How To Dispose of Leftover Grout and Thinset

Grout and thinset mortar are types of concrete and should never be rinsed down drains. That includes the muddy water rinsed from the buckets and trowels used to handle these materials. Remember concrete contains sand and can actually harden underwater, which makes it perfect for clogging pipes.

Most people find it easiest to wash up their buckets and trowels outdoors using a water hose instead of indoors using a sink. However, you still need to collect as much of the concrete in the rinse water as possible and dispose of it as solid waste for several reasons:

Sometimes weather will make it necessary to do all your work indoors, including concrete clean up, and so you might as well know how to clean up buckets and tools without using gallons and gallons of water to dilute the concrete and wash it into the lawn.

Also, if you mix up concrete frequently, the calcium in concrete rinse water can build up and kill vegetation by raising the pH of your soil. (I have used concrete water to balance the pH of my compost heap, which is highly acidic due to all the decaying organic matter.)

Rinsing Buckets and Trowels with Minimal Water

Use the trowel to shovel and scrape as much left-over concrete as possible out of the bucket and into a lined trash can.

Use old plastic grocery bags and newspapers to wipe out the bucket as cleanly as possible. Add 1 cup of water at a time. Stir the bags and newspapers around the bucket with a trowel. Dump the moist dirty mess into the trash. Repeat.

Do the same for your trowel.

It is possible to use this method to get your buckets and trowels sufficiently clean to do a final rinse in a sink without fear of harming plumbing in any way.

What To Do With “Muddy” Water

However, sometime things will not go to plain either during the mosaic work or the clean up. Sometimes your hand-rinsing bucket or some other bucket will end up with a lot of dirty water with concrete on the bottom.

Waste slurries such as this should never be poured down a drain. Even if you dilute the concrete so much that it could never form a bond, the sand in it will remain a solid and accumulate in low spots in the piping.

There is a solution that doesn’t involve throwing away the whole bucket: Stir up the slurry so that it can be poured out into a disposable basin such as an old plastic milk jug with the top cut off or a plastic trashcan lined with a garbage bag. The concrete will harden over night, and you can pour off the water in the morning and discard the disposable container in the trash as solid waste.

13 thoughts on “How To Dispose of Leftover Grout and Thinset

  1. Janet

    I have many bags of mastic and grout. I didn’t know until just recently that it’s not good after a short period of time. I’ve had it for about ten years. I was wondering if there is any way to use it instead of disposing of it. I was told that I can set the bags, unopened, in the yard as curbing. The rain, in time, will cause the bags to disappear and I will be left with a curb. If this isn’t a good idea, please let me know. If you have any other ideas, also let me know. It’s driving me crazy.

    1. Joe Moorman

      I don’t know about mastic, but I wouldn’t think so because it isn’t a concrete product. The grout is a portland cement product the same as concrete, but it would need gravel added for tensile strength to make it concrete.

      I hope this helps,

  2. Nancy

    I have many bags of sanded and unsanded grout that are more than a year old. According to this article, I guess I should just throw them out? I don’t want to damage the environment. Some of the bags are so heavy I can’t lift them! Any ideas about safe and environmentally sound disposal is appreciated.

    In addition, I have many bottles of mosaic grout sealer. The handling of this needs to be very safe. I’m looking on the different bottles and it does not say how to dispose of? Thanks again for any advice… ! ~ Nancy

    1. Joe Moorman Post author

      The grout is concrete, and so it is about the safest thing to put in a landfill. You might soak it with water so that no dust is created during handling and transport.

  3. Nancy

    I have many leftover plastic bottles of mosaic grout sealer (with sealer inside). Not sure how to dispose of this safely. Any ideas? Thanks! ~ Nancy

    1. Joe Moorman Post author


      NO. While I routinely pour any grout-clean-up water out in my lawn and garden, I make sure that the sludge at the bottom of the bucket dries out and is disposed of as solid waste. Grout and thinset have polymers in them, and you want to minimize the amount of that you put outside.

      If you have a bag of old grout that is too old to use and questionable, then spray water on the bag, allow it to harden, and dispose of solid waste.

  4. Mike Jones

    If you have mortar mix that you will not be able to use for mosaics before its expiration date, do you think it could be used to make something decorative like stepping stones or concrete bowls?

    1. Joe Moorman Post author

      I try to make sure all the solids go in solid waste, but I will often rinse off the last of the thin residue into my grass followed by some more water as a precaution just to make sure it doesn’t burn the grass. If you are cleaning up correctly, over 99% of the material should be solid waste, and the extra water as a precaution really isn’t necessary.

      Keep in mind that I live somewhere with frequent rains, and so I can be sure that whatever residue is broken down by a lot of soil microbes. If I lived in an arid climate, I would take care and not dump anything out. Instead, I would have a final waste bucket and simply let the water evaporate from there.


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