Revised January 23, 2009
Selection and Use of Notched Trowels and Other Tools for Installing Ceramic Tile
American National Standard Specifications for Installation of Ceramic Tile are intended to describe the minimum requirements of materials and workmanship for the installation of ceramic tile. The amount of coverage or average contact to the back of the tile and the thickness of bond coat after the tiles are installed and beat-in varies in each installation. Refer to the proper ANSI specification according to the installation method selected for the exact amount of coverage necessary. The corners of all tiles are required to be flush and level with the corners of adjacent tile and a minimum of 2/3 of joint depth open for grouting.
THE PROPER SELECTION AND USE OF NOTCHED TROWELS AND OTHER TOOLS IS ESSENTIAL TO OBTAIN BETTER OF MINIMUM ANSI REQUIREMENTS.
TYPES OF TROWELS
The type of trowel used for a particular tile installation depends on the kind of setting material being used and the size and type of tile being installed. Each installation must be considered individually and the installer must always follow the directions given by the manufacturer of the setting material being used. There are however, a few general guidelines to follow in choosing the type of trowel to use for a particular installation.
The notched trowel is a measuring device and a spreader that gives a bead (rib) pattern that establishes both uniform thickness and full contact with the tile after beating in. Vitreous tiles, including ceramic mosaics, need enough mortar to grip the edges as well as their backs because these types of tiles have a hard smooth surface, which does not provide for a good mechanical bond.
V-notched trowels are typically smaller trowels and usually used with organic adhesives that are not sanded and can be readily compressed when tiles are beaten in. The use of organic adhesives is limited to walls and residential floors because they offer little compressive strength. (Compressive strength is the amount of downward pressure a tile can withstand before it breaks.) Also, organic adhesives dry by evaporation and most floor tile are large and vitreous, which would not allow drying by evaporation.
Square notched trowels are usually recommended for use with sanded dry-set, latex-Portland cement and epoxy mortars because the square beads (ribs) of mortar break open easily during the beating–in process and give better bond and coverage. These types of setting materials offer greater compressive strengths and are recommended for jobs requiring superior floor performance levels beyond residential and light commercial use.
U-shaped notch trowels are sized similar to square notch trowels and typical from ¼” arched openings to as large as ¾” openings. These larger trowels are required for medium bed thin set mortars used with larger tiles.
Unique shaped trowel notches of alternating teeth heights and different sized openings are becoming popular with the intent to spread bonding material in new configurations that make achieving required bonding material coverage and thicknesses under the tiles easier to attain with normal setting practices.
APPLYING THE BOND COAT
One of the most critical steps in the installation of ceramic tile is the type of bonding material used and the manner in which it is applied. (Refer to Trowel and Error Training Video By NTCA). The following spreading technique is now part of each ANSI installation standard. The application of the bonding material shall always be made first to the substrate with the FLAT SIDE of the trowel to work the material into the substrate (burn in coat) for the best mechanical bond possible. Then, with the proper size notched trowel held at a consistent angle, comb the bonding material in ONE DIRECTION leaving straight rows of material. Quickly press tiles into the freshly combed material and move them perpendicularly ACROSS the ridges, forward and back approximately 1/8” – 1/4” to flatten the ridges and fill the valleys. This also helps achieve a mechanical bond to the backside of the tiles. This method can produce maximum coverage with the corners and edges fully supported. Periodically remove and check a tile to assure that proper coverage is being attained. There must be sufficient bonding material under the tiles to permit beating in the tiles to result in a level surface (no lippage or high corners), as well as to provide for the required thickness of bonding material under the tile and the required coverage (80% - 100%).
GUARDING AGAINST BREAKAGE
A 1/2” square-notched, a 3/4” half-moon or similar large-notch trowel may be necessary to spread the bond coat for button-back and certain rustic, hand-molded, uneven back tiles. Properly used, these larger trowels provide enough mortar between the tiles and the substrate for secure bond and bedding. Generally, the more uneven the back of the tile, the deeper notched trowel is needed. With extremely uneven-backed or key-backed tile, it is often necessary to “back-butter” setting material on the tile as well as the substrate to insure full coverage and complete contact with the substrate.
Bonding materials have maximum and minimum thicknesses that must be observed during installation. Some bonding materials may be inappropriate for use in deeper thicknesses or with larger size trowels. There are new bonding materials available that have flow-characteristics such that achieving maximum coverage on large tiles is easier with normal setting practices. There are also special bonding materials called Medium Bed Mortars that are designed to be used thicker than traditional bonding materials in thin-set applications. Most bonding materials should not be used thicker than approximately 1/8” - 1/4” after beat-in as shrinking and cracking of the mortar and tile may occur. A medium-bed mortar can be used up to approximately 3/4" in total thickness after beat-in without the adverse effects of shrinking.
It is especially important to get sufficient setting material beneath uneven-backed tile to guard against later breakage. Later breakage is common with imported button backed tiles that have been installed with an inadequate amount of mortar beneath them. The depth of the “button” determines the size of the trowel needed. Generally, there should be the depth of the button plus the ASNSI required thickness of bond coat (3/32”-1/8”) material after it has been compressed (beaten-in) to insure good contact. To insure 100% contact, back-butter each tile. Unless completely backed with mortar, button-back tile may crack under concentrated force such as the spiked heel of a woman’s shoe. This concentrated force is known as “point loading” and is particularly common in kitchens and dining areas where thin legged chairs and tables are used.
A small test area is recommended to select the proper tools and procedures for the job. Determine the ANSI requirements for the tile and specific material, then select the tools an installation method to meet these requirements.
It is equally important to set the while the setting material is still open, (before it has skinned over). To test for this, touch the setting material that has been spread on the substrate with your finger. If the ridges depress but no mortar material comes off on your finger, it will not make a proper bond to the tile. In this event, immediately remove the material on the substrate and apply fresh adhesive, dry-set or epoxy mortar, whatever it is you are using. If the setting material has skinned over, even though you may be able to depress the ribs, the wet tack, critical for achieving bond is all but gone.
Always beat in the tile to seat it firmly in the adhesive, mortar or epoxy. The amount of beating in determines the amount of contact between setting bed and tile. The more beating in, the better the bond. The most common tools used for beating in tiles are hardwood beating blocks and hard rubber floats. Check the tiles from time to time during installation to be sure they have been properly beaten in and that there is a strong bond. Do this by removing a tile to see if the mortar is adhering to it. If it is, you’ve got a good, strong bond.
WHEN TO GROUT
Different bonding materials have unique drying and curing characteristics and times. For example, organic adhesives dry by evaporation. Small, porous tile on a porous substrate will allow organic adhesive to dry and cure relatively quickly. Larger, denser tile on a less porous surface will trap moisture inside and take much longer to dry out and cure. A large porcelain tile set with organic adhesive over a non-breathable membrane may never dry and cure. For dry set and latex mortars, drying and curing can vary with product categories. Highly modified standard latex mortars may take longer to dry and cure than unmodified standard dry set mortars. Fast setting mortars may dry and cure in hours rather than days. Epoxy mortars cure chemically and require no evaporation, therefore the size and density of the tile is less of a factor. With the wide variety of bonding materials and tile types available today, each installation must be considered individually. ANSI requires minimum cure times for all bonding materials and all products should meet these standards. Consult the bonding material manufacturer for specifics on each installation. If grouting is done the following day, although the dry-set mortar seems hard and brittle, it has not yet developed full strength. Tile might be sheared from the setting bed by forcing the grout into the joint to a point where it actually lifts the tile. If the tile has not yet bonded sufficiently to the mortar, contact with the setting bed may be broken.
Maintenance of tools is equally important. For example, V-notches wear down very quickly when used on concrete, more so than square notched trowels.
The ANSI A108 minimum installation requirements are the real guides for the proper selection, use and maintenance of tools. Develop your skill to meet these requirements first, them improve your speed and productivity.
TROWEL NOTCHS AND SHAPES:
The mere selection of the proper sized notched trowel will not in itself insure the specified results. The installer must not only use the trowel correctly (flat side first, followed by combing with the correct notch held at the correct angle, back buttering if necessary, etc.), but also must maintain the tool (keeping it clean during use; re-file notches when necessary, etc.). Too large a trowel and excess bonding material will be forced up into and overfilling the grout joints during installation. Too small a trowel and not enough bonding material will be spread and the tile will not be properly supported and loss of bond or breakage could occur. Select the trowel that produces the required thickness of bonding material with the required coverage after typical setting, embedding and beating in of each tile. There is no hard and fast rule of which trowel to use in each situation, just determine which one yields the required results. The ultimate goal in every installation must always be 100% coverage with no voids.