Hi,
I’m thinking of using concrete to make a one gallon size kettlebell. I’ve read that concrete weighs approximately 20 or 25 lbs, depending on whether one uses an American or British gallon. My question is, how much weight will it loose after it sets?
Thanks,
… john
Not much. . . interior water will “weep” towards the surface, and the water near surfaces will evaporate, but it’s a negligible percentage compared to the fine and coarse aggregates, and cement. It also depends on admixtures introduced.
Tripler
Ballpark estimates depend on the league of accuracy requested. 
There are several videos on Youtube about making concrete weights, including kettlebells. This is the first one I watched that seemed like a good one - 5 Awesome To Make Homemade DUMBBELLS Kettlebells And Barbells Gym At Home - YouTube
The water you’re adding is for the most part a reactant that is consumed in the reaction that results in a solid product. I always thought of it as “drying” but that’s incorrect. You’re forming new minerals that incorporate water molecules as hydrates.
This doesn’t answer the OP. But it made think of this guy who had an unfortunate incident when he failed to calculate the weight & density of cement.
Also, it will likely slowly absorb CO2 over time as it continues to cure. I don’t expect this to be a large weight percent but I don’t actually know the numbers off the top of my head.
Thank you. This is a far better characterization than my simplisting “weeping” and “evaporating.” [sub]I’m a crappy Civil Engineer, and pretty rusty on my concrete.[/sub]
Tripler
Electrical Engineer
I’d be surprised if the weight change was anything significant. As a test, make a small batch and weigh it wet and dry and see how they compare. Keep in mind that mixing cement does not always use exact measurements anyway. Each batch of cement will have varying amounts of aggregate and you may add more or less water depending on the consistency. Use a scale to ensure the weight of the cement is what you want rather than using any sort of volume measurement.
Holly Crap!!!
… john
Hi all,
Yes, it seems like the consensus is not much change. So it probably depends on how much water, over and above what reacts with the ingredients, I use. It’s probably not too critical as long as it doesn’t turn out like a sloppy Joe.
Yes, that’s the best video I’ve seen too. I was thinking of doing it that way, since it seems so simple; but I’m looking for something in the +20lb range, and I read where the ball thing won’t give me that. However, I will use the handle idea. Thanks.
Thank you all, and stay safe.
… john
Do you have a scale so that you can ensure a consistent weight? Just filling a container or ball won’t be very exact. If you’re trying to make 2 kettlebells of the same weight, make sure you weigh them while filling rather than just filling a container to a certain line. It’s more important that the 2 matching weights weigh the same rather than they are exactly 20#.
Hi filmore,
No, I’m just trying to make one kettlebell, between 20 and 25 lbs.
… john