I'm building a sandbox for my three-year old. It will probably sit on the deck, so it needs some kind of bottom. Ideally, we should be able to move the sandbox around the deck. Is it necessary for water to drain out of the sandbox, or will the sand absorb enough water? What should I use for bottom?
Ideas:
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Landscape fabric: allows water to drain through, but may not be strong enough to move.
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Regular plywood: allows movement, but may rot and does not drain.
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Redwood plywood: I don't know anything about, but I saw it at Home Depot, and it may be more resistant to rot.
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Edit: Combination: plywood with a few drilled holes, covered by landscape fabric.
Best Answer
The sand will definitely not absorb/release enough water if it's ever open to the rain. If your box doesn't drain, you'll have a small pond (as we do if we ever forget to put the lid on).
Your landscape fabric idea sounds pretty good. I'd just build that on top of decking slats or something like Trex (which might be perfect for this). Some gaps between the slats will allow drainage. Look into what the decking material is treated with. I'm in the camp that believes that the fears of CCA pressure treated wood are overblown, but even I probably wouldn't use it in a sandbox for a three year old.
Keep in mind regarding sliding it around: Sand is heavy, especially when damp (100-130 pounds per cubic foot). We have a pretty small plastic sandbox in our yard and I can't move it without dumping the sand first (but then "small" to me is something that holds three boys :D and I'm sliding across grass). You might want to think about furniture glides if you can find something that will slide reasonably on your deck, or even castors. Those will require that your base be much more rigid of course.