Not a boat question :(

Hey guys, apologies for being on a boat forum and not asking about a boat...fiberglass forums are blocked here in Iraq (Soldier) and I can't get on any of them.

I am planning on building my own fastback fiberglass top for my bronco, and am curious about how much mat and resin to use.

I am first going to cut the old square fiberglass top all around the edges, so I am left with just the part the connects to truck. Then I was planning on building the new frame on that, either out of 3/4 foam glued and shaped how I need it, or out of some chicken wire type mesh 16ga or thicker to hold the form, or out of conduit.

Then I will be using some 1 1/2" mat from US composite, chopped strand.

I have no idea how many layers I will need to put on to make it strong, or what type of resin to use. It isn't structurally integral, and the only thing it needs to do is keep the elements out and look good

I'd like it to be light, and not super expensive to create.

Its going to slant back from the cab to the tialgate, instead of being a big square like the stock top is, and I plan on adding a window in the rear and a window on each side, however I have not decided on using glass or some type of plastic window...I feel the plastic may degrade and fade/get beat up over time, and glass might be too heavy. Not really sure.

I was originally looking at buying 50"x25YD of mat, but I think that will be way too much.

http://www.aro2000.com/bronco_camper.htm

That is the top I will be copying for the most part. The window will be the same size and I will add two small triangle windows to the sides. It is roughly 6' long and maybe 3' tall at the highest point.

 

Funny that they don't allow you to read about fiberglass, it doesn't seem like a dangerous topic to me.

Styrofoam is not suitable if you intend to use polyester resin, with epoxy it is OK. Four layers will do the trick, with some reinforcement every 2', like a strip of plywood covered with a few layers of glass.

Typically, you need equal quantities of glass and resin (by weight), if this is your first project you need 10-20% more resin.

There is acrylic glass that withstands UV very well for more than 10 years, but it scratches easily.

 

That's what I thought...even yahoo answers about fiberglass are blocked

Thanks for the reply by the way

I will probably use polyester because it is cheaper to be honest.

I have no idea how sturdy wet fiberglass is...what could I build the frame out of, or should I be building the top out of plywood and then putting the fiberglass over the plywood? I was hoping to make it 100% fiberglass so it would be lighter, but if that is possible I still need to figure out somthing to make a frame with, that I could remove later, just something to hold the fiberglass in place while it dries.

I was reading somewhere on this site also that mat is not very sturdy at all, and you should put layers of woven cloth in between.

How thick will 4 layers be when finished?

I plan on doing the windows after the top is finished, so they are easily removed. Probably will end up being some type of rubber grommet around the window to seal into the hole, but might just be bolts covered with trim.

Is fiber glass cuttable? I have ideas to make the flat portion of the top like a hatch that will pop up for slightly better cargo space, should I be making pieces and then fab them together or should I make one solid piece and then cut it?

 

The normal procedure for a one-off is to make a mold from plywood, fill the corners to the required radius with putty, paint the inside, sand and polish, then carefully wax it. Then apply the gel coat in the desired color, build up the laminate, put the reinforcement strips in and laminate 2 layers over them.

The gel coat must be cured before the 1th glass layer is applied, the rest can be done wet on wet.

A laminate with woven cloth is stronger, but for a car hood chopped strands will do. There are light, medium and heavy glass mats, the latter gives approx 0.3" thickness with 4 layers.

Fiber glass can be cut with a knife in 'green state' only (partly cured), once hardened you need a hacksaw.

Attempts to make an object on a wire mesh form either end in misery or require so much filler to get an acceptable finish you need a crane to lift it.

 

Thanks CDK!

If I am reading this correctly You just told me how to make a mold to put the top into right?

The gel coat on the inside of the mold ends up sticking to the fiberglass when you remove it?

I have a feeling if this application goes welll I will do more projects out of fiberglass!

I am now thinking of building the top out of plywood first as a proof of concept type thing, and then covering it up with fiberglass, and leaving the wood...I think that would eb the only "frame" type thing that would work right? 1/4" would be plenty to hold its form, then I could just do fiber inside and out, or just do a bunch of layers of fiber outside, and then pull/sand off all the wood inside?

 

Dont build in ply first. I comes out very heavy (at least twice the weight), and has other issues too. The poly resin does not stick well on wood. 1/4 btw is not holding shape at that size.

Either build a male mould out of foam (you will have to test the foam if it stands the styrol, don´t use Polystyrol foam it disappears immediately).
You than apply your layup. Now you have a rough surface which must be faired and sanded. A lot of putty and a lot of labour! It then can be painted / sprayed.

Or you build a female mould where you can use a gelcoat as first layer, giving a smooth finish without filler, and paint. But of course the fairing is done on the mould instead.

The 4 layers of mat are insufficient on such a structure. Especially when there are cutouts for windows!
Do 2 layers mat, one layer woven fabric of at least 300 gram m² and 2 or 3 layers mat again.
Assuming the mat is about 240gsm you end up with 1300 to 1500 gram glass per m². As CDK said, there is about the same weight of resin in that layup + 10- 20%.
That will do the trick.

 

Ah ok, male mould is where I have a structure made of foam and then lay the glass on top right?

Windows will be tinted plexi, I am still waiting on the measurements of the stock top so I can do a scale concept design, which I'll upload.

I've looked for foam to use, it was my original idea. Would foam insulation work? Talking about the 3/4" stuff at like home depot. Glue that stuff together or even use wood dowels to hold it?

 

http://www.lowes.com/pd_42729-236-263063_0_?productId=3033432&Ntt=insulation+foam&Ntk=i_products&pl=1&currentURL=/pl__0__s?newSearch=true$Ntt=insulation%20foam

Like this stuff

 

No idea about the Home depot stuff except that it is usually very cheap stuff.

You need PU foam or polystyrene (some qualities do, some not), and you will have to test the latter.

Plexi will not stay clear for long, Lexan would be better, but of course it depends how long the car will last, if worth the effort.

Regards
Rchard

 

Not like this right?

http://www.foamdistributing.com/products/poly.html

Seems very soft and flimsy.

where is a good place to purchase this, or should I look locally when I get back to the states?

 

I've used extruded polystyrene foam (styrofoam) for a couple of times with polyester resin. The foam board is stiff enough for your application size. It can be sanded smooth enough for a male mold. I've used PVAc (ordinary wood glue) to protect the foam against the resin. Poly resin sticks to PVAc so some sort of mold release wax is in order.

http://en.wikipedia.org/wiki/Styrofoam

Building a small Trolling Boat #88

Hope this helps.

Lurvio

 

Sure you can use that foam,

for matresses.

I have no idea where you could find the foam you need, but Lurvio gave you the right hint which one will probably the cheapest to use.

Regards
Richard

 

Luvio, that was a perfect answer! I'll have to work out the protection for the foam, but PERFECT!!!!

I got measuerments for the top as well, it is 60" long 24" tall and I am waiting on a width measurement, but I will guess at 45" or so.

So one board of Dow insulation (blue stuff the sell at hardware stores) will be plenty. I start up the concept drawing tomorrow!

I am thinking make a full concept model out of the foam, using 2-4" wood dowels to hold it together, with a bit of glue. That way I can work out all the bugs and fit the panels together perfectly before wasting a bunch of resin. I am very excited!!

 

I think good old Elmer's glue will protect the foam from the resin, but make very sure you did not miss any spots or the resin will dissolve the foam into a little lump.

 

Thanks guys! I will upload my concept drawings on here when I finnish them