There are countless online tutorials that will cover building a resin river table in detail. I recommend watching a bunch of them, and finding a method that will work with your available tools and space. I'll go briefly over the steps I took to build this one and point out a few of the mistakes I made, in hopes that you, dear readers, can avoid them.
I got a slab of live-edge walnut from a local supplier. I asked them to cut the wood to give me enough for a 36" square table -- the size of the ratty old card table previously in residence in my kitchen dining area.
I took the wood to my local makerspace, Hackerlab, and ran it through the drum sander until I had an even thickness on both pieces and the wood was as flat as I could make it. This took approximately 100 years. Next time I will use the planer.
I went to my local Tap Plastics and asked them to cut me a sheet of polyethylene plastic that was 36 inches square, plus four side panels that would fit around the edges to build a mold for my table. Polyethylene is perfect for this, since the resin will not stick to it and it's not too expensive. I used hot glue and aluminum tape to hold the sides to the bottom.
It was tricky to get this built water-tight so the resin wouldn't leak through, since the bottom of the mold was the exact size I wanted to end up with. If I were to do it again, I'd make the bottom of the mold a few inches bigger. I would make a 38" square and then secure the sides set-in by 2" to create a 36" box. This would have given more plastic for the hot glue to grab around the edges -- I could have really piled it on to stop all the leaks -- and made my life easier.
I placed the wood into the mold and then filled the empty space with something I could easily measure the volume of. Rocks, sand, or gravel would work great here. What I had a lot of on-hand was cat food. So I filled the river with cat food, then measured how much I'd used.
For my 36" square table I ended up needing around 4 gallons of resin. I ordered extra! You'll need extra. Order extra.
Clamp the wood down into the mold so it doesn't float up on top of the resin. Be sure it's level, using shims to adjust the mold where needed.
Vacuum out ALL the dust. Dust is the enemy! The cleaner you can keep your environment, the better. Every speck of dust that gets in the resin will show.
A lot of beautiful live-edge hardwoods have knots and cracks throughout the grain. This makes them especially beautiful and unique, but will be your worst nightmare during a resin pour. If you don't get all these holes filled up with cured resin, you'll get very annoying bubbles in your final pour as the resin seeps into the cracks.
Before you do your first pour, mix up a small batch of resin and fill all the cracks and holes in your wood. If the resin drips all the way through, put a piece of aluminum tape on the back side of the wood to hold the resin inside until it cures.
You may be surprised at how much resin the wood will swallow up! Some of these little holes apparently lead to other universes.
Read and follow the manufacturer's directions carefully. Resin can be finicky and if mixed incorrectly will remain a sticky mess forever! That's the last thing you want on your expensive beautiful live-edge wood. Each type of resin varies, but some general rules you don't want to bend include:
- Measure precisely. Don't guesstimate! You can get disposable graduated mixing buckets at any hardware store, so buy a stack of them and pay attention to the markings.
- Mix Thoroughly. Mix for far longer than you think you need to. Pour into a new container and mix again. Unmixed resin will give you sticky spots.
- Pay attention to the temperature ranges and don't try and mix resin on a freezing cold day, or it won't ever set up.
- Pour the resin in multiple layers. A too-thick layer will cause problems -- bubbles will get trapped in there, and it won't set up as well. I found a 1/16" to 1/8" layer was about right.
I got my resin from several different sources. Some, I had on-hand from earlier craft projects. I found some on Amazon and ordered some directly from the manufacturer. For the final pour I used resin from the craft store (since I ran out of the other stuff). I was nervous the different kinds might not play well together, but they worked just fine. I'd probably still advise to use just one kind of resin if you can, but being a bit promiscuous with resin types didn't hurt my project any.
I added some blue mica powder and some dye to my very first layer, to make it a little bit more opaque for better LED diffusion. This looked lovely! I made each subsequent layer more and more clear.
After each pour, I used a propane or butane torch just above the surface to pop any bubbles. I tried using a heat gun at first, and that worked okay, but then I switched to the torch and it worked SO much better. The open flame changes the oxygen / CO2 balance in the air which yanks the bubbles right out of the resin. This part was so satisfying!
Cover between pours to minimize dust and hair getting into the resin. Let each pour cure for the time recommended on the directions. Longer works fine too, but if you do leave it longer you'll want to sand each layer (and vacuum up all the dust) so the next layer has something to grab. Don't worry about putting scratch marks in each layer. The next layer will render them invisible. This is handy -- you can sand out any bubbles or dust that snuck into any previous pours.
I filled my resin river and then did a final pour where I covered the whole table top with resin. Unfortunately I got a little greedy here and poured my last layer too thick. I also hadn't adequately sealed every hole and crack in the wood. The result was that my top layer looked horrible. It wasn't smooth, and there were dozens of ugly bubbles trapped just below the wood. I got my rotary sander and tried sanding them out, but the resin was tough and I nearly gave in to despair and scrapped the whole project.
But, after asking the advice of some local woodworkers at my makerspace, I decided to try using the CNC router to plane the table down and give the top layer another try.
I used a Shopbot CNC router to mill down both the top and the bottom of the table so they were perfectly flat. This took off the bottom opaque layer of resin, but I could live with that.
I used a table saw to neatly trim 1/4" off each side of the table. This cleaned up the edges where the resin was uneven, and gave me four 1/4" edge pieces that matched the edges of the table perfectly. I later used these as a "skirt" underneath the tabletop to hide the acrylic sheet and electronics.
I sanded down the bottom of the resin but did NOT do another thin coat of resin on the bottom of the table. This might have looked beautiful -- it would make the whole table clear and see-through. But I wanted a bit of cloudiness for diffusion so I left it sanded and not refinished.
The CNC router had reopened some of the holes in the wood, so I resealed using some resin, and where that didn't seem to work, I used a few dabs of 5-minute epoxy glue. It didn't dry perfectly clear, but it did work to block the holes that would not fill up with resin (because, apparently, they led to some other dimension).
For the final pour, I moved the project into a dust-free room (my wine cellar), micromanaged the temperature, and did everything I could to create the perfect environment for a smooth pour.
I warmed the resin in a hot water bath to thin it and lower the viscosity. I used a squeegee to spread it as evenly as I could to all four corners, and a foam brush to add a thin coat to the sides.
It's not perfect.. but it's good enough for me. And for Biskit.