How to build this DIT concrete and wood bench out of some two by fours and a 60 pound bag of concrete. I’ve been wanting to build a bench for my backyard, and I wanted to see what I could put together using minimal materials.
How To build This DIT Concrete And Wood Bench:
I came up with this design that I put together in SketchUp. It’s made up of a couple basic concrete legs and a top made of redwood two by fours.
I piked up everything I needed to build this bench from Home Depot, and all in, the materials for this project cost me just over $100. If you’d like to follow along with this project step-by-step and make your own version of this bench.
To get started with this project, I wanted to start with the concrete legs. I created the basic design and shape for the legs in SketchUp, and then I could build a form for the legs out out melamine.
Building the form was basically the same process I used when I built my concrete sink form a few years back. Now, if you haven’t seen that project, I’ll leave a link down to that down below, as well.
To build the form, I just ripped the melamine down to 2-1/2 inch strips and created the basic shape by cutting the 10 degree angled pieces and screwed it all together with drywall screws to match the dimensions of my SketchUp rendering.
I built two identical forms because I wasn’t sure I’d be able to reuse the form once I poured the concrete in it, and it would allow me to pour both legs at the same time. Once the forms were built, use some silicone to seal all the seams and also spread it on the exposed edges of the melamine and the screw holes.
If you don’t seal the exposed ends of the melamine, the water from the concrete will soak into the end of the forms, and it’ll cause it to swell, which will compromise the form.
Once the silicone’s set up, I cleaned the forms with some denatured alcohol and sprayed them with this Crete-Lease spray, which I had leftover from my sink project.
You probably don’t need to use this spray, but I had it around, and it helps release the concrete from the form. Before pouring the concrete, you need to build thr rebar skeleton that will serve as the structural support for the concrete.
I used some number three 3/8 inch rebar to build a basic shape to match the form and wired it altogether like the diagram in my SketchUp plan. Once that was done, it was time to pour the concrete.
The concrete a simple, cheap bag of concrete mix from Home Depot is totally fine. This is a 60 pound bag of Quikrete concrete mix. There’s nothing fancy about it.
I like the industrial look of it. You can use GFRC, which is glass fiber reinforced concrete, and it’s used a lot for countertops if you want to.
Then add a bit of concrete to the bottom of the forms, and insert the rebar skeleton and then filled the forms to the top with the remaining concrete.
These legs are perfectly sized to use a single bag of concrete for the two of them. Once poured, the key to getting a nice smooth surface for your concrete is to get the trapped air bubbles out of the concrete, so you have to vibrate it well.
I chose to take the blade out of my Sawzall and just shake the hell out of it to release all of the bubbles, which seemed to work really well. Then, I could just let the concrete cure for 24 hours.
While that set up, I moved on to building the seat of the bench. The bench seat is just made of redwood two by fours. I like the idea of alternating spaces between the two by fours, so I cut some 3-1/2 inch long blocks to go in the spaces between every full length run.
This bench is six feet long, so I added the blocks on the ends and in the center. I glued the two by fours together with some exterior rated wood glue and shot them together with two inch brad nails before clamping it together to dry.
I glued it up in two big pieces because I plan to feed it through my planer to take the rounded edges off the two by fours and give it a more modern polished look and I couldn’t fit the full thing through my planer in one pass.
You could also rip the rounded edges off of the two by fours on a table saw before gluing it up if you wanted to rather than feeding it through the planer or if you don’t have one.
Once it was put together, I sanded it down to 22 grit and added the first of several coats of tongue oil finish to it.
Then the next day, pop the forms on the concrete legs. The form side of the concrete was super smooth and came out really nice. I gave it a quick sand to expose any additional bug holes, but there weren’t many.
The other side required a bit more work. Since both sides of the legs are visible, I spent a bit more time on that side, sanding it down and then applying a slurry coat, which is just plain Portland cement and water to try and smooth it out.
Even after sanding, it’s not as nice as the form side, but I still think it looks cool. I’m not sure how you’d be able to get two perfectly smooth sides unless maybe you built a two-sided form and poured it in from the top, but even then, it might be tricky and more work than it’s worth.
But I’m really happy with the way that these legs came out as is. To finish up the legs, I added a couple coats of wet-look concrete sealer, which darkened them up and gave them a really nice finish.
Then, I finally had to figure out a way to mount the top to the base. Now, I had a couple ideas here, but I decided to go with concrete anchors, so I added a few bounding blocks to the underside of the seat and then drilled out the holes for the anchors.
I mocked the top up onto the legs and drilled out the matching holes on the legs with a masonry bit, added the concrete anchors and then tightened them down.
Ideally, I’d let the concrete cure for a couple weeks before tapping into it, but since I’m on a time crunch for this build, I went ahead with it anyway, and it worked out just fine.
Finally, I added a few more coats of tongue oil to the seat, and that was it, finished product.
To be honest, I wasn’t sure how stable this design would be, and I thought I’d have to add a stretcher between the legs to keep it from racking back and forth, but once I cranked down on the bolts and I gave this thing the old hip wiggle test, it’s actually super solid. And now all I need is someone to paint me like one of their French girls.
So that’s it for this project. I hope you guys enjoyed it, and I hope it inspires you to tackle your own outdoor furniture project.