Replies

1. 
   Mike_Maines_ | Jun 29, 2001 01:36am | #1

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   In college I was on a team that built and raced concrete canoes. We made forms that were cross-sections of the canoe on 12" center, then ran thin pine strips along the cross-sections (like an inside-out cedar strip canoe). We bondoed the form, sanded it down, oiled it with form oil (or maybe kerosene), and layered on the concrete. Actually it was more like morter, as the aggregate was very small. We added perlite to reduce weight, air-entraining admixture, and some other stuff I forget now.

   We would smother on a layer of this mix maybe 1/8" thick, then embed a mesh, something like fiberglass window screen. Maybe it was fiberglass window screen. Then another layer of concrete, and another layer of mesh, etc., for about 5 layers altogether. After stripping the forms, we'd have a canoe that was fairly rigid and between 50 and 100 pounds.

   The same techniques would work for a tub, I would think, just make the walls thick to resist the weight of the water, and paint the tub with epoxy paint or something, because concrete is not by itself waterproof.

   Another way to do it would be to cast it in place, with a stiff mix of concrete you could mold it pretty well, then use bondo for the final smoothing.

   This is a pretty tricky undertaking, do you have experience building or with concrete?

   Mike

1. 
   David_Giuliani | Jun 30, 2001 06:39am | #2

   *You will be amazed what a super plasticizer, like Rheobuild 1000, will do for your mix. It will flow like hot oatmeal and cut your water requirement by 25%. Another additive for increasing strength and decreasing permeability would be silica fume, Rheomac SF 100. Call up Master Builders: 800-992-9950

1. 
   augey_ | Jul 04, 2001 12:19am | #3

   *Definitely post an update when you're finished. I was once asked to make one, but the project never happened.We were going to make forms that had a layer of polyuerethane foam which I was going to shape and then laminate with fiberglass and polyester resin (I used to glass surfboards). The intention was to have smooth curves and a nearly polished surface when it came out of the mold. We were also going to use white concrete. I still want to try it someday. My only advice would be to make a few samples and experiment with finished surfaces.

1. 
   Seaweedsteve_ | Jul 18, 2001 07:53pm | #4

   *I made a plastered in place tub a few years back for my own home. I did it like a morterbed shower pan with no tile. After getting the masonary walls in place ( framed could work) I shaped wire reinforcement and layed it in there. I plastered the bottom and sides to get a good drain into the bottom of a tile style shower drain. Then I put a pan in: heavy 40 mil PVC glueable ones are sold for this, though I used roofing tar and plastic with fiberglass reinforcement on curves. All this drains into the lower, backup tier of the tile drain.I was concerned with losing heat to the large masonary mass, so I then layed in that insulating bubble stuff to isolate the inner shell.I then plastered a second layer with it's own diamond lathe reinforcement (should it have been plastic mesh?) This is the really the tub, the previous is support and drainage backup. Last, I painted it with a tinted masonary cement paint on for the final finish. My finish is rustic, your may be able to sponge this or any high cement thin coating for a smooth finish.- small pool trowel is useful- the floating inside shell has showed hairline cracking. Crack free mesh and fiber reinforcement may help that.Have you considered that your tub size will be difficult to fill with enought hot water, and wasteful? Smaller, or at least a tapered bottom is much more manageable.Steve

1. 
   d_j_k | Jul 20, 2001 04:41am | #5

   *I saw a picture of a concrete tub in one of the new Koelher catalogs ( or was it Grouhe?) anyway it was a retangle shaped one placed in side a another one ,which created some kind of moat. So you could fill it up to the top. Naturally they were displaying a fancy faucet.Looked real neat, but was a major sq footage hog.

2. 
   D_Lambertson | Jul 20, 2001 04:41am | #6

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   We want to build a concrete soaking tub measuring 4'x28". Would appreciate advice about best way to do it. We're thinking about casting it and then placing it. What are the thinnest walls we can make?; any good additives to reduce the water used? Best way to get a curved base/bottom? ANY adivce is most welcome. Thanks