Replace 1x6 old boards with plywood? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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07-22-2009, 12:54 PM
My installer told me to just put 1/2 durock over 1x6 old angled boards which are on 16oc, 2x12's, 13' span....will this be enough strength or should I replace the old 1x6s with 3/4 plywood....I want the floor to be strong enough to hold the ceramic/porcelain.

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07-22-2009, 12:59 PM
You can either replace the planks with 3/4" plywood or OSB, or you can put 1/2" plywood over the planks, then an underlayment and your tile.

07-22-2009, 12:59 PM
Hi Rick,
You've got a few choices but all of them add up to having plywood.

Removing the existing planks is a good option then add 3?4" T&G plywood long edge perpendicular to the joists. Follow that with 1/4" Durock or 1/8" Ditra and you will be ok.

Another option - make sure the 1x6's are secure, add screws as needed. Add 1/2" plywood, perpendicular to the joists and screwed into the 1x6's only. Top with 1/4" Durock or 1/8" Ditra.

I'm a big fan of Ditra but it will cost you more. Weighs a lot less, no fasteners, just thinset down and then tile on top.

07-22-2009, 01:12 PM
I already have the 1/2" durock at the house...I will install the 1/2" plywood over the planks into the I need tar paper under the pw to prevent any squeaks?
Do I need to thinset the durock to the plywood?
My installer says not.

07-22-2009, 01:23 PM
Welcome to the forum, Rick.:)

You most certainly do need thinset between the Durock and the ply. It's not so much for bonding as it is for filling voids that would lead to tile-destroying movement.

07-22-2009, 01:28 PM
Thanks for all of your answers and advice....
I will go with the tar paper (30lb), 1/2" pw, thinset, 1/2" durock....this should do the trick....
Now to convince my installer and see how high his bid goes up...ahhahah
Any type of thinset better than others that I can get at Home depot/lowe's?
Plywood type??

07-22-2009, 01:33 PM
Rick, this is the one time where thinset quality doesn't matter that much since the bond isn't really needed. VersaBond from Home Depot is a great all around thinset, but if you can find something cheaper to use under your Durock - use it.

I'm not certain about the need for tar paper. It may be more trouble than it's worth.

I'm also concerned about your installer. He doesn't seem to know about industry standards.

07-22-2009, 01:38 PM
I will for go the tar paper and use the hd brand thinset....what type of plywood do I need?

I might need another installer.

07-22-2009, 02:16 PM
No tarpaper. If you screw the plywood down well enough, there will be no squeaks.

Use AC, BC or CC grade, exterior rated plywood.

07-22-2009, 02:18 PM
Another option you might consider is pulling up the 1x6 planks, and laying down 1 1/8" Tongue and Groove subfloor ply, long edge perpendicular to the joists. It runs (barely) under $30 a sheet at HomeDepot.

Then you could just put the durock on top of that (with thinset in between).

For the plywood, next time you go to HD, look at how the subfloor plywood is made - it has a lot more plies than the sheething plywood, and that translates to being stiffer. I don't know what a good piece of 1/2" ply will run you, but you want stuff that doesn't have voids in it otherwise what's the point?

Now my disclaimer - I'm not a pro by any means. Just telling you what makes sense to me. Hopefully the resident pros will correct any errors I've made.


07-22-2009, 02:24 PM
If a fella's gonna tear out alla way to the joists, Fab, I'd still recommend he use two layers of plywood rather than that 1 1/8th" stuff. Gives you the opportunity to orient the layers such that there is no joint over a joist that goes all the way up through the subflooring. That's the most likely point of failure of a tile installation due to subflooring deflection.

Not to mention that it's far easier to actually survive handling 3/4" ply than that 1 1/8" stuff. Give a thought to the older people, won'tcha? :D

07-22-2009, 02:37 PM
Hi CX, good point about the staggered joints.

What about the quality of the plywood? Is sheathing plywood suitable? The stuff I've seen had voids on one side, who knows what in the middle layer. I would think you'd want something with all voids filled, doesn't matter if it has footballs as long as they're filled. Not sure what grade indicates whether the internal plies have voids/knot holes...

07-22-2009, 03:01 PM
See Injineer Bob's post #9

The stuff you're seeing with the open voids in the face grain is no better than CD and not acceptable. The grades Bob cited are all suitable.

My opinion; worth price charged.

07-22-2009, 03:40 PM
Is sheathing plywood suitable?

Nope. Never use sheathing as part of your flooring.

07-23-2009, 05:20 AM
Because of height restrictions at the sliding door....decided to go with:
tearing up planks and replacing with 3/4" subfloor grade pw @ $32/sheet
then thinset the 1/2" durock (with taped joints) to the pw
then appying the tile.....
this is on 16oc, 2x12, max length of 13ft....
Is there anything that I missed?

07-23-2009, 05:29 AM
If height is a concern, you can use 1/4" cement board. You won't be sacrificing any structural integrity by doing so. You can save even more height by using Ditra (

07-23-2009, 05:45 AM
I am mostly concerned about the strength of my subfloor and I already have the 1/2" durock on site--I would use the ditra but found out about it too late.

...we are going to live in this home for a long time and just want to make sure the subfloor will be sufficient so we have no problems.

07-23-2009, 05:37 PM
If the floor is too high, you'll be kicking yourself for as long as you're in the house. Backer board is pretty cheap, so the fact that you already have it shouldn't dictate how you build your floor. Build it right, and if you have to write off $200 worth of backer board, so be it.

07-24-2009, 09:36 PM
Hi Rick,

I completely agree with Fab above. Spend the extra time or money now, if necessary, getting the floors you want and you'll be thankful you did for years (decades?) to come.

If the 1/2" Durock is not the best material thickness for you, there are thinner options available as mentioned above. Have fun:)

07-27-2009, 08:14 AM
Thanks to everyone for the advice....the height issue is not an issue....
I am going to proceed as follows:
Remove old 1x6 flooring
Glue and nail 3/4" T&G subfloor
Thinset 1/2" durock
then install tile

Question: Part of this floor is over a VENTED crawlspace....I plan on:
installing insulation between the joist with the face touching the subfloor, using metal stiffeners to keep the insulation from falling, and then putting a plastic layer on the dirt crawl space floor.

Should I put anything on the bottom of the floor another vapor barrier?

07-27-2009, 08:24 AM
If height is not an issue, Rick, I would still strongly suggest you add another layer of plywood and go with a thinner CBU or other substrate.

Yes, if you have proper drainage under the crawl space, covering it with a vapor barrier membrane and doing your very best to seal around all penetrations of the material is your best bet for moisture control under there.

For containing the under-floor insulation I like to staple chicken wire to the bottom of the joists after installation. Can't tell what part of the country you're in, but I'd still likely recommend no vapor barrier under the un-faced insulation.

My opinion; worth price charged.

07-27-2009, 11:05 AM
Do you need to let the plywood on top of planks acclimate to house temp/humidity prior to screwing down to planks?

07-27-2009, 11:09 AM
Welcome, Kim. :)

One always wants her plywood to acclimate if at all possible. How essential is will be for your particular application depends upon a lot of things, but if you have the option, definitely bring the stuff into the room in question for a couple days before installation.

If you'll have additional questions about this project, please start a new project thread of your own. Tends to get very confusing with more than one project being discussed on a single thread.

My opinion; worth price charged.