Using Dominos for an Epoxy Waterfall Joint


TomInNC
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I'm working on the waterfall table guild project, and my plan is to use dominos to reinforce the waterfall joint. Given the layout of my slab, there will be a significant amount of epoxy spanning the width of the miter that would accept the Dominos. At this point I have 2 concerns. First, how well does the Domino cut mortises in resin? Unless I only want to reinforce the far left and right side of the joint, I will likely have 4-6 dominos that are solely embedded in the resin. I have never used the Domino on resin before, so I'd appreciate any feedback on what to expect from anyone that has. My second concern regards aesthetics. The resin is tinted an opaque blue, and I am wondering if the outlines of the dominos would be visible in the waterfall joint.

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So you have a front slab a rear slab and resin in between? If that's the case I'm not sure that the domino in the resin would add anything other than being a potential eyesore if you can see it through the resin. A large reason for the domino in the wood on miters is end grain is not an ideal glue surface and can suffer strength consequences as a result. Resin doesn't have the same properties and epoxy along the 2 joining surfaces of the resin would be similar to a long grain glue joint in wood. I would make sure that the resin glue surface had plenty of rough texture for the adhesive to get a good bite between the 2 surfaces and forgo any sort of reinforcement.

As far as cutting joinery in resin. There is no reason the domino won't cut a perfectly decent mortise in it. Resin acts similar to a dense tropical hardwood with minimal grain and the domino works just fine on that material. I could get deep in the weeds on mechanics of materials on why joinery in resin wouldn't be as effective as in wood but I'm sure no one wants to read about that. Just know that woodworking joinery in resin/plastic/cured epoxy will not work as well as the same joinery in wood.

6 minutes ago, drzaius said:

Or If loose tenons are used, I think you'd want some bigger than dominos.

I would agree with this. I would make shop stock much wider than the festool stuff and make multiple plunges close together to make a wide slot. As i mention above I'd keep the woodworking joinery in the wood and would just use epoxy on the resin edges.

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On 9/20/2022 at 10:19 AM, Chestnut said:

So you have a front slab a rear slab and resin in between? If that's the case I'm not sure that the domino in the resin would add anything other than being a potential eyesore if you can see it through the resin. A large reason for the domino in the wood on miters is end grain is not an ideal glue surface and can suffer strength consequences as a result. Resin doesn't have the same properties and epoxy along the 2 joining surfaces of the resin would be similar to a long grain glue joint in wood. I would make sure that the resin glue surface had plenty of rough texture for the adhesive to get a good bite between the 2 surfaces and forgo any sort of reinforcement.

As far as cutting joinery in resin. There is no reason the domino won't cut a perfectly decent mortise in it. Resin acts similar to a dense tropical hardwood with minimal grain and the domino works just fine on that material. I could get deep in the weeds on mechanics of materials on why joinery in resin wouldn't be as effective as in wood but I'm sure no one wants to read about that. Just know that woodworking joinery in resin/plastic/cured epoxy will not work as well as the same joinery in wood.

I would agree with this. I would make shop stock much wider than the festool stuff and make multiple plunges close together to make a wide slot. As i mention above I'd keep the woodworking joinery in the wood and would just use epoxy on the resin edges.

Yes on the question about the slab arrangement. I just took a look, and the area where I will be putting the joint would be roughly 5 inches of wood, 5 inches of epoxy, and then 5 inches of wood spanning the 15 inch width of the table. 

Good point on the glue for the domino in the resin. I guess I didn't even think of why I would be using the Domino in that section, just that it seemed natural to do so. 

 

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On 9/20/2022 at 1:21 PM, Mark J said:

A random thought:  Unless the resin is opaque, I think you're going to see the miter joint in the resin section pretty clearly, no matter the adhesive.   Anyone ever try this before?

I haven't done it on something this large, but gluing together pieces of epoxy resin can be done more or less seamlessly if you very carefully clean the mating surfaces (high-percent alcohol, gloves, lint-free cloth, and a dust-free environment) and match any colorants. Fundamentally similar to pouring in multiple lifts.

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Thanks for the feedback. Regarding the opacity, I am going to be using the same pigment-resin ratio that I used a recent table build, and the resin was quite opaque. That was a flat table top and did not have a waterfall joint, however, so I was a little concerned that the resin might look different when its cut and joined at 45 degree angles. 

 

Bon Pacific, what did you mean in the comment above about "high-percent alcohol"? Was this just a reference to wiping the surfaces down with denatured alcohol before the glue up?

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On 9/21/2022 at 6:30 AM, TomInNC said:

Thanks for the feedback. Regarding the opacity, I am going to be using the same pigment-resin ratio that I used a recent table build, and the resin was quite opaque. That was a flat table top and did not have a waterfall joint, however, so I was a little concerned that the resin might look different when its cut and joined at 45 degree angles. 

 

Bon Pacific, what did you mean in the comment above about "high-percent alcohol"? Was this just a reference to wiping the surfaces down with denatured alcohol before the glue up?

Just for cleaning the joint. 90+ percent isopropyl is my preferred resin cleaning liquid, for both UV and epoxy resins. Denatured alcohol has a risk of softening/deforming the epoxy which would throw off your joint.

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Just an FYI for anyone that might find this thread in the future. Before posting here, I asked the folks at Festool about using the Domino in resin. Their response is below.  So in addition to the approach not making a lot of sense from a structural standpoint as Chestnut pointed out, it sounds like the Dominos might not properly bond with the resin anyway. 

 

 

"Thank you for contacting Festool. Festool does not recommend using Dominos for the application described. Festool has not seen success in connecting epoxy resin materials even after they cure. This is not an application suggested by Festool."

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