High density ferrocement

RECIPE FROM http://www.youtube.com/watch?v=EgOXCjRdHBU

Two full buckets of sand - 10 gallons - lots of fines. If you shake it out, you get half large rounded pebbles

1 bag portland cement

2.5 gallons of water

16-20 oz of yukon SBJ - magic - be patient and let it mix - wait for it to turn into a lava texture

add half a bag - 12.5 pounds Micron 3 - more than 12.5% cementous we are good.

use as little water as possible to create plaster.

Add two more buckets of sand

PVA Fibers - RSC 15

Forte Ferrell Fibers - 3/4"

1. 1 bucket sand
2. 1 bag portland
3. 2.5 gallons water
4. 16 oz eucon sPJ
5. WAIT for watery consistency (cement is all hydrated)
6. 12.5 lbs Boral Micron 3
7. 1.5 compacted quarts fibers of PVA rec 15- 8mm
8. 1 compacted quart of Forta Ferro 3/4" fibers
9. MIX
10. 2 more buckets sand
11. 5 gallon bucket of properly aerated Mearlcel 3532 foam

YIELDS 3 Cubic Feet of plaster mix

Comments

Why is a low water mix important?

Not only does the low-water content enhance compressive strength significantly, more importantly, it substantially reduces the shrinkage of the cement during curing. This allows several unique advantages: A second coat can be applied without waiting for the first coat to cure and shrink; Cold joints with older plaster bond well, No expansion joints are needed, Cracking is reduced or elliminated, The low-water mix gives up water more slowly and so is easier to cure. All of these makes this mix more forgiving for less experienced plasterers.

Doesn't the 40 ounces of water added with the Mearlcell 3532 boost the water content for the cement hydration?

No. Aerating compounds such as these provide a stable solution for a stable bubble that will survive past the initial set or initial hydration of the cement.  The compression strength drops from 17K psi to 11Kpsi when the 12 to 17 percent aeration is added not because of the extra water, but because hard mineral based aggregate is replaced with air bubbles. This can be proved by simply measuring the shrinkage percent, which is an accurate measure of water content during initial hydration. Also, if the 40 ounces of water were released for the initial hydration phase, the compressive strength would not likely exceed 10,000 psi as test cylinders reveal.

at 2:45 of http://www.youtube.com/watch?v=JtmKLVVAgbc

they build a 260000 gallon insulted tank out of ferrocement lamination, but don't discuss the insulation. Inquiry made.