Thread: Quck question on working with fiberglass

Originally Posted by djvillar

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?

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.

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.

Thanks for the explanation, djvillar

What kind of resin are you using?

Laminating resin? or a finishing resin?

laminating resin will retain a tacky feel to it *contains no wax in the resin

finishing resin will retain a smoother feel when cured *contains wax in the resin. Bondo/3M is a resin that contains wax btw. With this type of resin you will need to sand in between layers otherwise you will have bonding issues between your layers of chop mat. Not sure if you knew or not but its good to know when trying to lay down multiple layers of fiberglass.

I honestly would start all over, tear your pieces of chop mat up with frayed edges all around. Small 4x4in pieces, 6x6in pieces,12x12in pieces etc. when you get into certain areas it will make layup much easier. Do a 30-50% overlap of the layers as you put them down. Never over saturate chop mat, just enough to penetrate through the fiberglass fully. This can be difficult sometimes when using crappy thick bondo/3m brand resin or really old resin.

You need to get a fiberglass roller too so you can work those air bubbles out as you go. Keep a jar or tin can around, something that can handle acetone and be sealed good so acetone wont evaporate, keep the fiberglass roller in the acetone before/during/ and after you use it. Once your done glassing I usually let my roller keep soaking in acetone for a while then I take it out and let it dry, and hang it up for later use.

Again once you are done laying up a layer or so and if you may or may not be done for the day be sure to sand that layer of glass before adding more layers for a good bond, 80 grit is fine but I usually knock stuff down a little or just rough it up with 40grit or lower, just personal preference.

Another way to help things go a little easier is a little tip I picked up from bobwires aka Nelson on FG forums with plate glass.

Get yourself a nice sized cooking pan, saran wrap, razor scraper, and get a piece of plate glass that will fit right inside the cooking pan.

lay down a piece of chop mat fiberglass onto the plate glass, stipple the ***** outta the chop mat with resin and get it nice and saturated. Then roll over it a few times with your fiberglass roller to get out any bubbles.

pick up the piece of chop mat off the glass and just lay it down onto your taped up area you want to make a mold from or lay it into your already made mold.

This method is quick and easy, less of a mess and is great when trying to lay glass up into tight/uncomfortable spots like trying to make kick panels. Doesn't hurt to roll over the glass again once you place it where you want it, again make sure the roller is soaking in acetone before you roll it over fiberglass.

Wait now I'm not done yet, pour acetone into the cooking pan and place the plate glass in there when done. Cover the pan with saran wrap to keep the acetone from evaporating and let the glass soak in it so it can eat up the resin. Use the razor to scrap off any resin thats still trying to hang around. This is also good to mix body filler on.


Once last thing, ditch the rope thing. You don't need it, just make sure you have laid down enough layers of fiberglass before pulling the mold and you should be fine, how many layers you need will depend on the glass your using 3/4oz? 1oz? 1.5oz mat? etc etc.

Thanks for the input Rell,

Although starting over is TOTALLY out of the question -- the fumes from the resin has set off my wife's asthma and added to her cold. That removes my house as a place to work on said project... I'll be lucky to finish what I have started. Hopefully, people will use the search function and read up on all your suggestions!

So....

Given all the issues, I was wondering if it would be worthwhile to add a couple of layers of rubberized undercoating on the inside of my box? I came across the suggestion somewhere on line, and wondered if it would add a layer of sealing to the box (and I have the air space for it).

One final question on this...

As everyone has noted, "air bubbles" weaken the fiberglass. Got that. It's also said all over the place that if you can stand on the box with out it flexing it's strong enough. My 230 lbs body (with steel toed boots on) could stand on it with no issues. Does passing the stand test remove concerns about "air bubbles"? ie: did I put enough layers to compensate for my poor fiberglassing skills? Or is there something else I am missing...