Improve the bond - Fiberglass/Epoxy to Home Depot foam (extruded polystryene)

[turbothrush]

I did some testing on adhesion last winter and found rough sanding the foam was not the best solution for adhesion at least not with the materials that I used. Sanding may work fine on urathane foam, I don't know.

I should also say the test was only a peel test and I used the exact materials that I was using on my build. Foamular C-300 from Home Depot / U.S. Composites 3 to 1 thin epoxy 635 / 6 oz e glass fiberglass. I tested various grits of sandpaper from 220 down to 20 grit (had to glue the 20 grit to a block of wood and kind of twist it into the foam) as well as drilled holes and holes poked with a scratch awl also with and without 3m super 77 spray glue.

The only sample I saved was the one I found to give excellent results which was scoring the foam not rough sanding. I scored the surface of the foam with a stainless steel pet brush from the dollar store. This only seems to work well if you score lenghwise and what you are looking for is score lines like in the pic . If you use a plastic squeege to spead the epoxy it seems to "key" into the foam quite nicely and gives a really strong bond. So strong you can rip the cured skin of fiberglass (6oz.) before it will detach from the foam.

If you don't have a dog or cat then a gang of utility knife blades with some thin wood spacers between them works at least as well as the brush.

I realize that there is lots of other methods as well, like holes drilled or cut and wood dowels or blocks of wood inserted to join the two skins but the scoring method is nice if you have a large area to do like I did.
Just thought this might be of interest to someone since this bond is so critical to success.

[nateshuntsvegas]

This is great, this is exactly what I have been thinking of making for a long time. I have a 2000 Nissan frontier and its a 4 cylinder so not much power, also even so called light weight fiberglass campers are upwards of 2000lbs. Do you mind if I asked a few more details on the construction process? Did you use stringers or anything else to reinforce the foam or is it just fiberglass and foam? How many layers of fiberglass did you do inside and out? How much fiberglass and resin did this project take? Do you have any video of the process? Do you have more pictures of this project? I saw more on your other post but had more to do about aerodynamics than actual construction.
TIA
Nate

[Christ]

Neil's gonna have some scratching to look forward to methinks... lol

And after all that time spent nicely smoothing everything.

[turbothrush]

Originally Posted by nateshuntsvegas

This is great, this is exactly what I have been thinking of making for a long time. I have a 2000 Nissan frontier and its a 4 cylinder so not much power, also even so called light weight fiberglass campers are upwards of 2000lbs. Do you mind if I asked a few more details on the construction process? Did you use stringers or anything else to reinforce the foam or is it just fiberglass and foam? How many layers of fiberglass did you do inside and out? How much fiberglass and resin did this project take? Do you have any video of the process? Do you have more pictures of this project? I saw more on your other post but had more to do about aerodynamics than actual construction.
TIA
Nate

I know what you mean about heavy campers.

Don't have a video but questions are no problem. Camper is still not done but I still work on it when I have time.

There is no stringers . I made all the panels on a large flat table made from used hollow core doors joined with biscuits(no glue). The table is important since all the panels index off the table if you want a camber in the panels or if you just want a flat panel. I used formular 300 foam from Home Depot which is 30lbs/sq inch crush strength.This seems to be enough with 2 layers of 6 oz cloth when weave is filled the microbaloons/cabisol on the outside. Inside just 2 layers of cloth.

I used duct tape for clamps and Gorilla Glue for gluing the panels together.
Attachment 12673

I let in hardwood blocks into the foam before glassing for attachments points for jacks , ladder , table ,tiedowns etc.

I will have used about 10 gal of epoxy and about 1600 sq. ft of fiberglass cloth(400 sq ft of panel area x 4 layers total ) and probably 3 or 4 gallons of microballons and 1 gal of cabosil for filler and gap filling glue.

Bare shell comes in at under 400 lbs. with windows
Fun project but big in more ways than one.

[Xist]

Originally Posted by Christ

Neil's gonna have some scratching to look forward to methinks... lol

And after all that time spent nicely smoothing everything.

Heh.

Hey, if I finally went out and ecomodded, would I earn disapproval if I shaped foam, but did not smooth it until after I laid fiberglass? Could you ever tell if it was as smooth as an android's bottom?

[3-Wheeler]

I wonder if it might be better to mix up a batch of micro-balloons and epoxy, and then work that mix down into the "grooves", then layup the glass and epoxy as usual? That way, the mix will weigh a little less than pure resin.

Thanks for the nice write-up !!

Jim.

[nateshuntsvegas]

Originally Posted by turbothrush

I know what you mean about heavy campers.

Don't have a video but questions are no problem. Camper is still not done but I still work on it when I have time.

There is no stringers . I made all the panels on a large flat table made from used hollow core doors joined with biscuits(no glue). The table is important since all the panels index off the table if you want a camber in the panels or if you just want a flat panel. I used formular 300 foam from Home Depot which is 30lbs/sq inch crush strength.This seems to be enough with 2 layers of 6 oz cloth when weave is filled the microbaloons on the outside. Inside just 2 layers of cloth.

I used duct tape for clamps and Gorilla Glue for gluing the panels together.
Attachment 12673

I let in hardwood blocks into the foam before glassing for attachments points for jacks , ladder , table ,tiedowns etc.

I will have used about 10 gal of epoxy and about 1600 sq. ft of fiberglass cloth(400 sq ft of panel area x 4 layers total ) and probably 3 or 4 gallons of microballons and 1 gal of cabosil for filler and gap filling glue.

Bare shell comes in at under 400 lbs. with windows
Fun project but big in more ways than one.

Do you think it will be strong enough to have a walk-on roof?
What are your material cost so far?
How many hours do you think you have into the project so far?
Thanks for all the answers.
Nate

[Varn]

If you put a peel ply on any layer that you want to add reinforcement to it makes an excellent bonding surface for the secondary layup. It also adsorbs some of the epoxy which adds minimal strength. The strength is the fiberglass.

[turbothrush]

Originally Posted by 3-Wheeler

I wonder if it might be better to mix up a batch of micro-balloons and epoxy, and then work that mix down into the "grooves", then layup the glass and epoxy as usual? That way, the mix will weigh a little less than pure resin.

Thanks for the nice write-up !!

Jim.

Hi 3-Wheeler, Thanks for responding . I have done exactly what you suggest but only where I scored the foam on the tablesaw for bending. And I must say it creates the ultimate bond. Kind of like micro dovetails.
To be honest I never tried micro mix in the pet brush grooves but I will.

I'm trying to say away from polyester fillers entirely. After a sanded micro layer I am thinking maybe System Three epoxy primer then System Three lpu top coat. Manufacturer says it can be wet sanded and buffed which is something that I am already familiar with . I don't really need to go automotive topcoats since I don't need to do any color matching....Any thoughts or comments ?

[3-Wheeler]

Originally Posted by turbothrush

....I'm trying to say away from polyester fillers entirely. After a sanded micro layer I am thinking maybe System Three epoxy primer then System Three lpu top coat. Manufacturer says it can be wet sanded and buffed which is something that I am already familiar with . I don't really need to go automotive topcoats since I don't need to do any color matching....Any thoughts or comments ?

Yes.

I use either West System Epoxy or U.S. Composites Epoxy.

I do NOT use any type of polyester resin. It smells, hard to mix because of having to count multiple drops, and eats the Foamular foam on contact.

The epoxy I use is mixed 3:1, and I use pumps, so it's super easy and pretty fool-proof too, works great with micro-balloons, and is very predictable in it's operation. Oh, and it does not eat the foam!

Jim.