How to Install a Cast Iron Tub

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Welcome to Showersly!

If you’re wondering, “How to Install a Cast Iron Tub?” you’re not alone.

Many home owners fall in love with cast iron tubs for their bathroom re-models, but due to their added weight, more questions naturally arise.

I’m here to answer those questions, and also, as an added bonus, give my pro tips along the way.

If you need help selecting a cast iron tub, check my guide to the 11 best cast iron tubs of 2019. You won’t want to miss it.

I hope that this page lifts the curtain of mystery on, “How to Install a Cast Iron Bathtub,” and that you enjoy yourself while you’re learning. Now lets get started.

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What You’ll Need

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How to Install a Cast Iron Alcove Tub

#1Remove Old Bath

• Disconnect drain with pliers
• Remove old wall material that may get in the way
• Slip wooden boards underneath old tub’s feet, to protect floor
• Slide out old tub

#3Prepare Subfloor

Make sure your subfloor is level. Also, check if it needs repairs, and/or reinforcement.

#4Determine Framing

• Take the height, width, and length of your new tub, then mark off where your tub will go on your subfloor
• Mark off area where drain will go, allow clearance
• Construct a framing recess for your particular tub, most commonly using 2x4s, making sure to allow room for sub & finished wall

#5Determine Draining

• Cut a 6″ x 12″ hole for the drain (unless it’s an above-the-floor drain install)

#6Partially Install Bath Drain

• Install your drain on your new tub (per drain manufacturers’ instructions)

#7Protect Bath Unit

• Put a towel down at the bottom of your new tub (prevents surface scratches)

#8Install New Cast Iron Alcove Tub

• Carefully slide new tub into frame
• Insert drain tailpipe into drain hole
• Level bath, using metal shims (as needed) underneath support feet
  • Bath must be resting on all 4 support feet
• Check level along top, and drain side of tub
  • If bath is still unlevel, you may have to move your tub in & out of the recess area, until it’s shimmed properly

#9Install Plumbing

CAUTION: risk of damage to subfloor & bath bottom

• Make sure all drain connections are watertight
• Once the bath is set, and secure, connect the drain to the trap
  • PRO TIP: Having an “access panel” will simply future maintenance

#10Complete Wall Finish

• Protect the bath surface
• Install gypsum wallboard, covering frames and walls
• Apply a bead of silicon sealant where the gypsum wallboard meets the tub
• Install the wall covering (subwall), go down until 1/16″ from tub surface
• Install the finished wall material to the subwall
• Use your silicon sealant to seal the joint between the rim of our tub, and the wall
• Install the finished floor
• Apply silicon sealant to bottom edge of your bath apron

#11Install Faucet Handles & Spout

• Install your faucet handles & spot, according to manufacturers instructions

#12Clean Up

NOTE: Avoid abrasive cleaners! (may damage or dull your tub surface)

• Use warm water + liquid detergent to clean surfaces

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How to Install a Cast Iron Drop-in Tub

#1BEFORE You Begin

• Inspect new tub for damages / imperfections
• Place tub on drop cloth to prevent scratches
• Make sure subfloor is level & can support the full load (weight of the tub & water)
• Ensure you have proper access to final plumbing locations

#2Site Prep

• WARNING: Do NOT support drop-in tubs by their rim, support by their feet
• Check plumbing supply lines for leaks, then cap
• Construct 2×4 or 2x6 stud framing for tub, allow room for finished wall

#3Suggested Framing

• Frame the floor (2×4 or 2×6) stud framing
• Provide 1/16″ gap between framing & bathtub rim (for finished wall)
• Position the rough-in plumbing
• Verify subfloor & framing can support tub, also make sure their level

#4Install Drain

• CAUTION #1: Do NOT lift without assistance, cast iron tubs are some of the heaviest tubs out there, so you’ll need help
• CAUTION #2: Do NOT support your cast iron drop-in tub by it’s rim
• Install your drain, according to drain manufacturer’s instructions
• Place drop cloth inside tub to protect from scratches

#5Install Cast Iron Drop-In Tub

• CAUTION #1 & #2 still hold true
• Using help, move your bathtub into postion, within your frame
• Once in position, verify that your tub is level
  • Using your metal shims, adjust if necessary under feet
• PRO TIP: For future maintenance allow access to plumbing

#6Install Plumbing

• CAUTION: Ensure your connections are watertight, prevents leaks & property damage
• Connect your drain to your tap, according to drain manufacturer’s specifications
• Install your faucet valve, according to faucet manufacturer’s specifications
• Open your water supply, check ALL connections for leaks
• Fill your new cast iron drop-in tub to the overflow, check for leaks

#7Complete Finished Wall

• Install finished wall material / tile, leave 1/16″ gap for silicon sealant
• Seal with silicon sealant
• Install faucet trim, according to faucet manufacturer’s instructions

#8Clean Up

• CAUTION: AVOID acidic & alkaline based cleaners, will damage cast iron enamel
• Use a neutral detergent, soft cloth, and warm water to scrub away any dirt / imperfections

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How to Install a Cast Iron Pedestal or Clawfoot Tub

#1BEFORE You Begin

• Make sure your floor can support your new tub’s load
• Verify floor is level
• Once you receive your new tub, with a pencil, mark your dimensions in the floor where your new tub will go

#2Place Your New Tub In Your Desired Location

• Once into place, drop a plumb line from your new tub’s overflow drain
  • Determines your drain location
• Mark your drain hole location on your floor

#3Move Tub To Install Plumbing

• Once your tub is out of the way, install your drain & waste pipping at the appropriate height
  • To determine this, pre-install your drain pipping to your tub, and measure length to the floor (where your drain will be)

#4Set Tub Back Into Position – Level

• Carefully, set your tub back into position, level with metal shims if necessary
  • For cast iron pedestal tubs: apply a bead of silicon to leveling feet once into place, to prevent future movement

#5Trim Drain & Overflow Pipes

• Once your tub is set into place, trim your drain pipe, and overflow pipe to the required length

#6Use Plumber’s Tape To Prep Drain & Overflow Pipes

• Once your drain & overflow pipes are properly trimmed, put plumbers tape around the threads at all ends

#7Apply Silicon Sealant To Drain Flange

• Now that your tub is in place, and your pipes are prepped, apply your silicon sealant to the drain flange underneath your tub
• Next, get your drain flange, and thread it through your tub, to your drain pipe
  • Use silicon sealant, or plumbers tape, to ensure a watertight seal
  • CAUTION: Failure to provide a watertight seal, with your drain, can lead to significant water damage, so be careful
• Tighten your drain flange by hand, wiping away any excess silicon sealant

#8Install Overflow Piping

• Install your overflow assembly (overflow plate, beveled washer, and mounting screw)
  • Use your silicon sealant underneath the flange, to ensure a watertight seal

#9Connect Waste Drain to Overflow Pipping

• Using sealing washers, and slip nuts, connect the waste & overflow tee
  • Beveled end of the washer should face the tee

#10Connect Waste & Overflow Tee to Floor Drain

• Beveled end of the washer should face the tee

#11Now That Your Tub Is Set, Check for Leaks

• Once tub is in place, and all connections are made, check for leaks
  • This can be done by slowly filling up your tub with water, making sure the overflow drain, and waste drain are watertight

#12For Cast Iron Pedestal Tubs ONLY

• Apply silicon sealant around the base of your pedestal tub, wipe away excess sealant

#13Clean Up

• Same goes as the other tubs, AVOID acidic & alkaline based, will damage your tub
  • Instead, use warm water, a neutral detergent, and a soft cloth

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Summing it up

There you have it folks.

After reading this page, you should have a good idea on how to perform your cast iron bath installation.

Again, as we’ve said many times throughout this guide, cast iron tubs are HEAVY, so you MUST check if your floor / subfloor can support this significant amount of added weight.

Once you get the green light, that your floor can support the weight, you’re all set to enjoy LONGER, and WARMER baths.

After taking your first cast iron bath, good luck trying to go back!

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