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Old 09-30-2010
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Thickened epoxy really necessary?

I'm re bedding my grab rails and am therefore doing the old drill out and fill routine with epoxy to seal the deck core. I've always poured epoxy in to seal the core, drained it out and replaced it with thickened epoxy (per Don Casey). I've got a lot of holes to fill this time, and it it occurs to me that regular (un thickened) epoxy is probably many times stronger than the balsa it's replacing. Since the rails are through bolted, the epoxy is acting strictly as a filler. Is it really necessary to do the extra step with thickened epoxy?
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Old 09-30-2010
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The epoxy in the holes is in compression and thickened epoxy is stronger. It takes little extra time to thicken the epoxy. I would and do mix colloidal silica with it.
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Old 09-30-2010
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non-thickened epoxy is pretty brittle.
if I was doing this, I would skip the non-thickened epoxy "wash" and just fill holes with thickened epoxy and re-drill. Seems to work quite well for me.
You don't need to thicken epoxy too much - just getting it to slightly viscous consistency where it is still quite liquid, improves it's flexibility a lot (easy to check - let it cure as a single piece elsewhere, then try to bend it, compare to non-thickened epoxy), while still letting it permeate the surrounding core somewhat.

Always remember that you don't want those holes to outlive the rest of the boat
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Old 09-30-2010
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Straight epoxy is actually very brittle, and relies on the binding to something to give it shatter resisting strength, so as Brian pointed out, thickened epoxy will be stronger where it will be in compression, and possibly have sideways forces pushing on it and trying to crack it.

Further, I have filled a few small screw holes in my deck, just trying to seal them up and due to the ssmall size, I just put a few drops of epoxy in them and used a small sliver of wood to work it down into the hole and get the air out. Without a thickening agent, I found the epoxy still dipped down in the whole once dried. A few that where really bad (Like the epoxy was absorbed somewhere) I refilled, and still ended up with a depression in the top. I have worked with thickened epoxy a lot and have not noticed nearly as much of an issue getting a nice flat fill.
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at the other end of the application.. there are super thin and "penetrating" epoxies out there too. "get rot" is one I believe. They do have the ability to do just that. penetrate. I just don't know if trying to stabilize core material like balsa would work without hundreds of holes for drying it out. I read that acetone saturation helps dry the balsa but I really have no idea if anything really works other then taking the skin off and replacing the core.
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The reason you wet the wood with unthickened epoxy before filling with thickened epoxy is to saturate the wood surrounding the hole so it doesn't "steal" epoxy from the thickened epoxy, which can lead to problems. Thickened epoxy is far stronger and resists chipping and compression far better than unthickened epoxy does. Also, properly thickened epoxy is far more viscous and less likely to drip. You can vary the viscosity by varying how much thickening agent you add to the epoxy.
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Git Rot is ok, but a far better product is Smith's CPES (clear penetrating epoxy sealer) if you want to penetrate and seal the wood before using thickened epoxy.
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I found a cake decorating kit at the dollar store, with several interchangeable tips. I load my thickened epoxy in a ziplock bag,and stick it inside the decorator.I can reach to the bottom of the hole with it. As it fills i draw up slowly, leaving no voids. If you have ever tried to router any quantity of these holes with the crappy little dremel bit, you know how useless it can be, so get yourself a allen wrench, sharpen the leg to a knife edge, and use it in your drill to oversize the core. I use compressed air, and the shop vac to clean em out good. I use a large syringe to fill and after time to soak, empty the holes before filling with the thick stuff.
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You may want to give West a call about their new product.
WEST SYSTEM | Specialty Epoxies - G/flex
G-flex
It is sort of thick but also is good for wetting.
May be a one step solution.
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I use a dremel bit for small holes (1/4" or so for bolts) and for a larger hole like hatches or deck fills I use the router bit shown below in a laminate trimmer - a smaller one handed router. My deck core is 1/2" so it does a perfect job.
For filling holes I use West syringes. With thickened epoxy you can't fill the syringe from the tip so I fill it from the back end. The cake decorating kit is a good idea and has the advantage of throwaway - the syringes are hard to clean.
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