I decided to try my hand at building a cast concrete planter as research for a potential magazine story on the subject. The folks at Dremel recently sent us a new tool to try out called the Ultra-Saw. It’s a multipurpose saw that cuts with abrasive cutting wheels instead of blades. It struck me as a versatile tool, and I decided to give it a try on my planter project. There are other accessories available, but the saw came with a wood-cutting wheel, a metal-cutting wheel, a wood flush-cutting wheel, and a grinding wheel for grinding down thin-set or removing paint from concrete.
The construction of the planter cast is pretty straightforward. It’s basically a box with a smaller box on the inside. I used scrap 3/4-in. plywood for the outside box and scrap 3/4-in. melamine for the inside box. The base of the form was larger so the outside box could be braced up at the bottom.
The Ultra-Saw cut the wood without any problems. I chose to install panels on all four sides made out of 3/4-in. pine boards with a 45-degree angle on them. This would result in a recessed area once the forms were removed. I had to use my circular saw for those cuts, and that’s when I realized how well the Ultra-Saw cut. The sight lines were much better. It created less sawdust, and it didn’t chew up the edges of the wood nearly as bad as my circ saw. It also weighed half as much, which was nice because that circ saw seems to get heavier every year.
I made the inner form so it was 1-1/2 in. smaller than the outer form. It seems a little thick but the recessed areas end up only 3/4 in. thick. I screwed the boxes together so they could be removed easily once the concrete set. That meant using inside corner braces for the inner form. I cut a hole in the center of the base and installed a wood dowel that stuck up 1-1/2 in., the same thickness as the concrete at the bottom of the planter—this would be the drain hole.
Before mixing the concrete, I cut two chunks of 3/8-in. rebar to reinforce the bottom. It probably wasn’t necessary, but it made me feel better. Once again, I got to try out the Ultra-Saw. I installed the metal-cutting wheel and it ripped through the rebar like nobody’s business. I sprayed the outer form with vegetable oil and wrapped the inner form in a plastic bag.
I used a sand/topping mix concrete because it has no large aggregate, which could create voids. I filled the bottom with concrete to the top of the dowel and then set the inner form box in place and filled it with sand to keep it from floating to the top. I pushed a stick into the concrete and repeatedly whacked the outside of the form with a hammer to eliminate voids in the concrete. I waited a full day before removing the forms.
There were a couple of voids here and there, but not too bad. The corners of the planter were a little rough and jagged, and there were other areas that needed smoothing, so once again I got to use the Ultra-Saw. I installed the grinding wheel and smoothed the corners and knocked down the rough edges. It worked great.
The whole project took me almost a full day, but of course it would have gone much faster if I'd had the forms already built. I’m going to try to stain the planter, but I’m not sure if the motor oil on the forms will make that possible. Maybe I’ll premix color into the next batch. Things didn’t go exactly as planned, but I think I learned enough to pitch the idea to my Senior Editors. Look for the full story next spring.
The Dremel Ultra-Saw is available at Home Depot for $129. The saw worked especially well for this project. The only wheel I didn’t try out was the flush-cutting wheel, but I just happen to have a flooring project coming up that’s going to require trimming the bottoms off a couple doorjambs. Nice!
— Mark Petersen, Contributing Editor