Installing a cast iron tub

[NetWareHead]

Any pointers on installing a cast iron tub into a 3 wall alcove in a bathroom? The tub will be surrounded by wall tile on 3 sides. The open side of the tub will have a visible apron that touches the floor.

I've been doing alot of reading about this and have so far come up with some ideas I would like to incorporate.

1. The tub has tiny but pointed feet. They are basically skinny points underneath the finished surface. Have been seeing alot of advice to set the tub on metal shims. The idea being that these pointed feet will bear the entire load of the tub, occupant and water. Eventually when set on a plywood subfloor, some compression of the wood is possible leading to the tub shifting. Metal shims under these feet will better resist these loads.

2. Ledger board under the long section of the tub against the wall opposite the apron. Not trying to support the weight of the tub by its lip but more or less integrating the tub with the wall surface. Do all sides of the tub that touch a wall need a ledger or just the long side? And how above above the lip of the tub? The ledger will sit under the lip but is there anything to secure the top of the lip? Or is that a function of the tile underlayment which leads to my next question.

3. Tiled surface. The hardibacker (or similar underlayment) will be nailed to the studs above the bath tub and the bottom edge of underlayment will touch the tub. There was a bathroom reno thread here http://forums.anandtech.com/showthread.php?t=2460295 where some methods of waterproofing the edge of a tiled surface to a shower were discussed but wondering if a bathtub is similar. Also, any similar recommendations for where the apron of the tub will meet the floor tile and how to install that underlayment?

Thanks for any comments/advice...

 

[gururu2]

1. Seems to be a common instruction from most installations when shimming. Others favor placing some thin steel squares under each foot. See John Bridge or Terry Love forums. Tons of good information.

2. Just the long side. Helps prevent shifting of tub. Top of lip will have a vapor barrier hanging over it secured down with some caulk and tile over it.

3. You should use screws instead of nails. I used Durock with Kerdi over it. Durock was ~1/8" above lip and the Kerdi went over lip (affixed to the lip with Kerdifix). Instead of Kerdi you can use Redguard, but this wont reach over lip as its a "paint". Fill in the lip gap with caulk. This creates a flexible link between the tub and the wall. Tile direct over the redguard and over the lip (tile should not contact the lip). Caulk in seam.

 

[gururu2]

For the floor, I used DITRA over plywood and tile on the DITRA. That rides up to the apron bottom and the tile/tub seam can be caulked. I did end up stacking another sheet of plywood on top of the old one because it was starting to bow and for tile it needs to be rock solid.

 

[Micrornd]

We get around the point loading problems by bedding all (metal or other) tubs in a bed of mortar when we install them.
This spreads the load over all the possible joists and greatly decreases any deflection or point load.

 

[NetWareHead]

We get around the point loading problems by bedding all (metal or other) tubs in a bed of mortar when we install them.
This spreads the load over all the possible joists and greatly decreases any deflection or point load.

Ok so I read about this and it looks like this would support the tub uniformly under it and not just on its little feet. Seems like this is the most recommended method to best support the tub

Instructions I found were to mix up some brick mortar, stiffer than you would use for laying bricks. Recommended was home depot's "mason mix", structo-lite or topping cement. Dont use plaster of paris bc it sets up too quickly.

Make 2-3 inch high mounds (that will reach higher than the floor of the unit) strategically placed around base of tub and set it into the mortar. Set the tub down into this and smoosh it into the mortar. Level the tub. Use nails above the lip & butt somethign up against the apron of the tub to lock it into place.

Questions:

1. Can I just set this mortar straight down onto the plywood subfloor?

2. How do I keep all of this mortar contained so it doesnt spill out to the sides when I set the tub down into it?

3. Read some recommendations to keep out of the tub for 24 hours while the mortar bed sets up. Should I put some weight in the tub while it sets? Read somewhere that they filled up the tub with water while the mortar bed cured...

 

[gururu2]

I did the mortar bed with an acrylic tub. It adds 50-100 lbs to the weight, which you have to consider with a cast iron (especially on second floor). I think its heavy enough to not need the mortar, but it would certainly distribute the weight.
I used a regular mortar (noone seemed to carry the recommended structo-lite) and just put one large mound right on the plywood pretty much dead center. I placed the tub on and stood on it until it seemed stable and the legs were all on the floor. I didnt have any seep out of the edges. The apron helps contain it. In my case the tub center was above floor so I had to add a lot of mortar so it maintained good contact between floor and tub as it spread. I didn't keep any weight on it while it cured.

 

[skyking]

We insulated our cast iron tub with the spray foam. It holds a warm bath a bit longer.

 

[Micrornd]

Questions:

1. Can I just set this mortar straight down onto the plywood subfloor?

2. How do I keep all of this mortar contained so it doesnt spill out to the sides when I set the tub down into it?

3. Read some recommendations to keep out of the tub for 24 hours while the mortar bed sets up. Should I put some weight in the tub while it sets? Read somewhere that they filled up the tub with water while the mortar bed cured...

1. We put down a separate sheet of 1/4" plywood on top of the subfloor, nailed in the 4 corners only, beyond the mortar bed.
(Just to make it easier, if someone remodels in the future)

2. Only put the mortar directly under the bottom of the tub, you can see where it will contact and how high it should be.
Make a stiff mix.

3. We do not put weight in. The idea is for the tub to be in constant contact with the mortar bed and not pull away from it when empty.

As skyking said insulation is a good thing.
I used a heavy combination of fiberglass and rigid foam on our own acrylic jetted tub, and the wife says it stays the same temp for 2 1/2 hrs. +.
( I wouldn't know, I prefer showers )

 

[Hilary Andrews]

Thank you for sharing your valuable experience. It will be helpful for most of us.I am also planning for bathroom renovation and one of my friends suggested me to contact professionals for renovation. I am planning to install walk in tub bend, as my mother was unable to climb traditional bath tubs.If anyone ever used these type of bath tubs please share your suggestions.