Why grey grout turns white in spots: Latex leaching and efflorescence

latex leaching in groutKersten’s Retro Renovation blue bathroom turned out beautifully, but she also was honest in sharing some of the problems she ran into. One of them was how the gray grout started to whiten in some spots. When I published her story, I promised to look into the issue, and I think I found the answer. The problem is a relatively common concern in tiling and grouting: “Efflorescence” and “Latex Leaching”. The darker your grout, the more you need to be aware of these issues. 

I’m not going to try to explain the phenomenon completely here. Instead, I found two online fact sheets that seem to lay it all out. Reading through them, I speculate that Kersten experienced latex leaching. Latex leaching can occur when too much water (or water with chemicals in it) interacts with colored or grey grout mix, causing polymers in the grout to rise to the surface and whiten.  A similar phenomenon is efflorescence, in which minerals in the subfloor (often concrete) below the tile rise through the grout and leave a white residue on the surface.

  • Tile USA Efflorescence FAQ  — This FAQ makes a clearer distinction between efflorescence (which seems to come from the substrate) and latex leaching (which is an interaction between the grout and water.)
  • Mapei Fact sheet — Lots of good tips here on mixing and applying grout to avoid latex leaching.

Solutions? (1) The Tile USA fact sheet suggests some acids might fix latex leaching; sounds iffy to me, and what would happen to your tile? (2) Use a professional so when it goes wrong you can make him or her do it over. (3) Shop til you find a time capsule, so you don’t have to renovate anything. (4) Another possibility: Use a sand-based grout — presuming there are no polymers — ???? — I don’t know. That’s another story. (5) Lay down a rug, and move on. <– A wise solution.


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  1. Jana says

    Hi Pam,
    You are correct in urging caution implementing the Tile USA fact sheet solution suggesting some acids might fix the problem of latex leaching. My experience with muriatic acid is that it lightens grout. I used it on my mosaic ceramic tile bathroom floor to remove some dark stains from the white grout in the tiles. The muriatic acid did not hurt the ceramic tile, but it did lighten the grout in between the tiles. I don’t know if the Tile USA fact sheet suggested some specific types of acid to use, but muriatic acid would seem to produce the opposite effect that Kersten is looking for.

  2. says

    Some antique tile dealers use muriatic acid to melt the grout off old tiles. Using too strong a mixture will etch the surface glaze as well. My solution as a man would be to stop cleaning the floor so well and eventually the grout will darken 🙂

    • Patty says

      I like the stop cleaning the floor suggestion. My first thought was find something else to worry about. Perfection is over-rated.

      • Wendy M says

        I agree…don’t worry about perfection, especially in a mid-century home. The flaws make it seem more authentic!

  3. Kersten says

    What a fun surprise to see my bathroom floor up on the blog today! Pam, it’s wonderful you found an answer to this puzzle. Although my floor is too late, I’m sure this will save many retro-renovators the same irritation that I faced. We did try the muriatic acid, a couple times, and although at first, it seemed to even out the color, as it all dried, it basically went back to the same issue. Someone else recommended some type of grout marker (I’m picturing a sharpie type thing), but I feel hesitant to try it. The other strange bummer is that, you might be able to notice in the photo, the small 1″ square tiles grabbed onto the grout more than the 2″ square tiles. It is very obvious when you look at the floor. We can’t figure out why the 1″ ended up holding onto the grey grout, and appear darker. In the end, we opted for Pam’s option #5. “Put a rug on it!”

  4. Ann-Marie Meyers says

    I am not sure I like this. This is happening in the corners of my shower floor, and I am about to put my house on the market (my 1986 house, not the mid century one). Now there is one more big problem to fix.
    Oh, well, thanks for alerting me to something that might be major before I find out from a potential buyer. I’ll get it checked out.

    • Ann-Marie Meyers says

      BTW, it is the corners on the exterior wall of the house, so it sounds like it is efflorescence to me.

  5. TappanTrailerTami says

    I have experience with the dreaded efflorescence effect. After grouting the new tile on our bathroom floor, within two days…..all the grout was white, and it should have been a med. to dark gray color. We ended up having to remove all of it and re-do it. Tedious. Second time around was fine, and we sealed all of our grout really well. I think we had trouble the first time for using too much watr in the grout.

    I found this quick trick online to determine if efflorescence may be a problem before you grout (provided you are renovating and doing a new floor):

    To check for efflorescence, tape a small piece of plastic (polyethylene film) on the slab to be tiled. Make sure the tape seals all of the edges. If water condensation appears under the plastic within one or two days, efflorescence will most likely occur. To avoid grouting problems a waterproofing membrane may be necessary.

    Since the efflorescence effect evolves from the upward or outward movement of free lime to the surface of the grout (through the evaporative process) during curing, reducing the amount of moisture (the carrier) will reduce, if not eliminate, the possibility of efflorescence.

    The primary source of controllable moisture in a tile installation is the water used when mixing grout, mortar, etc. Therefore the ideal situation calls for working as dry as possible, especially when grouting, during the original installation. (Pay particular attention to the “Application” section of “How to Grout Properly”, above.)

    For small areas on existing floors – I’d probably go the acid route (I know, I know) to get rid of it, and then….there are sealers on the market that specifically prevent the minerals from floating to the surface again. One of the products I read about was EverBlock and EverSeal Extra….never used it, but these products are out there once you get rid of the white.


  6. Elizabeth Mary says

    Also on the subject of grout, but an opposite problem — white grout discoloring . When I re-did my bathroom in 2003 I wanted white tile and grout on the shower walls. A good friend had just done that in her house nearby and the grout was already turning yellow, so that concerned me. To prevent that, the contractor used Kerapoxy Grout — and the grout is still white and has never needed any special cleaning in spite of being hit by our very hard water constanly. To get the grout, I had to drive over 70 miles round trip — more than once — but it was well worth the effort.

    • Elizabeth Mary says

      Addendum: Going back through my records I see that the same brand of grout was used on the hexagon tile floor, in Pearl Grey. Just looked over the floor and I see no sign of any change in that grout color either. So, Yeah Kerapoxy!

  7. says

    I used to work in the concrete business awhile back. And I’ve heard of similar issues with polymer modified cement products. The whitening could be from efflorescence or from polymers within the grout. It’s hard to say.

    The efflorescence could probably be removed with white vinegar and a little bit of elbow grease. Not to mention, white vinegar is cheaper and safer than muriatic acid. If the vinegar doesn’t remove the white stuff, then it’s polymers that have leached out. This is probably due to the grout being overwatered or overworked. The only way to fix the polymer issue would be to remove the grout and re-apply. Or possibly paint the grout to match?

    • Ann-Marie Meyers says

      Thanks, Amanda. In my case, since my tile is in the shower, anything is possible. I am going to try the vinegar before I go for any of the more severe possibilities.

  8. Clare says

    Thanks for solving this mystery. I had tile very similar to the one featured here in my previous condo. When we went to sell, my husband went to town cleaning and used a steam broom several times over on our bathroom floor. After that the grout turned white in areas and I could never figure out why. After all, we had been taking showers in there for five years and had a small child who splashed around in the tub. But the concentrated steam must have put it over the edge. Having just installed dark grout in our new bathroom, I’ll be careful not to make the same mistake.

    We solved our condo problem with your last suggestion: strategically placed bath mats!

  9. Joe Felice says

    And here I always thought this happened because someone didn’t sufficiently mix the water & grout. Have you ever read the contents of modern grout? You almost need a respirator & a hazmat suit to use it! I would say it is very carcinogenic, so, if I had a large area to do, I’d leave it to someone else. There is silica in it that is as bad as asbestos. The U.S. Product-Safety Commission just hasn’t found out about it yet. Wait till it does. We’ll probably have to start tearing out all our grout. Lord help us! How did those of us who are old enough to remember the ’50s ever live to the ripe old age of. . . Well, never you mind, dearie.

    • says

      Silica isn’t as bad as the warnings make it out to be. If silica were to become like asbestos, you’d never be able to go to the beach or lake again as sand is made up of silica!. The silica warnings on grout packages (along with bagged concrete, sand, and gravel) are required per OSHA. As I mentioned previously, I used to work in the concrete industry and the product my employer sold had similar warnings on it, which I had to explain to customers.

      Breathing in the dust while mixing grout (or other cement products) is bad for you, so wear a respirator of some sort, have adequate ventilation. And long term exposure to silica dust can cause a serious health condition caused silicosis. Incidental exposure to silica dust probably won’t cause harm to most people, granted you don’t have a pre-existing lung condition or smoke. But people who work with grout, cement, sand blasting products, etc., on a regular basis are going to be more susceptible to silicosis. And once the grout has hardened, there is no need to worry about any silica dust being released. Unless you start grinding away at the grout for whatever reason. And then you’d obviously want to wear respirator again.


  10. lynn says

    I grouted my bathroom floor with a medium gray grout and it was fine, dried to the right color. I waited for the recommended time to cure and then sealed the grout. As the sealant dried, the grout turned white. Since no water was used in the sealing process and the grout was already perfectly dried and the right color, the process of turning white must have come from the sealing solution itself. I actually don’t mind the white grout lines, but if I ever am tiling again, I’d like to know what happened and if there is any remedy.

  11. Joe says

    I suspect this discoloration is due to minerals in tap water that may be considered “hard” water. My floor has the clouding in the dark grout. I used distilled water to mix the grout for my backsplash tile, and got no such clouding. I therefore believe that dissolved minerals in my tap water caused the lightening/clouding effect in my floor grout.

  12. Paul says

    After reading all the comments it sound like I have latex leaching!!
    What ratio of water and vinegar to I use and also the ratio of muriatic acid. My contractor recommended acid but no ratio, he also is to busy now to come and help me. You think I choose the wrong contractor??

  13. Jamie says

    Okay so recently my wife and I have “gone to town” with a steam mop (as stated above) on the tile in our entry way. We noticed white spots on the grout as well as the tile itself afterwards. A couple of the spots where the still hot mop was left for a minute or so and some spots just from using the steam mop and then moving it off of the tile afterwards. The spots where the mop was left standing on the tile look a little worse than the others. The grout color is dark gray I think. (It is 56 years old, assuming it has never been re-done so it’s a little hard to tell.) So is this efflorescence? The wifey has been pushing for replacing the tile for a while now and this has only accelerated that discussion. I was hoping that steam cleaning this tile would give it new luster but it sure has made it look worse. Any help/ideas would be greatly appreciated!

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