So, i just made two attempts to build an atlas stone. I bought a kid’s playground ball (15") and covered it in plaster of paris to make a mold. The first time, the plaster shattered when I was trying to path a smallish hole. The second time made it as far as pouring the portland concrete, and then blew a hole in the side of the stone. Much swearing, huge mess. Any ideas?
Thanks
Peter
PS Thanks to whoever suggested kiddlietoys.com! Awesome site. My big rope ships out tuesday!
I’m not sure how this would work because I’m not a costruction guy and I’ve never tried this but it seems to me that your problem is in the weight distribution. Simply, the weight INSIDE is way too heavy for the integrity(sp) of the mold.
So to even that out, maybe grab a large garbage can, and fill it four or five inches of sand, then set your plaster mold in the can on top of the sand. Now fill the sides (between the mold and the can) with another two inches or so of sand, then pour two inches of concrete INTO the mold. Repeat with the sand on the outside and conrete on the inside, alternating and inch or two of each in an attempt to keep equal strength on both sides of the mold wall.
I think the next problem you’re going to see there is the concrete is going to take a while to dry. Take the Hoover Dam as an example. If they poured that as one piece it still wouldn’t be dry today. So maybe pour and let it dry in stages? Not sure if that would create gaps and cracks between the layers.
Hope this helps. If not, hopefully my bad idea will spawn a good idea on your end(?).
oddly enough that is one of the better ways to do it once you have the mold. Plaster of Paris does work, you just need to cake it on THICK. again, these things are heavy. if you are making a bunch, like I am grab a slater stone mold. they rock and Steve Slater is a great guy. With those you can make a number of stones, and they come out really really nice.
Yeah, Slater molds might a good idea next time. Initially, I thought it would be cheaper to make my own. But, a boat load of concrete and plaster later, not to mention a lot of time and effort, the wisdom of DIY starts to pale. Anyway, I made the plaster mold, buried it in sand, filled it halfway, buried the rest of it, and s far so good. Now the concrete has to cure. The guy at Home depot said it’ll take abut a week to set up. THen, I guess it’s some more quality time spent with a hammer and chisel. THe really agravating thing is, I’m not actually sure I’ll be able to lift it when it’s done!
you could wrap a whole bunch of duct tape or fiberglass tape around the outside of your plaster mold to distribute the stress also. (just in case you don’t have a huge can and a bunch of sand)
So, after playing with the first stone for a while, It quickly became too light. So I thought I’d take advantage of all the mistakes I made with the first and build another one. I went to the store, and couldn’t find a larger kiddie’s play ball. So I stopped by Les Schwab and picked up a bunch of those lead weights that they use to balance tires out.
(They have to pay to recycle them, so they’re happy to give them away…) I made the plaster mold (Including wrapping it with tape, before I deflated the ball. I put the plaster cast in a big sink and filled up the sink with sand until it was halfway up the ball. After mixing some cement (Actually, quite a back workout as it turns out…) I filled the ball about half way with cement, then added the weights, then the rest of the concrete.
This made kind of a cool Death Star looking thing. I used cheaper concrete which didn’t really conform well to the mold, so there’s this flat spot on the top, and this fissure running around the circumference where the lead weights settled out.
It isn’t that much heavier (maybe 20 lbss) and I think it will eventually break in half where the fissure is. Plus, the weights occasonallion slip out. I might try to patch it up with more cement, or crack it in half, remove the weights and give my goats a new toy.
Sorry, I don’t really have a way to photograph. I’m also making a climbing wall… I’ll let you all know how that goes. Oh yeah, and I found a larger beach ball at the dollar store! I’ll make a larger stone soon!
Use plaster of paris BUT SOAK RAGS IN THE PLASTER and layer the ball in rags and plaster…this is the key! you have to use rags or bandages. 2-3 layers is what I have used in the past.
All the stones I’ve made were using slater molds and they’ve turned out beautifully. If you go the route of making your own mold usually you have to bury them otherwise the mold will collapse/deform. Slater’s definitely the way to go though since you can tape the mold instead of burying it and put it on a tire. This way you can vibrate the mold and get out all the air bubbles and water for a much smoother stone.