We just finished installing approx 150 sf of stone pebbles in a large turett area over ditra over slab, the we grouted using sanded natural grout from customs, came out just fine even thought we needed to use an additional heater to get the grout to set. This is the delemma, certain areas due to missing grout stayed wet longer than needed, and as a result produced minor staining of the grout, I suggested to the grout installer that she needed to come back and heat gun the wet areas in a resonable time so this would't happen, anyway we still have these minor areas that need to be dealt with. I was thinking of 1-4 mix of muriatic and water using a window brush and immediatly wet vack this up and than resealing the grout to get rid of the minor stained ares, what do the experts think

I'm not really sure I understand what you have going on here. Let me get it straight.

First you put in the stone. Then you grouted using natural grey grout. Then you heated the room so that the grout would dry so that you could seal it?

From here it sounds like the sealer coat wasn't as uniform as you would have preferred and you are concerned about the places where the sealer was heavier drying a different colour from the rest. Is this right?

If it's a sealer issue, you need to use a stripper to get the sealer off. You don't want to go there if you can help it. If I were you, I'd wait a while to see how it all dries. Over the next couple of weeks, it may even out. If there are minor colour variances, go over the whole thing (stone and grout) with another coat of sealer, or maybe an enhancer. That may very well blend the whole thing together and make it all beautiful. Anything to avoid stripping.

The truth is, the sealer shouldn't be applied to the grout until it has cured for 28 days. Otherwise, you're taking the chance of it all drying with different colour blotches.

A mistake that people often make is in reading the sealer bottle to know when to apply it. The sealer manufacturer can say that the sealer can go on in 2 days or in 2 weeks, but their opinion doesn't matter. It's not the sealer that will discolour if it is applied too soon, it's the grout. You need to read the grout manufacturer's spec as to when the grout is ready to be sealed. The rule that I use is the 28 day concrete curing time, because grout is a concrete based product. Applying heat won't help the curing process. The surface may be dry, but it has not fully cured. As long as the temperature is above 50 degrees farenheit, let it set up naturally on its own at a consistant rate. Coming back a month after the tile is done so that you can seal it is inconvenient, but it is a billable service. Quite often, I supply the sealer and leave it with the customer to apply a month later, if they choose.

Forgive me if I misunderstood your issue. I hope this is helpful.

I'm also confused about the question.
What I read, is that this is a grout drying issue and there has been no sealer used at this point.

The worst thing you can do to any concrete based product is apply heat or fans to dry it out in the initial curing stage. This will NOT help in curing or preventing staining. It's quite detrimental to the curing process.

It sounds to me that this is a grout issue. Too much water in the mix or too much water in the clean up or a combination of both.

Remember that this is a pebble floor and the grout spaces are quite large and deep in some areas. These areas will take longer to dry naturally and may look as though they are stained.

The last thing you should be doing is using muriatic acid on a fresh install.

I would wait a few more days to see if it is a drying issue or a grout installation/cleanup problem.

After that time frame it would be more helpful for you to post photos of the problem so that we can see whats going on.

Since you mentioned "resealing" the grout, I'm assuming it's already been sealed. Although you don't mention the time lapsed between grouting and sealing, it's possible that the cure time wasn't long enough, as mentioned earlier. It's even more likely since the job is over Ditra, which requires a little longer drying time than jobs done over a slab or cement board, and the fact that this is a pebble job which involves larger amounts of grout.

I also agree that muriatic acid shouldn't be used on this job.

Just out of curiosity, how big are these pebbles, on average, and what type of thinset did you use?

The pebbles are about 1x2, 1x1 mixed sizes, small. We used hydromet ditra thinset. The issue is that certain areas there was grout missing and in the process of grouting the water from the clean up got down to the thinset and sat on the ditra so the dry time in these areas took longer to dry than the rest, in some areas were still not dry. I should have put a heat gun on these areas but did not and decided to let all cure, these areas are a slightly different color.

Its not a grout issue as the overall color of the grout was uniform. The issue was that in certain areas the water from the cleanup got down uderneath due to small voids in the grout and stayed wet for too long of a time, I thought about using a heat gun but decided to let all grout cure and see. This has been 14 days since. The client wanted us to seal so the plumber could do his thing. I should have known better than to allow someone else to dictate my jugement on this. The overall apperance is excellent, with the exception of a few areas.

This is a little off topic, but aren't those pebbles too small for Ditra? I think 2x2 is the minimum size for Ditra.

Grouting pebbles can certainly be a challenge. I try to allow myself plenty of time to grout pebbles, since they're a lot of work. It's important to let the grout set long enough, but not too long before washing it. Knowing the right time can be difficult, sometimes it requires experimenting in a small area.

If there was grout missing in places, it should have been addressed at that time as opposed to later. I own a heat gun, but I've never considered using it for any of my tile work. I would suggest you save it for glue removal or something of that nature. You shouldn't even have a fan blowing across the grout while it's drying.

As Kman mentioned and although off topic you may have bigger issues than just some stained grout.
Schluter is adamant that no tile,stone or mosaic smaller than 2" x 2" be installed over Ditra. Its a potential point load issue within the Ditra structure that the waffles can not support small pieces of tile. You may see cracks forming once the floor starts to see traffic.


You really need to post photos of this problem. It would be more helpful than verbally trying to explain what the real issue is.

Am I correct in assuming you personally did not grout this floor and it was subcontracted out?

Rick, I really hope you don't reply with a comment about how the same Schluter rep (you know what I'm talking about) told you it was ok to install those small tile over Ditra.

Okay! Here we go, I did in fact install ditra over the concrete slab and than installed a thinset bed over the top before I installed the pebbles, I than pre sealed the pebbles using " Aqua Mix " enrich and seal, imediately wiping off the excess, I figured that the sanded grout would dull up the sealer upon application, which it did. J@D was right, I installed the sealer without the 28 days of cure period which was needed due to the fact that because of the amount of grout that was required this installation turned out to be covered by the conctcete cure method of at least 28 days, not by the sealer specs. So this is where we are at as of now. I instructed my grouter to acid wash all existing stone areas using a 4-1 ratio and hot water with muriatic acid to cut the water based sealer and than to wet vacumn this up right away, worked just fine. She than used a hair dryer to finish up the still damp areas, this also worked. The summary would be, do not install pebbles over " Ditra " and than seal all without the cure time required. Floor looks excellent now. Also just a note, I assume that because we used a water based sealer we just dodged a bullet, I think that by using the reduced acid that this opened enough pores in the grout to save our asses !
Never intalled pebbles before over anything but shower pan areas which of coarse are over hard pack. Thank You again

RC I did not contact my schluter rep on this, I just assumed that I could install small pebbles in a grid over this membrane after thisetting the ditra material before setting, even though this would probably negate the whole purpose of the " ditra specs", seems to me that any tile over ditra needs to be installed at the same time to ensure bonding with the waffles in this system.Just going by gut instincs. I also did not want to install pebbles using a 1/4" x 1/4" trowel without filling the ditra first. Also as stated in " my too much thiset " I was on the hook to continue to install ditra on all floors, I would have installed " Mapeiguard # 2 " peel and stick. If you are not supposed to install small pebbles over ditra and the job insists on it what are you supposed to do ?

The only reason that we had a fan going which was 15' away from our grouting with a propane heater was due to a couple off reasons, # 1 the in floor heat was not in this area and this is coldest part of the house # 2, I wanted to make sure that any water used in the grouting clean up did not sit on top ! I have had in the past, especially on floors an efferesence left in the grouting process from customs sanded grout. Also we used a hair dryer instead of the heat gun to show the owner that all grout would blend in if waited the full cure time, this dryer steped up the actual apperance, I know does not make any sense.

This area with the pebbles came out just fine, using the propane heater and acid washing this area twice and letting the grout cure worked. Just another note, we suggested that an Island stone for the pebbles be used and the owners went with a cheaper stone which took 30% more grout than what we are used too, the fact that the in floor heat was not installed and presented major problems. I had to return approx 500.00 dollars to the clients because of the time involved in getting this area to look perfect, this is a t/m job, what are you supposed to do. Weigh the balance of the work that still needs to be done and eat this minor glich.!!!!!! They are saving money compared to by the square foot for these areas. Also on the hard pack over ditra to fix the remainder of the floors as stated before, this system worked out better than I thought. We ended up with 3/8" average of hardpack and two yards to fix, than as stated before a diluted redguard solution only to insure that the hard pack would not deteriorate durring the installation of the marble, I think that this held together the hard pack.

Just an FYI for future installations with any radiant or electric under tile floor heat. They should NEVER be turned on before or during a tile/stone installation. As I have stated before, no extra heating or fans should ever be used during an installation.

Until full curing of thinset and grout has been achieved (approx. 21 days)no radiant systems should be activated.

Sorry to hear you lost money on this job. Sometimes you win, sometimes you lose. The joys of contracting.

Done deal,Thank You for the information on the curing time for grout, we ended up using 150# natural grey customs sanded grout and needed to acid wash x 2 to secure the color because of the ditra over slab and the teperature conditions of this area were not right, cold part of the house. We still need to seal all work and will be using aqua mix gold and after set will put the floor machine on to clean up, and hopefully blend in the finish of the pebbles. Any advice on the final step would be welcome.