Replacing a bathtub is a major bathroom project — typically the central piece of a bath remodel. The work involves removing the old tub (often by destruction), prepping subfloor and walls, setting the new tub, plumbing connections, and finishing walls and floor around it. Most replacement scenarios are like-for-like (same drain location, same alcove dimensions); replacements with different fixtures or layouts add structural and plumbing work.
This guide covers a typical 60×30 inch alcove tub replacement — the most common Canadian bathroom configuration.
Before you start
Three things to settle:
1. Tub material drives weight and finishing. Acrylic: lightweight (40-60 lbs), warm to touch, shows scratches. Fibreglass: cheap, lightweight, less durable. Cast iron: heavy (250-400 lbs), needs reinforcement, premium feel. Steel-enamel: heavy, durable, traditional look. Match material to budget and use.
2. Drain location must match new tub. Old drain rough-in: 16-18 inches from one end (varies by tub). New tub's drain location may differ. Verify match before tub purchase.
3. Wall structure access. Removing tub typically requires removing tile or wall panels above tub. Plan to retile or rebuild walls during install. Tub-only replacement (without retiling) requires careful demo to preserve existing wall.
What you'll need
Tools
- Reciprocating saw or oscillating tool
- Drill with bits and driver
- Pry bar
- Tape measure
- Level
- Adjustable wrench
- Bucket and old towels
Materials
- New bathtub (matched to alcove)
- Drain assembly matched to tub
- Cement board (1/2 inch — for tile walls)
- Plywood subfloor (if old subfloor damaged)
- Pipe nipples and elbows (for plumbing reconnection)
- Plumber's tape
- Plaster of paris or quick-set mortar (for tub setting bed)
- Construction adhesive
- Silicone caulk (100% silicone)
Old cast iron tubs: cut up to remove
Cast iron tubs are too heavy to lift out (250-400 lbs).
Score with grinder or use sledgehammer + chisel to break into manageable pieces.
Wear safety glasses + dust mask. Cast iron shards are sharp.
Cardboard or plastic over old tub before breaking — contains the chips.
Step-by-step instructions
Shut off water and disconnect plumbing
Whole-house main water shut-off (or local at bathroom).
Drain tub (open faucet, plus open lowest fixture in house if needed).
Disconnect tub spout, shower head from valve.
Disconnect drain (typically pipe runs to overflow drain at end of tub).
Cut wall above tub
Cut tile/drywall on each side of tub up to where new tub deck height will be.
Allow access to plumbing behind tub.
Save reusable trim if possible.
Drywall and tile dust everywhere — protect rest of bathroom.
Remove old tub
Acrylic/fibreglass: remove screws securing tub to studs, lift out.
Cast iron: cut up with grinder + chisel to manageable pieces.
Steel: heavy but lifts out (3-4 people).
Inspect and repair subfloor
Look for water damage, rot, mould around drain location.
Replace damaged subfloor.
Verify floor is level and structurally sound.
Prepare drain rough-in
Verify drain pipe is in correct location for new tub.
Adjust if needed (cut, extend, reroute).
Pressure test new drain plumbing.
Set tub bedding (mortar bed)
Mix mortar (plaster of paris or quick-set) on subfloor where tub will sit.
Bedding supports tub bottom — prevents flexing under weight.
Spread evenly across the tub footprint.
Set new tub in place
Lower tub onto mortar bed.
Verify tub is level (front-back, side-side).
Drain aligned with rough-in.
Tub flanges (the lip on the sides and back) sit against studs.
Anchor tub to studs
Most tubs have flanges or mounting holes.
Drive screws through flanges into studs.
Don't overtighten — flanges crack.
Connect drain assembly
Drain components per tub manufacturer.
Plumber's tape on threads.
Tighten drain trim from above; tighten lock-nut from below.
Don't overtighten.
Reconnect water supply
Tub spout and shower trim per fixture install.
Apply plumber's tape.
Hand-tight + 1/4 turn with wrench.
Install cement board around tub
1/2 inch cement board around alcove walls (for tile finish).
Edges overlap tub flange.
Cement board screws into studs.
Tile walls and floor
Tile per tub spec.
Waterproofing membrane (Schluter Kerdi or RedGard) over cement board first.
Grout, caulk in corners (silicone).
Test for leaks
Restore water.
Fill tub. Drain. Watch for leaks at all connections.
24-hour leak test.
Common mistakes that cost you
- Drain location mismatch. Doesn't connect. Verify before purchasing tub.
- No mortar bedding. Tub flexes under weight, may crack. Always mortar bed.
- Skipping subfloor inspection. Rotted floor under new tub = unstable. Repair first.
- Wrong tub for alcove dimensions. Doesn't fit. Measure carefully.
- Skipping waterproof membrane. Walls leak around tub. Always waterproof before tile.
Frequently asked questions
What drives the cost of replacing a bathtub?
The biggest cost drivers are tub material (acrylic, fibreglass, cast iron, or steel-enamel), the extent of any plumbing modifications when the new drain location differs from the old rough-in, and how much wall and floor finishing the surround needs.
A direct tub-only swap with no layout change costs far less than a full bathroom replacement that includes new tile, waterproofing, and fixtures. Site conditions — subfloor condition, access, and reinforcement for heavy cast iron — also affect labour. We provide a detailed written breakdown before work begins so you see exactly what is included.
Should I replace the tub or refinish?
Refinishing (resurfacing) is the lower-cost option and typically lasts 5-10 years.
Replacement: longer lasting, more involved.
Refinish if structure is good and you like the size; replace if material is wrong or fixture is damaged.
Do I need a permit?
Like-for-like tub replacement: typically no permit required.
If plumbing rough-in changes, or if structural changes: plumbing permit required.
Check with municipality.
When to call us instead
Tub replacement is part of every bathroom renovation. Our team handles plumbing, tile, and fixture install as fixed-price work.
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