Using Foam as a "mold" for Fiberglass or CF Teardrop

[shootr]

As you can see from the post count, super-noob here, wrought with teardrop fever and planning on a build this summer/fall.

I've built a few small things with epoxy/fiberglass (roof console for a jeep, surfboard, etc) but nothing bigger than that. I'm up for the challenge of using this material if I can get some advice/opinions/critiques of a few thoughts. Otherwise I'll go foam/plywood route.

I'd like to create a 8' x 4' shell for a traditional teardrop design, then layup 2 layers of FG or CF mat/epoxy. The floor would be traditional plywood/stud buildup. The kicker is after the fiberglass is cured, I want to remove the foam and leave the shell behind. Lateral support would come from the bulkhead between the sleeping area and galley. The galley door would be cut out of the shell and reinforced, and RV style shorty doors used in the cabin. I worry about fatigue cracking, getting enough support for the galley door hinge, stuff like that. I guess it's just an attempt to be different...

I don't need the insulation of the foam - heat is more the issue here in AZ, and even if I camp in the winter, blankets in a tent always worked before.

Anywho, if you're bored, feel free to share your thoughts. Thanks!

[KCStudly]

Nothing wrong with embedding some hardwood ribs in the hatch area to act as screw blocks for your hatch hinge and give some depth of section for adding stiffness to the FG structure.

Take a look at the Pico Light thread where the guy in Alaska is building a mini to be towed behind a motorcycle. i think the key is to do an inner and outer lay up over foam core. Separating the inner and outer skins is where the strength comes from.

Good luck and remember, post lots of pic's!

[mezmo]

Are you planning on using foam sheets to build the 'body'?

I'd consider it a waste of time to glass over that and then take the
foam out. Insulation works both ways - can keep heat out as well
as in. Otherwise, just consider it construction material used to
delineate the shape and volume of the TD. Put in
some hard points the same thickness as the foam in the correct
places in the foam and it'll be easier to attach the doors and hatch
and bulkhead etc.. The interior would need a covering over the
foam but that'd be easy to do by just using 1/8-1/4 ply or even
plastic laminate and the 3M green contact cement Steve/Linuxmann
(sp?) recommends. I'd use the effort you'd take to tear out the
foam to do that. Also you're spending the money for the foam already
so it'd make more sense to keep it. Also glassed foam may be lighter
than a built up, thick enough, fiberglass shell. Glassed foam may
therefore be cheaper as less epoxy and fiberglass would be used
than for only a fiber-glass shell.

A South African forum member - can't find the build at the moment -
built a TD using 3ply corrugated cardboard as the shape/volume core
for the TD and then epoxied and fiber-glassed that. It turned out
great. He left the cardboard intact - no reason to take it out. [Oh I
should also mention that the polyester resins melt foam, so they say,
when fiber-glassing is being discussed.]

The main thing is to do it the way you want to do it after evaluating
the comments you asked for. It's your money and time, so use it
as you wish.

Cheers,
Norm/mezmo

[Oldragbaggers]

+1 what Norm said.

Not only will you get insulation from heat and cold by leaving the foam in, but sound insulation as well, which can be nice when in a crowded campground or when you are trying to sleep with rain beating on the roof. If you're in AZ you'll need something to insulate you against that sun beating on your roof or your camper will be like a toaster oven.

Just to clarify, polyester resin melts foam, epoxy resin does not. I did an experiment in another thread where I layed fiberglass cloth over the rigid pink foam made by Dow. It had no ill effects on the foam, was very strong and very light. The foam adds more structural strength than you might think, therefore less fiberglass and less weight.

It certainly is your build, your money and your time, but you might more carefully consider the advantages of leaving that foam in place. And as Norm pointed out, you've already paid for it, why waste it and lose all those benefits.

Will be anxiously waiting to see what you build.

[shootr]

Are you planning on using foam sheets to build the 'body'?

I'd consider it a waste of time to glass over that and then take the
foam out. Insulation works both ways - can keep heat out as well
as in. I was thinking of dissolving the foam with solvent after 'glassing. My fixation with just a shell and no foam is clouding my ability to see the whole picture you aptly describedOtherwise, just consider it construction material used to
delineate the shape and volume of the TD. Put in
some hard points the same thickness as the foam in the correct
places in the foam and it'll be easier to attach the doors and hatch
and bulkhead etc..When using the wood for hardpoints, it will bond to the fiberglass same as the foam, yes? (Become an integral part of the structure?) The interior would need a covering over the
foam but that'd be easy to do by just using 1/8-1/4 ply or even
plastic laminate and the 3M green contact cement Steve/Linuxmann
(sp?) recommends. That was a big fear, trying to 'glass the inside. Your recommendation is an excellent answer to that challenge. I'd use the effort you'd take to tear out the
foam to do that. Also you're spending the money for the foam already
so it'd make more sense to keep it. Also glassed foam may be lighter
than a built up, thick enough, fiberglass shell. Glassed foam may
therefore be cheaper as less epoxy and fiberglass would be used
than for only a fiber-glass shell. Another unknown - how many layers of 'glass to make it strong enough, the wood interior would be the aesthetic I'm looking for, and the smooth seamless exterior the 'glass provides is as well.

A South African forum member - can't find the build at the moment -
built a TD using 3ply corrugated cardboard as the shape/volume core
for the TD and then epoxied and fiber-glassed that. It turned out
great. He left the cardboard intact - no reason to take it out. [Oh I
should also mention that the polyester resins melt foam, so they say,
when fiber-glassing is being discussed.] I've researched so many materials over the years, I just haven't nailed down what is possible yet. Like this stuff: http://www.outwatercatalogs.com/lg_display.cfm/page/683/catalog/Master_2012 I'd love to add some uniqueness with unusual shaping of the roof and/or sides. I also have visions of carbon fiber shell with the pattern showing through.

The main thing is to do it the way you want to do it after evaluating
the comments you asked for. It's your money and time, so use it
as you wish. Thanks for taking the time Norm, this forum has been a lot of fun this week, and I look forward to this build, even if the direction is a little fuzzy right now!

Cheers,
Norm/mezmo

[shootr]

Nothing wrong with embedding some hardwood ribs in the hatch area to act as screw blocks for your hatch hinge and give some depth of section for adding stiffness to the FG structure.

Take a look at the Pico Light thread where the guy in Alaska is building a mini to be towed behind a motorcycle. I studied his build a lot before starting this thread (didn't want to hijack his), that is what gave me hope I am on the right track - but leaving the foam is quickly becoming obvious as to the way to go i think the key is to do an inner and outer lay up over foam core. Separating the inner and outer skins is where the strength comes from.

Good luck and remember, post lots of pic's!

[shootr]

+1 what Norm said.

Not only will you get insulation from heat and cold by leaving the foam in, but sound insulation as well, which can be nice when in a crowded campground or when you are trying to sleep with rain beating on the roof. I was considering that when looking at the aluminum sheeted ones - how loud it must be with rain beating on it - you're right, though - the foam would quiet things down nicely. If I went wood instead, I was considering shooting the entire shell with bedliner to weatherseal and sound deaden it.If you're in AZ you'll need something to insulate you against that sun beating on your roof or your camper will be like a toaster oven.

Just to clarify, polyester resin melts foam, epoxy resin does not. I did an experiment in another thread where I layed fiberglass cloth over the rigid pink foam made by Dow. It had no ill effects on the foam, was very strong and very light. The foam adds more structural strength than you might think, therefore less fiberglass and less weight.

It certainly is your build, your money and your time, but you might more carefully consider the advantages of leaving that foam in place. And as Norm pointed out, you've already paid for it, why waste it and lose all those benefits.

Will be anxiously waiting to see what you build.

Still months away from realistically starting (I'm a little OCD when it comes to laying projects out) but will document it well, rest assured.

[atahoekid]

Welcome to the madness. I'm using 2" foam and plan on glassing the outside. I've used 5mm lauan mahogany (sold as underlayment) for the interior walls. Yeah, I'd leave the foam in place. Provides thermal and sound insulation. You may want something thinner than 2" foam for your needs. The hard points are an integral part of the walls now that they are epoxied in place.

[Wobbly Wheels]

Similar to Mel above, I'm using glass and foam but my layup is two layers of 6oz cloth on the outside and 1 on the inside of a 1" foam shell. My interior bulkheads and cabinet carcasses will also be the same layup. The overall weight of glass that I'm towing with the sandwich will be less than what it would take to build a single-skin shell. By separating the skins with foam coring, both skins combined can be thinner than a single skin of the same thickness. Sandwich panels were a no-brainer for what I wanted to do.

I've placed red cedar backing blocks strategically in the foam: they are lightweight, they soak up epoxy REALLY well and are rot resistant. Many racing sailboats use cedar coring in their epoxy layups.

There's a blog floating around by a woman who built a 'camp-and-surf' trailer that would haul her gear and give her a place to sleep at night. She used a single skin and I think she mentioned how hot it got during the day...like camping out of a pickup canopy I'll bet. Of course, one can do a lot with ventilation & site selection....but insulation is going to make a huge difference.

Welcome, and always feel free to post any questions you've got. I'm keeping an eye out for your build thread.