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What is the standard for determining the size of a grout joint?

We are often asked what is the standard for determining the size of a grout joint – can it be bigger or smaller – does it need to be a specific size, etc.

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.

For cementitious grout, joints smaller than 1/8″ generally should only be grouted with unsanded grout, and joints of 1/8″ and larger should only be grouted with sanded grout. Joints larger that 3/8″ usually need a more heavily sanded grout to accommodate the large joint.

Some manufacturers sell a “wide joint” mix (for joints bigger than 3/8″), but you can make the same thing by adding coarse sand to regular grout. For the exact amounts to add, you should check with the manufacturer of the grout you plan to use.

Generally, sanded and unsanded grout should never be mixed and absolutely never with marble or any other surface that can be scratched by the sand in grout (note: marble is a cut product, manufactured to extremely tight tolerances and usually designed to be installed with 1/16″ spacing).

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.

What is the standard for variations in grout joints?

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

  • Variations in the size of the tile
  • Changes in the plane of the substrate
  • Changes in the thickness of the tile (often this applies to hand-molded tile)
  • 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.

When do you use caulk instead of grout?

Technically, anywhere there is a change in substrate or backing surface such as the joint between walks and floor and wall joint, caulk should be used in place of grout since these surfaces move independently of each other. However, it is important to recognize and make the end user aware of some important points.

Often, installers use grout in place of caulk for these reasons:

  1. The caulk may not exactly match the grout color.
  2. Even when the caulk exactly matches the grout color when installed, it may not match six months later (caulk will “age” differently from the grout).
  3. Caulk will need to be maintained more often than grout.
  4. Mold may grow more easily on caulk (except caulk treated with mildewcide) than on grout.
  5. Acrylic caulks break down in horizontal wet applications. Silicone, urethane, or multi-polymer caulks are better choices but can be harder to apply.

However, when grout is used in place of caulk, the grout can cause structural and aesthetic problems.

  • The grout will crack allowing moisture to penetrate.
  • Where the grout is sufficiently strong, movement in the walls, floor, or countertop can damage the tile.
  • Grout cannot hide corner cuts as well as caulk.

In summary, caulk is the better choice, but the customer needs to understand its limitations.

How do you remove grout that is adhered to a tile floor?

Removing grout that is adhered to a tile floor can be difficult. The type of tile greatly affects the difficulty of grout removal. Also, if the grout was polymer modified, it may be more difficult to remove.

In general, the more porous the surface, the better grout will adhere. Conversely, grout is more easily removed from dense impervious tiles (e.g. porcelain).

To remove the grout, start with an alkaline cleaner and a nylon scrub pad. Make sure to check that the scrub pad is not damaging the tile. Normal floor tile will not be affected by a using a scrub pad, but some decorative tiles do not have the same surface hardness. It is best to check your decorative in a secluded area.

If the scrub pad is not effective, there are specialty cleaners on the market that chemically attack the grout. Typically these are weak acids. As with all acids, follow the manufacturers warnings carefully and use caution. Always check the tile in an inconspicuous spot first in case the cleaner affects the tile.

Again, these specialty cleaners will not affect most floor tiles; however, it is prudent to check. Some tile installers use stronger acids that they carefully dilute. While experienced professionals can do this, there are great risks in doing so. There is the possibility of bodily harm as well as damage to the surroundings.

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