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Refinished concrete floor: Xylene off-gassing duration

LloydPDX | Posted in General Questions on

The surface of our stained basement slab was damaged during some extensive waterproofing work; in order to repair it, it was recommended to have it re-ground and newly stained. (We are keeping the slab as vapor open as possible.) The cleaning process required(?) xylene, but we had no idea how *!?!!* bad the offgassing was going to be. We had to vacate the house for two days and nights, but the basement is still aromatic. Two questions: with ventilation how long might this offgassing take, and will the penetrating stains (with much lower VOCs) being applied in two weeks do anything to mitigate this? I’ve learned so much about concrete and its traits and behaviors, more than I ever wanted to know, but I sure hope we’re going to be able to use the space in a reasonable time frame.

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  1. Expert Member
    Michael Maines | | #1

    Lloyd, I don't have an answer for you but consider this a bump.

  2. LloydPDX | | #2

    Thank you. As info for others wondering, it’s finally imperceptible after a week. Relieved. Had two window fans exhausting, two air doctor filters running (with charcoal filters) and some incoming hvac (heat) moving into the space. I suspect the filters might have been overkill but we had them, so why not use them.

  3. Expert Member


    You have my sympathies. Xylene is awful to work and live with. Is there a final sealer coat after the staining? If so try and make sure it isn't also Xylene based. I did my own house with that and it basically locks you in to using the same product when you need to re-seal down the road.

    1. LloydPDX | | #6

      I know the stains are very low VOC, but will ask about the sealer. Thanks.

  4. walta100 | | #4

    Xylene is very volatile so consider closing the windows and cranking up the furnace heat the house up to 90° for 12 hours then air it out.


    1. LloydPDX | | #7

      Didn’t think about this approach- will keep it in mind for other situations. Thanks.

  5. Expert Member
    BILL WICHERS | | #5

    Xylene is a volatile organic solvent. I wouldn't really call the evaporation of the solvent "offgassing", at least not in the sense that the term is usually used, since normally "offgassing" refers to various things slowly leaving a material. In the case of a volatile solvent like xylene, the *entire* product evaporates. Either way it makes for a stinky process though!

    You can expect ALL of the xylene to evaporate in a relatively short period of time, but you DO need good ventilation for this to happen. What you want to do is open all the doors/windows in the enclosed space where the solvent was used, then setup some fans to blow OUT from one side of the room. The idea here is to get "cross flow", which is airflow coming in one side of the space and exhausting out the other. Leave this setup for several days and you should notice a huge improvement.

    As long as you didn't seal the slab before the xylene evaporated, you should be in good shape and I'd expect 2-3 days of good ventilation and you'd be mostly done with the "de-stinking" process. If a sealer was applied prior to the xylene fully evaporating, it could take longer. Note that you might also smell the stain or a sealer (if one was used), and not the xylene. It's common for noses to become desensitized after a while if exposed to high levels of stink, so it's easy to confuse one stink for another when everything just has a "chemical" smell to it.

    My recommendation is to keep the cross flow ventilation running for 2-3 days, then shut it down and see if things are improved -- and I expect you'll find it to be much better. Close things up, then wait a few days to see if the smell comes back. If it seems to start smelling more after a few days closed up, repeat the ventilation process. Keep repeating this cycle until you get the smell under control, but I doubt you'll need to do it more than two or three times at most, and one cycle may well be all you need.


    1. LloydPDX | | #8

      Thanks for the deep dive. It was in fact better after three days, and finally after a week, I’m not noticing any smell, even after closing the place up for a bit. I did have exhaust fans blowing out of two different windows instead of flow through, so I might do that differently next time as you suggest.

      1. Expert Member
        BILL WICHERS | | #9

        It's always best to have air moving through the ENTIRE space, and cross flow helps to ensure that's what happens. The reason this is best is that you don't want any dead spots with still air. Moving air keeps the concentration of the "bad stuff" in the air low, and the lower that concentration, the faster the rest of the "bad stuff" will leave from wherever it is, since the relative concentrations affect the rate of evaporation.


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