Newbie Questions About Subfloor Requirements

Dave Bishop · May 31, 2009, 05:04 PM

I'm new to the forum and hope to get some answers that will help me decide what type of flooring I can install as part of my kitchen re-model. My supervisor wants ceramic tiles, which I have installed in a previous home. However, the current kitchen may have limitations that prevent this. Here's what I have to start with:

1. 5/8" plywood subfloor on 2x8 joists on 16" centers.
2. A second layer of 5/8" plywood over the subfloor, to which sheet vinyl has been glued directly.
3. Two more layers of vinyl glued to two layers of luaun, each of which is stapled down. (The house was built in 1987, we're the third owners, and everybody got a new floor!)
4. Joist spans of 12' in one part of the room and 15'-6" in another part.

The second and third floors can and I know must be pulled up (I have tested in a couple areas) and this will leave thousands of protruding staples. These will need to be pulled out (impractical, I think, given that this is a 350 sq ft space) or hammered down. If hammered down, the staples would prevent me from stripping the original vinyl, if that is necessary. So...if it were your house, what would you do?

Dave

rgfloor · May 31, 2009, 05:48 PM

First, welcome!!

Second you seem to have some ideas already so lets talk about them. For ceramic tile you need to make sure that you have two layers of 5/8 plywood. That is unusual for newer construction. OSB is pretty standard, but plywood is much better. Two layers of 1 1/4 inch total is sufficient for C-tile.

Joist span is next, C-tile requires a rating of L-360. There are all kinds of calculators around, this one is quick and easy. You need to know the joist material and size, imput it and tell us what you have. The Amazing John Bridge Forums Deflect-O-Lator :-)

The two layers of luan must come up, but you knew that. Take the time to pull the staples, a broad bladed ice scraper will probably remove most of them. Then strip the first layer of vinyl.

If it were my house, I would do what the supervisor (wife) wants.

Peter Kodner · May 31, 2009, 05:57 PM

Even not knowing the species of your joists, your 15'6" span puts you at less than L360. Some of the other pros here will give better advice on how to deal with the overall issues including the rip up off the existing..

Kman · May 31, 2009, 08:35 PM

Your subfloor is more than adequate, it's your joist span that is the problem. The 12' span is easily fixable by sistering the joists with 2x6's, or you could even rip down some pieces of plywood to strengthen them.

Tell us about the area under the joists that spans 15'6". Is there a basement or crawl space? Is it possible to add support underneath to shorten the span?

And yes, you'll have to take all layers of vinyl off. Sorry.

Dave Bishop · May 31, 2009, 08:55 PM

I was afraid that the spans were too long for ceramic tile. I have a crawlspace under the kitchen, and a roughly 13' long support beam could be placed to shorten the 15'-6" span to about 10'-6". However, sistering anything to the joists to strengthen the 12' joists is practically out of the question because of all the pipes, wires, HVAC ducts and fiberglass insulation that run over, around and between the joists. I guess it will be vinyl for us, for we already have stained oak strip floors in the adjacent rooms, and to lay any more wood would be too much, I think, plus it would necessitate removal of that second 5/8" plywood layer to keep from building up too much. Thanks to all for your help.

sodak · May 31, 2009, 09:48 PM

Have you considered DuraCeramic or Konecto Tiles? After you take it down to the second plywood layer, either of these should work and give you the ceramic look w/o the weight issues.

Kman · May 31, 2009, 10:20 PM

Dave, if you're able to add a support beam under the 12' span, that would work also. The maximum span for a 2x8 is 11 feet, so you could conceivable add support anywhere in that 12 foot span, as long as it is at least one foot away from the original support, thereby shortening your span to 11' or less.

Another important factor is the grade and species of your joists. If you intend to go any further with this project, you need to know that bit of information.

Dave Bishop · June 1, 2009, 03:14 PM

In response to the last couple replies, it's not practical for me to add support beams so that I can use ceramic tile, and I have considered Duraceramic tiles. I would want to grout the Duraceramic, so can anyone tell me how stiff the subfloor must be for this application? Is this more forgiving than ceramic? Thanks.

Ken · June 1, 2009, 03:25 PM

The grout for Duraceramic is flexible and is designed for use over a wood subfloor/underlayment.

Dave Bishop · July 17, 2009, 09:30 PM

I'm back ... to ask a few more questions. Please see my earlier posts in this thread. I have stripped the top layers of lauan plywood and vinyl, am down to 1/2" plywood subfloor covered with 5/8" plywood, to which the original vinyl is glued. Turns out there are at least two ridges in the floor that will probably prevent my using a laminate snap-together floor, for specs call for a fairly flat base for laminate. So I'm back considering what it would take to prep for ceramic tile.

How best to scrape off the original vinyl, which is glued to the plywood? Some areas are fairly loose, while others are stuck well. I have removed ALL staples that held down the upper two layers. It took several days!

If I decide to add a beam in my crawlspace, to shorten the 15'-6" joist span, the beam would need to be about 13' long. I assume that two 2x8s glued/screwed together, supported at both ends and in the center would be sufficient. Can this beam be supported on concrete deck pads set on the soil floor of the crawlspace? Or how else? Are 4x4 posts OK or 6x6 needed? Posts would be about 4' high.

Kman · July 18, 2009, 02:21 AM

The same ridges that prevent you from having a laminate floor can also prevent you from having a tile floor.

Do you know what is causing the ridges?

Ken · July 18, 2009, 02:33 AM

Setting the deck pads on the soil will allow for movement and settling of the new support beam, you should give the pads a firm base that will not settle with the added weight and movement.
At the very least I would dig out a 8/10 inch hole and add a 3 to 5 inches of
21AA and pack it down tightly then set your pads on them.
similar to the base used for brick paver walkways/driveways.

mcbrides · July 19, 2009, 02:01 PM

Dave Bishop said

Turns out there are at least two ridges in the floor

How best to scrape off the original vinyl, which is glued to the plywood?

Dave, there was a reason that the existing floor you have now was sheeted again, the 1/4 ply smoothed out those ridges.

Stop messing around with structural issues, just sheet it again with 1/4 ply and install DuraCeramic (my favourite ... ). If your wife wants ceramic tile, this product will send her over the moon, not cold, dropped items don't break, nor the tile, and she can spend the whole day on it without her legs starting to hurt. I have a retired lady (a repeat account) that I installed DuraCeramic for 5 years ago; she tells me she can spend the whole day on it, when she goes to her daughter's house, she only lasts an hour on the ceramic tile.

I'm installing about 1500 square feet of DuraCeramic tile in a new custom house in September; the new homeowners are Italian, and you know how much they like their ceramic tile ...

Deb