pulled mortar bed out, replacing subfloor

Old 03-16-06, 05:43 PM
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pulled mortar bed out, replacing subfloor

I need some information about laying a standard plywood subfloor as a replacement for the old 3 1/2" mortar bed in my bathroom. Recently I asked a few questions on a tile forum and I received some good information. But I'd still like a little more help. If you guys can push me in the right direction, simply respond with a link, book, or IBC that could help. Here're the posts I've been making.

Thank you in advance!

A few days ago I decided to put a new pan in. Unfortunately I discovered that the previous redo was a half-butt job. Basically they hot mopped the pan and half the damn; allowing the original lead pan to remain the barrier over the damn.

After pulling the entire damn out due to water damage I realized that the mortar bed for my tile floor in the bathroom was cracked right down the middle. It must have happened during the removal of the shower pan and damn.

Regardless, I have already removed the mud bed and wanted to know about my options for a sub floor. The joists and beams have been trimmed to a point on the top for adding lateral strength to the mud bed; or commonly known as 'hatched'.

Is another mortar bed my only option?

I was planning on doing a simpler method, but I wanted some professional input prior to asking a bunch of hourly paid ‘clerk-contractors’ at HD.

A thought that had past my mind was using a hand planner to level the tops of the joists then add the subfloor to that. I have no problem with being able to plain the joists and beams to a level top; I’m confident in my carpentry ability. But I’m more or less worried about what I would use to fill the space and structural integrity of the joists. I’m sure I could use some pretty thick cement board and use thinset/mortar to modify the thickness to +/- ¼”.

The joists are 2x10 with plenty of room to work with. There’s also a 4x10 running directly through the bathroom at 16” with the other joists. That too has been “hatched”. My primary reason for wanting to add a new subfloor is due to the fact that there’s another bathroom directly next to mine with the same adjoining walls. I would like to tear down the alcove wall between them and make it one bathroom. The time and money isn’t available yet.

Would adding 2x10 sister joists or perpendicular joists to the joists/beams, give enough strength to hold a new subfloor or would there not be enough support on the current joists?

Could I take the peaks out my 2x10's and drop 5/8” plywood down or could I leave the peaks and just glue & screw 2x10 sister joists and then add the new subfloor to those?

I guess the question in a simple format is would the sister joists alone hold the subfloor? There isn’t going to be much of a live/dead load besides one toilet and a wall mounted sink.

Thanks for any help.
Old 03-17-06, 10:06 AM
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WOW! Boy I've seen more than my share of this type of thing and of course I can't see what you are dealing with for sure but in my thinking I would sister the existing joists and be done with this mess. Sistering is usually the lessor-of-the-eveils.

Lessor joists could be used and I would bolt them to the original joists I think.

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