Why is my Unsanded Grout Cracking and how do I fix it?


We want to regrout our kitchen floor that has ceramic tiles. We installed the floor in Feb 2020. we used Mapei unsanded grout from Lowe’s. We heard afterward it’s best to use sanded grout). It was the kind that you ADD WATER to it. Within a week or two the grout started to crumble and crack in many places & got worse in the past month. Huge stressor!Some sections of the floor the grout looks good in that it hasn’t cracked or crumbled but other areas there is a lot of pieces loose or cracked. So we have taken out the visually loose & cracked grout pieces. Some places look in tact and food... So left those alone. However we wanted to regrout the whole floor with sanded Mapei grout of the same color. Would the new sanded grout bond with the previous unsanded grout? My husband said we don’t have to regrout the whole floor just problem areas but I worry that if the currently nice areas are in good shape now that they may crack or crumble overtime like the others have. We recently purchased a premixed grout of Fusion Pro that has a sealant in it. Is that best to use or use the unsanded Mapei grout since the original grout from Feb 2020 is sanded Mapei? Also would it be more beneficial to regrout the entire floor which would cover the problem areas and fill some grooves that don’t have a lot but would cover nice grooves?


ANSWER - There are many reasons why a grout will crack and come loose.  Unsanded grout is recommended for grout joints 1/8" wide down to 1/16" wide.  Sanded grout is recommended for grout joints that are 1/8" wide up to 1/2" wide unless you use the special grout for wider grout joints. If the grout joint is 1/8" wide I will always use sanded grout.  If the grout joint is less than 1/8" wide then the sanded grout doesn't fit in the joint to full fill it up.

If the grout joints were larger than 1/8" then you might get some shrinkage cracks, but it shouldn't come loose.  Often grouts fail because there might be too much deflection in the floor.  Or sometimes too much water is used in mixing the grout and/or in cleaning the grout right after it is installed.  Too much water weakens the grout causing it to crumble.

To remove all of the grout is a big job and you might chip some tiles during the process, unless if the grout is so weak it can easily be removed..  If there is at least 1/8" depth left in the grout joint it is possible to grout over it with a polymer modified grout and maybe the premixed grout will work too.  Before you do anything check with the grout manufacturer to make sure they approve of how you use their product.

6 thoughts on “Why is my Unsanded Grout Cracking and how do I fix it?

  1. Shaina Harris says:

    Need your help!!!! So I used sanded grout with a grout maximizer additive (didn’t use any water) on our porcelain tile floor and I put it on too thick ;( so now I have areas that have hardened on the tile because by the time I got to those areas it dried up. How do I remove hardened grout on tiles? ;(

    • Donato Pompo says:

      First I would try to carefully scrap off any excess grout if you can without scratching it. If there is just a grout film haze on the tile you can first try some diluted vinegar to remove. But first test it out to make sure it will work to your satisfaction. To test saturate the grout with clean water then take a diluted solution of vinegar and test a small spot and see if it works before proceeding.

      If it doesn’t work then you might need to use a latex remover because you used an additive. Test it out first to make sure it works before proceeding. Follow the same instructions above by first saturating the grout joints with clean water. You should be able to buy the latex remover through a tile distributor or a Home Center.

  2. Rod Moss says:

    We recently tiled our kitchen backsplash using sanded walnut custom grout. Came out beautiful. About 2 weeks later we decided to add another section of tile using same grout color but new bag and it dried darker so now we have 2 different looks. One darker than the other. It’s a small section but stands out when you see it.
    Is there an epoxy colorant you can suggest to use on the darker Custom Walnut grout section that will lighten it to match the rest?

    • Donato Pompo says:

      That can be a problem with cementitous grouts. The color can change from batch to batch. Even when you grout with the same grout out of the same bag at a different time under slightly different conditions the grout can come out lighter or darker depending how much water was used to mix and clean up, and how fast it dries.

      Custom Bldg Products does sell grout colorants that match their grout colors. Home Depot use to stock them or go to a tile supplier who might sell them.

  3. Denise says:

    We have a custom Home in N. Idaho that has 2 tile showers built on exterior walls. The home is 5 years old. The showers have hardibacker board, thin set and tile I believe. Every year both showers in both corners along the ext. wall split in the Wall tile corner grout joint. The space is wide about 1/4″ inch but it only splits about a foot from the top of wall to about a foot from the bottom, basically in the middle of the joint. We have had the builder come out several times and tile installer and the tile installer had a so called expert inspector come out and his report said it is settling. There are no visable cracks on the outside or inside walls by the showers or in the stem wall foundation in these area’s. It expands in winter cold months and summer contracts back together. I have for the past 3 years every jan/feb had to refill the gaps in with a sanded silciconized acrylic latex caulk that the tile installer gave me because the gaps are to wide to just leave open. What do you think the problem could be and is it possible to fix without having to demo both tile showers and start over.

    • Donato Pompo says:

      If I understand you correctly, you are saying that the inside vertical corner of your shower has cracks. That is a condition where there is a change of plane from on wall to the adjacent wall that is subjected to differential movements and stress.

      Industry standards require those joints to be filled an ASTM C920 sealant (caulking) over a closed-cell foam backer rod or over bond-breaking tape. These sealants are normally either a 100% silicone or a polyurethane sealant. Siliconized acrylic caulking does not meet the standard is does not perform well. The ASTM C920 sealants (caulking) bonds extremely well and can mitigate a lot more movement if installed correctly.

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