Strengthening bathroom floor to support a cast iron bath

[Jamesjf1]

(Sorry if this subject is already on here, but I can't find it. Please point it out for me if it does).

I've bought a big, old cast iron bath (very heavy, but couldn't give any sort of accurate weight) to fit in our ground floor bathroom. It's approx 6' x 34", with the usual 4 ornate feet.

The bathroom has a suspended floor of 28mm floorboards over 6.5" x 2.5" joists spaced at approx 18" centres. Does anyone have any thoughts on whether the joists/floor would need strengthening and, if so, how?

The feet of the existing acrylic bath are each supported on short lengths of 2" x 1", which spread the load on each foot across the width of 4 160mm wide floorboards each. I wouldn't want this with the new bath, as the underside is exposed and on view. Would adding a second layer of floorboards on top of, and perpendicular to, the existing floor serve any load-bearing/spreading benefit (as I would prefer an exposed floorboard finish)?

Thanks

 

[DAZB]

I don't think you have too much to worry about with the floor you have. Generally flooring isn't as thick as the one you have and the joist spacing is adequate so I'd consider it ok to take the load.

 

[Richard C]

You should be OK with the joist size & spacing you have but the unsupported span & where the bath sits within that span is also a factor. If the feet don’t sit directly over a joist, I would add some 4” x 2” noggins to provide additional support; it’s a relatively simple job to sister the joists under the bath if necessary.

 

[Jamesjf1]

Thanks for taking the time to reply, Daz and Richard.

If I go for a tiled bathroom floor, would you install the bath and then tile around the feet? (The weight of it means that getting into position might cause damage to any tiling already done).

Thanks

 

[Richard C]

That’s a tricky one for me; I'll admit I’ve never actually done a bathroom that’s been tiled under with ornate bath feet resting on the floor tiles. Floor tiles must always be laid on a thick solid bed adhesive (no air voids) or point loads (even feet) can cause the tiles/grout to crack. Now in theory, with a solid adhesive bed, a reasonably flat tile & no unevenness or projections on the feet that would cause a dramatic point load on the tile then you should be OK. It’s certainly not a problem with appliances & I’ve supported some pretty heavy ones on kitchen floor tiles but the point loadings on a cast iron bath filled with water & one (possibly 2 ) people in it will weigh somewhat more than that.

Hopefully one of the other guys on here who have done it before, will spot this & confirm or advise what they usually do.

As before, I would ensure you have either a joist or noggin under each foot.