Fiberglass and cardboard

[Forrest747]

With not much going on until next week an idea came to me while researching fiberglass.

I have a freind that ships machines and they use 6 foot by 12 foot boardboard panels. so thinking hey i could have him aquire a couple of them. thye are about 3/4 of an inch thick and I could fiberglass overthem, cut to shape and screw into the side of the floor.
Do both sides in fiberglass and paint the interior.

Your thoughts.

[chief5]

Several years ago, I read a book on composite aircraft construction. In it, one of the aircraft designed by Molt Taylor was constructed using "card stock". It was wetted, bent to the desired shape, allowed to dry, then fiberglassed on both sides. Entire wings and fuselages were constructed with internal bracing and gussets of cardboard "card stock. The theory was, that the strength of the part being built was was in the 2 layers of fiberglass cloth. the small separation of the cardboard gave the part rigidity.

The method was named "Taylor Paper Glass"

I see no reason why you can't build with this method. I will do a search and see if I can find and link some info on this building method.

Good Luck, Lorn.

[bgordon]

Hi,

Yes, you could easily work with cardboard, form the teardrop as you would like, and then fiberglass over it. For a very good explanation on how to do it, look here:
http://microship.com/resources/cardboard-core-composites.html

However, the problem lies with the finishing. You wil have to apply body filler, and sand, sand, sand, and sand! Honestly, the sanding alone will probably take you longer than building the entire structure! (That's of course, if you want a decent looking finished product.)

You should heed Andrew's (Angib) advice about this. He always tells people that you should have a good reason to want to work with fiberglass, since it is a much harder, and longer process than working with plywood.

[Forrest747]

i think due to my first attemp i am just going to use plywood, fiberglass the joints to ceiling and walls and such to water proof. the plywood out here i have found has a MDF core. i do not want it to get wet.

[kennyrayandersen]

Yeah, getting cardboard or mdf wet is a disaster. I can't recommend cardboard as a build material -- even when it is covered by fiberglass, and I'm pretty darn sure Andrew would back me up on this one. First, the core of cardboard is only slightly structural (enough to support box construction), but nothing like a tear, second – wet boxes are crap in a matter of seconds. If ANY moisture got in there it would basically fall off the frame. By the time you got enough epoxy somehow forced into the center of the core to stabilize it against moisture, it wouldn’t be light anymore, nor cheap, since epoxy isn’t so cheap.

There are special fiber reinforced honeycomb cores and what not, but they are expensive and a LONG way from cardboard and can be a real challenge to fabricate with. Thin plywood is pretty easy to work with and the only real reason to use the fiberglass is to do a glue and stitch –type construction (reinforce the joints), seal over a woody or before paint to keep it from cracking and letting moisture in, or as some part of a serious weight-saving effort. I think Andrew is pretty right on this one (if I’m remembering his comments correctly)

[Forrest747]

yeah i was looking at the cardboard and the enginer wheels started to turn just wonderin.

Just because you can go mach 3 in a cessna doesnt mean you should.

[bobhenry]

A paper mache teardrop can not be far away !

[Trackstriper]

A paper mache teardrop can not be far away !

From the odd edges of automotive history of the late '50s....I bring you the Paper Mache Special:

http://books.google.com/books?id=oZempfWXoe4C&pg=PT220&lpg=PT220&dq

[bgordon]

Hi,

Mmm, I just want to make sure that my previous post was not understood in a wrong way. When I mentioned that you could build with cardboard and then fiberglass over it, I meant fiberglass in the sense of "applying resin, then at least 3 layers of 6 ounce fiberglass (chopped strand or weave), and wetting it out between each layer".

I want to stress that the cardboard has NO structural function other than to give the wetted out fiberglass mat/chopped strand it's form. When the resin has cured, (within an hour or sometimes less), the cardboard has NO further function, and can easily be removed if you wish. The fiberglass and resin shell now forms the basis for the structure, and is VERY strong. Many, many fiberglass trailers are out there with nothing but three layers of 6 ounce fabric and resin to form the structure.

The cardboard, if correctly used, will last for the hour or so to provide the form. For proof of this, see the link in my previous post.

And to latch on to others, you could just as well build a paper mache teardrop and cover that with fiberglass (3 layers of 6 ounce at least), to form a very strong, structural body. Again, the paper mache will not give the structural strength that is required for highway speeds, but the fiberglass shell will.

But again my further point. When you wet out fiberglass, the surface is fairly rough, and to get that 'mirror' look like the one you have on your car bonnet, will call for (seemingly) endless sanding, body filler, and sanding.

To prove this point, look at this page:

http://www.rqriley.com/frp-foam.htm

Almost at the end of the page, you will find this paragraph:

The process of leveling and smoothing a fiberglass body is the most labor-intensive part of construction. Literature on fiberglassing describes various techniques for producing a gelcoat finish. At Quincy-Lynn, however, we used conventional autobody repair techniques and filler materials instead. The fiberglass body is first smoothed with a Surform file to remove large fiberglass drips and surface irregularities. It is then covered with lightweight plastic body filler (such as "Bondo") and leveled using traditional body-working techniques.

Although every word in this paragraph is true, I believe it does not really spell out the work that is required. As mentioned before, the sanding stage alone will often be more work than the entire structure building process!

I hope that clarifies my previous post somewhat!

[kennyrayandersen]

OK there are two approaches, one is to use it like a mold and just lay a bunch of glass over the top. You can do it this way, it’s not the lightest construction, but you could certainly get enough glass (like a boat) to make it strong enough. However it would take a bit of material and epoxy to do in the scale of a teardrop trailer so it wouldn’t be so cheap.


So, with that regard, it’s doable; however, lighter is to use some type of core material like NOMEX honeycomb or foam (which is mostly air) that can react the shear between the two outer surfaces – this type of construction is much lighter and stronger. Some in the past have suggested using cardboard as the core, but as I pointed out it is really non-structural that way and if you get enough epoxy to make the core rigid, then it’s heavy. Cardboard just wasn’t designed to take that kind of loading or any exposure.

Actually, plywood is pretty good for this application being fairly lightweight and thick enough that it doesn’t fail in a stability mode (it’s pretty stiff for its weight). It going to be hard to beat for strength verses cost etc. unless you are willing to get into some more sophisticated building techniques.

[bgordon]

Actually, plywood is pretty good for this application being fairly lightweight and thick enough that it doesn’t fail in a stability mode (it’s pretty stiff for its weight). It going to be hard to beat for strength verses cost etc. unless you are willing to get into some more sophisticated building techniques.

Yes, I agree. As a matter of fact, I understand that fiberglass is about 6-7 times heavier than plywood, so going the plywood route is not a bad idea.