As far as the cement curing, a full cure usually takes a few days, depending on the mix that you use... I have used portland cement/sand mix when creating faux rock, with great success... However in your situation, you will probably find that the cement will have a hard time adhering to near vertical walls, without some kind of support... You can use 1/4" hardware cloth, chicken wire, or best yet, diamond lathe... THis way, the cement will squeeze in between each hole, thus making it stronger, and more stable, than resting on a vertical smooth surface...
As far as coloration goes, there are a few techniques that you can use for coloring, including cement stains, which are usually extremely messy and damaging to furniture, clothing, carpet, etc... The easier method is to use latex exterior paint, diluted to a milk-like consistency, and then sprayed right onto the rock with a handheld garden/plant sprayer.. Cement is rather porous, so it will suck the color right into the rock, where fading doesn not really occur, unless perhaps it's over the course of many years, exposed to natural weather conditions...
Working with cement is fun, but you also have to compensate for the weight that it will add to the enclosure... Using resins, epoxies, and elastomers is more flexible in design, lightweight, and you can achieve more realistic looking rockwork when using this stuff.. However, it is not for everyone, as it has a short working time, and puts out noxious fumes... Not for the beginner..
I am currently working on some more rockwork for a customer of mine, as well as a cage for my soon to be aquired pair of black water monitors... but Here are some examples of some of the rockwork I have done...there are others, but I have yet to compile all of them onto one page/site... Cheers, best of luck to you in your creativity...just go with the flow....hahaha.. Take care, have a wonderful day..
BOb
the odatriad
http://www.geocities.com/odatriad

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