Interesting project. A model Ferocement boat.

Portland cement and 60-70 seive sand will make a strong fine grained
plaster. You will have to experiment with the ratio but about 4 parts sand
to 1 part cement should work. It needs to be a very stiff mix so add water
sparingly. For reinforcing I think you have two options. You can use a
chopped fiberglass available from any ready mix supplier and occasionally at
Home Despot or a fine (.016") wire 20x20 plain steel mesh available from
McMaster for about $1.50/sq.ft. If you go to your local ready mix plant
and explain what you are doing they will either laugh you out of the office
or get interested and give some good advice and maybe even a quart of cement
and some fiber.

You will need a form. Styrofoam will work but you will need to seal it well
to prevent it from sucking water out of the mix. A wood form would be
better but harder to shape. Mount the form on a painted board and apply a
thin coat of grease.

If you use mesh, shape it around the form and staple it lightly in place
around the edges only. Smear on the cement mix and work it in well to a
thickness of about 3/8". (assuming a total volume of 1 cu.ft.) If using
fiber it should probably be a little thicker.

The key is to make the cement mix as dense as possible. As Brian said, a
vacuum will help the ultimate strength a lot. You can make a bag from 4mm
poly sheet folded over and sealed at the edges. Make it about twice the
size of the board so that it fits very loosly over the mold. You don't want
it to stretch over the top or it will thin out the cement. You can use
nylon tube and one of those plastic suction cups used to stick things to
windows for a vacuum port. Drill through the middle and fit the tube
tightly in the hole. Borrow a vacuum pump and suck the bag down as tight as
possible.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

wrote in message
oups.com...
I have to build a cement boat that will hold as much weight as
possible. It must be made completely out of cement, no styrofoam, wood,
or anything that would provide buoyancy. It can be 1 cubic foot
maximum. How would I go about doing this??