sanding alone wasn't the best. I recall someone with a build thread on here as well who got delamination from sanded XPS+FG layup when it got hot (sat in the sun).

 

[steelhd]

Apologies if somebody already pointed this out, but the foamie forum seems to be what you are looking for.
http://www.tnttt.com/viewforum.php?f=55

 

[stomperxj]

Apologies if somebody already pointed this out, but the foamie forum seems to be what you are looking for.
http://www.tnttt.com/viewforum.php?f=55

Those guys are using paint and canvas over foam. Apples and oranges.

 

[steelhd]

Those guys are using paint and canvas over foam. Apples and oranges.

True. But lots of good info about adhesives, surface prep, materials, methods, etc.

 

[turbothrush]

As for foam prep... No need for a silly dog brush.
60 grit on a DA is plenty, much faster, easier to be consistent, and is more than enough for epoxy to grab well.

Adding "grooves" doesn't do much for bonding, assuming you are using a proper adhesive.
Sanding off any residual film/residue and scuffing the surface sure, but by no means do you need to gouge the panel.

And yes, binding to the foam is critical, but to imply that it is more important than bonding to the skin is just ignorant.
You are bonding two materials together. Bonding to both materials is EQUALLY as critical.

Hi. Dog brush guy here.. Original thread here
http://ecomodder.com/forum/showthre...ass-epoxy-home-depot-foam-extruded-24820.html

I guess it is important to test the marterials that you plan to use in any build to avoid disappoint later. When dealing with
epoxy/foam/fiberglass as far as adhesion goes what works with with one density of foam may not work so good for
another. Here is my peel test of Owens Corning Foamular C-300, 2 layers of 6 OZ e glass, U.S composites thin 635 epoxy
resin. The foam was scored with a dog brush and the epoxy applied with a plastic body fill squeegee

Using these materials the foam is definitely the weak point but still it was very difficult to peel the skin off. It may be overkill
but I felt more comfortable with the result than just sanding with 60 grit. i guess it just depends on what you are comfortable with.
My goal with this method is to hopefully prevent any delamination issues

The white dots above the shadow in the pic shows where the epoxy ripped off the fiberglass cloth but mostly it was a one way transfer of
material

 

[rruff]

Hi. Dog brush guy here.. Original thread here
http://ecomodder.com/forum/showthre...ass-epoxy-home-depot-foam-extruded-24820.html

Thanks for coming by!

Have you ever posted your build online? I haven't been able to find it if you have. Would love to see what your finished product looks like.

 

[IdaSHO]

Try it and see!

There was a lot of discussion of this regarding surfboards (I'll see if I can find links), and sanding alone wasn't the best. I recall someone with a build thread on here as well who got delamination from sanded XPS+FG layup when it got hot (sat in the sun).

Certainly find some links if you can.

I've heard the same, referencing the same supposed case, but I've never seen photos or even a link of such a case.


Epoxy in itself isn't so simple either.

LOTS of different grades and types of epoxies.

So what might have failed in the case you refer to, may have simply been the wrong epoxy for the job.


FRP has proven over the years to be very tough to bond to. Most FRPs are epoxy based polymers, but it still takes a pretty rough FRP surface to provide enough for the epoxy to grab.

PU has some incredible tack and grab strength, but the expansion of the good moisture cure options is a problem.

 

[IdaSHO]

Hi. Dog brush guy here.. Original thread here
http://ecomodder.com/forum/showthre...ass-epoxy-home-depot-foam-extruded-24820.html

I guess it is important to test the marterials that you plan to use in any build to avoid disappoint later. When dealing with
epoxy/foam/fiberglass as far as adhesion goes what works with with one density of foam may not work so good for
another. Here is my peel test of Owens Corning Foamular C-300, 2 layers of 6 OZ e glass, U.S composites thin 635 epoxy
resin. The foam was scored with a dog brush and the epoxy applied with a plastic body fill squeegee

Using these materials the foam is definitely the weak point but still it was very difficult to peel the skin off. It may be overkill
but I felt more comfortable with the result than just sanding with 60 grit. i guess it just depends on what you are comfortable with.
My goal with this method is to hopefully prevent any delamination issues

The white dots above the shadow in the pic shows where the epoxy ripped off the fiberglass cloth but mostly it was a one way transfer of
material

I appreciate you for stepping into the thread!


If I read this correctly, you are referring to glass lay-ups over foam?

If so, its related, but not directly applicable to the discussion with regards to adhesives and panel construction.


I myself love the glass over foam method, but it is extremely labor intensive compared too a composite core panel

 

[IdaSHO]

For reference I also tried Loctite UK 3173/3182 2 part and it was pretty good but way too thick and was over $300/gallon. The stuff Styromax uses isn't available in anything less than a 55gal drum in the US which was well over $5k. I don't need 55 gallons

Similarly, loctite PLP Premium (caulk tube) is INCREDIBLE stuff for general bonding duties.

But similarly, it is much too thick for panel bonding as it simply doesn't flow.

it also expands (moisture cure) but that helps when bonding the types of materials it is designed for.


Wood, pocket holes, and a small bit of PL Premium will result in a joint considerably stonger than the parent material.

Thats how the entire wood frame of our camper is constructed. Major overkill :Wow1: