Porcelain tile install in 1945 kitchen. Am I doing this right? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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03-24-2015, 11:27 AM
Hi, all,

Been reading a bunch on here and trying to learn as I go along.

Trying to prepare my kitchen floor for porcelain tile. Small area, about 80 sq. ft.

1945 house, 2x8, 16” OC floor joists.

What I’ve done so far:
- Used a nail set to set all the original nail heads in the original 5” T&G floor boards.
- Added an extra deck screw in between each pair of nails used to attach each board to the joists.
- Laid 5/8” exterior plywood with 1/8” gap between sheets and around edges, used 1 5/8" deck screws, 4" spacing on edges, 5-6" in the field
- Primed ply, laid down some diamond mesh and poured about half a bucket of LevelQuick RS into two low spots, to fill in dips that were about 1/4" over a 4’ span

What I’m about to do:

- Lay down Ditra over modified thinset
- Tile over Ditra… no details necessary here? Well, I'm considering 12"x24" porcelain tile. But maybe 6"x12", not sure yet.

What my problem/question is:

This was my first ever time using SLC. I think it came out to be about 90% perfect, in that it filled in the dips in the floor. However I did muck with it a little too much, so the other “10%” is what is bothering me. The two dips were in two different areas of the floor. I did not use SLC on the entire floor, but simply tried to feather it out. There are some small ripples in the SLC that had set, and there are some small bumps on the top that dried from the drips that dripped onto it from my screed tool. I took to use 60 grit sandpaper on a drywall sanding block to smooth out those areas and I think I should be able to with a little bit of elbow grease, to smooth out those spots.

All I really need I think from this place is some reassurance on what I have done so far, I guess. I’m not sure how much time I should spend trying to perfectly feather out and make the SLC areas smooth, or if the 1/8” thinset + Ditra + the thinset on Top of Ditra will make those small 1/16” – 1/8” irregularities pretty much insignificant?

Thanks for reading!

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03-24-2015, 11:43 AM
Hello, Geneus. Welcome to the forum. :)

If you have a little bump where the SLC terminates, that needs to be knocked down to a feather edge. With a tile the size that you plan to use, your floor should not be out of plane more than 1/16" in any two feet, or 1/8" in any ten feet. So a 1/8" is a little much if it's abrupt.

Since you had only 1/4" to build up, is the lath covered completely?

The little bumps you have from the SLC dripping should be knocked down, however you can get that done. If you have a scraper, that might work for you.

03-24-2015, 11:44 AM
You provided most of the specs of your support structure except the unsupported span of those 2x8s (true 8" or 7.25"?). Did you plug your numbers into the handy-dandy Deflecto located in the blue bar near the top of every page?

Were the 5" boards laid on an angle or perpendicular to the floor joists?

Otherwise, assuming you meet the deflection requirements, it all sounds good.

I have OCD and I'd probably continue smoothing out the SLC. Your tiles sound like they might be on the largish size so the flatter the floor, the better. A rub stone could also work to smooth things out.

03-24-2015, 12:06 PM

The lath is covered 99%; I can see in one spot just the tiniest amount of protrusion from one or two rows of the lath, barely above the surface of the SLC.


I did plug my numbers into the deflection calc before I started anything, and it did tell me that I should be fine for porcelain tile, but not natural stone. I don't remember the unsupported length but if that's one of the parameters that was asked by the calculator, I must have measured it. I want to say it's about 9'.

The 2x8s are 7.25".

The 5" boards are laid perpendicular to the floor joists.

Thank you for the rub stone suggestion, i've never heard of it but it sounds like it would do a better job than sandpaper!

03-24-2015, 12:13 PM
The orange and blue box stores should have rub stones in the tile section.

03-24-2015, 06:41 PM
The orange and blue box stores should have rub stones in the tile section.

I looked on both of their websites and I can't find anything by that name. They call them anything else? My OCD is kicking in on the CBU seam mortar, needs to be blended down a little :bonk:

03-24-2015, 08:44 PM
Welcome, genEus. Please change that permanent signature line to a first name for us to use. :)

Dan, try "tile rubbing stone." Homer's carries a two-grit stone from QEP that I've never tried, but they usually also have a blue one that I've found useful for breaking tile edges.

But for course work like knocking down CBU joints, look for a "rub brick" (see picher).


03-24-2015, 09:17 PM
Thanks CX. That tile stone just looks like your garden variety sharpening stone like you would use for knives/scrapers. The creatures that inhabit the local HoDepot aren't too friendly or knowledgeable, except when they're being audited by customer service @ the corporate level. Then they're on you like stink on a monkey. That's why I like to find it on their website since it will tell me where it's at in the store.

03-24-2015, 10:00 PM
Much different grit on those than on sharpening stones, Dan.

Now, back to your project thread with your additional questions and let's leave this fella's thread to his project questions, eh? :)