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Thread: First time Fiberglass questions

  1. #11
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    The mat and fiber give it strength. If you're not using the fiberglass for structural purposes then you don't need the mat each time. But are you just planning to paint resin to the outside of this box and smooth it down? Are you going for curves? Ever thought about simply carpeting the boxes?

  2. #12
    Wants to make it harder monkeyracer's Avatar
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    I honestly think that fiberglassing the box you have is really more work than it will be worth in the end.

    I know you want to learn more about using fiberglass, and want to seal the box, but I really think that the result you are after is not easy, especially for a newbie.

    To seal the box, you should build the box from the sub hole piece first, that way you can seal the opposite side from the sub hole. Silicone, wood glue, whatever seals the air would be sufficient. For the outside, if you want a perfectly smooth surface to apply vinyl or carpet, or even paint, you can countersink the screws, and then use bondo or some kind of filler, and sand it down.

    Fiberglass is usually better used when you want more curvy shapes, and in fact it's strongest when it's curved.
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  3. #13
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    Quote Originally Posted by guizai View Post
    The mat and fiber give it strength. If you're not using the fiberglass for structural purposes then you don't need the mat each time. But are you just planning to paint resin to the outside of this box and smooth it down? Are you going for curves? Ever thought about simply carpeting the boxes?
    Yes I do plan to paint it after I fiberglass it/sand it down. I don't really like the look of carpet or I would use it.


    Quote Originally Posted by monkeyracer View Post
    I honestly think that fiberglassing the box you have is really more work than it will be worth in the end.

    I know you want to learn more about using fiberglass, and want to seal the box, but I really think that the result you are after is not easy, especially for a newbie.

    To seal the box, you should build the box from the sub hole piece first, that way you can seal the opposite side from the sub hole. Silicone, wood glue, whatever seals the air would be sufficient. For the outside, if you want a perfectly smooth surface to apply vinyl or carpet, or even paint, you can countersink the screws, and then use bondo or some kind of filler, and sand it down.

    Fiberglass is usually better used when you want more curvy shapes, and in fact it's strongest when it's curved.
    so your just recommending to use bondo to give it a smoother look and then paint it? How would I seal it from the inside though? Should I use fiberglass resin and brush it on in the inside? Like roflcopter said?

  4. #14
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    Quote Originally Posted by PBFreak817 View Post
    so your just recommending to use bondo to give it a smoother look and then paint it? How would I seal it from the inside though? Should I use fiberglass resin and brush it on in the inside? Like roflcopter said?
    I would take the panel opposite the sub hole off, then apply silicone sealer around all the edges. Then, put that panel back on, and apply the silicone to the remaining edges, since you will have access to them from the sub hole. Once it's sealed, I would make sure no screw head protrudes past the mdf, and fill all dips and crevices with bondo, then sand down to a smooth finish. Next, I would use a high-build primer, then sand down, and start painting the box. The smoothest finishes require wetsanding, but you'll want to make sure that the box is sealed and that the bare MDF doesn't get wet. If it does, it will swell and ruin the entire project.

    Adding the FG to the box really only complicates things. You would need to make sure there aren't any air bubbles, and once it's dry and cured, you would still need to use filler to get it perfectly smooth.

    One thing I noticed with your design is you used braces on the corners. On a box this small, that is really not necessary. It appears you've got 1/2" mdf (recommend 3/4", but 1/2" will suffice, but nothing thinner really) and there is enough on the edges to pre-drill and just screw into the edges of the wood. So, I would remove all the little corner braces you have, and that would make sealing it a whole lot easier.

    Hope this helps a little bit.
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  5. #15
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    Quote Originally Posted by monkeyracer View Post
    I would take the panel opposite the sub hole off, then apply silicone sealer around all the edges. Then, put that panel back on, and apply the silicone to the remaining edges, since you will have access to them from the sub hole. Once it's sealed, I would make sure no screw head protrudes past the mdf, and fill all dips and crevices with bondo, then sand down to a smooth finish. Next, I would use a high-build primer, then sand down, and start painting the box. The smoothest finishes require wetsanding, but you'll want to make sure that the box is sealed and that the bare MDF doesn't get wet. If it does, it will swell and ruin the entire project.

    Adding the FG to the box really only complicates things. You would need to make sure there aren't any air bubbles, and once it's dry and cured, you would still need to use filler to get it perfectly smooth.

    One thing I noticed with your design is you used braces on the corners. On a box this small, that is really not necessary. It appears you've got 1/2" mdf (recommend 3/4", but 1/2" will suffice, but nothing thinner really) and there is enough on the edges to pre-drill and just screw into the edges of the wood. So, I would remove all the little corner braces you have, and that would make sealing it a whole lot easier.

    Hope this helps a little bit.
    I cant take anything apart because it is glued. But of course the glue didn't do such a good job with sealing it. I have all the screws couter sinking with the MDF. I think I'm going to just use bondo to make everything smooth and even. Then sand it down like you said.

    But with the bondo, can i round out the edges with it. Like where the MDF comes to each other and forms a 90 degree angle (|__)?

    Yes I did use braces. Because I messed up on the one end when a screw separated the MDF when I predrilled and everything. And Im using 3/4 not 1/2. And again, the braces are also glued to the rest.

  6. #16
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    bondo is in no way a structural material. If the joint area is not solid, the bondo will crack in no time.

  7. #17
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    OK


    But will hot glue work for sealing? Cause I have a small enough hot glue gun to get inside the box.

  8. #18
    Wants to make it harder monkeyracer's Avatar
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    He's not trying to use the bondo for structure, the cracks are small, and the bondo will work, but there are better materials. Silicone caulking (like what they make for bathroom cabinets) will work great, and they make small tubes that will get into the box. Once it's well sealed, the bondo will work just fine to fill in the outside cracks.

    The best way to get a rounded edge would be to use a router. The problem comes in with the screws though. You would have a hard time getting a radius larger than the closest distance from the edge of the screws to the edge of the wood.

    It might be worth the time and effort to just start over from scratch. If you want a round edge then you would want to use braces, but you would need a screw about every 3 inches along each edge. Seal each joint with the silicone caulk as you make the joints. Work from the face that has the sub hole first. That way when you place the opposite face, each other edge is sealed, and you cat reach through the sub hole. When everything is all joined and sealed, then you can take the router to it to give a nice even round edge. Then fill in the screw divots and sand and paint.

    This enclosure is going to be subject to some fairly high stresses, so having a well built and well sealed enclosure is key to having a perfect paint finish and a lasting finish.
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  9. #19
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    Heres what I decided to do.

    IM going to goto Home Depo later and try to find the smaller tubes of silicon caulk. If thats no there, then I will buy some more wood glue. I pretty much bagged the whole painting it thing over night and decided to just carpet it. Due to the fact that the outside looks like ****. Hopefully, I can find some small tubes of silicon caulk.

    Then I'm going to mess around with the fiberglass in another part of the car where I can mount some subs. Making a mold, ext.

  10. #20
    Wants to make it harder monkeyracer's Avatar
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    The ones I got from HD were little red tubes about the size of toothpaste tubes, about 2-3 bucks each. I had less edges, so I only used most of one tube, but you might need two.

    I think it's just called clear silicone sealant or clear silicone caulk. It holds its shape and stays put a lot better than wood glue.

    I think carpet would be the best option for the box, so while you're at the depot, you might want to pick up a can of spray adhesive. Super 77 or Super 90 should work just fine. I usually get my carpet from a local auto upholstery shop.
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