Bathtub Installation

In this section, you’ll learn how to tile a bath tub with ceramic tile, porcelain tile or stone tile using the “one coat” mortar method. If you’re interested in reviewing a similar installation using backerboard, click on Bathtub Installation with Backerboard.

Ceramic, porcelain, and stone tile tubs are the focus in this how to section.

Note that a prefabricated 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 Manufacturer’s instructions for the products that you choose to use.

What You’ll Need for this Tile Installation Project

  • ½” water resistant gypsum board also called “green board”
  • Heavy contruction paper and duct tape
  • 15 pound roofing felt
  • Tile for the job (in this case 4×4 tumbled marble with an accent strip)
  • Pencil
  • Straight edge
  • Level
  • Razor knife to cut felt
  • Wire reinforcing (2.5 pound minimum)
  • Metal lath cutting shears
  • 2″ galvanized nails
  • Mortar tools:
    • Level
    • Mortar board
    • Hawk, finish and margin trowels
    • Buckets
    • 6 foot metal feather edge
    • Wood float strips
    • Wheelbarrow for mixing mortar
    • Mortar dry ingredients: 1 part cement, 1 part hydrated type s lime, and 7 parts damp sand
    • Scratch coat tool or 1/2″ “notched trowel

The One Coat Mortar Method for Installing Tile Around a Bathtub

The following photographs and text will detail one method for erecting mortar bed walls to receive tile in a tub surround using the one coat mortar method where 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 also called “green board”.

Check that the installation is plumb and square, with no variation in plane exceeding ¼” in 10 feet. Also, make sure to check the tub surface for damage that might have occurred during previous construction.

Next, you’ll want to protect the tub from damage during your work by draping multiple layers of heavy construction paper down into the tub and holding it in place with duct tape.

Position the first layer of tape to allow for the expected mortar thickness of ½.” This will protect all areas of the tub including the front apron.

Then prepare the membrane that will cover the solid backing. In this case, use 15 pound roofing felt. For this step, you’ll need to establish the dimensions of the two side walls.

Since the tile for this job was 4×4 tumbled marble with an accent strip, the tile was laid out on a floor to establish a full tile measurement.

The accent strip makes 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.

To this measurement, we added the depth of the back wall making the total 32 ½”.

Two lines, one on each side of the enclosure, were penciled in to represent 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 can be cut. Don’t forget to add the required 4″ overlap.

The pieces were cut to approximately 36 ½” and a tight fold was made at 32 ½.”

Since the wall above the tub measures nearly 7 feet, four pieces of felt were cut per side.

This insures 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 to make sure that the pieces are all cut square to one another.

You can similarly cut pieces for the back wall so they extend to either side wall without a fold.

Once cut, the pieces are 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 by 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, assemble the mortar tools! These include a level, mortar board, hawk, finish and margin trowels, buckets, and a 6 foot metal feather edge.

Moisten the wood float strips with water and cut them 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 feather edge is set against the back wall to establish the lower and upper float strip location. The float strips need to be set where the feather edge can reach both the upper and lower ends of the wall when placed against the strip.

Here, 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 ensure 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.

Mix more mortar and begin the filling process.

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 feathe redge 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 feather edge 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 feather edge.

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 make sure 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 you’ll only need one vertical layout line on the back wall in the exact middle of the wall. No ledger was necessary as the tub was installed level by previous trades.

Next, latex modified Portland cement mortar was mixed per the Manufacturer’s 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.

Important Tip: When setting the first two rows, be sure 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 can be trowelled and the tile 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, tile the side walls in a similar fashion from the bottom to the top. Since this is a full tile installation, very little cutting is necessary.

However, the side wall with the protruding valves requires 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 to force 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, we made the trim by cutting tile into 1″ pieces of the marble into trim pieces.

Also, we made an upper “crown type” trim to accent the installation. In the case of the pre-cut 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, using a product such as Starlike Bathroom Grout.

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 we completed the installation, it was possible for the plumbers to install the necessary finishing trim.

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