concrete effects on orchids?

[james mickelso]

I used to make bonsai pots of cement and color added as it cured. Planted in it not too long afterward. Also used tile grout for slabs then planted bonsai trees on it after it cured dry. Just cut 1/4 inch hardware cloth and spread colored tile grout on top and once dry wired small and large trees to it with soil and moss on top. Sold lots of them and had a few for over 20 years. Have a pic somewhere of a nice pinus thunbergia planted on a nice tile grout slab. About 20x36 inches across and 3/4 inches thick. Once the cement dries, it is inert for the most part. Crushed up to fines and soaked you might get some alkalinity out of the drained water.

[Ray]

As a ceramic engineer (cement is considered a ceramic material), we went to a manufacturing plant when I was in school. Wow! I've never seen whole rail cars inverted to dump their contents before! Anyway....

Described in its simplest form, when water is mixed with the calcined cement, calcium hydroxide crystals begin to grow. They are needle-like in shape, and as they grow they "interlock" with each other, which is why it is so hard and strong. The unreacted calcium oxide is very basic, so will be damaging to plants. In pure cement, it takes over 20 years for the hydroxide crystals to fully develop, and for the strength to maximize.

Aging of cement in a wet environment is accelerated, reacting that surface lime, making it relatively inert. Acid treatment reacts with the "unaged" material to do the same.

[Yukonphal]

OK....so...to break that down into something we can use.......vinegar in water to soak the cement?????

[Ray]

Originally Posted by Yukonphal

OK....so...to break that down into something we can use.......vinegar in water to soak the cement?????

I suppose, but vinegar is not a very strong acid, so won't have that much effect.

[Yukonphal]

Muriatic acid in the first bath then? and clear water for the second and third??

[Ray]

I think a single rinse would suffice.

[james mickelso]

Ray, do you engineer ceramic armor? My friend in Mass. MIT studies ceramics for that purpose. I used to lay tile and liked working in that material. Very hard. I even used tile and glass for making knives and arrowheads. What do you study regarding ceramics?