How to Install an Alcove Bathtub
Learn how to prep alcove framing, install supporting ledger boards, lay a mortar bed, drop in the tub, and anchor the flange level and plumb.
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🧰 Required Tools & Equipment
- ✓ 4-foot spirit level
- ✓ Drill and driver bits
- ✓ Tape measure
- ✓ Mortar mixing paddle and bucket
- ✓ Pencil
📦 Materials & Supplies
- ✓ Alcove bathtub
- ✓ 2x4 lumber
- ✓ 3-inch structural wood screws
- ✓ Mortar mix
- ✓ 6 mil plastic sheeting
- ✓ Tub drain and overflow kit
⚠️ Safety Checkpoints & Warnings
- • Clear subfloor completely of protruding nails and debris before laying mortar to avoid tub puncture.
- • Use two people to lift and lower the bathtub into the alcove to prevent back strain and tub cracking.
- • Wear safety glasses and work gloves when mixing mortar and driving structural screws into studs.
📋 Step-by-Step Guide (6 Steps)
Dry-Fit Tub and Check Studs for Plumb
Slide the bare bathtub into the rough framing pocket until the back and side flanges touch the studs. Check all framing studs with a 4-foot spirit level and confirm the subfloor is flat and free of debris. Mark the exact height of the tub's top flange and bottom supporting lip against the wall studs with a pencil.
- • Bathtub resting fully inside framing pocket with clearance at drain hole
- • Clear horizontal pencil marks across all rear and side wall studs matching tub lip height
- • Skipping the dry fit, resulting in flange clearance issues or pipe alignment errors after mortar is laid
Mount the 2x4 Support Ledger Boards
Remove the tub from the alcove. Measure down from the pencil marks by the thickness of the tub flange to locate the top edge of the 2x4 ledger board. Fasten 2x4 lumber horizontally across the back wall and side studs using two 3-inch structural screws per stud.
- • 2x4 boards fastened horizontally across rear and side studs
- • Spirit level bubble centered along the top edge of the newly mounted ledger board
- • Mounting the ledger board at the overall flange mark instead of compensating for the bottom lip thickness
Install the Waste and Overflow Drain Assembly
Install the tub shoe, drain gasket, and overflow pipe onto the tub body while it is tilted outside the alcove. Thread the drain basket into the shoe with plumber's putty or manufacturer gasket under the flange, and tighten securely with a drain wrench. Connect the vertical overflow pipe to the drain tee so all compression joints seat squarely.
- • Drain basket seated flush against tub floor with excess putty squeezed out evenly
- • Overflow cover plate and gasket seated firmly against tub overflow opening
- • Overtightening the drain basket and squeezing out all putty or cracking acrylic
- • Cross-threading plastic slip-joint nuts on the overflow assembly
Mix and Lay the Mortar Support Bed
Lay a piece of 6 mil poly plastic over the subfloor to prevent dry plywood from pulling moisture out of the wet mix. Mix mortar in a bucket with water until it reaches a thick, peanut-butter consistency that holds its shape. Shovel 3 to 4 thick mounds (about 2 inches tall) across the subfloor where the tub basin floor will rest.
- • Plastic sheeting covering subfloor below tub footprint
- • 3 to 4 distinct 2-inch mounds of wet mortar spaced evenly across basin support zone
- • Mixing mortar too watery, causing it to flatten out and provide zero load-bearing support
- • Placing mortar over the drain cutout, blocking plumbing access
Set Tub into Mortar and Verify Level
Carefully lift the tub and drop it straight down into the alcove, sliding the back edge over the ledger board. Step into the tub with socks on and apply steady downward foot pressure to squish the basin base firmly into the wet mortar mounds until the rim rests solidly on the ledger. Place the 4-foot level along the front deck and side aprons to confirm absolute level in both axes.
- • Tub bottom rim resting flush against the 2x4 ledger board without gaps
- • Level bubble dead center on both front ledge and side ledges
- • Letting the tub sit high without walking it down into the mortar bed before mortar sets
Secure Flange to Wall Studs
Fasten the tub flange to every overlapping stud along the top perimeter. If the flange lacks pre-drilled holes, drive pan-head screws with galvanized washers directly above the flange lip so the screw head clamps the edge down, or pre-drill oversized clearance holes through the flange. Ensure no screw heads distort or pinch through the acrylic.
- • Pan-head screws or washer-backed screws holding flange snug against every stud
- • Flange held tight to framing without visible cracks or bowed plastic
- • Driving drywall screws directly through un-drilled acrylic flange, instantly shattering the lip
Credit: inspired by an original tutorial by Home RenoVision DIY — watch the original on YouTube.
Don’t have everything?
- No Mortar mixing paddle and bucket? Trowel or small shovel in a heavy-duty wheelbarrow
- No 4-foot spirit level? 2-foot spirit level placed on top of a straight 2x4 board