How to Mortar Under a Bathtub

Mortaring under your bathtub will help to keep it from dislodging from the wall.

Mortar, or a mix of sand and cement, is typically installed beneath a bathtub to create a base to support the tub. Bathtubs can expand when filled with water due to the added weight and heat. This expansion can move the tub and cause it to dislodge from the wall if it's not secured to a mortar base. You can mortar under your bathtub yourself and save the cost of hiring a professional service to do the work for you.

Things You'll Need

• Tape measure
• Mortar mix
• Plastic tub or other container
• Water
• Trowel
• Chalk line
• Wooden beams
• Carpenter's glue
• Trowel
• Towel
• Wooden mallet
• Work gloves
• Safety goggles

Instructions

1. Measure the width and length of your bathtub, using a tape measure. Snap chalk lines matching these measurements around the area where you will install your bathtub.

2. Measure the tub’s height from the base of the tub to your bathroom floor. Position wood beams against the chalk lines. Each beam you install should be 2 inches thicker than the tub’s base height. Use carpenter’s glue to secure the beams together to form a rectangle.

3. Mix mortar in a plastic tub according to the manufacturer’s instructions. Pour the mortar into the area between the wood beams. Allow the height of the poured mortar to reach about 1 inch below the top ends of the wooden beams.

4. Level the mortar with a trowel. Position the tub on the mortar base. Let the tub sink down to the height of the skirt you intend to attach. Position additional wood beams against one side of the tub to help secure it against the wall.

5. Use a damp towel to wipe away any excess mortar from the wall. Allow the mortar two days to dry. Use a wooden mallet to tap the beams and loosen them enough to easily free them from around the tub.

Tips & Warnings

• Use thermal mortar to achieve the best results. This type of mortar expands and contracts when exposed to heat and is less likely to crack than standard mortar.

• Always wear safety gloves and safety goggles 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