DIY Concrete Dumbbells

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In this Video I show you how I made concrete dumbbells for the less than $30 per set.

Calculator for tubes other than 8″ – http://ustesg.com/calculate.html Credit: Ustes Greenridge

Tools

For this project you will need:

• A razor knife
• Hacksaw (for cutting the metal handles if using conduit)
• A marker or pencil
• A rubber band
• A Tape Measure
• A mixing bucket
• Duct Tape or AC foil tape (if re-using forms)
• OPTIONAL:
• Drill and mixing bit
• Cooking Spray (if re-using forms)
• A concrete trowel or similar forming tool

Materials and cost

• High-strength Concrete Mix (or crack resistant if you can find it) 80lb bag ~ around $5 Dollars
• 8″ Concrete form tube – sold in 48″ lengths ~ about $10 Dollars
• 1″ metal conduit – sold in 10ft lengths (or iron pipe if you don’t have the means to cut it) ~ $11 dollars
• Duct Tape ~ $5 Dollars
• Total Cost with materials to spare: Less than $30 Dollars
• An 80lb bag of concrete will yield one set of 40lb dumbbells (makes sense right?). You will have left over form tube and conduit so the best value here is to make more than one set. The Crack-resistant concrete is the best because it has tiny fiberglass fibers in it that make it stronger. You definitely don’t want to use any fast-setting concrete or motor mix. I made sets 40’s, 45’s, 55’s, and 65’s and used 5 80 lb bags.
• You could also use the same concept to make barbell weights if you want.

A quick note on the 8″ Form tubes, not all tubes are created equal. These two came off the same shelf, same store, same day, even same bar-code. One of these is just under 8″ in diameter and the other over 8 and 1/2. They are still labeled exactly the same so you’ll want to measure these in the store if you plan on buying more than one. They are designed for large scale construction where 1/2 inch variance is negligible but for what I’m doing, 1/2 inch would throw off my calculations and change the weight of the dumbbells. They are sold in 4 ft lengths so you will have enough to make more than one set of dumbbells.

If you want to re-use the form tubes, I know that can be done at least once with good success. It will cost you a razor blade or two and you will need that optional cooking spray and tape I mentioned earlier but it does work. Since these are optional and I didn’t include them in the cost.

If you plan to leave these outside you’ll want to remove the cardboard form anyway. The first time they get wet they will fall apart.

The Conduit also comes in 10 ft lengths and since I’m using a 12-16″ piece for each dumbbell I will have enough material to make more than one set.

You can also use iron pipe if you don’t have a way to cut the EMT but this will cost a bit more.

Concrete weighs about .087 lbs per square inch so to figure out how large each dumbbell needed to be I have to do some quack-ulating. If you’re not using the same 8″ form tubes that I am, you’ll want to solve for the volume of a cylinder and then multiply that by .087 to determine the weight of each side of the dumbbell (remember you’re splitting the weight in half for each end). You can also just click this link to download a PDF chart I made. It’s free! I also wanted the dumbbells to be about the same length overall. That was possible until I went above 55lbs. I still wanted about 5 inches of handle to grab onto so I wound up making the heavier dumbells a little larger.

I was actually surprised by how accurate the turned out to be. I figure within a pound or two is close enough for me.

If you’re one of those people who has to have matching plates and the gym because you think it makes a difference then concrete dumbbells probably aren’t for you. Also, don’t weigh the dumbbells you bought at the sporting goods store, or your gym for that matter. Unless they’re calibrated competition quality, you will be very disappointing in their consistency.

Since my forms were just shy of 8 inches I made my cuts about an 1/8th of an inch larger. I made multiple marks around the tube so I could use a rubber band to mark the tube and try get the most accurate cut possible. The best way to do this is actually with a chopsaw but I wanted to show this could be done with minimal tools.

I used the hack saw to start the cut and then transitions to a razor knife. The hacksaw wanted to bind in the cardboard and seemed counter-productive. I used sort of a sawing technique with the razor knife and inched it along rather than trying to force the blade through. Again, the cardboard wanted to pinch and made cutting more difficult. The end result should be a fairly straight cut that won’t leak if you place the cut side down.

Taking the overall length into consideration, I figured I needed about a 14-16″ piece of conduit for the handle. I want the handled to be submerged in the concrete but not to poke out the end. I also want to keep that 5 inch minimum handle size too.

For the 40’s and 45’s I used about a 14 inch piece and for the 55’s and 65’s I measured about a 16 inch piece. With that cut I’m ready to set the form tube up and mix concrete.

Start mixing the concrete is small batches. I know a 65 lb dumbbell will be a little less than half a bag (37.5 lbs per side). It’s important to work the concrete into the form and sift it down in small batches. I’m trying to get as much air out as possible to reduce any kind of flaking or scaling against the form. A slightly wetter mixture will help with this but too wet and you will weaken the concrete.

Once I have the form mostly filled I’ll add the handle and position it as close to center and I can. I’ll then fill the handle with concrete to help add strength. Work the concrete flat on top and remove any excess. As the water starts to come to the surface and the concrete begins to set up, I reposition the handle and check to make sure I haven’t set it too deep. I want enough room for a 5 inch handle and to set at least half way into the other side of the dumbbell. Once I’m satisfied with the placement I’ll add my alignment board to center the handle.

I cut a board in an 8 inch square and drilled a hole in the middle to help me align the handle. you can use a level if you want it to be perfect but there’s nothing wrong with eye-balling it either.

Let this cure for at least 12 hrs and leave the form tube on. I had to do some re-taping from the moisture in the concrete. Set up the other side of the form and have your spacer ready.

I cut the spacer before hand and taped it back together just so it was easier to get off. Repeat the steps from the first side and use the space to hold the top half dumbbell in place. This set is 65 lbs (so a little over 30lbs per side) and its probably the max for the cardboard spacer.

This was the second time I used these tubes and they actually got rained on so it ruined the form tubes.

After a few hours you can remove the forms but you’ll want to let these fully cure before you start throwing them around.

You’ll also want to sand these down a bit to at least knock the burrs and loose chunks of concrete off. You don’t want pieces falling in your face when you lift them over your head.

You can take this a step further and even paint them with some oil-based or concrete paint. That would help them hold up to the elements especially if you plan on leaving these outdoors.