I bought some play-sand for our new sandbox on a rainy day, then left the bags unopened on our patio to dry for a few days.

It's been about a week and they haven't dried, and now my wife is wondering if they're growing dangerous mold/bacteria/what-have-you and should be discarded.

So, my questions:

  • Is this fear justified? Should we get new sand or treat the sand we have somehow?
  • Are wet bags of wet play-sand actually common and we should just dry them out going forward?
  • Is the sand likely to dry adequately by leaving it in a sandbox for another week with its cover on?
  • 3
    When you buy playsNd it will not be dry - it will have some moiusture in the bag. Very dry playsand is hard to play with and you'll probably be adding water to sand when it gets very dry.
    – DanBeale
    Commented Jun 19, 2014 at 17:07
  • 2
    The stores around here have the bags out on pallets in front of the store all summer, which is no different than leaving it out through a rain storm on your patio. I really don't think it is a problem.
    – michelle
    Commented Jun 19, 2014 at 17:52
  • Most sandy beaches get wet.
    – DA01
    Commented Jun 19, 2014 at 17:55
  • 2
    I would just give it a smell test. If it doesn't smell moldy, it's probably not moldy enough to be dangerous (most of the real danger from mold will be the allergic asthma it can cause). If it does, then empty it out into the sandbox and let it air out (maybe stir it up periodically).
    – Joe
    Commented Jun 19, 2014 at 18:31
  • 1
    For the record, mold grows on organic surfaces. Not sand.
    – DA01
    Commented Jun 20, 2014 at 20:30

5 Answers 5


The ultra-violet component of sunlight is anti-microbial and anti-fungal. If you're worried about the wet sand, spread it out in the sandbox and the next bright sunny day will disinfect it.

Unless the sand is very pure, and thus empty of any nutrients, you're probably right that it's a breeding ground for bacteria right now. But I doubt it's anything that could hurt your child since bacteria and fungi are vital parts of all soil that your kids walk over and play in every day.


I'd say it's far cleaner now than it will be the first night you leave it open to the neighborhood cat. If I were you, I'd add a tablespoon of bleach to a couple of gallons of water, just enough that your wife can smell the "disinfectant" you're going to mix in with the sand, mix it in and forget it.

  • Yeah, we would only leave it open if we were nearby to discourage neighborhood cats from checking it out.
    – Ed Brannin
    Commented Jun 22, 2014 at 13:56

Bacteria, mold and other things need a medium in which to grow, something with nutrients, like humus (decomposed organic matter, not the chick pea mash). Good quality sand (and it is usually washed before it's bagged) has no humus in it; there is almost nothing to it but little lumps of silicon dioxide.

In time it will collect humus (cat feces can be considered infected humus) in the form of leaves, grass clippings, etc. If you're not afraid of these, no need to be afraid of clean, wet play sand.

other considerations about play sand from the American Academy of Pediatrics


To ease your mind you can clean the play sand. This can be by boiling it for at least ten minutes. Yes, this is messy and needs big pots and lots of water and energy.

You can find a child safe antisceptic. One brand name in the UK is "Milton". Use the manufacterer recommendations and wash the sand, through a sieve, into another bucket. Then wash the sand with water back into a different bucket. Drain it, spread it on an old towel in a dry place to let it not be soaking. Then either let it dry or put it where ever it's going.

  • 6
    I guess you could do this, but kids play in sand and dirt all the time. Unless you're sanitizing the entire yard, cleaning the sand seems a bit pointless.
    – DA01
    Commented Jun 19, 2014 at 17:56
  • 1
    If the wife is insistent on disinfecting the sand, a cheaper and more convenient method is to water it with diluted sodium hypochlorite bleach, using a shovel to ensure thorough mixing. However, if there is no odour or visible change in the appearance of the sand to indicate activity by microorganisms or algae, even that would be overkill (for the reasons other commenters have given). The OP's wife is obsessing for no good reason.
    – Erik Kowal
    Commented Jun 20, 2014 at 12:07
  • 2
    @Erik - Keeping a spouse happy is worth a bit of trouble. That's why I suggested a bit of bleach in water, just enough to smell, mixed in with the sand. Placebos have their place!
    – Marc
    Commented Jun 22, 2014 at 2:29

Sand for sure can grow mold (even in bags). I’ve had bags of sand sitting for 8 months (for a paver project that has yet to be started) and there is definitely visible large mold spots growing in the bags. I will just spray it with bleach water when I put it down.

Whoever said mold only grows in organic matter is wrong. Hello... mold grows on grout, tile and plastic in the bathroom ALL the time.

  • 2
    Grout in the bathroom collects skin flakes and water that has run over our skin, causing there to be organic matter in it. Dust is organic matter usually so unless you make sure there is no dust or water on the grout at any point it is considered organic matter. However the same will apply to the sand after it has had someone touch it even once...
    – Vality
    Commented Aug 26, 2019 at 19:20

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