Tile How-To: >> Bathtubs
Ceramic, porcelain, and stone tile tubs are the focus in this how to section. Bathroom tile be it stone tile or ceramic tile is hugely popular. This section will detail methods used in the tiling of tubs using ceramic tile, porcelain tile, and stone tile. As noted in the Tile Doctor General Information section, "Showers and Tubs," a pre-fabricated shower pan is treated in a very similar way as the tub built in this section.
Keep in mind what you have learned in other sections concerning the choice of tile intended for use, layout considerations, and desired methods. Also, remember to follow the Manufacturers instructions for the products that you choose to use.
MORTAR BED:
The following photographs and text will detail one method for erecting mortar bed walls to receive tile in a tub surround. This is a "one coat" mortar method. This means that the mortar wall is applied in one coat without a scratch coat. This requires that a solid backing cover the studs. In this case the solid backing consisted of ½" water resistant gypsum board. Other craftsmen prior to my arrival installed the board, also called "green board".
The installation was checked for plumb and square, proper installation, and no variation in plane exceeding ¼" in 10 feet. Also, the tub surface was checked for damage that might have occurred during previous construction.
The first order of business was protecting the tub from damage during my work. This was 
accomplished with multiple layers of heavy construction paper held in place by duct tape. Note that the first layer of tape was positioned to allow the expected mortar thickness of ½." The paper was then installed and draped down into the tub. All areas of the tub including the front apron were protected.
The next step is preparing the membrane that is required to cover the solid backing. In this case 15 pound roofing felt was chosen. In order to accomplish this step, it is necessary to establish the dimensions of the two side walls.
Since the tile for this job was 4x4 tumbled 
marble with an accent strip, the tile was laid out on a floor to establish a full tile measurement. The accent strip made it necessary to set the tile with a 1/8" joint to make everything match up. By laying out the tile with the accent strip, 32" side walls were necessary. This measurement needed to have the depth of the back wall added making the total 32 ½".
Two lines, one on each side of the enclosure, were penciled in and represented where the membrane would end. A six foot level of six foot straight edge and four foot level can be used for this step. The important thing here is that the lines are plumb. The reason for this is that the membrane and wire will be used to set the float strips later.
At this point the roofing felt could be 
cut adding the 4" overlap that is required. The pieces were cut to approximately 36 ½" and a tight fold was made at 32 ½." Since the wall above the tub measured nearly 7 feet, four pieces of felt were cut per side. This insured plenty of overlap for each piece and plenty to overlap both the tub flange below and ceiling above. The felt is cut with a razor knife and straight edge insuring that the pieces were cut square to one another.
Pieces were similarly cut for the back wall so that the pieces would extend to either side wall without a fold. Once the pieces were cut, they were placed on the walls from the bottom up in shingle fashion held in place by a few staples.
The lower pieces of felt are allowed to drape over the tub flange approximately 1" to 2" and are folded tightly into all 90° corners. 
The felt is then taped to the 
tub protection to hold it tightly against the wall. After the mortar process the felt is cut where it meets the tub. This allows the membrane to be continuous behind the mortar into the tub over the flange.
Next the wire reinforcing (2.5 pound minimum) is cut using metal lath cutting shears. Be careful!
Once the wire is cut, it is sharp! The lath is measured and cut so that there is a break in the wire at all 90° corners. This acts as an expansion joint to deter the tile at the joint from cracking later in the life of the enclosure.
The reinforcing is applied and temporarily held in place with staples. Each piece must overlap each other 
the required 2" (or more). The reinforcing is then nailed into the studs with 2" galvanized nails bent over to catch at least three strands of width. These nails are spaced 6" on center.
Next the mortar tools are assembled and include a level, mortar board, hawk, finish and margin trowels, buckets, and a 6 foot metal 
feather edge. The wood float strips are moistened with water and are cut to the appropriate size. In this case the float strips are to be placed horizontally. This is a matter of preference.
The wall mortar is mixed in a wheelbarrow with the dry ingredients mixed prior to adding the water. The mixture consists of 1 part cement, 1 part hydrated type s lime, and 7 parts damp sand.
The mortar is mixed to a workable consistency where a furrow made in the mortar will not collapse. Be sure to use some measuring method like a small bucket. Fewer problems are the result of accuracy.
The mortar is taken to the enclosure and the wall mortaring process is started. In the one coat method, it is best to start the process when there is enough time to finish each section of wall at once. If there is doubt, do one wall section at a time.
The wire is fully embedded with mortar by firmly pressing the mortar into the wire with the finish trowel. Work on the area directly above the mortar board, which is resting on the protected tub top. This will keep falling mortar from being wasted in the bottom of the tub. Once the wire is fully embedded, score the mortar with a scratch coat tool or 1/2" ”notched trowel to allow the finishing coats of mortar to grab the original coat.
The next step is the float strip application. The 6’ metal featheredge is set against the back wall to establish the lower and upper float strip location. The float strips need to be set where the featheredge can reach both the upper and lower ends of the wall when placed against the strip.
In this case the lower back wall float strip is set first. A Column of mortar is placed on the wall where the float strip will be placed. The float strip is placed with the use of a level or straight edge.
This allows the float strip to be imbedded in the column straight and on plane. Measurements are taken from either end of the strip to the end of the side wall membrane.
In this case, the rear float strip measures 32” from the side wall membrane and wire making the back wall ½” thick.
The procedure is repeated for the upper float strip. The upper float strip is checked for plumb using a spirit level. This is the time for any minor adjustments to be made to insure that the back wall float strips are accurately placed and plumb.
Next, the procedure for setting the side wall float strips. They are similarly placed in a column of mortar and are measured from the adjoining wall to insure that the mortar bed is approximately ½” thick.
Then the float strip is squared against the back wall float strip. This represents the reason for the horizontal float strips. This process is repeated until all the float strips are in place.
More mortar is mixed and the filling process starts. Fill the areas surrounding the float strips with mortar applied with hawk and finish trowel. Fill the areas to a little above the float strip height. Use the metal featheredge to cut off the excess mortar filling any imperfections as you go.
Work around the enclosure filling and cutting until all the walls are completed.
You will notice that the side wall with the exposed shower valves is the hardest one to float. Use the metal featheredge at angle to cut off as much excess mortar as possible. It is quite common to use a finish trowel to remove the small patches of excess mortar in the areas not reachable by the featheredge.
For the outer edges, use a combination of finish trowel, margin trowel, or wood float to make the outer edges straight and uniform.
Once the walls are floated, remove the float strips by cutting the mortar at their edges float strip depth and carefully pull the strips out. Use caution not to disrupt the adjoining mortar bed. Fill the recesses with fresh mortar once the strips are removed and cut off the excess with a wood float or finish trowel.
Give the walls a careful final rub down with the wood float and insure that any imperfections are filled and the finished walls are flat.
In this case the mortar was allowed to cure (minimum 20 hours at 70° f) prior to the installation of the tile. At this point the felt was cut and the protective paper with the mortar process debris was removed. More protective paper was applied to the tub bottom and apron. From this point on the installer must exercise due caution, as the only protection is the bottom and the apron of the tub.
The beauty of this full tile installation is that the only layout line necessary was one vertical line on the back wall. There was no ledger necessary as the tub was installed level by previous trades.
The layout line was established in the exact middle of the back wall. Next, latex modified Portland cement mortar was mixed per the Manufacturers instructions.
The thin set was applied to the mortar bed with a ¼” notched trowel held at slightly less than 45°. First the thin set was “keyed” into the mortar bed using the flat side of the trowel.
The thin set was then combed to a uniform depth with the notched side of the trowel.
Only enough thin set was applied to set the first two rows of tile. These first two rows will be leveled and shimmed to exact level and will support the rows of tile installed above. A level is used to insure that these rows are straight and level.
Be sure to lightly beat the tiles in and to check periodically that the coverage of thin set is greater than 90% due to the “wet” enclosure. This tile actually has 100% coverage.
Dr’s tip: When setting the first two rows, it is important to space the tile 1/8” above the tub height. This space is an expansion joint and will be filled later with a sealant.
Once the first two rows are set and the installer is happy that the rows are set properly, the area above is trowelled and the tile is set in a similar fashion. The working line should not be covered with thin set. This allows a reference line for the additional rows of tile. Also, a level is continually used to maintain the straight and level application of each successive row of tile.
Next, the side walls are tiled in similar fashion from the bottom to the top. Since this was a full tile installation, very little cutting was necessary. However, the side wall with the protruding valves had some interesting cuts. There are two or more ways to handle this situation. In this case the valves were nearly in the center of full tiles. The tile was back cut and the center was punched out.
Note that this method leaves deep saw cuts on the back of the tile. Be sure to back-butter the tile forcing the thin set into the saw cuts. Then set the tile in a normal fashion.
This strengthens the back-cut tile.
It is possible to mark the tiles that fit over the valve and use a diamond hole saw for this step if you wish.
Note that this installation is from tub top to the ceiling. The minimum tub surround height needs only to extend from tub height to 70” above. Also note that tumbled marble has no manufactured trim pieces. It is the installer’s responsibility to fashion his or her own trim pieces. In this case, the trim was made by cutting tile into 1” pieces of the marble into trim pieces. This was the choice of the home owner. Also, an upper “crown type” trim was made to accent the installation.
In the case of the precut trim, the pieces are back-buttered and set into place with the appropriate spacers. The upper “crown” type trim needs to be supported by a ledger carefully and temporarily nailed into place. The ledger is removed after the thin set has cured.
Next is the grouting process. Be sure to keep the joints as clean as possible during the tiling process. This can save you time later when you prepare to grout. Remember that the 90° joints between the side walls and the back wall need to be left open for the installation of sealant not hard grout. Also, the interface between the tub and tile as well as the interface between the tile and drywall will receive a sealant not hard grout.
A total of two buckets will be needed. One for wash water and one for grout. Mix the grout per the Manufacturers instructions in a clean bucket mixing only enough grout that you will need. For small installations like this one, a margin trowel works very well for mixing the grout. The amount you will need comes with a little experience.
Grout small areas of tile at a time. Pre-moisten the tile with a sponge and water before the application of grout. Leave no standing water in the joints. Apply the grout with a rubber grout float held at a 45° angle diagonally across the face of the tile.
Be sure to force the grout fully into the joints.
Use the same grout float diagonally again to cut off the excess grout placing the excess back into the grout bucket. Use a good quality grout sponge wrung out thoroughly and rub the area using only enough pressure to “tool” the joints to an even depth. Be sure to fill any pin holes and even out any depressions as you go.
Clean out the grout sponge and wipe the tile face diagonally again cleaning the grout off the face of the tile. Repeat this process until the area is free of grout residue. This process can be mastered in a short time. Try not to over tool the joints and do not apply too much pressure to the sponge. The idea here is to clean off the face of the tile, not to re-tool the joints.
Once the field and trim tile has been grouted, make sure to clean out the areas that will receive the sealant. Follow the Manufacturers recommended curing process. In this case the Manufacturer recommended a misting spray for three days following grouting. This was accomplished with a household sprayer with the nozzle adjusted to a fine mist.
The next day it was possible to fill the required joints with a sealant that matched the grout color. The sealant was allowed to cure and final cleanup was possible. This tile needed to be sealed and this was accomplished following the Manufacturers instructions.
After the installation was completed, it was possible for the plumbers to install the necessary finishing trim.
Please keep an eye on this section for the two coat mortar method without solid backing and the use of backer board.
