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  • Quck question on working with fiberglass

    Hi,

    I am creating a sub box for my accord and have progressed pretty far with it... However, I have noticed that I have a lot of "air pockets"/"air bubbles" -- or that is what I think they are. Essentially, they are areas of white amongst my brownish mold. Most of the spots are hard to the touch (ie: don't flex with the thumb test). Some are actually separated from the mold. The mold has 4 - 5 layers of matting on it and for the most part feels pretty strong, although I haven't gotten brave enough to do the body weight test on it yet. And there are some areas that are still *tacky* -- it's below 50 here so curing has been slow, even when adding more hardener. So, all that said, what needs to be repaired and what doesn't? And for the items that need repair, how do I go about fixing them? Thanks in advance,

    Nasa

  • #2
    Heres what I would do... But it depends on the bubble type in my opinion.

    1. Big bubbles that protrude from the acutal mold, I would hit with a knife, dremel, or grinder and rebuild the area.
    2. Big bubbles that don't protrude from the mold, i would drill a hole and brush some resin in the to fill the void.

    With the larger bubbles I would toss another layer or 2 of glass over the bubbles with 2" over lap if possible.

    Smaller bubbles that protrude you can probably leave from a structral point of view and the even smaller bubbles that are in the layers don't even worry about those.

    A 1/16" layer of fiberglass can bridge a 1" hole and with hold approximately 80psi. 1/16" layer is roughly 1 layer of 1.5oz chopped strand mat. 2 layers at roughly 110mils will take 100psi over a 1" hole. So from a structral point of view the bubbles don't truely matter too much. However I don't think you want your sub box to flex at all, especially if you are going to paint it.

    Hope this helps.

    Mike
    Last edited by celeryman22; 01-03-2012, 05:14 PM. Reason: spelling

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    • #3
      Upload pics. Not sure what you're talking about. You are working from a "mold" , so you're making a positive from a negative? Doesn't matter really just want to clarify. Not really sure how you'd fix it other then to drill in to expose it then fill in with resin, but really the issue is why its happening in the first place.

      It happened to me the first couple of times working with resin. It usually means your trying to work with it too long, its starting to cure and your still trying to spread it on the glass. What happens here, is that the surface of the glass gets resin, but its not viscous enough to saturate through the surface. This is not good, especially for a sub box that will be under a lot of flex. Don't put more catalyst. or if you do, have MEK or Acetone around. In addition to the 2 parts, dump some of this in there. It will increase the work time by not allowing the catalyst to react until the MEK/Acetone has evaporated. And as soon as it starts getting hard... stop using it. Make a new batch.

      If you use either, especially MEK, where a fume mask in a well ventilated space. NOT KIDDING, its harmful to breath in. And to help curing, getting a space heater on that thing with a vent pulling fumes outside.

      Happy New Year!!!

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      • #4
        Thanks djvillar,

        I will post some pictures tomorrow, as it still puts off some fumes so I can't bring it into the house. I am working on it in my backyard (cause it was to strong in the garage which is attached to the house). I think my biggest problem is the cold, the resin was thick right from the can -- I have started to warm it up prior to using and the weather is also being a bit more helpful.

        The other issue I have been running into is around some curves, where the matting isn't forming the way I would hope. The prime example of that is around some nylon rope I added for strength (a little googling can be a dangerous thing). I couldn't for the life of me get the mess to stick around the rope -- even though I had soaked the rope with resin prior to putting it down.

        Oh, I am referring to the popped out form from my trunk as the mold. If you look at my accord thread here: http://www.mp3car.com/worklogs/11769...ml#post1465342 you'll see what I am referring too.

        Thanks again,

        Comment


        • #5
          So I lied... Here's some example pics (see my thread to put them somewhat in context),

          Click image for larger version

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          This shows the area around one of the threads...


          Click image for larger version

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          Lots and lots of *white* most of which is hard (can't flex with my thumb). Comments?

          Comment


          • #6
            When you applied the matting did you pat it down with a paint brush soaked in resin. We used steel rollers and brushes to make sure the layers of matting had no air pockets. You could just try and soak those areas with more mixed resin. SNO

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            • #7
              SNOtwistR,

              Yeah, I have been trying to apply the dab the mattng with a wet paint brush this whole 1st attempt. I think I am getting better at, but then again... When you suggest soaking the areas with more resin, do I need to drill/cut open the areas to let the resin in (I'm guessing that's the case)?

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              • #8
                prolly a good idea to open up the area abit to get resin under the air pockets and even on top of the matting to hopefully soak in. Very good for first attempt! SNO

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                • #9
                  So,

                  Mike posted the following, which for some reson hasn't show up here -- and it good stuff...

                  Heres what I would do... But it depends on the bubble type in my opinion.

                  1. Big bubbles that protrude from the acutal mold, I would hit with a knife, dremel, or grinder and rebuild the area.
                  2. Big bubbles that don't protrude from the mold, i would drill a hole and brush some resin in the to fill the void.

                  With the larger bubbles I would toss another layer or 2 of glass over the bubbles with 2" over lap if possible.

                  Smaller bubbles that protrude you can probably leave from a structral point of view and the even smaller bubbles that are in the layers don't even worry about those.

                  A 1/16" layer of fiberglass can bridge a 1" hole and with hold approximately 80psi. 1/16" layer is roughly 1 layer of 1.5oz chopped strand mat. 2 layer of at roughly 110mils will take 100psi over a 1" hole. So from a structral point of view the bubbles don't truely matter too much. However I don't think you don't want your sub box to flex at all, especially if you are going to paint it.

                  Hope this helps.

                  Mike
                  Thanks Mike

                  Comment


                  • #10
                    Yeah, that's def air pockets. Get those bags of brushes from home depot brushes from home depot. A trick I picked up, cut them down so the bristles are only 1" long. This makes makes sure the you're not holding a ton of resin in the brush. Also it s makes it easier to stipple of matte.

                    As for the nylon, if you want to add strength, you should be using thick cord (like 1/2"). The trick to not getting air bubbles is, mix and put on one coat of resin, that's it. Wait for it to become tacky. If you press a dry piece of matte against it, it should stick. This will also make putting the first layer of matte on, because you can lay in all on first then just stiple in the resin till saturated. Also, don't put full, in tack pieces over the rope or sharp edge. It stead, chop up that matte and place the serrated edges there so that the strands conform around the sharp turn.

                    Comment


                    • #11
                      Originally posted by SNOtwistR View Post
                      prolly a good idea to open up the area abit to get resin under the air pockets and even on top of the matting to hopefully soak in. Very good for first attempt! SNO
                      Thanks -- I try...

                      As far as the suggestion goes, I attempted doing as you said in a number of spots. I came away with a couple of observations. Unless I make the holes fairly large, the resin doesn't seem to flow through/in them, and once the fiberglass is semi-cured the resin doesn't seem to soak in (that would have made my life way too easy)

                      Comment


                      • #12
                        Originally posted by djvillar View Post
                        Yeah, that's def air pockets. Get those bags of brushes from home depot brushes from home depot. A trick I picked up, cut them down so the bristles are only 1" long. This makes makes sure the you're not holding a ton of resin in the brush. Also it s makes it easier to stipple of matte.

                        As for the nylon, if you want to add strength, you should be using thick cord (like 1/2"). The trick to not getting air bubbles is, mix and put on one coat of resin, that's it. Wait for it to become tacky. If you press a dry piece of matte against it, it should stick. This will also make putting the first layer of matte on, because you can lay in all on first then just stiple in the resin till saturated. Also, don't put full, in tack pieces over the rope or sharp edge. It stead, chop up that matte and place the serrated edges there so that the strands conform around the sharp turn.
                        Thanks for the hints, djvillar. putting the matting down after the resin is *tacky* seems like it would be easier -- I tried that (not related to getting rid of air bubbles) and it did seem to work OK, will have to do more of it. One question on this, what do you mean by "stiple"?

                        As far as where I am at -- based on Mike's comments and that the structure withstood me standing on it, I think I will basically leave it alone (the back won't be visible and I plan on using fabric for the covering of it) and move on. Any issues with doing that?

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                        • #13
                          I would think you would be fine. But you still need to make sure there are no holes in the structure. Cause if there is you will get a whistle sound from the pressure the sub creates.

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                          • #14
                            Sorry I misspelled. Stipple, is what it should have been. faux-paint-stippling Stippling is when appling your finish by pushing the bristles into the surface rather then dragging the bristles of a brush across a surface.

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                            • #15
                              Thanks for the explanation, djvillar

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