Both products have a fine aggregate, usually fine silica (quartz) sand, as the foundation of the product. This sand is what really produces the strength and durability of grout. Silica has a hardness of seven on the Mohs scale, and not too many naturally occurring things are harder than quartz. When sanded grout is dry and you rub your finger across it, you feel this sand.

Urethane grout is premixed. You open a bucket, stir it to fold in any of the urethane polymer that’s separated during shipment and immediately get to work. Cement grout is a powder you mix with water. If you add too much water, you can significantly reduce the final strength of the grout. Unequal amounts of water in different batches can lead to mottled coloration of the dried grout. Cement-based grouts also release dust into the air when you pour and mix them.

Urethane grout use polyurethane resins and polymers as the binder to hold together the sand particles. Traditional grout uses Portland Cement.


The pigments in urethane grout are a special coating that’s permanently bonded to each of the fine sand particles. The finished colors of the grout are solid colors that are ultraviolet stable. They will not yellow nor fade when exposed to harsh sunlight that might stream through a patio door. Pigments in traditional grouts are powder additives that colorize the cement which then coats the silica sand. It can wear off over time. You’ll see this on older grout floors as the sand particles look light, even white in color.


Because urethane grouts air dry, you have to wipe off any excess grout film quickly from the tile surface. It’s best to just work a small area of probably 10 square feet at a time. Always squeeze all the water from a sponge as you gently wipe and film from the surface of the tile. Excess water can weaken urethane grout.

The drying or curing time for these urethane grouts is about the same as cement-based grouts, however in very humid locations the curing time will be longer. They’ll not achieve a great hardness until the water in the emulsion has a chance to evaporate. Simply follow the instructions on the product label and you will be fine.


Urethane grouts are slightly more expensive than cement-based products. However, factor in that the urethane grouts are more flexible than traditional grout. If there is future movement, a cement-based grout will usually develop a hair-line crack. The urethane grout is more likely to withstand that stress without cracking.

If you are a novice and don’t know how to mix grout, the urethane grout takes away all that worry. You simply open up the bucket, mix and spread. If you have any leftover, you can save it if you follow the directions on the label. Once traditional cement-based grout is mixed with water, it will harden. You can save leftover dry cement-based grout, but you must tightly seal it so that humid air will not react with the cement powder.


There is a relevant standard in the ANSI A108/A118/A136.1 manual. You will see that it is not specific however, this is the only part of the standard addressing joint spacing.

ANSI A108.02, Section 4.3.8 – Nominal centerline of all joints should be straight and of even width with due allowances for hand-molded or rustic tiles.

In general, there is not a specific standard for the size of a grout joint. However, there are many relevant parameters that should be considered.

  1. What is the amount of variation from tile to tile?
  2. Are the edges of the tile linear or irregular (e.g. “hand-molded”)?
  3. How big is the tile?
  4. What is the surface of the tile; can it be easily scratched?
  5. Where is the tile being used?
  6. Is the surface level?

Ultimately, the project owner should choose the grout joint they desire, keeping in mind that a tighter grout joint will show more variation from tile to tile. Many people feel that a joint smaller than three times the average variation from tile to tile (or two times the maximum variation) tends to look irregular and poorly installed.

Also, grout accommodates differences in the angle of the surface. Where the floor or wall is not level, the grout will slope from one tile to another. When tiling over a hump, the grout joint opens up; and when tiling across a depression, the top of the grout joint narrows.

Tile spacing is measured between tile edges – not from the top edge of the bevel on the tile. The majority of tile made today has a beveled edge and grout should not be installed on the bevel. The bevel is often a glazed surface which is intended to transition from one tile to another. On some tiles, the installer must “hand-tool” the grout to keep grout off the bevel.

A common mistake is to set the tile too close. Often, the finished results look sloppy due to variations in the floor or wall and in the tile. Even small variations can throw off the pattern of the tile if adjustments are not made in the grout joint. Although 1/16″ of an inch may seem unimportant (for example, on a 12″ tile), it represents a 50% variation in a grout joint 1/8 inch wide. This would be immediately noticeable and unattractive.


When evaluating grout joints, it is important to consider that grout is used to adjust for differences in the following:

  1. Variations in the size of the tile
  2. Changes in the plane of the substrate
  3. Changes in the thickness of the tile (often this applies to hand-molded tile)
  4. Variations in the rustic profile of the tile

The standards for the manufacture of tile allow for variation from tile to tile. While the standard details this exactly, it is not uncommon for some manufacturers to ship tile with about 3/32″ difference between the largest and smallest tiles in a box.

Grout must adjust for these differences between tiles so understandably there can be some variation in the width of a grout joint.

Generally, it is advisable to use a grout joint at least two times the average difference between the largest tiles and the smallest tiles. A smaller joint will exacerbate the differences between tiles as the human eye can readily see very small differences as a percentage of the total grout joint. For example, while a difference of a 1/16″ of an inch may seem small on a 12″ tile, this is readily apparent compared to a 1/8″ grout joint.

As the plane of the tile changes, the grout joint allows for this change. Should tile go over a hump in the floor, the grout joint will open; when tile follows a depression in the floor, the grout joint will narrow.

Clearly, grout joints also accommodate both changes in the thickness and profile of rustic, hand-molded tile.

Perhaps due to these variables, there is not a numerical standard to which the tile grout joint must conform.

ANSI A108.02, Section 4.3.8 of the ANSI A108 standard says, “Nominal centerline of all joints should be straight and of even width with due allowances for hand-molded or rustic tiles.”

ANSI A108.02, Section 4.3.10 addresses variations in the plane of the tilework. This section states, “Finish floor and wall areas level and plumb with no variations exceeding ¼” in 10 feet from the required plane.”

However, it should be noted, elsewhere in the standards the plane of the subfloor is required to be similarly flat.

Tile installed by the thinset method is really a surface finish that will follow the plane of the substrate. As such, variations in the substrate will be reflected in the tile layer, unless additional leveling is performed.

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