VCT tile odd staining looks like mold/mildew coming through from ground set slab

Discussion in 'Vinyl Flooring Q&A' started by jhbubba75, Sep 27, 2017.

  1. jhbubba75

    jhbubba75 Member

    Aloha All!

    Has anyone see this before? attached pic.

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    Looks like moisture coming through the ground set slab and is causing this staining or growth within the tile and showing through the top surface. Is this curable? Is it hazardous and we need to replace asap? If in the future we install vct tile in another home in a high moisture area is there something that you can treat the slab with before installing vct over it to reduce or eliminate this from happening? It seemed like the areas affected were along the exterior wall edges and wherever the tenant had furniture placed in the room. Any insight on this is greatly appreciated.

  2. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    Could be, hard to see if it will scrub off surface. I see this in supermarkets, mold can grow in, on, and below. I bought a white vinyl 50 ft drinking water hose, white, and mold grew under the jacket liner, back to Home Depot it went.
  3. kwfloors

    kwfloors Fuzz on the brain Charter Member I Support TFP Senior Member

  4. Incognito

    Incognito No more Mr. Nice Guy! I Support TFP Senior Member

    I've dealt with VCT by the millions of square feet-----demoliton, moisture barriers, prep and install over 30-40 years now. Your staining is something very peculiar. It may be mold. I also may just be high alkalitity salts collecting under the tile and eating up the glue, patch and surface of the concrete. This process tends to disfigure the tile and makes it extremely difficult to clean.

    Take a piece of steel wool or sandpaper to a darkened area and see if that dark stain is THROUGH the tile or just on the surface.

    Regardless, this is a severe moisture problem. There's no VERY cheap solution to moisture passing through concrete. There are good, better and best methods. Unfortuneately, the solution kwfloors suggest is the only one I can recommend wholeheartedly. The cheapest way out that I know "works"------at least for a good many years is a product called Versashield. It's a fiberglass membrane that is rolled out and taped together at the seams. When you glue the VCT over the membrane moisture will not be able to penetrate the Versashield so your VCT will perform well for many years.

    The reason I prefer Koster is that there's not EVER going to be a problem under the epoxy membrane that has penetrated the pores of the concrete. So this avoids any unhealthy accumulation of moisture and salts under the moisture membrane. I've also see dramatic failures of underlayment (patch) under the Versashield. So Versashield can be used if your substrate is in relatively good condition AND your moisture and alkalinity measures just modestly above the tolerances of the manufacturers (flooring, glue and patch).

    If the moisture tests show high moisture and alkalinity its stupid to install resilient flooring without shot blasting and applying a premium quality moisture barrier.
    • Agree Agree x 2
  5. jhbubba75

    jhbubba75 Member


    Thank you for your reply, and sorry for the delayed response, I wasn't getting email notices that i had replies waiting. I believe it's growing through the tiles.


    Thank you for mentioning Koster as i do install vct often.

    It's good to hear from someone that has been dealing with these types of flooring for so many years and to say this one is peculiar. Thank you so much for your input.

    Last edited by a moderator: Oct 3, 2017
  6. Mike Antonetti

    Mike Antonetti I Support TFP Senior Member

    You have replacement tile? Pop one up and see f there is a source for mold growth.

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