How to Do the Mortar Base for a Bathtub

Most modern bathtubs are comprised of fiberglass, or glass-reinforced plastic, which is lightweight and easy to transport. Fiberglass tubs expand slightly when filled with warm water, which can result in the entire tub shifting out of position. Installing a mortar base secures the tub in place and helps prevents movement. Installing a mortar base is a relatively simple DIY project, and the work can typically be completed in one afternoon.

Things You'll Need

• Plastic sheeting
• Tape measure
• Utility Knife
• Mortar mix
• Bucket
• Trowel
• Level

Instructions

1. Position the tub in the center of your bathroom. Measure the distance from the bottom of the tub to the rear, drain area, and middle of your bathtub.

2. Measure the length and width of your tub. Mark a sheet of plastic to match your tub measurements. Cut the sheeting with a utility knife.

3. Lay the plastic sheeting across the floor against the wall where you intend to install the tub. The plastic will keep any moisture from the mortar contained, preventing it from seeping into your bathroom subfloor.

4. Mix mortar, according to the manufacturer’s instructions, in a bucket. Use a masonry trowel to scoop out the mortar and spread it over the plastic sheeting. Follow the contour of the bottom of your tub as you spread the mortar. Add one inch to each of your previous tub measurements to determine the correct thickness for your mortar.

5. Lift the tub and position it on top of the mortar bed in the desired final position. Press down on the tub until the tub skirt sinks down entirely and comes into contact with your bathroom floor.

6. Level the sides of your bathtub with a level. Allow the mortar to dry for 48 hours.

Tips & Warnings

• Ask a friend to help you place the tub on top of the mortar bed to make the job go faster and more smoothly.

• Always wear safety gloves when working with hand tools to prevent injury.

References

• TMPorterLtd: Mortar Bed How-To
• "Audel Plumber's Pocket Manual"; Rex Miller, et al.; 2004

Resources

• "The Plumbing Apprentice Handbook"; R. Dodge Woodson; 1993