# Looking for tips on fiberglass techniques



## jaspersk (Jun 26, 2008)

I have my battery racks welded and painted. They are basically frames of 3/16" steel. They look great and a very sturdy.  

For sides and floor, I plan to use fiberglass sheets with insulation inside of that. I need to go about building this fiberglass box within the metal rack. Like a lot of things on this project, I am learning new skills and fiberglassing will be one of them. I am looking for tips or suggestions from someone that has done this.

I already bought supplies. They might not be the ideal materials but they just opened up a new Lowe's by me with unlimited coupons for $10 off $25 purchase. 

I bought three of these 4x8 sheets for $20/each (with coupon)
http://www.lowes.com/lowes/lkn?action=productDetail&productId=8566-293-77096&lpage=none









I also purchased a gallon of resin/hardener and a bunch of fiberglass cloth from Lowes. It was around $40 before coupon if I remember correctly for resin and cloth. They don't have this stuff listed on the website but it is in the paint section if anyone wants to look for it. This didn't seem priced too high with coupon versus cheap kits you could buy online but I could be wrong. It is certainly more expensive than calk or foam though but I wanted something that would hold up my fiberglass panels.









(This is a picture from another forum).

The fiberglass sheets are the flimsy stuff you'd use for a shower stall. It will go up against the steel so it is only there to provide a moisture barrier. What technique should I use for fiberglass on the corners? Things I am scratching my head on. 

1). Will the resin bond to the fiberglass sheet or do I need to stitch or glue the corner together first?
2). I was planning to only fiberglass the inside since I have a limited amount of space in the rack for insulation and batteries. If I do it on the inside the insulation can mold to the form of the fiberglass. This should work, right?
3). I need to form the fiberglass in the shape of a box. Should I just apply the resin with the fiberglass inside the box frame? 
4). How should I go about holding the panels while the resin dries?
5). If I put it together inside of the frame, will the resin bond to the painted metal surface?
6). Is there any kind of glue or paste I should put in the corners before resin and fiberglass?

Any other tips on would be much appreciated. Thanks!


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## aktill (Jun 18, 2008)

jaspersk said:


> The fiberglass sheets are the flimsy stuff you'd use for a shower stall. It will go up against the steel so it is only there to provide a moisture barrier. What technique should I use for fiberglass on the corners? Things I am scratching my head on.
> 
> 1). Will the resin bond to the fiberglass sheet or do I need to stitch or glue the corner together first?


Depends what sort of resin you bought, and what the panels were originally made with. If you bought polyester resin and the panels were made with that as well (likely), then you're okay. If you have epoxy and the panels are poly you're okay. If you bought poly and the panels are epoxy, you miht have bonding issues.

You'll want to tack the panels together so that they're easier to work with. You'll go nuts trying to hold them together while a bonding strip dries.



jaspersk said:


> 2). I was planning to only fiberglass the inside since I have a limited amount of space in the rack for insulation and batteries. If I do it on the inside the insulation can mold to the form of the fiberglass. This should work, right?


Not quite following. Are you putting the fibreglass sheets between the foam and steel, or are the sheet going against the steel, the foam inside, and then a layer of cloth over the foam? At any rate, I wouldn't put the foam beside the batteries, since I doubt that the acid would do good things to it. No idea how acid reacts with resin.

I've not done this for my project yet, but I plan to place the batteries in the steel racks with the foam and fibreglass outside of that rack with steel carrythroughs that bolt to the car frame. I'm probably going Li, but I'll still line the steel racks with plastic sheet of some sort.

Are you planning to line the entire inside with cloth, or use strips 4-5" wide to bond the edges of the preformed sheets? You'll probably want strips inside and out, for strength. Also remember that wet cloth doesn't like sharp corners, so they should ideally be radiused.



jaspersk said:


> 3). I need to form the fiberglass in the shape of a box. Should I just apply the resin with the fiberglass inside the box frame?





jaspersk said:


> Probably overkill to line the whole thing. If you just want the liner to stay together, then strips of cloth ("Seam tape") should be okay, but you'll need something wider if you want the fibreglass box to be structurally weight bearing.
> 
> 4). How should I go about holding the panels while the resin dries?



I'd tack them together with a bit of superglue in dots, if I were you. The resin won't like to cure right over the superglue, but if you keep the dots small, it shouldn't be a big deal.



jaspersk said:


> 5). If I put it together inside of the frame, will the resin bond to the painted metal surface?


Probably to some extent. A bit of vaseline or mold release wax will keep them apart if that's what you want.



jaspersk said:


> 6). Is there any kind of glue or paste I should put in the corners before resin and fiberglass?
> 
> Any other tips on would be much appreciated. Thanks!


I'd build a little fillet using ultralight spackle, if I were you. It'll help the fibreglass strips to conform to the inside radius, if that's the way you're doing things. Might make battery fit tricky though.

If you're doing the seam tape method and cutting the glass yourself (buy a dressmakers circular cuting wheel to cut the glass, not scissors), cut your seam tape diagonally to the weave of the cloth ("on the bias"). The tape will conform to the bend much better if you do.

Just some thoughts. I've done tons of composite work, just not on a car yet.

Cheers,
Adam


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## jaspersk (Jun 26, 2008)

Great advice! That is exactly what I was looking for. Thank you!!!



aktill said:


> Depends what sort of resin you bought, and what the panels were originally made with. If you bought polyester resin and the panels were made with that as well (likely), then you're okay. If you have epoxy and the panels are poly you're okay. If you bought poly and the panels are epoxy, you miht have bonding issues.


I am pretty sure the cheap Lowe's/Elmer's resin is poly. I have read that large volume manufacturing is usually poly so hopefully the panels I bought are poly as well. Would you recommend that I sand the areas where I need it to bond like they sometimes recommend for fiberglass repairs?



aktill said:


> You'll want to tack the panels together so that they're easier to work with. You'll go nuts trying to hold them together while a bonding strip dries.


Sorry for being such a newbie but I have no idea what this means. Are you referring to superglue method that you mentioned below? After my original post, I read some stuff on boat building which lead me to think that using duct tape on the outside while I resin the insides would work well.



aktill said:


> Not quite following. Are you putting the fibreglass sheets between the foam and steel, or are the sheet going against the steel, the foam inside, and then a layer of cloth over the foam? At any rate, I wouldn't put the foam beside the batteries, since I doubt that the acid would do good things to it. No idea how acid reacts with resin.


That would be ideal but I am not planning to go to that extent. I am simply going to have painted angle iron on the outside, fiberglass panels against that, and 1/2" EPS insulation laying loose on that. I realize that will be tough on the insulation but insulation is cheap and easy to replace. I kept the tolerances fairly tight so I am expecting the insulation to deform to make up for things like bolts or my fiberglass and to allow for some expansion of the batteries when they get hot.



aktill said:


> I've not done this for my project yet, but I plan to place the batteries in the steel racks with the foam and fibreglass outside of that rack with steel carrythroughs that bolt to the car frame. I'm probably going Li, but I'll still line the steel racks with plastic sheet of some sort.
> 
> Are you planning to line the entire inside with cloth, or use strips 4-5" wide to bond the edges of the preformed sheets? You'll probably want strips inside and out, for strength. Also remember that wet cloth doesn't like sharp corners, so they should ideally be radiused.


This is great advice. I am only planning to run strips on the edges to bond the corners and provide leak tight box. I have two 1/8" sheets that meet at a hard corner. I can radius the inside curve with some spackle like you mention below. How do I do that on the outside?

The only small concern is that I left just enough room in my rack for the batteries, the insulation, and the fiberglass sheet and maybe 1/8" of extra space. I am counting on the insulation to deform to make space for my fiberglass work. Can I keep the fiberglass fairly thin?



aktill said:


> I'd tack them together with a bit of superglue in dots, if I were you. The resin won't like to cure right over the superglue, but if you keep the dots small, it shouldn't be a big deal.
> 
> Probably to some extent. A bit of vaseline or mold release wax will keep them apart if that's what you want.


I am not sure where to get mold release wax short of ordering online but as long as vaseline works that sounds good.



aktill said:


> I'd build a little fillet using ultralight spackle, if I were you. It'll help the fibreglass strips to conform to the inside radius, if that's the way you're doing things. Might make battery fit tricky though.


This might be a stupid question but is this just the standard lightweight spackle that I would buy in the drywall section? Obviously, I need to allow it to dry. Hopefully my duct tape and/or super glue will be strong enough to keep that from being a mess prior to putting the resin down. I won't have the same problem with the resin curing, right? (such as you suggested it might with super glue?)



aktill said:


> If you're doing the seam tape method and cutting the glass yourself (buy a dressmakers circular cuting wheel to cut the glass, not scissors), cut your seam tape diagonally to the weave of the cloth ("on the bias"). The tape will conform to the bend much better if you do.
> 
> Just some thoughts. I've done tons of composite work, just not on a car yet.
> 
> ...


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## aktill (Jun 18, 2008)

jaspersk said:


> I am pretty sure the cheap Lowe's/Elmer's resin is poly. I have read that large volume manufacturing is usually poly so hopefully the panels I bought are poly as well. Would you recommend that I sand the areas where I need it to bond like they sometimes recommend for fiberglass repairs?


You'll definitely need to scuff the surface, at the minimum, and wiping it down with acetone would be a good idea as well. The panels will probably have a bit of mold release wax left on them from the factory, which would decrease your bond strength.



jaspersk said:


> Sorry for being such a newbie but I have no idea what this means. Are you referring to superglue method that you mentioned below? After my original post, I read some stuff on boat building which lead me to think that using duct tape on the outside while I resin the insides would work well.


No worries, you're not a mind reader. Yes, I meant the same thing as I wrote later on (sorry for the order mixup!).

If your tolerances are as tight as you say they are, use some form of glue rather then tape. Spritzing the super glue with a mist of water will cure it almost instantly. Tape can creep, especially since the resin gives off heat as it cures, which will stretch the tape and possibly cause the tape adhesive to lift.



jaspersk said:


> That would be ideal but I am not planning to go to that extent. I am simply going to have painted angle iron on the outside, fiberglass panels against that, and 1/2" EPS insulation laying loose on that. I realize that will be tough on the insulation but insulation is cheap and easy to replace. I kept the tolerances fairly tight so I am expecting the insulation to deform to make up for things like bolts or my fiberglass and to allow for some expansion of the batteries when they get hot.


Really, I'd be worried about acid and foam getting to each other. Do an experiment to check. When I've intentionally melted foam out of molds and such the insulation releases all sorts of ugly vapours, heat, and turns into toxic goo. Even a thin poly liner would be a good idea. Also, the insulation won't really deform much if it's dense enough to be a decent R value.



jaspersk said:


> This is great advice. I am only planning to run strips on the edges to bond the corners and provide leak tight box. I have two 1/8" sheets that meet at a hard corner. I can radius the inside curve with some spackle like you mention below. How do I do that on the outside?


Hard to do. I wouldn't really bother. Just know that you might go a bit nuts trying to keep the tape against the box (maybe use some waxed spare angle as a form to press against it?)



jaspersk said:


> The only small concern is that I left just enough room in my rack for the batteries, the insulation, and the fiberglass sheet and maybe 1/8" of extra space. I am counting on the insulation to deform to make space for my fiberglass work. Can I keep the fiberglass fairly thin?


Sure, the cloth will most likely be negligable. If you're using Dow extruded polystyrene insulation, thought, it probably won't deform as much as you might think. I also suspect it will react badly with acid...really badly.



jaspersk said:


> I am not sure where to get mold release wax short of ordering online but as long as vaseline works that sounds good.


Not sure where you live, but in any moderately sized area there's probably a composites/plastic supplier. There are a few here in Calgary. Model shops that specialize in radio control stuff is another option.

Vaseline is probably easiest, just a bit messy.



jaspersk said:


> This might be a stupid question but is this just the standard lightweight spackle that I would buy in the drywall section? Obviously, I need to allow it to dry. Hopefully my duct tape and/or super glue will be strong enough to keep that from being a mess prior to putting the resin down. I won't have the same problem with the resin curing, right? (such as you suggested it might with super glue?)


Yep, same stuff (Polyfilla etc). A heat gun will speed the drying, but might warp your 'glass sheet. It should stand up without dripping - it's quite stiff, since it's designed to not run down vertical walls etc.

Leaving it overnight is the best bet. 'glass will go right over it...I used this when repairing dings in foam cores for composite aircraft wings.


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## JRP3 (Mar 7, 2008)

I don't think I'd use spackle, I don't think it's very strong and will probably crack if there is any flex in the panels. You can use a fiber reinforced polyester filler from an auto supply place, sometimes called tiger hair. Basically just chopped up fiberglass thread mixed with polyester resin. Polyester resin shouldn't give off all that much heat when curing so I'd think the duct tape would be fine to hold it all together while it cures.


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## grayballs (Aug 27, 2008)

JRP3 said:


> You can use a fiber reinforced polyester filler from an auto supply place, sometimes called tiger hair. Basically just chopped up fiberglass thread mixed with polyester resin. Polyester resin shouldn't give off all that much heat when curing so I'd think the duct tape would be fine to hold it all together while it cures.


Try to stay away from tape in the finished joint, of any kind,,, the resin doesn't like the adhesive and prevents complete cure in most cases. Bondo or any other body filler will work for glueing the panels together,,, use a tounge depresser for the radius. And, by all means clean and sand the panels. The bond, to cured poly is mechanical, rather than chemical.


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## JRP3 (Mar 7, 2008)

I'm assuming the tape is holding the panels together tightly on the outside and the resin/fiber mixture won't leak through, but if it's a concern you can use a thin strip of wax paper or plastic in the middle of the tape over the joint. I would not use bondo as it's not structural at all, where as the fiber reinforced resin is.


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## Technologic (Jul 20, 2008)

Answers in bold:



jaspersk said:


> 1). Will the resin bond to the fiberglass sheet or do I need to stitch or glue the corner together first?
> *Resin will soak into the glass itself if it's polyester or epoxy resin... it will effectively harden that way inside of the molecules in the glass*
> 2). I was planning to only fiberglass the inside since I have a limited amount of space in the rack for insulation and batteries. If I do it on the inside the insulation can mold to the form of the fiberglass. This should work, right?
> *You're fiberglassing steel or what?*
> ...


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## aktill (Jun 18, 2008)

JRP3 said:


> I don't think I'd use spackle, I don't think it's very strong and will probably crack if there is any flex in the panels. You can use a fiber reinforced polyester filler from an auto supply place, sometimes called tiger hair. Basically just chopped up fiberglass thread mixed with polyester resin. Polyester resin shouldn't give off all that much heat when curing so I'd think the duct tape would be fine to hold it all together while it cures.


I didn't intend there to be any strength in the filler - it's just a lightweight means of providing a rounded surface into a sharp corner. We're only talking a few ounces, probably, but it still counts. Plus, working with anything polyester is something I personally avoid when at all possible.

I don't think you'll get much of any bond between the filler and a pre-cured panel - that's why when laminating resin companies will tell you to lay up layers in short sequence (ie within a few hours). If I'm remembering the chemistry right, when poly cures it flashes off amines, which inhibit bonding if they're not cleaned off. When I laid up molds (in epoxy, I hate the smell of poly), I only waited about 20 mins between consecutive batches of 4 layers of cloth - enough time for the initial heat to dissipate, but not so much that there wasn't a chemical bond between laters.

Still think tape is asking for trouble - if something shifts there's a gooey mess to wrangle back into shape. Plus greyballs brings up a good point - adhesives in tape will mess with the bond.

Only things I'd comment on from Technologic's post is that the resin won't soak into precured panels (though I doubt he meant that?), I love bagging but you can't easily bag a hollow box without distorting it, and that I've not experienced any issues with melting c/a with epoxy. It takes a lot of layers of cloth to build up enought heat...5-6 layers of 4oz cloth or higher was where the molds started getting a bit toasty. That many simulataneous layers of poly would be flammable, but I doubt that the OP is talking more then a couple of layers of cloth at once, if that.

Anyway, different roads to Rome and all that...


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## JRP3 (Mar 7, 2008)

I'm pretty sure amines are only present in epoxy resin, not polyester. Secondary bonding will be mechanical in either case, not chemical, which is why you need to rough up the surface before bonding if it's fully cured. Polyester resin is air-inhibited, unless it's specifically treated otherwise. This means that the surface will remain tacky for a long time allowing chemical bonding. If you've ever tried grinding laminating resin that hasn't been wax covered or something else you'll gum up your grinding discs with the uncured surface resin. The panels he's working with were probably cured in a mold so that's not an issue.


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## Wirecutter (Jul 26, 2007)

Wow, this is a great thread. Jaspersk, I'm very interested in hearing how this goes. I've been considering similar construction, but so far it's barely even a paper exercise. 

-M


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## 1clue (Jul 21, 2008)

My experience is only with epoxy resin, but I do know people who have used polyester.

Those prefab panels have almost no strength. You will get serious sagging if you dump more than a gallon of water or so in the box, if there are large unsupported areas. If that's not acceptable, then I might suggest that you use the panels only as a disposable mold for a stronger box.

Mold release wax is ideal, but I have used a high-carnauba car wax when I didn't have mold release wax. With mold release wax it takes 3-4 coats of wax (if you're glassing to a mold) and with the car wax you would need twice that for the same effect. Cover the mold with wax, dry for 20 minutes, cover again, wait 20, etc. Still can't figure out why you want it here.

You might consider hot glue to hold panels in place. Put it on the side NOT getting fiberglass. Another idea is to make a 1x2 frame to support everything.

Polyester resin dissolves polystyrene foam. Polystyrene foam is either the white bead board or the pink, blue or yellow extruded foam you get at home improvement stores. Once it is cured you are OK for the most part, but Do Not Let the resin hit your foam while uncured. It turns into a big pile of extremely sticky goo and will stay that way for days or weeks. I imagine similar things will happen if you get battery acid on the foam.

Curing: Both polyester and epoxy resins have several cure states.

You have the cup life, which is how long after you mix the cup that you can work it. The cup life of the stuff I use is around 10 minutes, which is just an estimate which varies wildly based on conditions. If the resin heats up and starts getting tacky, the cup life is over and you have to throw it out if it's in the cup, or stop working it if it's on your project.

Next you have soft cure. This is the state where the resin is hard enough to handle the project without leaving fingerprints or deforming it. The stuff I use varies between 10 and 12 hours.

A hard cure is when the resin is completely cured. In my cases with the epoxies I've used and the temperatures I've done it in, this takes several days to two weeks, depending on the type of epoxy and the temp, moisture and other things. Your container will have some of this, and the manufacturer will have more on their web site.

Glass: The top package of what you show looks like matte. Matte has a random fiber pattern. Cloth is woven the way a shirt is. Cloth is stronger than matte, and generally you want cloth for taping seams. Matte is for when you don't want a cloth pattern to come through. I never use it, but depending on your strength requirements it might be OK, it will just be really difficult to bend around corners because it's so thick.

Bagging: This is probably out of your league. Vacuum bagging is good in a manufacturing process or if you need to clamp things down really well, but it takes practice to get it right. I've vacuum bagged large hovercraft hulls, you can use a shop vac for the level of clamping I needed. In order to get actual weight savings you would need a hard vacuum and the know-how to handle vacuum infusion. And you would never have gotten those prefab panels.

If this was my truck, I would use the prefab panels to make a male mold, then add 2 or 3 layers of 4-oz cloth over that, then add a couple layers of heavy cloth, the stuff that looks like it has 1/4" strands. I might vacuum bag it, but I've done that before.

Then I would put the foam outside the box.


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## aktill (Jun 18, 2008)

Bit of an aside, but for anyone looking to build a small vacuum bagging unit, these are good instructions (they're basically what I used):
http://www.badger.rchomepage.com/vacbag.html


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## JRP3 (Mar 7, 2008)

If you need longer working time with your resin, whichever type you're using, put it in a large shallow container so it can spread out and not build up heat. With polyester you can vary the amount of catalyst somewhat depending on temperature. Not so with Epoxy which needs a precise ratio of resin to hardener to allow cross linking. Some companies make hardeners with different cure rates for their expoxies.


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## 1clue (Jul 21, 2008)

Good point, JRP3.

Another think to keep in mind is that, if this is your first epoxy project, use a smaller cup. You will spend all your time trying to figure out how to mix it and apply it, and you will have problems at first. Make no more than a cup of it, at first.

The "cup life" is dictated by heat dissipation. If it's cold in your shop, the cup life is longer. If it's too cold, you just won't get a cure, possibly ever depending on your chemicals. Or you could get a substandard cure. Same thing goes for too hot. The ideal for my setup is about 70 degrees, as far as curing goes. That makes the cup life pretty short though, so you gotta get it down on the project as soon as you mix it.


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## aktill (Jun 18, 2008)

Another good habit to get into is to start measuring resin and catalyst by weight with a small electronic scale. For a few years I relied on the pumps that come with West System or MGS and the results were okay, but I got a better product when I switched to measuring by weight.


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## JRP3 (Mar 7, 2008)

Yeah I don't love the pumps, if it's cooler they don't pump well, sometimes they get air bubbles which mess up your ratio. I usually go by volume using little cups, 5 cups to 1 for West system, but if you had a good scale that's probably the best.


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## 1clue (Jul 21, 2008)

From the photo, this guy is not using epoxy. It looked like Polyester resin to me.

Even so, be careful about the measuring technique. I measured by weight a lot at one point (now I'm back to it) but the brand of epoxy I was using had a significant density difference and the mixes all turned out bad. I went back to look at the data sheet, and it said, "do not mix by weight." You can go by weight or volume, but make sure your chemicals are good for what you want to use first.

Another alternative to the pumps is to use measuring cups. I used to use one cup for hardener and two cups for resin, just pour them full. It's best to have 2 different colors so you don't accidentally swap cups. You have to have a fourth mixing cup of course, and a squeegee for each for resin and hardener. That's a lot of work, so I switched brands and measure by weight now.


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## JRP3 (Mar 7, 2008)

If you can find a straight sided plastic or paper container, make 6 evenly spaced marks on the sides, then fill to the first one with hardener and the next 5 with resin, or vice versa, mix it up, then toss it when done.


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## jaspersk (Jun 26, 2008)

Thanks for all the guidance! This is very helpful!!

I went ahead and bought some tiger hair and mold release from my local autobody shop. I plan to work on the project this weekend. I'll be sure to take some pictures and post them here on what hopefully will be success.

One other note, I got involved in a discussion on battery boxes over on EVDL and came to the conclusion that I will also need some special protection for the iron I will be using to hold my batteries down. I didn't realize that anything conductive on top of the batteries is a really bad thing since acid will pool at top and provide electrical path to metal. I purchased a quart of "Glyptal" which is an electrically insulating paint used for motor parts. It claims to be acid resistant so I'll let folks know how that goes as well but that will be in a few weeks.

I caught one other good tip on evdl which was to provide a hold in the bottom of the box so you can wash off the batteries occasionally.


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## jaspersk (Jun 26, 2008)

Well, I went ahead and finished my battery racks. Overall, the fiberglass went well. I was impressed by how much strength they had. The tiger hair worked great and I'd recommend that for corners. Putting the actual fiberglass down went about as expected except I didn't realize how sticky everything would get in the process. It reminded me of the scene from National Lampoon's Christmas Vacation where Chevy Chase has wood sap on his hand and it sticks to everything. 

I did make a couple of mistakes. The individual sheets each fit perfectly in the box before hand but after fiberglassing they wouldn't fit. Grumble.  You can see in one of the pictures that one of the sheets cracked and I had to put new fiberglass over it. Once I finally got the boxes in, the batteries were hard to fit as well. I planned for 1/2" styrofoam and thought I had 1/8-1/4" spare but obviously I didn't leave enough extra space for wiggle room. Getting the batteries back out some day will be tough but right now I am just glad the batteries are in. Next step, wiring.


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## JRP3 (Mar 7, 2008)

Good work!


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## dtbaker (Jan 5, 2008)

jaspersk said:


> I have my battery racks welded and painted. ...
> For sides and floor, I plan to use fiberglass sheets with insulation inside of that.


wow, I was thinking about this... and decided to go with 'welded' prolypro plastic sheeting. A little higher material cost, but looks like LOTS less labor.


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