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Old 01-03-2016, 21:10   #1
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Polystyrene pellets added to epoxy to fill void?

Hi, I need to fill a void that is approx 500 cu-in, or about 2 gallons, through a 5/8" hole. I want to pump epoxy in and think I could save weight and money by adding small polystyrene pellets, 1/16"-1/8" diam. I'm also concerned that it may be brittle and crack, so thinking of adding some chopped glass fibers. Does anyone have experience with this? I'm using a pressurized jar rig to feed the epoxy through a 1/2 tube and am concerned the pellets may cause flow problems. I could buy a larger pellet, like 1/4" and pour that into the hole and then pump epoxy over it. Probably couldn't put the glass fiber in doing it that way though? Will this work? What do you think?
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Old 01-03-2016, 22:47   #2
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Re: polystyrene pellets added to epoxy to fill void?

How do you plan to prevent things from going exothermic? And where is this void, plus why does it need filling?

Also, yeah, if you fill in something that big, even with epoxy thickened with structural fillers, you're asking for trouble. Either in that the fill will be brittle, or that you'll create a hard, tough block, which has physical properties that far exceed the material surrounding it. So then, you'd be faced with a stupidly hard, hard spot.

There are some epoxy compounds which might, repeat, might work; if you had better access to the space in question. That, & if you have a bigger access point, there are far better space fillers that you could use. But... not knowing any particulars on this, coming up with any wisdom to offer, escapes me.

So, barring filling us in on details, good luck.


PS: Why not just fill it with foam? Or for that matter, why fill it at all?
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Old 01-03-2016, 23:20   #3
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Re: polystyrene pellets added to epoxy to fill void?

There was a small aft bilge compartment above my shaft tube that some Po filled with a few litres of resin and the rest with foam. It was a nightmare getting it out so I could deal identify and deal with the actual problem that had just been buried instead of fixed
I wouldn't even consider filling your void with foam or resin unless you have some really thought out reasoning


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Old 01-03-2016, 23:24   #4
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Re: polystyrene pellets added to epoxy to fill void?

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How do you plan to prevent things from going exothermic?
Several ways: 1. by pouring in a quart or so and waiting an hour or two and repeating, 2. using a slow hardener, 3. the added Styrofoam pellets should slow it by spreading it over more surface area.
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Old 01-03-2016, 23:50   #5
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Re: polystyrene pellets added to epoxy to fill void?

Still not clear why it needs to be filled but bad idea trying to fill an enclosed space with even a quart at a time of epoxy. There is nowhere for the heat to go and the pellets won't absorb any significant amount.

Also, how to you stop the pellets from simply floating to the top?

If you just need to fill some space, 2 part expanding foam makes much more sense.
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Old 02-03-2016, 07:27   #6
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Re: polystyrene pellets added to epoxy to fill void?

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... the pellets won't absorb any significant amount.

Also, how to you stop the pellets from simply floating to the top?

If you just need to fill some space, 2 part expanding foam makes much more sense.
I want to through bolt a folding step to a FRP cabinet that has a good 1" gap behind it, then another FRP wall. So the hollow is like 22" x 20" x 1". The issue is the through bolt can't be tightened b/c the fiberglass wall just flexes. I think I need something stronger than foam with the weight of a person standing on the step. And I have nearly a gallon of epoxy that's 3-4yrs old on-hand and would like to use up vice buying foam, which I have no experience with using.

I wasn't thinking the pellets would absorb heat as much as spread out the bulk of epoxy to slow the reaction. I don't know if the pellets floating will be an issue? The small ones may stay put b/c the viscosity of epoxy. With the big ones, I may only use enough epoxy to cover and fill the voids between beads, and since I'm filling in stages, I'm not sure floating will be a problem..?
thanx
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Old 02-03-2016, 07:50   #7
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Re: polystyrene pellets added to epoxy to fill void?

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I want to through bolt a folding step to a FRP cabinet that has a good 1" gap behind it, then another FRP wall. So the hollow is like 22" x 20" x 1". The issue is the through bolt can't be tightened b/c the fiberglass wall just flexes. I think I need something stronger than foam with the weight of a person standing on the step. And I have nearly a gallon of epoxy that's 3-4yrs old on-hand and would like to use up vice buying foam, which I have no experience with using.

I wasn't thinking the pellets would absorb heat as much as spread out the bulk of epoxy to slow the reaction. I don't know if the pellets floating will be an issue? The small ones may stay put b/c the viscosity of epoxy. With the big ones, I may only use enough epoxy to cover and fill the voids between beads, and since I'm filling in stages, I'm not sure floating will be a problem..?
thanx
They do make structural foams that would work. The epoxy will work fine except the complication of actually pouring it. I suppose you could do a cup or two at a time and wait for it to cure before doing another cup or two. (you did check that there is a bottom to this void and it won't just leak out into the bilge...right?)

I would expect the pellets to float to the top of each layer. It doesn't set that quickly that they won't have time to float up. Also are they compatable with epoxy. I have no idea but could easily see them disolve and mess up the epoxy.

Any chance you could cut an access hole and insert a piece of wood or starboard to take up the space?
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Old 02-03-2016, 08:03   #8
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Re: polystyrene pellets added to epoxy to fill void?

I have filled a bigger space with cheap epoxy, no fillers. However, our case was a very long grp tunnel - so most resulting heat went into the atmosphere.

The filler you use can be anything, just mind if the part is structural, a stronger filler creates a stronger bond (only where it counts). If you just fill a void, this will likely be irrelevant - use a light filler then.

PS Micro-balloons and cotton are cheap, light and problem-free. Or use chopped glass. Etc.

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Old 02-03-2016, 09:15   #9
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Re: polystyrene pellets added to epoxy to fill void?

Or use a shoulder type bolt, or construct a structural "tunnel" that would allow you to tighten the thru bolts without compressing the bulkheads.
Flanges on either side to disperse the load, and so on.
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Old 02-03-2016, 09:49   #10
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Re: polystyrene pellets added to epoxy to fill void?

This is a very round about way to solve an easy problem. Drill a hole thru both sides, then insert a G10 tube as a sleave, and epoxy it into place with structural filler. Then thru bolt the part with a backing plate. It is identacle to how spreaders are bolted in place.
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Old 02-03-2016, 09:59   #11
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Re: polystyrene pellets added to epoxy to fill void?

Instead of filling the void, consider drilling oversize and bonding in blocks to fasten to. If not that, use 2-part foam of a high density, and make sure it has room to escape. If you really want to mix styrofoam beads and epoxy, try a quart of it in a plastic cup, and evaluate what happens and the strength of the result. You may have invented something, or you may just get a fire and a really gross result.

There's a reason people do things certain ways in boat maintenance. Thousands of people have already spent millions of dollars proving what does and doesn't work.
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Old 02-03-2016, 09:59   #12
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Re: polystyrene pellets added to epoxy to fill void?

There are lightweight products meant for this. I filled the rudder in my 44 footer with it. The stuff I used was surplus mil spec product for casting powerboat rudders without layup. It was called "ruddercast". It has disappeared from the market though. There are likely other products around. I doubt Polystyrene bonds with epoxy...?
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Old 02-03-2016, 10:08   #13
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Re: polystyrene pellets added to epoxy to fill void?

Bond backing pads where fasteners are located.Somewhere on the website the Gougeon Bros explain how to insert oversize pads blindly thro' oval shaped holes.
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Old 02-03-2016, 10:10   #14
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Re: polystyrene pellets added to epoxy to fill void?

Or if you want to keep it real simple, drill a big hole, say one inch, through one side for each mounting bolt, dip a 1" wood wood dowel, longer than needed, in epoxy and shove it in until it reaches the opposite side. It will stick to the far wall and the one hole you drilled. Let cure. Chisel off inserted end flush. Then drill a hole through the wood dowel for the mounting bolt. The 1" dowel will act as a compression sleeve and not allow the fiberglass to flex.
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Old 02-03-2016, 10:21   #15
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Re: polystyrene pellets added to epoxy to fill void?

If you want to use the epoxy with pellets, mix it well and use just enough epoxy to wet all pellets.

That way there will be enough epoxy to glue the pellets together but not enough to run off. Consider adding a thixotropic agent to reduce viscosity.
Pour few cups at a time.

Try it in a cup outside your compartment to check if it's to exothermic.

Alternatively there are pourable two component closed cell foams.
Make sure they are closed cell.

Beware that styrofoam absorbs some water over time.

The glued in inserts seem a better solution.

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