*
The type of plywood or the rigidity of the floor are neither of the main concerns here. Movement destroys tile either vertically or horizonally. The 2×6 flooring should prevent any deflection in the substrate; however, ther is nothing to stop the horizontal movement.
The installation should start by taking the plywood up. Then install a “membrane” such as Composeal Gold on top of the 2×6 planks. Then install the tile directly to the membrane. This allows tile to move as a unit, independently from the substrate. You could leave the plywood down if you needed it to bring you to the height of your hall flooring.
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One important piece of info is missing from Tom's original post: the span of the 2x6 flooring. Are the supporting beams two feet apart, three feet, or more? Deflection could be a problem.
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2X6 or 2X8 T&G, #3 and btr, Doug Fir has been used for very many years around here on 4' centers as subfloor. The 300 plus feet of tile in my home has that as the basic structure. 10 years here with absolutely no tile movement of any kind.
I'm not crazy about plywood versus tilebacker but it is good enough when paired with an appropriate thinset.
joe d
*If floor height is restricted, patch all ply joints then use a trowel on membrane such as Ultraset. Get some literature first before you even contemplate using it...I've never used it over ply, so check it out to see if it's a suitable application. That will protect your ply from any water migrating through the grout. Cement board in itself will not protect the ply, water passes right through it.Attach your tiles using thinset over the ultraset. There are time restrictions once the Ulraset is troweled on (48-72 hours??), so have your ducks lined up. If the mix doesn't already have it, use an acrylic latex modifier in place of water when mixing the thinset.Seal all grout lines.
*Supporting beams have a 2ft and measure 3x7. The whole room is only 8x8 ft. The floor seems real solid. I'm most concerned with the adhesion and longevity of tile to plywood vs. cementboard. I do appreciate all the input.... It's given me alot to consider.
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I am finishing up a bathroom project in the upstairs of our log home. The new bath is directly over the downstairs bath. The original upstairs floor was 2x6 t&g planks over exposed beams, however, I have laid oak flooring over the whole upstairs with the exception of the new bath. My wife would like a mosaic ceramic tile floor in the bath, and I have been unsure how to apply it. I have planed out the uneven spots on the plank floor, then glued and screwed 1/2" plywood down, and that is real solid. An engineer at the log home mfg. told me to apply the tile directly to the plywood, in fact he had done the same thing. I would prefer to do this, so I can keep the bath floor somewhere near the same height as the hall, but there are strong recommendations to use cementboard over the plywood.
Does anyone out there have experience with this? Years ago, I laid slate over plywood in our entryway, and there's been no problem, but I really don't want to do this job twice. I suppose another consideration is moisture from the downstairs bath migrating up(?) I can't stall this much longer, wife is restless......
*No problem.
*2x6's with 3/4 ply should be plenty stiff for tile. I have done with 2 layers of 3/4 material screwed tight and never had a problem. You have at least twice the stiffness, assuming supporting structure is as stiff as normal floor framing. Good luck with the floor and the wife. Rich.
*Tom,I agree, that's plenty solid enough for the installation of tile but I would still recommend concrete board over that. Thinset and 1/4" concrete board fastened properly would give me a lot of peace of mind in a bathroom application, especially with mosaic tile. That is a lot of grout lines to possibly crack and accept water over time. I like concrete boards chances with a little water better than plywood, even if it is CDX, which it should be.If it was anything but a bathroom, I'd say you could get away with it if you felt you needed to. There is too good a chance of a substantial amount of water getting to the floor with a toilet, tub, and sink involved.Red dog
*Red Dog,Just curious... Why do you say that when using plywood it SHOULD be CDX? Why not BC, or AC fir?CDX is the lowest grade of plywood, and leaves a lot to be desired when you need a smooth, flat surface. It would be the last choice for vinyl because of it's voids, pits, and bad spots. Why would it be the best for tile?Just curious... you might very well know something I am missing.James DuHamel
*James,
Tom,
Joseph FuscoView Image© 1999"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*James,Joe said it, it's the exterior glue. I also like the rougher surface of CDX as opposed to the sanded surface of AC or BC. Seems like the mortar would hold better to it. I haven't bought any pine plywood in a long time. The fir is so much nicer to work with and is more stable than pine.Thanks for asking.Red dog
*CDX is not true exterior plywood. It is interior plywood with exterior glue. The quality of the inner plys is not enough for it to be used in exposed locations. The minimum grade for exposed use is CCX which is a true exterior plywood.That being said, I would never apply tile directly to any grade of plywood in a bathroom. The potential for moisture is always present. Although not waterproof backer board will not be damaged by the moisture and can be attached over a layer of building paper. If you don't want the extra thickness of backer board, consider using a waterproof membrane such as NobleSeal TS, also sold as DalSeal TS. Follow the instructions to the letter.
*Mike,
Joseph FuscoView Image© 1999"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*According to the Engineered Wood Products Association formerly the APA "The minimum gradeof veneer permitted in Exterior plywoodis C-grade. D-grade veneer is used inpanels intended for interior use orapplications protected from permanentexposure to weather." See the attached.
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Joseph Fusco View Image© 1999"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Joe,First off, the stuff that happens outside is called weather, not whether. Second, you have contributed to some BS discussion of plywood that has nothing to do with the original question. Try to stay on track.Tom, I would expect a 2x6 wood underlayment to be quite stable. Had it been me, I would have installed cement board over it instead of the plywood, then applied the tile. The methods are well described in Byrne's "Setting Tile" available from Taunton or cheaper from Amazon.com.
*Weaks,
Joseph Fusco View Image© 1999"The first step towards vice is to shroud innocent actions in mystery, and whoever likes to conceal something sooner or later has reason to conceal it." Aristotle
*Tom,Since you don't really want to raise the floor any higher, "tile it, and forget it." A friend of mine has been tiling for years over plywood using latex base thinset, with a latex additive (by Thoroseal I believe) to help with the adhesion and has always claimed to get good results.You said your engineer friend did the same to his house? Well check it out and see how it looks. Ask him how old his tilework is and what products he used. Everyone is "hip" on using cement board or Dens Shield these days, but years ago they didn't make these products. Tilework used to be embedded in full beds of mortar; but this took a lot of skill and patience....therefore the rise to thinset mortars. Thinset mortars have been on the market longer than manufactured cement boards. Moisture proof drywall was used for tile work on walls and plywood was the underlayment choice for floors in the past. If you want that extra margin of "safety", then go with the cement board, trim off the bottom of your bathroom doors and raise your thresholds. If you don't want that hassle, then tile it the way it is, and find out what type of silicone treatment is best recommeneded for applying to the tile after grouting is complete. There are several silicone based waterproofers on the market, which may provide you with ample protection against common bathroom moisture and the occaisional bath tub spill.As long as you have a solid, strong floor, with little flex and few voids, your tile should not experience much movement; which is the real cause of cracking. Also, latex based adhesives (thinset) will help the tile to "give" a little in those rare instances where movement may occur, and helps to further keep the joint from cracking.Don't fret the small stuff, just do it! Good luck Tom.Davo
*Hey Joe,I have a neighbor that is a foreman at the Louisiana-Pacific plywood plant about 3 miles from my house. I asked him about all of this, mainly because he actually makes plywood everyday.Here is his explanation, although it only pertains to Louisiana-Pacific plywood. Since he doesn't work in another plant, this info may or may not pertain to them.The plywood produced at this plant includes CD, BC, AC, particle board, and Oriented Strand Board (OSB).He stated that they dropped the X from the CDX plywood a few years ago. Now it is simply called CD.As far as glue goes, ALL of the plywood that they produce is made with EXTERIOR glue. There is a reason. They used to have to clean all the machines, and insert a different glue every time they switched between interior and exterior grade plywood. It was time consuming, and expensive for them to do this. The bean counters figured they would actually save money if they just used the exterior glue on ALL of their layered plywood (OSB and partricle board are made in different parts of the plant). He said they only shut down once a month now to clean out the machines. His statement about the quality difference are: CD plywood is made with the lowest grade of veneer. It has voids, holes, knots, etc... and would otherwise be wasted. It is structurally sound when the layers are glued together, but the layers themselves are poor quality for smoothness and finish.BC is sanded 1 side only, and it may contain "patches". They use huge machines that sand the face (much like a giant roller sander). AC is the most expensive plywood for them to produce. They have to have the for veneer shipped in, (we don't have fir here) and they don't make much of it at all.This is according to the Louisiana-Pacific foreman.In regards to the pine versus fir plywood. Fir is readily available here, but it is a different brand name than Louisiana-Pacific. It is indeed more structurally sound than pine, but DAMN is it expensive here ($45.00 a sheet for 3/4")Just some more info to add to the stew...James DuHamel
* James,
Joseph Fusco View Image "The price of apathy towards public affairs is to be ruled by evil men." -- Plato
*Tile is not waterproof, and water if left on the surface will migrate through the tile and grout joints onto the substrate. If the substrate is wood, it will swell and will de-laminate, and you tile job will be ruined.Assuming this is a dry location (it doesn't sound like it though), one can tile over plywood. The key is a smooth surface so the tiles bond well. I would use ACX. As a precaution, you can waterproof the plywood using a trowel on waterproofing membrane, which is basically expoxy and fiberglass mats, and then tile over it.For bathroom floors, I assume that it will get wet, and pick a substrate that is waterproof. My recommendation would be to place 30 lb tar paper over the CDX with cold patch roofing cement and staple it down. Then I would apply Hardibacker, which comes in thicknesses as little as 1/4". Screw it in place with stainless screws or galvinized nails. This has to be dead flat. Then tile as ususual.In wet locations,
*Steve, Yeah, I agree that the 2x6 subfloor has enough rigidity, but I was concerned about seasonal movement of the planks, and what kind of an interface this would make with the cementboard. Living in a log home makes one very aware of wood's instability. We use a woodstove for most of the Vermont winter, and this caused alot of movement. I could visualize the planks shrinking and swelling, crumbling the cementboard as the screws move with them. (Perhaps I have an overactive inagination) Anyhow, the plywood seemed like a more forgiving interface. Also, as I said, the planks had some cupping and uneven spots that I planed as smooth as I could, but if I were to put cementboard directly on them, I probably would need to use a leveler in spots. Well, the plywood is there now, and I guess the safe thing is to use cementboard, chop the door, and install a threshold. Oh well........
*The type of plywood or the rigidity of the floor are neither of the main concerns here. Movement destroys tile either vertically or horizonally. The 2x6 flooring should prevent any deflection in the substrate; however, ther is nothing to stop the horizontal movement. The installation should start by taking the plywood up. Then install a "membrane" such as Composeal Gold on top of the 2x6 planks. Then install the tile directly to the membrane. This allows tile to move as a unit, independently from the substrate. You could leave the plywood down if you needed it to bring you to the height of your hall flooring.
*As long as floor deflection is within limits, I'd use a water proof thinset, getting a good bond and a waterseal at the same time.Dave