I'm putting in a shower prepan, and I'm following directions to make a thin, sandy layer. Mix: portland 1, sand 5. Next day, much of the concrete comes up with a wisk broom. What have I done wrong? Should I rip the rest of it up? I live in arizona, should I cover the concrete with tarp while it dries?
You don't mention water. What directions are you following? Your underlayment could have sucked some moisture from your sand mix. I would rip it up and do it again. Dampen the area under the crete first or seal it.
Cement 1 to 5 sounds like "drypack" to me. What you mixed is a far cry from concrete. Last time I did this I started laying on the mix while it was wet.
I was attempting to make "Deck Mud".
Water: minimum amount for consistancy of sand-castle mix - not too dry, not too wet. I did not wet down the underlaying concrete pad before laying on my mix.
I'll rip up my bad lot, clean up, wet down the pad, and try again. Thanks!
also: Is there a minimum thickness for a such a mixture? Does anyone recommend a layer of thin set on the pad, to help the drypack stick?
If the weather is hot, then cover the mix while it dries. Concrete sets by chemical reaction initiated by the water in the mix; if the water evaporates before the reaction is complete the concrete will not harden properly and will be dry and sandy (exactly as you described your mix to be!)
I would go 3 sand to 1 cement
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