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  1. #1

    epoxy over resin, or resin over epoxy?

    I know one doesn't work over the other, but I can't remember which is which.

    Need to glass in some new motor mounts in the blaster for the longer engine. Just wondering what to use.


  2. #2
    Duke's Avatar
    Join Date
    Jul 2006
    Epoxy is always better and works on both. West Systems brand epoxy resin is a very good product.

  3. #3
    Mr Waverunner's Avatar
    Join Date
    Sep 2007
    Central Fla
    Automotive light body work and paint was a everyother day side job I kept for 20 years.
    I can share some info about Epoxies.

    Polyester resin does not cure properly over epoxy. Epoxy can be used over polyester, but there may be adhesion problems. It's best to stick with one or the other and not try to use them both.

    There are several liquids that are appropriate for applying glass cloth. I've used some, but not all of them. After trying a few different things, I found something that I like so I have no desire to try anything else. There are no set rules, it's just finding the methods and techniques that you do best.

    Epoxy is a two-part adhesive that cures by chemical interaction between the two parts. Is strong but heavy, expensive and is fuel proof. Epoxies are used for bonding high-stress areas as well as items that no other adhesive will bond together. Is used to apply fiberglass cloth and making fiberglass parts.
    There are two kinds of epoxy resin that I know of. The most common type is used as an adhesive. The second type is used for laminating and tends to be thin in consistency. There are also various epoxy putties, etc.
    Epoxy Finishing Resin (normally just called Finishing Resin or Laminating Resin) is designed specifically to apply composite cloths such as fiberglass and carbon fiber. It has a thin consistency and a slow drying time. It penetrates and saturates the cloth quickly and spreads easily.

    There are two ways to make epoxy less viscous. Both methods can cause problems and I recommend that you don't use either of them.
    1-Use a Reducer
    You should not use thinners because they alter the chemical curing process.

    Some people add thinners (some people called reducer) such as alcohol, acetone, lacquer thinner or MEK to the resin to make it easier to work with. The result can be a rubbery or brittle finish. Adding thinner to epoxy will cause it to shrink which it would not do otherwise. Additionally, some thinners, particularly drug-store alcohol, contain water that can become trapped in the resin with unpredictable results.
    2-Use Heat
    You should not warm epoxy because heat drastically speeds the curing process.

    The other way to make epoxy less viscous is to warm it. After the two parts are mixed, place the container into a shallow pan with warm water. Alternatively, a hair dryer can be used to warm the epoxy after it is applied which will make it watery and easier to spread. It will also soak in more. Do not over heat epoxy! The fumes are extremely dangerous. Heat can also make the epoxy very brittle after it has cured which significantly weakens it.
    You will have much less time to work with the epoxy due to the accelerated cure rate. The resin may suddenly set up in the middle of the job at which point you're in trouble.
    The only time I warm epoxy is when it is used as glue — not to apply glass cloth.

    Polyester resin is fiberglass resin. It is a two-part resin having a catalyst that I believe is peroxide based. The more drops of the catalyst added to the resin, the faster it cures. Polyester resin does not cure properly over epoxy. Epoxy can be used over polyester, but there may be adhesion problems. It's best to stick with one or the other and not try to use them both.
    Fiberglass resin smells horrible and causes bad rashes on some people. Polyester resin dries very hard and will sand better than epoxy resins sooner. By that I mean epoxy resins take longer to achieve the same hardness but epoxy is easier to sand. I don't mind waiting, so I have not had a problem using epoxies, but some people complain that epoxies do not sand well which indicates to me they are trying to sand too soon.

    In addition to the above methods that I have used, other people have claimed to use the following to apply glass cloth. I have not used any of the following, so I can't speak from experience:
    Epoxy Paint (clear)
    Polyurethane Paint (water or solvent-based clear)
    Airplane Dope (clear)
    Cyanoacrylate (CA or“Super Glue”)

    Some people will recommend that you use cyanoacrylate (super glue) to apply glass cloth. I think using CA is a really bad idea. First, the fumes created are enough to knock out a stable full of horses. Second, it is expensive and has a working time of zero seconds once it is applied. Lastly, you have absolutely no control of where it goes. It simple gets poured on and you hope for the best.

    West System epoxy is formulated for marine applications, and like Duke stated, it works on both.
    I've never used before, but is well recommended by a few body shops

  4. #4
    GP2500R stvdrag225's Avatar
    Join Date
    Sep 2006
    United States
    Go with the West Systems epoxy.

  5. #5
    to answer your question epoxy sticks to P/E and not the other way
    if its hand laid fibreglass use polyester resin, its a lot quicker to work with and wets out chop strand mat easier,
    but if its smc the you have no choice but to go with epoxy, plenty of brands out there but you will have to use woven glass or there is a chop mat with a different binder that also wets out better for better shaping

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