Kitchen floor, subfloor guidance please [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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03-09-2007, 09:00 PM
Planning Kitchen floor tile. Currently, 2X10 joists 16"OC, 11ft span, joists unknown wood, but good condition, house built in 1994. Deflectometer score L/525, .251 inches deflection. 3/4 OSB with 1/4 plywood and sheet vinyl now. Meets carpet at one end of room. Current vinyl is 1/2" below top of carpet.

Using 8 ft metal level as straight edge, discovered slight slope at one end of room perpendicular to joists. It is fairly consistent across the room. It drops 5/16" - 3/8" over 34" span leading into the carpeted area.

Intending to use a ceramic or porcelain 12"-15" tile.

1. Will this slight slope cause problems?
2. What subfloor is recommended from my OSB to my tile? Hoping to end up close to the carpet height to ease the transition, but know that skimping on the subfloor is a no-no.

Want to do it right and do it only once!

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Dave Taylor
03-09-2007, 09:47 PM
Thank you for joining us on the forum.

It sounds like your kitchen floor will be nice to work with for ceramic (not stone) and the slight slope it does have should be no problem. Flat is, however, important and I assume this is your case.

Folks here-a-bouts will recommend that you remove both the vinyl covering and the 1/4" Lauan beneath it..... neither is a great substrate mix for a ceramic covering. This will give you an additional 1/4" + to work with leaving your carpet 3/4 + above the kitchen floor.

I would like to see more ply on your kitchen floor..... 3/8" AC, BC or CC exterior grade glued, sanded and plugged at a minimum.

On top this use Ditra (1/8" properly installed) now leaving your carpet 1/4 + above your kitchen. Then apply thinset (height roughly 1/2 the trowel notch size) and tile at 3/8" or less.

This should allow for a gentle transition down from your kitchen to your carpet.

Hope this helps :---)

03-09-2007, 10:45 PM
What Dave said...and i'm thinking that you should be a moderator imo Dave

03-10-2007, 01:47 AM
Hi, new here, started to answer this earlier this evening but the phone kept ringing.

Yeah, like he said, you want flat, level is OK but flat is what you are after, you can't start re-building the whole house. If it is real important that you have no height difference from one tile to the next use the smaller size tile, that makes it a little easier. Sometimes a bend in a floor makes it about impossible to be absolutely flat. Use a high flex mortar, your tile supplier can recommend one from whatever line they carry.

Ripping out the vinyl and adding a new u-lay is probably easier (considering future failure) and safer than trying to go over the vinly although it can be done.

At the carpet you can get a transition to protect the edge of the tile if there is a little height difference when you are done. Hopefully where you get your tile can cut a piece for you. Schluter is one brand, there are other brands and a host of profiles to fit your need.
The Ditra matting is a good idea if you don't mind the expense, and easy to work with. There a few other systems out there that act as anti-fracture or uncoupling membranes.
Best of luck, Michael

03-10-2007, 07:28 AM
Will definately remove vinyl and luan. And will add 3/8 plywood in one of the grades listed above. Have used cement board in a couple of bathrooms with good success, but will give Ditra a shot in the kitchen. Sounds like a good investment. This is a bigger job in a higher traffic area than my previous projects.

About that slope... I guess I didn't describe it very well. The kitchen floor is 10 feet long. It is flat and level for the first 7 feet. Then, it very slowly slopes down about the last 3 ft, with a total drop by the time it hits the carpet of about 5/16".

1. With my improved explanation of the slope, is it small enough I'll be OK?
2. The luan is attached to the OSB with staples - lots and lots of staples. They are very narrow, but quite deep. Once I rip out the luan, is it OK to pound the staples into the OSB or do I need to pull each one out? (I'm remembering hours of work in my much smaller bathrooms removing these and now wondering if it was necessary.)
3. What is recommended for attaching the 3/8 plywood? Avoid matching joints with the OSB joints? Can I nail down with my framing nailer or are screws required? Spacing of fasteners?

Thanks so much. You guys are great!

Dave Taylor
03-10-2007, 01:10 PM
Your using a fairly large format tile and your floor needs to be quite flat; you may have some trouble at the point where your floor starts to slope. If that point is abrupt you will need to address it so the tile does not rock if layed over it.

Here are some quotes from injuneeer Bob Camp "bbcamp" in past threads that address your other questions. BTW... if you use the proper nails for fastening your 3/8' ply underlayment.... don't make no never mind if you use a nail gun or hammer :---) And yes.... you kin' hammer them narrow crown staples right into your subfloor. Do it all the time. Use either screws or nails to attach yer' 3/8" ply underlayment.... I am partial to using deck screws.

Hope this all helps

Bob C said the following at various times: The standard for floor flatness is 1/4" out-of-plane over a 10 foot span. To measure this, place a 10 foot straight edge on the floor and measure the gap between it and the floor. Move the straight edge around the room and at different angles and mark where you have more than 1/4" gap and where you have less than 1/8" gap. This makes a topographic map of the floor.

The screws you use for installing the plywood should penetrate the subfloor OSB so that the pointed part of the screw is exposed. That way, you get the most holding power the screw is capable of.

Use grade AC, BC or CC (plugged and sanded), Exterior or Exposure 1 rated plwood. Place the plywood with the face grain perpendicular to the joists. Use ring shanked nails or deck screws 4 inches apart along the edges and 6 inches apart in the field. The length should penetrate the subfloor. You don't need to worry about hitting the joists. Don't aim for 'em, don't worry about hittin' 'em.

PS: Here is a URL for a pdf that will tell you everything you never wanted to know about adding a plywood underlayment :---)

03-10-2007, 04:26 PM
So what is the word on glue or adhesive for putting down the underlayment? Not needed?
thanks, Michael

03-10-2007, 05:15 PM
Hi Michael, no glue on the second layer of ply if using Ditra. Also no screws in the joists and ply edges to span over the joist by 4".

03-14-2007, 06:10 PM
Thanks guys. Good info. I appreciate it!

08-07-2007, 07:01 PM
Finally got started on the kitchen floor project. Vinyl and 1/8 in ply removed along with a "million" staples leaving a flat and surprisingly nearly level 3/4 OSB subfloor. 3/8 BC ply underlayment installed with 1/4 inch perimeter gaps and 1/8 in panel gaps. Big roll of Ditra sitting in the hallway along with a bunch of thinset (modified and unmodified) and 12x12 and 6x6 tiles for Hopscotch layout. Now for a few questions before I start laying tiles this weekend...

1. Ditra calls for latex portland cement mortar to set the Ditra. I read somewhere else on this site (I think) to use modified thin-set under the Ditra so I bought Mapei Ultraflex 1 polymer modified mortar. Is this the right stuff?
2. Ditra calls for unmodified thin set mortar to set the tiles. I bought Mapae Keraset Professional Dry Set Mortar, since the other mortars seemed to be "modified". Do I have the right mortar to set the tiles?
3. My plan is to set the field tiles first, and then the next day cut and set the perimeter tiles. Is this the best approach?
4. How long after I set the tiles and grout before it's safe to move my fridge and stove back onto the tiles?
5. Since this is in the kitchen, and my tiles have a slightly beveled edge, I'm thinking a small grout line makes sense to avoid chair legs getting caught between tiles. How wide of a grout line do you guys use? I was thinking 1/4", but am wide open to suggetions based on your experiences.

Thank you.

08-07-2007, 09:18 PM
Hi Greg,

I know what you mean about those staples. I spend 2 hours removing an entire vinyl kitchen floor, then spend the rest of the day pounding staples. :bang:

1. yes, modified thinset to install Ditra to plywood.
2. right again, use unmodified thinset to set tile, even porcelain. Try to find Ditra-Set if possible.
3. Do it that way if you don't have a cutter or saw on hand if you want to. If you have the tools on site, you should do the cuts as you go.
4. If you're careful and have the proper equipment you could do it the day you grout, BUT I DO NOT recommend it. Wait about 3 days, after you have a chance to do the final cleaning, and the grout is sealed.
5. I don't consider 1/4" grout line narrow, it's pretty common. It all depends on the tile and your taste, I usually shoot for 3/16".


08-19-2007, 09:13 AM
Grouted my new floor yesterday with Polyblend unsanded grout. 1/8 spacing of tiles in Hopscotch pattern. I worked the grout in with a rubber float diagonally in all directions to try to ensure full and deep grouting. Wife hit the grout lines and wiped off the tiles 15-20 minutes after grouting with a grout sponge being careful to minimize the amount of water used. I followed this about 4-6 hours later with a damp microfiber cloth (rinsed wrung out repeatedly) to take off the haze.

This morning we noticed some cracks in a few of the grout lines - primarily at some of the intersections where the 6X6 and 12X12 tiles meet.

What's the proper next step? Caulk with matching caulk and then seal over it? Mix up a small batch of grout and grout over the cracks? Just hit it with grout sealer and call it good?

Thanks for your help!

Rob Z
08-19-2007, 09:22 AM
Hi Greg,

Was the grout mixed too loose?

You set with 1/8" joints, which is the upper limit for unsdanded, but I am guessing the tile is fairly thick, so you had deep grout joints for an unsanded grout. If this is the case, I would try to regrout those areas and see how it does. Use a grout saw to enlarge the areas slightly, dampen them and apply new grout.

08-19-2007, 10:19 AM

Do as Rob suggests, it's the best way to fix the cracks. The few times I've used unsanded under similar circumstances, I have seen cracks too.

You said the joints are 1/8", you might have used 1/8" spacers? If you did, the joints are min. 1/8" and some are wider. Next time use sanded.