1. More and more concrete substrates are smooth steel troweled and often have curing compounds added to the surface of the substrate. While curing compounds create a bonding issue for thin set mortars, that is addressed in other articles and publications. A smooth steel troweled floor shows to be far less absorptive than broom finish floors and that has an impact on grout curing properly and evenly in color.



2. Porcelain Tiles and Dense Bodied Ceramics have issues that equally challenge water management when grouting, especially those tiles in excess of 12x12.



3. When the two issues are found to be in combination, the problem of grout curing the same throughout the installation is exacerbated leading to probable color variation and alkali migration.

1. Several hundred grout installations have been viewed where the following conditions exist.



1. There is a steel troweled floor that is far less absorptive than we have traditionally experienced. Water should penetrate the substrate in less than a minute, and many smooth steel troweled floors cause water to sit for ten minutes and longer.



2. There is porcelain tile and/or Dense Bodied Ceramic installed. (These are tile that have absorption rates of 3% or less.)



3. Tile are installed which are in excess of 12 x12.



4. There is alkali or latex migration showing on the grout surface and often imbedded in the grout as well.



2. What happens when we set tile and install grout when the above conditions exist?


1. The substrate is almost impervious causing curing issues with the setting material.



1. The setting material cures slower allowing the alkalis and latex material in the setting bed to have the potential to migrate more freely. We have noticed that even in the most extreme heat, the setting material under the center of larger tiles is still way too wet for traffic or floating grout often after 72 hours and longer.



2. Thus, the setting material has not effectively attached to the substrate or the impervious tile which often results in hollow tile.



3. Equally, the setting material should cure for longer period of time before grouting.



2. The impervious substrate does not extract the moisture from the setting material consistent with most specifications set by manufacturers of setting material.



3. In like fashion, Pocelain and/or Dense Bodied Ceramics equally resist moisture absorption since they are at a 3% or less absorption rate.



4. The end result is setting material that is greener, for longer periods. In addition, the setting material expresses its alkalis and other chemical materials to the sides and up instead of having them locked into the setting material, bisque or substrate which would occur more completely with an adequate initial cure.



3. Steel troweled slabs tend to hold more moisture for longer periods of time than the broom finish. Still, the moisture in the slab will escape over time taking to the surface of the grout joints some alkali, and other minerals consistent with cementitious products. This was addressed at length by Gray La Fortune relative to a finding called Alkali Burn on Stone set on a Smooth Steel Troweled Floor.



4. Now, porcelain or dense bodied ceramic tile is set on the concrete substrate which was mixed with a higher water content. Then set tile which will not absorb water to any better degree than the substrate, and viola…you have a potential problem.



1. First, the salts from the setting material which has not properly reached its initial cure want to find their way out somewhere, and there is nothing better than a good grout joint…especially since the tile has an absorption rate of less than 3%.



2. The slab is equally unfriendly since it is still expressing moisture during this time, and does so with some degree of variation over the slab. So, the slabs moisture also finds it way into the grout joint taking with it whatever salts (alkalis) etc that it can find along the way.



3. Of course, grout has its own alkalis that when installed in a proper environment are controlled within the grout formulation itself. For example, latexes in grout were put there to even out the pores of the tile bisque (at the sides) and are essential for bonding grout to the denser tiles. If not mixed to manufacturer’s specifications, the latex in the grout may remain in suspension longer, and thus some of the latex will find its way to the surface of the grout joint.



4. This combination of wet substrate and improperly cured setting material and grout that is mixed a bit on the wet side is more than grout can stand. Curiously, this combination is alien to the way the grout was engineered to cure in the first place.



5. Let’s discuss grouts a bit. Most manufacturers realize that field conditions are not perfect, in fact far from it. So, manufacturers tend to over engineer the product with a “fail safe” margin for error(s). That way negative results for ineptitudes are minimized. For example, when installing a vitreous or semi-vitreous tile, make the grout a little on the wet side, that has been thought of. Don’t wet the tile ahead of you, well, that’s been thought of too. In fact, I have watched an installation where the grout was mixed to the consistency of pea soup, not allowed to slake, mixed with a high speed drill and put in the joints with a squeegee. Amazingly it worked.



1. However, over-engineering may not be enough when we have the aforementioned stack of issues.



2. The stack of issues we are discussing (smooth steel troweled substrates, larger tile with green setting material and 3% or less absorption of the tile) exceed the limits of what the manufacturer’s have concluded will be done in the field to effectively annihilate their product.



3. Thus, while people may have been effectively grouting their way for a million years, when all conspires against them, there is a strong likelihood of problems.



6. With this stacking of the tolerances, the end results are: 1) Grout that shows to have a “film on it”; 2) Grout that has alkalis on it (and/or in it) which are topically noticed and which are not consistent with efflorescence; 3) The alkalis show intermittently throughout the installation; and, 4) modeling.



1. Of course, the grout is blamed and the grout manufacturer blames the installer and all the while the consumer is upset. Better yet, some folks blame the problem on trade debris, which it often is at least in part, but not totally.



2. The alkalis are hard to remove. Often Sulfamic or Phosphoric acid will remove them, just as often they will not. Or they remove the “film”, but cause the alkalis to surface which didn’t quite make it to the top during the curing process. (Note: for the first 7-10 days one should try TSP rather than Sulfamic or Phosporic acid)



3. Curiously, it is noted when these conditions occur, the complaint will often be: “everything was fine for a few days and then, this whitish material appeared.” Obviously, this is because of the retarded curing process that has occurred based on the condition (smooth steel troweled floor poured wet, Porcelain/Dense-bodied Ceramics, moisture in the slab…) and the alkalis take time to surface.



4. Some have tried to resolve the matter after a few days by using TSP or Acid only to find the grout expresses pigment because the grout is still trying to express all the extra moisture and is not yet stable. Add a potent cleaner and you can extract pigments.

Summary:

When you find the following conditions: Smooth Steel Troweled Concrete substrates and Porcelain or Dense Bodied Ceramics (3% or less absorption) to be set over that substrate, caution in grouting must be exercised to prevent modeling, alkali migration and/or latex float/migration.

Prevention:

Before we go into prevention, we would be remiss to remind you that the above mentioned substrate is not acceptable and should be refused. Further, standard thin sets are not acceptable for the particular tile discussed. In like fashion, we know that the substrate will not be refused, but the wrong thin set for the application is suicidal and is worth the price of a few extra dollars per bag and the installer can control this part of the process without question.

1. Be sure to scarify, bead blast or etch the floor before setting the tile.



2. Be sure to use a premium polymer modified setting material.



3. Be sure you allow at least 48 hours between setting Porcelain or Dense Bodied Ceramics and the grouting process for 12x12 and 72 to 96 hours for tile in the 16x16 or 18x18 range.



4. Be sure the grout is absolutely properly mixed.



1. That is, the precise amount of water prescribed by the manufacturer.



2. No high speed drills.


3. Let it slake per the manufacturer’s directions…cover the grout bucket with a damp terry cloth rag, it helps the coalescing process and in extreme heat, increases open time.



4. Remix fully after the slaking period…and then, drop the bucket at least 2-3 times to eliminate air pockets.



5. Be sure to float the grout correctly.


1. Wet the tile ahead of you.



2. Use the float as a squeegee to remove excess material…do not allow more than a slight film to remain on the tile…this is essential with some of the more aggressive glazes found on the Dense Bodied Ceramics and Porcelains on the market today.



1. Many Porcelain tile have an aggressive glaze that will hold latex and other chemicals aggressively.



2. If excess material is left behind, this latex can be washed onto the grout joint in both the initial dressing and the final wash and even at some point in time after installation is completed.



3. Wait to dress the grout until the grout has become relatively hard to downward pressure…this assures that a good percentage of the alkalis and other chemicals have surfaced.



6. Dress and Finish Washing properly.



1. Obviously use clean water…equally obviously, if you must use a sponge instead of cheesecloth, use fresh one for each installation.



2. Change the bucket after every 100 square feet, or if there is a noticeable foam on the top of the water, or if you can not easily see the bottom of the bucket.



3. Dress only after the proper time frame…that varies by environmental conditions…from 20 minutes to an hour.



4. Final dressing should be after a couple hours. This will then get most of the remaining materials that surface.



1. Porcelains may retain more latex and/or other residue than conventional ceramics since they have a more aggressive glaze.



2. If one uses a medium bristle scrub brush with minimal water on the tile to get this material into suspension and then wipes with absolutely clean sponges, the likelihood of material finding its way into the joint is minimized.



5. Keep in mind, clean water and clean sponges. The water is dirty in this application when the slightest notice of foaming appears and/or you can not see the bottom of the bucket or you haven’t changed water in about 100 square feet; whichever occurs first.



6. Water Management inherent in grouts…there are many ways to manage water in grout. We would suggest that you ask you grout manufacturer for their specifications since there is more than one way to accomplish that objective. Water management with the smooth steel troweled concrete substrates and Dense tile (less than 3% absorption) is the manufacturer’s way to help offset potential problems, but unfortunately, they can’t do it alone.

An ounce of prevention is worth a pound of cure. By taking a little more time when the above stack of undesirable tolerances are present, the installer will reduce the potential for problems, reduce the need to address consumer complaints, and have a far more attractive job.