This instructable documents the process of building a coffee table from epoxy resin and white concrete. I’m calling this design my “Arctic Erosion” coffee table.
If you like this, I’d greatly appreciate your vote in the concrete contest! :) CONTEST LINK -https://www.instructables.com/contest/concrete2019...
High level view -- I used a CNC to cut out a layered topographic form from foam, sprayed and poured the concrete over the foam, then filled the cavity left by the foam with epoxy. This table was made using thick set epoxy resin with blue epoxy pigment, and a white GFRC concrete mix with white concrete pigment. Some have pointed out the concrete & epoxy coffee table somewhat resembles a Minecraft lake, although any resemblance is unintentional :)
I’m really happy how this table came out – the epoxy and white concrete both shine, and the design is probably my favorite thing I’ve made to date. So, let’s get to it!
\\ EPOXY //
o Total Boat Thick Set Epoxy Resin: http://bit.ly/31TDqOK
o Blue Transparent Pigment: http://bit.ly/31TDqOK
o Vacuum Pot: http://bit.ly/31TDqOK
o Vacuum Pump: http://bit.ly/31TDqOK
o Torch: http://bit.ly/31TDqOK
o Epoxy/Plastic Polish: http://bit.ly/31TDqOK
o Fine grit sandpaper (to 2000 grit): http://bit.ly/31TDqOK
o GFRC Concrete Mix: http://bit.ly/31TDqOK
o AR Glass Fibers: http://bit.ly/31TDqOK
o Cake Fondant Tool for perfect edges: http://bit.ly/31TDqOK
o Helical Mixing Paddle: http://bit.ly/31TDqOK
o Concrete mixer: http://bit.ly/31TDqOK
o Concrete pigments: http://bit.ly/31TDqOK
o 1-part concrete sealer: http://bit.ly/31TDqOK
o Black 100% Silicone Caulk: http://bit.ly/31TDqOK
o Paste Finishing Wax: http://bit.ly/31TDqOK
o “From Scratch” GFRC Recipes: http://bit.ly/31TDqOK
o Hopper Spray Gun (for spray-on face coat): http://bit.ly/31TDqOK
o Air compressor (for spray gun): http://bit.ly/31TDqOK
o Foamular: http://bit.ly/31TDqOK
o Melamine Sheet: http://bit.ly/31TDqOK
Sign up for a free Easel account: http://bit.ly/31TDqOK
o Inventables X-Carve CNC: http://bit.ly/31TDqOK
o Spektra Compression Bit: http://bit.ly/31TDqOK
o SawStop Table Saw: http://bit.ly/31TDqOK
o Kreg Miter Sled: http://bit.ly/31TDqOK
o Fine finish miter saw blade: http://bit.ly/31TDqOK
o Melamine blade: http://bit.ly/31TDqOK
o DFM Toolworks Mini-Square: http://bit.ly/31TDqOK
o Spektra Compression Bit: http://bit.ly/31TDqOK
o Hikoki / Metabo HPT Cordless Circular Saw: http://bit.ly/31TDqOK
o Hikoki / Metabo HPT (Insane!!) 36V Impact Driver: http://bit.ly/31TDqOK
o Hikoki / Metabo HPT Random Orbit Sander: http://bit.ly/31TDqOK
o Heat Gun: http://bit.ly/31TDqOK
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Step 1: Making the Concrete Form
We are casting this upside down, so the form is made in the mirror image of the final concrete shape. The form is just a melamine box, with a stacked foam knockout glued inside it. The foam is just ½” Foamular brand foam insulation that you can get at Home Depot for about $10 for a 4x8 sheet.
A. CUT THE MELAMINE PIECES
You can use a table saw or circular saw to cut your pieces to size. You’ll likely want to adjust the size of the table, but here is what I cut for a 48”x22”x8.5” concrete slab (conveniently, “4x8” melamine sheets are actually 49.5” wide, so you can just use the full width of them to save time). Note that I only made it 8.5” tall, because we’ll be making a 5.5” tall wood base for it to sit on.
(2x) long sides 49.5”x 9.25”
(2x) short sides 24”x9.25”
(1x) base 48”x22”
B. CUT FOAM
Note: if you don’t have a CNC, you can just print out the SVG file, and use it as a template to cut the foam pieces with a jig saw or band saw. If you want to go super budget, an electric turkey knife also works well for cutting foam.
I decided to make my own topographic shape from scratch. So, I first had to create a digital sketch of how I wanted the layers to look. I used Affinity designer to generate the 2D vector file of the layers, but you could use any software that can create SVG files, like Adobe Illustrator or Inkscape. I then imported the SVG file into Inventables Easel software. In Easel, I separated out each layer so I could cut the layers individually. I’m cutting each layer from ½” rigid foam, so when 8 ½” layers are stcked to the foam form will be 4” tall. Foamular can be cut really fast with a CNC. I did ¼” deep passes at about 60 inches per minute, so each layer only took a few minutes to carve on my X-Carve.
After each piece was finished on X-Carve, I used a 150 grit sanding pad to quickly sand off the tabs.
LINK - Inventables Easel Projects for Foam Knockout (might require some tweaks, but foam is cheap and cuts quick)
o Part 1: http://bit.ly/2IRCJht
o Part 2: http://bit.ly/2IRCJht
I attached one melamine end of the form to the melamine base. Note that I’m going to attach the other 3 sides after I’ve glued the foam to the inside of the form, which you’ll do after attaching the end.
To secure the foam, I just used some general purpose spray adhesive. I glued the bottom piece to the form first, and then glued the layers on one-by-one, to build up the 3D foam shape. I’ve been told that heavier duty spray adhesive can cause issues with concrete forms (e.g., eating away at them). The general purpose spray adhesive I used had plenty of hold, and didn’t dissolve the foam, so I recommend sticking with it.
I then applied a few coats of polycrylic to the foam. This helps a bit to prevent concrete from seeping into it and result in a cleaner surface. I’m told that brushing on a think layer of epoxy, and covering that in paste wax or some other release agent, works better. So you might try that if you do this, since I ended up having a fair amount of foam to scrape off the concrete.
After gluing the new foam knockout, I sealed the form by caulking the seams. I have a process that people seem to love for getting perfect caulk lines, so I’ll share it here. I apply a layer of paste wax to the melamine, lay down a generous line of 100% silicone caulk, and run a metal fondant ball tool over all the caulk lines. The fondant tool pushes excess caulk to the sides to leave a clean line over the seam. And, the layer of paste wax makes it easy to peel the excess caulk away once it cures, leaving a perfect caulk line.
Step 2: Concrete Spray & Pour
I used glass fiber reinforced concrete (or “GFRC” for short). Check out my previous Instructables on GFRC concrete for more details on mixing. However, for this project I made it easier using Fishstone's just-add-water GFRC mix. You mix it by adding 1 gallon of water for every 50 lbs (one bag) of mix. For this table, I needed about 170 lbs in total (between two face coats and back coats). The amount you’ll use will vary depending on the size of your table, but figure 11 lbs per square foot of table at 1” of concrete, and you’ll be good to go.
A. Face Coat
The first coat is sprayed on to provide a “beauty” coat or “face” coat, with no glass fibers. When mixing the face coat, you want to shoot for pancake-batter consistency, but it is important not to add too much water, which will weaken the concrete. If the recommended amount of water isn’t enough, I add a superplasticizer instead of more water, to get it right. If you scoop the mix with a trowel and hold it vertically, it should slide off the trowel, but leave a 1/8” layer on the trowel – this means it will be thin but still stick to the sides of the form when you spray it.
I used a hopper gun to spray the face coat, spraying corners first, then sides, then the middle of the form. I started by spraying with the form oriented vertically so it was easier to coat the tiered foam knockout. We then placed the form horizontally on the ground so I could spray the rest of the form. You want to spray in a U-pattern, towards the portion of the foam that is already covered, to avoid sand particles getting on the unsprayed surface.
After spraying, we brushed in the face coat with a chip brush, just to be sure there were no trapped air bubbles.
Optional: wait until face coat firms up but is still damp to touch, then spray second layer of face coat. If doing this, make each face coat layer no more than 1/8" (so 1/4" total).
Wait for the face coat to firm up before adding backer coat. You want it to be firm but still wet, so you can't push through it easily with your finger, but it still sticks to the back coat.
B. Hand-Packed Back Coats
The timing of your backer coat is important, so make sure your face coat has firmed up enough (but not completely dried out), before you start your backer coat. Usually this only takes 30-60 minutes.
You can wait until the face coat is ready to begin mixing your back coat, so long as you have everything measured out in buckets (so mixing only takes a few minutes). The process is similar to mixing the face coat, except you add glass fiber to the GFRC bag mix (between 1.0-1.5 lbs per 50 lb bag of mix). Also, you want to use less water and plasticizer, so the back coat is thicker and can be hand packed – it should be similar to playdoh or clay. (Again, see my previous instructables on GFRC for more details on the recipe and mixing process for the back coat.)
I mixed one 50 lb bag at a time, and packed it in by hand, working it into the concrete that is already in the form. To avoid slumping on the vertical surfaces, I only packed in about ¼” at a time. In total, we did 4 thin back coats, building up slowly until the concrete was ¾” thick on the verticals.
Optional: After the first layer was packed against the face coat, we added an alkali resistant (AR) glass mesh, which is made out of the same alkali resistant glass as the AR fibers in the mix. This mesh adds strength and also helps to keep slumping on the vertical surfaces to a minimum, making subsequent layers easier to pack in.
Step 3: Inner Base Support
Before flipping over the form, it was time to address the issue of how we would attach the inset base to the hollow table. Since the wood base will be inset from the edges of the table, you can’t rest it on the edges. The solution we came up with was to make inner cross pieces using construction lumber and 1” steel tube.
The steel cross braces will be supported by 2x4 or 4x4 lumber. I used a miter saw to cut scrap pieces of 4x4 and 2x4 to the size (sneaking up on the size by testing the fit in place).
I then cut the steel tube to length using my angle grinder. We used a drill press to create ¼” holes on the bottom side of tubes, and to drill larger holes on top of the tube. The larger hole on top allows the entire ¼” bolt, including the ½” head to be inserted into the tube, so it be bolted to the lumber via the smaller ¼” holes on the other side of the tube.
Step 4: Demolding the Concrete
I usually try to scrape of the excess concrete on the top edges of the form at 6-9 hours after pouring, when it is semi-hard, but timing didn’t allow for it this time.
When we came back the next day, the concrete was rock hard. I started trying to wet grind with an angle grinder, but quickly realized the dust storm would blind us before we could finish, if I continued. So we took a couple chisels and started chiseling…for over an hour. As we labored, we felt a bit like Michaelangelo’s assistants, doing the grunt work so he could come back and shape certain important parts of the David.
Once most of the edge was chiseled off, I could then use the angle grinder to grind the edges perfectly level with the form, for a clean crisp bottom table edge. Then we evacuated the shop my air filter did its work on the dust cloud.
Next it was time to flip the form and demold. This is pretty simple. Just remove the drywall screws and pry the sides off.
Note that the foam stuck to the concrete a bit more than expected. I think I should have put another layer or two of polycrylic on it, and probably used some form release spray, since parts of the foam stuck to the concrete.
Step 5: Pre-Finish the Concrete
To patch some imperfections in the concrete, I used a concrete slurry coat, which is just the same GFRC mix and white pigment as the face coat. I rubbed it in by hand, using circular motions to push it into holes in the concrete.
I let the slurry cure overnight, then came back and wet sanded with 400 grit sanding pads, and rinsed the table thoroughly. I then applied an acrylic sealer to the concrete. While I will be sanding and sealing again after epoxy, pre-sealing will help prevent any overflow epoxy from bonding to the concrete, and allow it to be more easily chiseled off.
Step 6: Epoxy
Before pouring the epoxy, I applied paste wax to the concrete at the open end of the topographic cavity, then used silicone caulk and a scrap piece of melamine to seal off the end of the topographic reservoir to hold the epoxy.
For this project, I used Total Boat’s new thick set epoxy, which allows for much deeper pours. I used Fusion 360 to calculate the volume of the topographical cavity – it came out to be 3.1 gallons.
I started by mixing up one entire 1 and 1/3 gallon kit of thick set. This was by far the largest amount of epoxy I ever mixed at once. I added blue transparent pigment to the epoxy, mixed thoroughly, and then poured most of the epoxy back to a smaller bucket that fit in my vacuum pot.
Using the vacuum chamber will pull the majority of the bubbles out of the epoxy, and reduce the chances of having bubbles trapped in it. I’m told it isn’t necessary with thick set, but I wanted to do everything I could to get clear epoxy for this project. After letting the vacuum pump run a few minutes, its time for the first pour.
After pouring and waiting a few minutes for any leftover bubbles to rise through the epoxy, I came back with a torch to pop the few bubbles that weren’t removed in the vacuum pot. The first pour ended up being about 2.5” at its deepest point, and I ultimately did two more pours to fill it up, letting the epoxy cure for 12 hours between pours.
Note that the painter’s tape I used to protect the concrete from epoxy turned out to be unnecessary. Some of the epoxy still got on the concrete. However, I was pleasantly surprised to find that, because I pre-sealed and waxed the concrete, the cured epoxy popped off really easily with a chisel, with no noticeable effect to the concrete surface.
When I removed the melamine from the end of the epoxy, I got another surprise, but this one wasn’t so pleasant. I’m not sure exactly what happened, but since the melamine only stuck in the deepest section that gets the hottest during curing….I think the epoxy actually melted the melamine and got into its MDF core. It wasn’t chiseling off….until I discovered that I could use the heat gun trick to soften the epoxy so the melamine could be removed. To make things more difficult, the chisel gouged the surface, which meant I had to go back use some fast-setting epoxy to patch things up.
Step 7: Finish the Epoxy & Concrete
To finish both surfaces, I started by dry sanding the concrete and epoxy from 120 grit up to 240 grit. I then wet sanded both surfaces to 400 grit. Since 400 grit is as high as I want to go on the concrete, I paused here to apply sealer to the concrete. (Note: if you sand concrete past 400 grit, some concrete sealers don’t take as well.) I let the concrete sealer cure overnight, then returned to finish the epoxy by wet sanding up to 5000 grit, and then using a plastic polish for the final shine.
Step 8: Make the Wood Base
The base is just a simple box, inset by 3.5” on the long sides, and 5” at the ends. I left one side open and added two dividers so you can store magazines or books under the table. I used butt joints and assembled with glue and brad nails. After filling nail holes and plywood sides with wood filler, I used white spray paint to paint all the exposed surfaces of the base.
Here is the cut list for a 38”x15”x5.5” base made from ¾” plywood.
(2x) 38”x15” – top and bottom
(2x) 4”x15” – side pieces
(2x) 4”x 14.25” middle dividers
(1x) 36.5”x4” inset back
Step 9: ASSEMBLE AND ENJOY!
The concrete and epoxy top weighs about 200 lbs, so I am just relying on its weight to hold it in place on the base. (You could use screws or construction adhesive to attach the base if you like.) So get a friend or two to help you move this piece, set it in place, and enjoy a piece of functional art in your living room!
This is an entry in the
Stone Concrete and Cement Contest