# Tile on plank subfloor



## CliffHollen (Jul 9, 2009)

Hey Guys,

I will soon be putting down some tile in an old house that has the original pine plank subfloor, which I have never put tile on. Some of the gabs between the planks are 1/2"ish. How should I deal with this? Can I just apply mortar and 1/4" hardibacker the way I would over a plywood subfloor? It seems like adding plywood and then mortar and backer would be nice, but that sounds pretty thick. 

Advice is appreciated.

-Cliff


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## angus242 (Oct 20, 2007)

An older home may not have the joist strength to handle a tile job. You first need to find out about the deflection. Chances are, you'll need an additional layer of EGP. If height is an issue, consider using Ditra instead of CBU.


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## N.Schiffer (Oct 24, 2008)

I'm not professional tiler but I would put plywood down, even if it only allows for 1/4" plywood. Any added thickness would help with uneven flex with planks. Just figure out how much thickness you can allow for, then go from there.


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## CliffHollen (Jul 9, 2009)

I'm not too worried about the deflection. Another room in the house has tile that must be 10 years old and still looks fine. I wish I could see what is under it.

The wood floor I will be butting up against is about 3/4" thick. Maybe I could use 2 layers of 1/4" backer?


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## davitk (Oct 3, 2008)

Cut the planks out and put down plywood.


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## WarnerConstInc. (Jan 30, 2008)

Ply wood over the planks, then 1/4" denshield.


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## angus242 (Oct 20, 2007)

CliffHollen said:


> I'm not too worried about the deflection.


Enough said.

Good luck :whistling


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## Celtic (May 23, 2007)

I don't know much about anything - ask anyone, they will tell you the same - but if your floor resembles this one in any way ~ I wouldn't put much faith in it:












A clean slate is so much easier to work with:


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## Splinter (Apr 5, 2005)

you should be worried about deflection, it'll cost you when the customer calls you back to fix all the cracked grout.... every year...

Don't base you decisions on the condition of a tile floor in another room of the house. There could be much better support under that floor. 

Forget using 1/4" plywood anywhere under a tile installation, it doesnt add any strength to the subfloor, and it's soft core can cause more trouble with deflection. Minimum 3/8" CCX plywood (BCX is better) for underlayment. 

Next, cement board is not meant to add strength to the floor, it's just a compatible surface to adhere tile to. So building up two layers of 1/4" backerboard is not a smart idea. 

It's usually not realistic to pull out the planks and replace with plywood. It adds a lot of time and materials to the project, especially since the planks always continue under interior walls, load bearing, and non-load bearing. If the customer is willing to spend the extra cash to save 3/4" in height, go for it. 

99% of my customers have no problem living with the height difference. A marble or granite saddle in the doorway makes a nice transition and alerts peoples subconscious to the slight step up into the next room. 

Go with 3/8" ply over the planks, Ditra membrane (1/8") and then tile.


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## Splinter (Apr 5, 2005)

Celtic- get some more screws into the field of that plywood, eh? :thumbsup:


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## Celtic (May 23, 2007)

Splinter said:


> Celtic- get some more screws into the field of that plywood, eh? :thumbsup:



Right now....there's mostly nothing under it :blink:

Not wanting to thread hijack [at least not yet :shifty:].....come visit me over here:
Butchered joists


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## angus242 (Oct 20, 2007)

1/2" EGP is the minimum underlayment. That's _over _a proper subfloor.

However, if your joists don't meet minimum deflection ratings for the type of tile to be installed, none of this matters.

You may not care. However, there are minimum requirements for a reason.


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## willworkforbeer (Mar 7, 2009)

angus242 said:


> You may not care. However, there are minimum requirements for a reason.


Yeah grout and stuff.


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## angus242 (Oct 20, 2007)

willworkforbeer said:


> Yeah grout and stuff.


and cracking tiles...:whistling


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## CliffHollen (Jul 9, 2009)

Allow me to rephrase- The condition of the tile in the kitchen has me feeling comfortable with the JOIST deflection. The 12" tiles in that room butt up evenly against the same hardwood. That tile is over the exact same subfloor that is set on the same joists as the bathroom in question- it's all over an unfinished basement. 

My original plan B was to cut out the planks and replace w/ 3/4" ply, but there wouldn't be joists to support the ends and there's way to much duct and knob-and-tube wiring to put more blocking between the joists to adequately support the edges of a new subfloor. 

Alex, your plan sounds solid. Thanks for the constructive advice. 

-Cliff 

-Cliff


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## davitk (Oct 3, 2008)

On second thought if you just caulk between the joists using Big Stretch, you should be fine.


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## angus242 (Oct 20, 2007)

CliffHollen said:


> Allow me to rephrase- The condition of the tile in the kitchen has me feeling comfortable with the JOIST deflection.


And how is _that _tile installed? My money is on a mortar bed :whistling

Look, do you want to do it right or just do it? Height is NOT what determines what is right. You've been given plenty of info to look at. You could do something goofy like 2 layer of 1/4" CBU or actually follow the recommendations of organizations that extensively test these methods. 

What kind of installer do you want to be?


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## CliffHollen (Jul 9, 2009)

CliffHollen said:


> Alex, your plan sounds solid. Thanks for the constructive advice.
> 
> -Cliff


Angus, did this not make clear "what kind of installer" I want to be?


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## angus242 (Oct 20, 2007)

Cliff, I'm not tryin to bust your balls but you keep replying and saying things that don't make sense if you want to do it right.

The TCNA says MINIMUM of 1/2" exterior-glued plywood. You said 3/8" sounds good.

The TCNA says MINIMUM deflection of L/360 for ceramic, L/720 for stone. You said you're not too worried about it and there's too much in the way to add blocking anyway.

You suggested the use of 2 layers of 1/4" CBU.....

I'm not making up the minimum requirements, I'm just stating what they are. You are the one who seems not interested in following them. If you spent $10 to get a copy of the TCNA Handbook, most of your tiling questions would be answered. All you have to do is follow the recommendations. IF you do that, then I'd say you're trying to do things right. If you choose not to, well then you tell me what kind of installer you're trying to be.


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## Splinter (Apr 5, 2005)

Angus- 

I'm not doubting the 1/2" plywood minimum, but I'd like to know where it says that... Can you quote from the TCA handbook?

This topic comes up regularly over at JohnBridge, and they recommend a minimum allowable underlayment of 3/8" for certain circumstances.


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