Can you post some links to the products you use? It'd be good to know what glues, paints, fillers, etc. I should be looking at buying.There's some of this weaved into the previous two tips because you can't really talk about building something without knowing what you'd use to do so, but I think a comprehensive list would be helpful for someone just starting out. There's a couple of different categories to materials so we'll tackle them that way. I'm going to use Amazon (usually not the best place to buy) and Tapp Plastics to provide links because between the two of them they've got everything I use regularly. Yes, I know there are cheaper places to get my supplies than Tapp Plastics but the store I go to knows me, knows what I spend, and therefore takes care of me and kicks me freebies on a regular basis. That extra couple yards of fabric or free bottle of PVA adds up. Sometimes it does pay to shop in your home town.
This is by no means an exhaustive list. If you're trying to join two materials or fill something in a specific way and it's related to a car there's probably an "exact right" product to use. I'm not a product reviewer so I'm just giving you the list of stuff I've actually tried or done enough research on to know whether or not it'll work. The point of this is to help you get started. You can get into exotic stuff on your own and report back to me when you've found the faults and applications.
Category 1: Fiberglass Resin
There are many different kinds of resin, what you choose to use is dependent on what you're trying to build and how big your budget is but in broad strokes there only two types: good stuff; and crap. Good stuff is what you get from Tapp Plastics and US Composites. Crap is what you get from your local hardware or autoparts store. Here's the funny thing: they cost about the same. No seriously - I've used enough of both to know.
One of the basic differences between the good stuff and the crap is the addition of wax. There's a lot of it in the Elmers and Bondo brand resins. At the end of the day you actually want some, but with the good stuff you typically need to add it yourself. The advantage of adding wax yourself and at the time of your choosing is that it allows you to take more time betwen layers and control when the piece will start fully curing. With the cheaper stuff it starts fully curing the second you add the hardener.
So for example, let's say you're making a car hood which is a fairly big piece. Let's further say that you add a couple of layers of resin in one go, but have to run out somewhere because you have a life. Now you get the pleasure of sanding the entire piece down before you add any additional layers or they won't fully adhere. I don't know about you but that sounds like a truely massive pain in the ass when you have the alternative of laying up the part with just resin, then doing the last layer with the surface curing agent (wax additive).
Bottom line: if you already have some cheap resin laying around - use it up - but only use it for an application where you can finish the layup all in one go or where it's small enough that you won't mind sanding the whole damn thing between layup sessions.
Now that we've discussed the differences between good stuff and crap, let's talk about the good stuff and the variations you can look for:
1. Polyester Resin: Your bread and butter resins. There aren't many things you could build where you absolutely shouldn't use a Poly resin of some variety. There are different grades as shown by the link and the price difference accounts for differences in the final material properties. Need more heat resistance? Isophthalic resin is your friend. Just need something for general use? I buy the Laminating Resin - Bond Coat B in 5 gallon buckets because it's the cheapest and it's strong enough for almost anything I need it for. For example I'm going to build the molds for the MR2 out of this stuff but may end up laying up the actual finished parts with the Structural Layup Resin because it's more flexible and will have less chance of just shattering under a small impact. But - it's also more expensive so building the molds and the parts out of it isn't financially sound since the properties it provides are actually undesireable in a mold. You don't need or want your mold to flex.
2. Epoxy Resin: Much stronger than your average Poly resin, on average much thinner than your average Poly resin so it's better for flow coating. The disadvantage is that it's far more brittle than the Poly stuff so I personally wouldn't use this for auto body parts. I would use it for interior stuff or Carbon Fiber applications where flexability isn't desired.
3. Surface Curing Agent: Because of the afforementioned lack of wax in the good stuff, you use this in your final pot of resin.
4. Hardener: AKA MEKP Liquid Catalyst. As far as I can tell these are all created equal so buy what's cheapest.
5. Talc: This is like adding breadcrumbs to your meatloaf because relative to the beef the breadcrumbs are dirt cheap. Talc bulks out resin so you use less to cover the same surface area. It also makes it thicker and reduces cracking. I don't use this in the first layer or two but I do use it on the non-visible side of whatever I'm making.
6. Cab-o-sil: Makes the resin more like a glue. Good for joining panels that are made of fiberglass.
7. Gel Coat: Regardless of if you're making a mold or a part from a mold this is the first layer you use. It's basically the fiberglass equivalent of primer and provides a smooth surface on your finished part. You need to spray it on to using a gel coat spray gun and those aren't cheap ($125 or more) but the good ones will save you tons of time you'd otherwise spend spreading the gel coat on with a paint brush. There's two kinds of gel coat - regular and tooling. Tooling is what you use if you're making a mold you're going to pull a lot of parts from. Since I'll only be making parts for myself I just went with the regular stuff.
8. PVA: I have no experience with this stuff yet but I've got a quart of it sitting on my supplies shelf. It's used as a parting agent when making molded parts. It's basically plastic dissolved in alcohol and it's only soluble in water so it will stand up to resin but you can spray water between your mold and molded part to remove it and help you pull the part off. I've heard it's a nightmare to spray on correctly - we'll see. The ease of parting benefit to me outweighs the risk.
Category 2: Fiberglass Fabrics
The problem with fabrics is there are tons of different kinds so if you're starting out it's hard to know what you should be using. I haven't tried them all so I'm only commenting on the ones I know. All of the cloth's I've listed are part of a product category called E-Glass. There's an S-Glass product set that's supposed to be stronger than E-Glass but I haven't used them yet.
Cloth is stronger than mat but it's only stronger in two directions so when you're applying it you should do it diagonally and overlap the direction of the strands to achieve maximium strength.
1. Chopped Strand Mat: CSM is the meat and potato's fiberglass cloth. You've seen it before at the hardware store. It looks like a bunch of strands interwoven together loosely which is exactly what it is. It tears easily by hand, gets fuzzy little strands everywhere, and generally makes a mess but it's cheap as chips, has equal strength in every direction, and is your most economical path to making just about anything out of fiberglass. It comes in different weights. I use .75 almost exclusively.
2. Surfacing Veil Mat: If CSM is meat and potato's this is apple pie. When used immediately after the gel coat layer srfacing veil mat helps reduce the visibility of the pattern of cloth you use after it. Think of it like a buffer layer before you start using cloth's with a looser fabric pattern.
3. Modified Twill Cloth: This stuff is good if you're trying to make a part with a wierd shape. Autobody panels are smooth enough that this isn't really necessary but molding parts with interesting angles is made eaiser with twill. It's far too pricey to exclusively use twill so you could use this as your first layer after surfacing veil mat to make sure you turn that corner well before you start on the CSM or Woven Roving.
4. Woven Roving Cloth: This is the heavy duty stuff. It's thick and is big enough that you can actually pull out individual strands of it by hand without completely ruining the fabric. This stuff is good to use in corners of a mold because it's sturdy and you need stength in bends and turns.
5. Core Mat: I'm not sure how to describe this stuff except to say it's sort of like a foam pad in it's dry state, and an iron plate when wetted out. You use this for parts when strength is a factor. I wouldn't use it in a mold because it's too pricey but if you need to make a hood a layer of this between a couple layers of Veil and CSM will ensure a super high strength part.
There's a ton more products in this category but the four above are your basics for beginners.
Category 3: Body Fillers
A lot of people just call this Bondo. That's bad because unlike Kleenex or Q-Tips the product that gave the category a name isn't the best option out there. Body fillers are what you use to fix a dent, fill a pinhole, or otherwise smooth out a surface with a small imperfection. You shouldn't build up body filler to more than 1/4" or so or you're asking for trouble because the stuff shrinks over time and with heat. Filling in that recess in your door with just body filler is a really, really bad idea. People can become partial to a certain brand of body filler over time and that's certainly the case with me. I love Evercoat products. I won't use anything else unless it's for a throw away application where I don't care about everything being perfect. I will never use Bondo brand filler again for anything but throw away stuff.
Within the category of body filler you have a couple of different types of products that are useful to the DIY guy:
1. Kitty Hair. This is body filler that has a paste like consistency and contains small strands of fiberglass which is where it gets it's name. You utilize it for things where you're either filling large issues in a fiberglass piece or where strength is a factor. This stuff is strong and reasonably light weight but it doesn't sand as well as other fillers and should therefore be used sparingly if posssible/practicle.
2. Light Weight Body Filler. This is your meat and potato's body filler. You use this for most jobs like filling slight imperfections or smoothing out a rough part. It sands better than kitty hair but is stronger than skim coat. If you're really in a pinch you can thin this with fiberglass resin and use it as a skim coat which will keep you from having to buy seperate products for different types of jobs like I do. If cost is a factor for you it'll get the job done and is cheaper than buying a seperate product.
3. Skim coat. Not as strong as Light Weight filler but it sands like it's not even there and is the best product you can use to fill in pinholes or other tiny imperfections before they come through during painting. As indicated by the name, you should use this very, very sparingly and in non-structural type applications. Think of this as the product to help you feather out your repair into the adjacent area of the body panel.
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