Outdoor Concrete Table

Lining the form wallNow you'll notice that the face of this is pretty rough. This texture will actually transfer onto the concrete if we were to cast concrete directly against it, which we don't want to do. So what we've done is actually taken a wall liner, this 2-inch strip of plastic material that has a nice satin finish on it, and we've laminated that to the curve and used that as our forming surface. The wall liner can either be applied with a transfer tape, or we also sometimes use the 77 spray adhesive. I'm going to set these off to the side.

Creating the umbrella openingBefore we get ready to cast, there are a few things that I want to point out: In the center you see here a knockout. This is just made from 1 ½-inch PVC pipe with a fender washer and a 2-inch drywall screw to hold it in place. What this is for is we're going to be using this tabletop outdoors and the client wants to put an umbrella into the tabletop, so this is the opening for the umbrella stand to go through.

Also, there are two seams in our wall liner. There's one right here, and then we've gone on the opposite side right across from it, where the wall liner material seams. It's important when you’re doing these seams, since they are going to be visible in the finished concrete, that you make them straight and very tight. We don't want any jagged, rough lines. We want a nice clean line there.

After we've sprayed the casting blend into the mold base and then sprayed up the sidewalls, we're going to be using a blend, a combination of both the casting blend and the backing blend. We're going to be mixing those together in a 50/50 proportion to give us a nice thick-consistency mix that's a little thicker than the casting blend on its own, but a little thinner than the backing blend on its own. And what that allows us to do is come on top of the casting blend that we've sprayed with a ½-inch layer of this combination blend and pour it into the form, quickly building up to our 3/4 inch thickness that we want the D-FRC to be on the base.

After that, we're going to go ahead and build a 2-inch-high rim all the way around the exterior, or the perimeter here. And we're going to make it about 3/4 inch thick. We'll also do the same around this knockout. And when we're done, what you'll see is the nominal thickness of this tabletop is going to be 3/4 inch, and at the edge there’s going to be a ¾-inch rim all the way around the perimeter.

Now when I get to the edges for my vertical walls, I'm going to press this material in not quite as thick as I want it to be for my finished casting because I don't want to add so much material on here that it sags or draws the face edge down. So I'm going to be placing maybe about 3/8 inch up here, which is thin enough where it won't weigh down the casting blend that I sprayed on the face.

I'm going to leave that probably for about 10 to 15 minutes, roughly the amount of time it takes me to go all the way around this form. By the time we're done with that project, we're going to have about 100 pounds of material in here -- 50 pounds of the casting blend and 50 pounds of the backing blend. I'm going to go ahead and finish up, and we'll be done with the casting part of this project.

We're ready to take this out of the mold now. I've ground down all the way around the perimeter of this tabletop. I want to point out, though, that I just took the concrete down to where this white line is, which is the wall liner, to where that white line has been exposed uniformly all around the perimeter. That's how I knew I had ground down deep enough. I was very careful not to grind beneath or to keep going deeper. Once I exposed that white line, I stopped grinding in that area.

At this point, we're just going to go ahead and find where the seam was, in one of these curved edge forms. Looks like one is here. I'm just going to peel this back. The curved edge forms I'm using are reusable, so I'm going to try to be careful to not shred these as I demold. Now that I've removed the curved wall sections, I'm going to remove the liners, and just kind of expose my edge here. The wall liners can also be reused. Looks pretty good. Well, we just popped these out of the mold. The piece looks great. We've got a little bit of lighter zones, some darker coloration, but all in all a really nice composition.

Just to recap here a bit, we are going to be placing this 48-inch tabletop on our spindle table base, and we've got roughly 100 pounds of material in this tabletop -- 50 pounds of the D-FRC casting blend and 50 pounds of the D-FRC backing blend, with the Green Tea SmartColor added in.

Mold designSo this is the mold that we’re going to use. I want to talk a little bit about this first, though, because what you see here is a very complex shape, and something that would be very, very difficult to build in your shop. So what we’ve done here is we’ve actually rendered this shape in a CAD file and sent it off to a foam fabricator who has a CNC machine. And what they’ve done is they’ve used the CNC machine to cut or to rout out this shape, and then coated the surface with an epoxy resin to give us a nice, smooth casting surface. For this project we need two of these molds. We’re going to spray into this mold - spray into a mirrored copy of it. And then, while the concrete is still wet, we’re going to stitch this, or seam these two together.

Table dimensionsA little bit about the shape here, though, and the design of this. What you’ve got is a table base that’s going to be 27 inches tall. The total diameter here is about 34 inches. And on top of it, a 48-inch tabletop is going to set. Our total height of this table, when we’re done, is going to be about 28 inches, which is the same as your typical kitchen table.

What I’ve got in here is the casting blend, mixed a little on the wet side, and I’ve tinted it with the D-FRC Smart Color green tea pigment, to match the tabletop. Let me go ahead and spray this into the mold about 1/8 inch thick on this first pass. Our second passes we’ll beef it up to maybe 1/4 inch at a time.

Applying the base coat

While I was spraying, you might have noticed that quite a bit of this material was running on these vertical walls, trying to slide down. That’s because the mix that I had mixed up was a little on the wet side, and I was spraying too heavy of a coat onto these vertical surfaces too quickly. So the timing issue comes into effect here where, if your material’s a little thinner or runnier, you’re going to want to spray it up in thinner applications than I did here. But at this point, we really can let this stand for 5 to 10 minutes, let it firm up and get a nice set to it, and then I can come back over it and spray on additional layers.

For this project, we want to have as few air bubbles as possible. So in order to insure that we minimize the amount of air bubbles on the surface, I’m going to use just a simple, disposable chip brush and lightly brush the surface to work out any air bubbles that might be trapped between our cement, or the D-FRC, and the surface of our form. I’m doing this very, very lightly, not a very firm pressure at all. You can see how if I use a lot of pressure it’ll force or agitate the material hanging on these vertical surfaces enough that it’ll actually start them to sag and run. You can see that, there. So if that happens, just step away and give it some time to set up a little bit. But on these horizontal surfaces back here, I can do some brushing while I wait for these vertical areas to up.

Applying additional coats

So this is the second half of the mold that we’re going to be seaming together. I’ve already applied my first coat of material, and now I’m going to come back and do the second coat. Typically, we would do this an additional three or four times until we had built up a thickness on this form 1/2 inch or more. At that point, then, we’d be ready to seam the pieces.

Okay. At this point, I’ve got three coats of the casting blend sprayed onto my form. But I want to check on this rim to see how thick of a build-up I have. On this top I want to make sure that I’m at least a ½ inch thick before I complete the spray application of the casting blend here. But a good way to check is to go ahead and cut this material off. And you can see, it looks like I’m about 3/8 inch thick here.

So that tells me I’m going to want to have a couple more coats sprayed on here. This material’s still pretty wet, so we’re going to let this set for about 10 minutes and then come back to it.

We’ve now assembled the two mold halves. So, if you take a look here, you can see that we’ve sprayed into the interior of each mold to about 1/2 inch thickness of the casting blend. And up along the top, we’ve built up a 1/2 to 3/4 inch rim, and have kind of flattened it off so it’s flush with the top of our form. I’ve taken the two halves and braced them together just using some luan strips and a couple screws. This is to hold the two mold sections tight. On the underside of this mold, we’ve done the same thing as well.

Reinforcing the seamsI have a few pieces here of glass fiber scrim. This is a 10 mil by 10 mil opening, and I’ve cut a few strips here to use as stitches. Essentially, this will add some additional reinforcing at my seams to make sure that the pieces hold together after they’ve been demolded. But before I place this fiberglass scrim, I’m going to go ahead and lay a little bit of my casting blend material into the mold, and then place the scrim over that casting blend, and then put another layer of casting blend over the scrim. So here’s how we do that.

Placing the casting blendMaterial’s nice and pliable. Lay this up, just kind of smoothing it out with my hands. This material is still a little on the wet side, so I’m going to wait a little longer to build up and flatten off this top edge. But I am going to go ahead and continue seaming this form, and then I’m going to move over to the opposite side and do the same.

So we’ve completed casting this piece, and we’re going to leave it cure overnight, for about 12 to 18 hours, before we demold this. And once we’ve demolded it, this will make a great base. Total material in this base is roughly 120 pounds of casting blend. And we’ll be installing this with a 48-inch table top on it.