Kitchen Tile - deflection issues

[jkk9]

To bbcamp:

"Pre-drill the new plywood and use a waterproof carpenter's glue spread with a small v-notch mastic spreader."

Do you mean pre-drill for the screws that hold down the new plywood?

[Houston Remodeler]

yes, so the new plywood doesn't rise up on the screw threads and create a void between the sheets.

[jkk9]

My kitchen subfloor squeaks. Do I use #9 deck screws on it everywhere before I lay the 1/2"? Or do I lay the 1/2" with glue and then use 2.5" #9s to hold the pre-drilled 1/2" and take care of the squeak?

[bbcamp]

You secure the subfloor so it doesn't squeak before you do anything else. When you install the second layer, use screws that penetrate the subfloor by 1/4". By using this length, you can drive the screws anywhere you want, so you do not have to avoid the joists. If you use longer screws, try to avoid the joists.

jkk9, please start a thread for your project, so we don't confuse bowtieman427 with his.

[jkk9]

Thinking of installing 1/4" ceramic in kitchen (225 ft^2). 3/4" T&G subfloor (after removel of vinyl and 3/8") Joists are 2x10, 16" oc, 15.5 feet from lip of plate to lip of beam, 18.5' total length (must be custom, no ink stamping). Deflecto calculation gives L/292. A 14' span would have beeen OK per the Deflecto. The floor feels very solid with just the 3/4 subfloor.

If I fix this with an additional support beam, what is required? A 4x4 on lallys? Wouldn't the lally posts need to have a footing for the base and not just sitting on the 4" floor? I read the posts about the TYW closet - is that built with just 2x4 stud walls?

I also want to do my 2 small baths - 25 and 35 sq ft. Can I run with the L/262 for such a small area?

[cx]

Welcome, Jim.

I brought your posts from that other fella's thread over here to avoid confusion there and to have the history of what's been asked and answered here.

If you wanna use a mid-span beam we'd need to know the length and how many support posts you would be willing to use.

The TYW closet can be framed as any other load-bearing wall with sheathing of some sort on at least one side.

Size of the room to be tiled has no bearing upon the floor joist deflection requirement. But it's your house and your tile and your dinero and you can tile over anything you like.

But I wouldn't recommend you do that.

My opinion; worth price charged.

[jkk9]

Kitchen size is 14x15, joists run the 15' length. Number of posts would be whats needed.

1/3 of baths is over finished basement; other 2/3 is obstructed underneath by plumbing and ductwork; hence the difficulty beaming the bathroom joists.

Thanks for the consolidation. Great memory!

[jkk9]

What are my choices on the mid-span (or 2/3rds span) beam/wall?

[cx]

Not sure what you're asking now, Jim. Choices? Like between a beam and a wall? I dunno.

I'm not an engineer, nor do I play one on TV, but my best guess is for a center span beam you would need doubled 2x10s across the 14-foot width with support at each end and the center.

Your very best option would be to pay a local structural engineer to come look at your application and make a recommendation.

My opinion; worth price charged.

[jkk9]

Had my brother (civil eng) look at my joists. They're actually 14.5' for unsupported span (L/247) with the additional ~32" hanging over the exterior wall. He said he could build an additional support wall under the floor but he said the additional trusses look brand new.

1/4" Durock was installed on the floor using modified thin set and screws. I then used a laser to measure floor heights. The attached PDF shows heights in 1/16", over 1 foot grids. Max difference in heights is 1/2". (The '0' was a point I picked that I thought was a high spot.)

So, using 12" ceramic tiles, I need to fill. Should I use Medium Bed Mortar to fill in the spots that are more than 1/8", then leveler to fill in the spots that are 1/8"?

[bbcamp]

I would recommend a self-leveling cement (something like Laticrete's 84 LatiLevel) or a trowelable patching compound (like Laticrete's 816 LatiPatch) to flatten your floor, rather than a medium bed mortar. You would use the SLC if you wanted a flat and level floor, the trowelable mortar if you had to maintain a slight slope. Both of these products can be applied over the backerboard you have installed.

[Scout123]

Interesting! Scout

[jkk9]

Bob: When you say to use a "trowelable patching compound (like Laticrete's 816 LatiPatch) to flatten your floor", is that partly because it's cheaper than the medium set mortar?

[jkk9]

Laticrete products don't seem to be available to the homeowner here in St. Louis. What are the suitable HD or Lowe's products?

[dhagin]

You've got to see what's available in the stores themselves. Different regions have different stock. Henry's/Ardex & Mapei make good products if Laticrete's not available in your local stores. Read the requirements on the bags to make sure they can be used from feather finish up to your maximum depth. Also, recommend mixing with a latex additive if it's an available option - Henry's/Ardex 547 mixed with their 546 is a good one.