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Quadra Fire Cube Design

Time: 02:36

A video transcript featuring Mike Heidebrink, Cheng Concrete

These are outdoor living projects made with CHENG D-FRC. I'd like to introduce you to the Quadra fire cube, by CHENG Concrete.

I designed this so that homeowners like yourself can have really good design that is accessible and, very easy to move around in your yard. And the style is adaptable to any environment. This unit is just made of two forms, cast from one mold with simple volcanic rock put in the center and a store-bought or a restaurant supply house wok simply placed in the center.

These simple components kind of amass together, comprise a look that looks much more permanent than it really is. If you wanted to disassemble this, it would be very easy because each one of these units only weighs 150 pounds because it's made out of our Cheng D-FRC lightweight concrete.

I designed this Quadra fire cube actually thinking about ventilation and things like that. And that's why there's this opening, sort of this gap. But the gap also helps show that kind of primitive fire volcanic rock; I wanted you to see more of it. And by exposing the sides, we let air pass through, and we have holes in the wok, so that you get air circulation and that way the fire would burn more evenly.

Design optionsThe Quadra fire cube is available in drawings that we have made really easily available to local artisans to use our D-FRC lightweight concrete to make this for you in your local area. And there's a lot of versatility there. For instance, you can change the color because we have an array of colors available in D-FRC.You can change the aggregate by using some sort of volcanic rock or some rock that's air-entrained like it is, that can absorb fire. Then you can also change the type of feel. It could be adapted to use with propane or wood, as we have it set up here.

Quadra Fire Cube Forming

Time: 08:41

A video transcript featuring Mike Heidebrink, Cheng Concrete

Let's start off by talking about the knockout that I've got here. What this is, basically, is a curved radius that is going to form the interior shape of our fire cube. The way that we built this is basically using a 3/4 inch sheet of plywood that we've gone ahead and cut to create the shape of this knockout. You can see here a couple layers that are laminated to this radius. What these are made up of are a couple items that I want to talk to you about. One is this flexible material called wiggle board. It's basically a plywood that is designed to allow us to create a curve, and we place this right over that radius. It's screwed into that position and that creates a shape to the form that we've already cut into this 3/4 inch plywood.

Making the knockoutNext, since I don't want to cast against something this rough, I want to line the surface with a material that I can cast my concrete against. And in this case we're going to use this satin-finish laminate that we then laminate to the surface. That creates a nice, waterproof casting surface that we can pour concrete against or cast our material against. When we're all done, we end up with a knockout that looks like this. To show you the backside of this, I want to point out that we've placed some ribs basically that separate the lower ¾-inch sheet of plywood from the upper ¾-inch sheet. This gives us our depth. If I was making a 24-inch-deep cylinder, these ribs that are back in here would be much longer than they are here. For this project, this entire box is only 15 inches high.

Attaching the knockout to the baseI'm going to move this out of the way for a second, and I want to talk a little bit about the base. The base that we've got here is actually a sheet of melamine. Working with melamine makes the project go a lot easier because we don't have to worry about sealing the surface of the wood. In this case it's already got a plastic coating to it. I've traced out where we're going to place our knockout. To mount the knockout, we're basically going to slide it into position, line it up, just like so, and screw this knockout to the base using a screw gun. This is step two in making our fire cube form.

Forming the wallsEarlier we made this knockout, and we've attached the knockout to our mold base. The next thing we're going to move on to are the walls. We want to form up the exterior shape of the fire cube, and for that we've gone ahead and precut our wall sections. This is, once again, ¾-inch melamine that we've cut on our table saw. A circle saw would do the same job. You'll notice that there are a lot of holes already in here. That's because we've already used this mold two times. This is going to be the third time that we've cast into this same mold.

To place our back wall here, I'm just going to position this so that the edge of my wall is in line with the base of my form. I'm going to just screw this in to hold this into position because I'm now going to move on to place my sidewall, which is going to go like this. I'm going to position this so you can see a little better. This kind of gives the general shape. I'm going to go ahead at this point and repeat the sidewall assembly over here on this corner.

Sealing the moldI've got my sidewalls up and I'm ready to seal the mold to make it watertight. In order to do this I'm going to use 100% silicone. This is a material that we can get a local home improvement center. In this case I'm going to use a black silicone to seal up my mold. The reason I'm using black, is that I'm using a white laminate material here, and I'll be able to see where I have excess to clean up.

We're going to start off by placing a bead of silicone at all of our horizontal and vertical seams. When we're sealing the seams we also use the silicone to shape our edges so that in the finished piece of concrete I don't have to do any sanding or shaping of the edge. I want the silicone to be shaped so nicely that that will create the finished edge on my finished piece of concrete. There's a silicone shaping tool that's basically an acrylic rod that's been beveled and polished on the face. These are available at CHENG Concrete.

I've got three different sizes here. I'm going to use a 3/8-inch rod that I'm going to use to shape the curve or the radius in the form. I'm going to start down here in the corner and I'm pulling the silicone with the shaping rod. I can either wait until the silicone is dried, but we'll go ahead and clean it up while it's wet using a razor blade.

After I've sealed the entire mold then we'll be ready to cast into it. I do need to let the silicone dry for about 24 hours, or overnight at least, before we move on to the next step, which is casting. There are a couple things I want to point out about this mold that make it different than if we were wet casting. When you're working with the CHENG D-FRC, we don't need a lot of excessive bracing on the sides of the mold to contain the concrete. Since all we're going to be doing is spraying the concrete into the mold, we just need to make sure that the walls are straight and vertical so the material can hang onto the sides when we go ahead and place our concrete.

When you're working with CHENG D-FRC one of the things that you want to remember is that we've really reduced the amount of time that we put into building a mold, as well as reduced the amount of material that we're actually using when we're building the mold. This keeps our labor costs and material costs low. The one main benefit, though, of working with a material like this is we can reuse a mold. We're not abusing the mold with heavy vibration or with a lot of reinforcing. We can reuse a mold like this up to 10 times.

You can find detailed plans and instructions for this fire cube online.

Quadra Fire Cube Casting

Time: 06:23

A video transcript featuring Mike Heidebrink, Cheng Concrete

We're all ready to cast the fire cube. Before we do, I want to talk about how we're going to be casting this. I've mixed up 25 pounds of the light casting blend and 25 pounds of the dark casting blend to create a cool gray color, nothing too dark or too light. And we're going to be spraying that into this form to about 1/8 inch thick on all the surfaces. After I'm done spraying the casting blend into this form, then we're going to go ahead and take what's remaining in this bucket, which will probably be about 30 to 40 pounds of material, and I'm going to mix that with another 50 pounds of the backing blend to create a thicker-consistency material to lay up onto the walls and into the base.

Applying the backing materialI've sprayed the casting blend into the form. Everything is covered by about 1/8 to ¼ inch, and roughly 15 to 20 minutes has gone by since I've sprayed it. In the meantime, I went over to my mixer and took the remaining casting blend that was in my bucket and added 50 pounds of backing blend, which is the thick fiber material, along with 1 gallon of the activator. And I've got a mix that has a pretty good consistency. You can see it's got a lot of fiber in it, it's pliable, but yet it's not super-stiff. This is the mix that I'm now going to put in the mold to build up the walls. These walls are still a little soft, so I'm going to be covering the vertical surfaces with a pretty thin layer initially, maybe about a quarter of an inch, wait 20 minutes between layups, coming back 20 minutes later with another quarter inch layup until I build up my walls to 3/4 inch thick.

I start with a handful, press it into the corner, making sure that I get it pressed pretty firmly into these edges. I don't want any voids or air to be trapped between this layer of my backing blend and the casting blend that I've already sprayed into the mold. I'm going to come up the vertical walls, no more than a quarter of an inch on this first pass. And see how the material wants to kind of sag down the wall? If I put it up any thicker than that, I'd surely have it peel or slump down into the bottom of the form. The rate at which I build this wall up, on a high vertical like this (this is a 15-inch-high wall), the timing of this is really important, because if I build too much material up too quickly, I could get all the way up to the top, turn my head for a minute, and turn around and this whole wall might have slumped down. So you don't want to get too far ahead of yourself. You'll also notice that as I'm up here at the top, I'm applying no more than 1/8 inch of material, so it's actually thinner up here at the top than what I was placing at the bottom. I'll thicken this up on later passes.

How to prevent saggingIf, as you're building up the wall, you get any area that starts to sag, pressing it back into place should work. But if it continues to sag, just try to thin it out, and then let it go, just let it set. Don't keep trying to pat it and hold it up because the more I agitate the surface, or this backing material, the looser it becomes. So it's only with a little bit of time passing that it's going to stiffen up to where it'll stand in place. Usually that's giving it about 10 to 15 minutes to get a little firmer.

Just to recap, the casting blend that we sprayed into the mold is going to be the surface that you see on the finished piece of concrete. This combination of casting blend and backing blend that I mixed up, this is where the structure is. There's a lot of fiber in here. That gives us a lot of the structure that we need for these vertical wall surfaces, as well as on the horizontals. This entire box here, or this fire cube mold, is going to take about 150 pounds of material. I've got 50 pounds of casting blend already in it, and another 50 pounds of the backing blend. The next batch that I mix will be 50 pounds of backing blend as well. So when all is done, we'll have about 150 pounds of material in this mold. I'm going to go ahead and finish this up, and that will wrap up the casting portion of this fire cube.

You can find detailed plans and instructions for this fire cube online.

Quadra Fire Cube Demolding

Time: 02:42

A video transcript featuring Mike Heidebrink, Cheng Concrete

We're ready to demold the fire cube now. But before we do, I've gone ahead and actually ground down any excess material that was left to be flush with the top of the form. So I've gone all the way around the mold here and the concrete is now flush with the top of the form. We're ready to start unscrewing our wall panels and peeling them off.

For demolding this knockout that we have in here, it's kind of tight and a little tricky to get it removed. I've already removed the screws that were attaching the knockout to the base, and now I've just put a couple sections of foam up against my concrete that I just demolded, and I've braced a 2x4 in front of that. And just by using these C-clamps, or bar clamps, I'm going to tighten this and pull that out of the concrete. Here we go. So now the whole piece is free.

You can find detailed plans and instructions for this fire cube online.

Quadra Fire Cube Polishing

Time: 04:49

A video transcript featuring Mike Heidebrink, Cheng Concrete

Well, we've demolded this; it's completely out of the form. We don't want this kind of matte finish. We want to polish this up to a high gloss. And what I'm going to be using here is Alpha's Universal Polishing System. It starts at a 60 grit and goes all the way up to 3000 grit. Since this fire cube here has only been in the mold 12 hours, the concrete is still probably a little soft, and I'm not going to need a very aggressive pad to polish down into this. So I'm going to start off with a 500 grit and then go up to the 1000 grit, and follow it with the 2000, and finish off with the 3000, to put a really nice, bright polish on the surface.

For the polishing, I'm going to be using my new favorite tool, Alpha's WDP-120 wet or dry polishing system. I'm going to be using it dry, and I've got it hooked into Alpha's HEPA vacuum, which does a great job of capturing dust that's being generated by this. So now I've switched out the 500 pad and I've put on the 1000-grit pad. So we're going to pick up where we left off there.

So, I just took the 1000-grit pad off, and I've now put the 2000 on, and you can see a lot of shine starting to come up to the surface. But over the next two pads, the 2000 and the 3000, you'll see this really get finished off to a bright shine. So, I've put the final pad, the 3000-grit pad, on my polisher, and I'm done with the 2000, so we're ready to finish this up. I'm finished polishing the top and I'm now going to go ahead and polish the sidewalls, the front, along with these little end pieces down here. I'm not going to polish the interior of the circle. I'm going to leave that as is, since we're not going to see that in the installation. Now remember, this is one half of the fire cube. There's going to be the same exact piece cast and fit behind it with a 10-inch gap between the two pieces. The gap is going to be filled with some mesh. This is a decorative 2-inch mesh that we're going to actually weld a 1/4-inch steel key stock to the top so that these pointy edges aren't sticking up where somebody could scrape themselves. And the entire bowl is going to be filled with some lava rock, which acts as a great heat barrier between the fire pit itself and the walls of our concrete.

For the actual fire bowl, we're going to be using a wok that we picked up at a local restaurant supply. The only modification I'm going to make to this is I'm going to drill some 1/2-inch holes in the bottom, to help facilitate airflow up through the lava rock and into the bottom of the bowl for my fire. Now this is a natural burning fire pit option. If, let's say, you wanted to do a gas burner, there are plenty of different models of gas burners out there that could be used in this fire pit, or there are even the alcohol or oil burners that could be used. But for this project, we wanted to have a natural burning fire pit, and that's what we're going to go ahead and install.

You can find detailed plans and instructions for this fire cube online.

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Quadra Fire Cube Design