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Brendon_t

Structural epoxy

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Not my area of expertise so I'll throw the question to the group.

Are most high volume epoxy products created equal?  

More specifically, I'll be using epoxy to bridge a gap between a few boards as many of you have seen in the "river table" builds. There will be all thread technically connecting the sticks but most of the holding together will be the epoxy. Are there formulations to stay away from? 

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Brendon, although epoxy is some pretty stout stuff, I wouldbe tempted to bridge the bottom gap with some clear material that is already solid. Lexan or plexiglass, maybe. Mostly to keep the pieces rigidly aligned while the epoxy cures. I would be less worried about the epoxy itself fra turing, than about it adhering properly to the sides of the gap, if there is any chance of shifting.

 

All that assumes the gap is through and through. If it is really a trench, then any of the popular epoxies or casting resins should work.

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In my experience with building model racing boats, the quicker the set time, the more brittle the epoxy.   I'm mainly referring to 5 min vs 60 min and times in between, but a 6 hour should be even stronger.   But then it also depends on the exact formulation.  Check each manufactureres site, they should have some sort of stress analysis' done. 

But I haven't dealt with epoxy in the scenario you describe, so I'll let others give you a better answer. 

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I don't have any idea what a river table is, but if I wasn't already invested in West Systems, I'd look into Jamestown Distributors store brand. It's gotten good reviews in boat forums, and used to be substantially cheaper than West, but I haven't looked at it for some number of years.  I think it's called TotalBoat, or something close to that.

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14 minutes ago, Tom King said:

I don't have any idea what a river table is, but if I wasn't already invested in West Systems, I'd look into Jamestown Distributors store brand. It's gotten good reviews in boat forums, and used to be substantially cheaper than West, but I haven't looked at it for some number of years.  I think it's called TotalBoat, or something close to that.

I've wondered how good Totalboat is for woodworking. It looks like the gallon kit sells for about $120 on Amazon with either fast or slow hardeners.  The quart kit is about $50.

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41 minutes ago, bleedinblue said:

I've wondered how good Totalboat is for woodworking. It looks like the gallon kit sells for about $120 on Amazon with either fast or slow hardeners.  The quart kit is about $50.

I use Totalboat with the slow set. No complaints at all. I've done several projects with it, both structural and fills. No failures so far. I got the quart kit about 2 years ago and still have 3/4 of it.

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That would be a LOT of epoxy.  I think regular epoxy, like West or TotalBoat would get too hot if you tried to even mix that much, and foam up.  There are resins designed for thick pours, but I've never had any reason to use any, so can't offer any advice.

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I've not used this before, but for the amount of volume you're looking to pour a regular 'standard' epoxy will end up being a disaster.  Very brittle, will shrink unevenly and leave a bunch of funky streaks in the clarity of the finish.  

 

This type of epoxy is designed for large pours (very large).  Think it would be a good fit for the project :-)  

https://www.smooth-on.com/product-line/crystal-clear/

Hope this helps!

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So that picture is about the right idea, except the maximum gap will be less than 2” wide, 1.5 deep and will be poured in multiple stages.

Most of the manufacturers of gallon plus size epoxy bottles list 12+ hours so I don't think any of those are quick set type.

I guess my main concern is that a 2”think gap of only epoxy won't just snap off of the boards and laugh in my face.

 

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Cool question. In my day job I've worked with actual structural epoxies by companies like Hilti, those generally aren't clear, in my experience, so a non starter there :).

I'm wondering if you did this in multiple pours, the risk is some sort of occlusions or dust between the layers, but I think it would cure better. Might be time for a test poor of a smaller sample of what you want to do.

 

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I have done a few tests of the concept and the main issues is getting the bubbles out from the goodies that will be submerged in the epoxy.. 

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3 hours ago, Brendon_t said:

I have done a few tests of the concept and the main issues is getting the bubbles out from the goodies that will be submerged in the epoxy.. 

Just spitballing, but try a test pour with one of the goodies having a film of a de-molding agent on it.  Like a silicone demolding spray.  That might lower the surface tension of bubbles on the goodies and let them escape. 

 

 

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Anyone used that stuff? I'm wondering how long it stays clear. My question comes from observing clear casting resins used to simulate water features in dioramas, model rail layouts, and the like.

Most I have seen tend to yellow, fog, or crack over time. I would hate to build a river table and have it look like a piece of grandma's old butterscotch hard candy in a couple of years.

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Personally, I think getting glass cut to span the gap is much better solution. Even with care, the epoxy is going to get scratched up & rough looking. At that point it just looks like a table with a piece of ugly, cheesy plastic in the middle. 50 years from now glass will still look great, & if it gets broken it's easily replaced. Having it tempered after cutting is a good idea too.

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1 hour ago, wtnhighlander said:

Anyone used that stuff? I'm wondering how long it stays clear. My question comes from observing clear casting resins used to simulate water features in dioramas, model rail layouts, and the like.

Most I have seen tend to yellow, fog, or crack over time. I would hate to build a river table and have it look like a piece of grandma's old butterscotch hard candy in a couple of years.

Reading the product info page, it's a UV resistant epoxy, so for indoor use, it should stay clear for a long time, but with prolonged exposure to UV light, they state it will yellow with time.   But they also recommend using coloring dyes, I would think that would mitigate the yellowing effect if it was already tinted in some color. 

A glass piece would work great like you said, but if I'm doing this type of piece, I would be stringing some Neopixel (WS2812 RGB) LED's inside the wood somewhere to use the refraction of the epoxy to glow and change colors over time.  Hard borders on the glass would be glaring, since you can never get glass to fit the natural edge perfectly. 

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Ive never worked with it before but you may want to look at a material called liquid glass I think the chemical name is sodium silicate.  I would definately do a test run of whichever system you decide on.  Also the liquid glass may only work as a filler than a structural element.

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