Supplies
Total Boat Thick Set Epoxy Resin
Blue Transparent Pigment
Vacuum Pot
Vacuum Pump
Torch
Epoxy/Plastic Polish
Fine grit sandpaper (to 2000 grit)
GFRC Concrete Mix
AR Glass Fibers
Cake Fondant Tool for perfect edges
Helical Mixing Paddle
Concrete mixer
Concrete pigments
1-part concrete sealer
Black 100% Silicone Caulk
Paste Finishing Wax
“From Scratch” GFRC Recipes
Hopper Spray Gun (for spray-on face coat)
Air compressor (for spray gun)
MATERIALS
Foamular
Melamine Sheet
CNC
Inventables X-Carve CNC
Spektra Compression Bit
OTHER TOOLS USED
SawStop Table Saw
Kreg Miter Sled
Fine finish miter saw blade
Melamine blade
DFM Toolworks Mini-Square
Spektra Compression Bit
Hikoki / Metabo HPT Cordless Circular Saw
Hikoki / Metabo HPT Cordless Angle Grinder
Hikoki / Metabo HPT 36V Impact Driver
Hikoki / Metabo HPT 12V Impact Driver
Hikoki / Metabo HPT Random Orbit Sander
Heat Gun
Step 1: Making the Concrete Form
You can use a table saw or buzz saw to chop your pieces to size. You’ll likely want to regulate the dimensions of the table, but here is what I cut for a 48”x22”x8.5” concrete slab (conveniently, “4×8” melamine sheets are literally 49.5” wide, so you’ll just use the complete width of them to save lots of time). Note that I only made it 8.5” tall, because we’ll be making a 5.5” tall wood base for it to take a seat 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’ll just print out the SVG file, and use it as a template to chop the froth pieces with a jig saw or band saw. If you would like to travel super budget, an electrical turkey knife also works well for cutting foam.
I decided to form my very own topographic shape from scratch. So, I first had to make a digital sketch of how I wanted the layers to seem . I used Affinity designer to get the 2D vector file of the layers, but you’ll use any software which will 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 froth form are going to be 4” tall. Foamular are often cut really fast with a CNC. I did ¼” deep passes at about 60 inches per minute, so each layer only took a couple of minutes to carve on my X-Carve.
After each bit was finished on X-Carve, I used a 150 grit sanding pad to quickly sand off the tabs.
C. ASSEMBLING FORM
I attached one melamine end of the shape to the melamine base. Note that I’m getting to attach the opposite 3 sides after I’ve glued the froth to the within of the shape , which you’ll do after attaching the top .
To secure the froth , I just used some general purpose spray adhesive. I glued rock bottom piece to the shape first, then glued the layers on one-by-one, to create up the 3D foam shape. I’ve been told that heavier duty spray adhesive can cause issues with concrete forms (e.g., erosion at them). the overall purpose spray adhesive I used had many hold, and didn’t dissolve the froth , so i like to recommend sticking with it.
I then applied a couple of coats of polycrylic to the froth . This helps a touch to stop concrete from seeping into it and end in a cleaner surface. I’m told that brushing on a think layer of epoxy, and covering that in paste wax or another release agent, works better. So you would possibly try that if you are doing this, since I ended up having a good amount of froth to scrape off the concrete.
After gluing the new foam knockout, I sealed the shape by caulking the seams. I even have a process that folks seem to like 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 edges to go away a clean line over the seam. And, the layer of paste wax makes it easy to peel the surplus caulk away once it cures, leaving an ideal caulk line.
Step 2: Concrete Spray & Pour
A. Face Coat
The first coat is sprayed on to supply a “beauty” coat or “face” coat, with no glass fibers. When mixing the face coat, you would like to draw a bead on pancake-batter consistency, but it’s important to not add an excessive amount of water, which can weaken the concrete. If the recommended amount of water isn’t enough, I add a superplasticizer rather than more water, to urge it right. If you scoop the combination with a trowel and hold it vertically, it should slide off the trowel, but leave a 1/8” layer on the trowel – this suggests it’ll be thin but still stick with the edges of the shape once you spray it.
I used a hopper gun to spray the face coat, spraying corners first, then sides, then the center of the shape . I started by spraying with the shape oriented vertically so it had been easier to coat the tiered foam knockout. We then placed the shape horizontally on the bottom so I could spray the remainder of the shape . you would like to spray during a U-pattern, towards the portion of the froth that’s already covered, to avoid sand particles aged the unsprayed surface.
After spraying, we brushed within the face coat with a chip brush, just to make certain there have been no trapped air bubbles.
Optional: wait until face coat firms up but remains damp to the touch , then spray second layer of face coat. If doing this, make each face coat layer no quite 1/8″ (so 1/4″ total).
Wait for the face coat to arrange before adding backer coat. you would like it to be firm but still wet, so you cannot erupt it easily together with your finger, but it still sticks to the rear coat.
B. Hand-Packed Back Coats
The timing of your backer coat is vital , so confirm your face coat has firmed up enough (but not completely dried out), before you begin your backer coat. Usually this only takes 30-60 minutes.
You can wait until the face coat is prepared to start mixing your back coat, goodbye as you’ve got everything measured call at buckets (so mixing only takes a couple of minutes). the method is analogous to mixing the face coat, except you add optical fiber to the GFRC bag mix (between 1.0-1.5 lbs per 50 lb bag of mix). Also, you would like to use less water and plasticizer, therefore the back coat is thicker and may be hand packed – it should be almost like playdoh or clay. (Again, see my previous instructables on GFRC for more details on the recipe and mixing process for the rear coat.)
I mixed one 50 lb bag at a time, and packed it in by hand, working it into the concrete that’s already within 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, build up slowly until the concrete was ¾” thick on the verticals.
Optional: After the primary layer was packed against the face coat, we added an alkali resistant (AR) glass mesh, which is formed out of an equivalent alkali resistant glass because the AR fibers within the mix. This mesh adds strength and also helps to stay slumping on the vertical surfaces to a minimum, making subsequent layers easier to pack in.
Step 3: Inner Base Support
The steel cross braces will be supported by 2×4 or 4×4 lumber. I used a miter saw to cut scrap pieces of 4×4 and 2×4 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
When we came back subsequent day, the concrete was rock hard. I started trying to wet grind with an angle grinder, but quickly realized the duster would blind us before we could finish, if I continued. So we took a few chisels and began chiseling…for over an hour. As we labored, we felt a touch like Michaelangelo’s assistants, doing the grunt work so he could come and shape certain important parts of the David.
Once most of the sting was chiseled off, I could then use the angle grinder to grind the sides perfectly level with the shape , for a clean crisp bottom table edge. Then we evacuated the shop my air cleaner did its work on the cloud .
Next it had been time to flip the shape and demold. this is often pretty simple. Just remove the drywall screws and pry the edges off.
Note that the froth stuck to the concrete a touch quite expected. i feel I should have put another layer or two of polycrylic thereon , and doubtless used some form release spray, since parts of the froth stuck to the concrete.
Step 5: Pre-Finish 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
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 quantity of the topographical cavity – it came bent be 3.1 gallons.
I started by mixing up one entire 1 and 1/3 gallon kit of thick set. This was far and away the most important amount of epoxy I ever mixed directly . I added blue transparent pigment to the epoxy, mixed thoroughly, then poured most of the epoxy back to a smaller bucket that slot in my vacuum pot.
Using the chamber will pull the bulk of the bubbles out of the epoxy, and reduce the probabilities of getting bubbles trapped in it. I’m told it isn’t necessary with thick set, but I wanted to try to to everything I could to urge clear epoxy for this project. After letting the air pump run a couple of minutes, its time for the primary pour.
After pouring and waiting a couple of 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 within the vacuum pot. the primary pour ended up being about 2.5” at its deepest point, and that 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 wont to protect the concrete from epoxy clothed to be unnecessary. a number of the epoxy still got on the concrete. However, i used to be pleasantly surprised to seek out 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 top of the epoxy, I got another surprise, but this one wasn’t so pleasant. I’m unsure exactly what happened, but since the melamine only stuck within the deepest section that gets the most well liked 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 warmth gun trick to melt the epoxy therefore the melamine might be removed. to form things harder , the chisel gouged the surface, which meant I had to travel back use some fast-setting epoxy to patch things up.
Step 7: Finish the Epoxy & Concrete
Step 8: Make the Wood 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: ENJOY!
