# Tiling over plywood floor 3 season porch



## matt7125 (Dec 2, 2009)

_2 threads on same issue merged_

I'm thinking of redoing the floor of my 3 seasons porch with tile but have a few questions. The current floor is raised above grade by 3 ft or so, all joists are 2X10’s 16 on center, it’s pretty much a porch/deck with walls and a roof. The room is completely enclosed with large windows and doesn’t get any rain or snow but because it doesn’t have heat I’m worried about possible issues. What is the best way to go about tiling, what should I use for mastic and grout, anything special? The original floor was ½ plywood with carpet, I tore the carpet up and installed ½ plywood running the opposite way for more strength, since there is no real threshold issues should I install another ½ cement board for strength or can I get away with ¼in cement board? The plan is to redguard the whole floor for protection against moisture. Let me know what you think??


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## Bud Cline (Mar 12, 2006)

Certainly do-able!



> what should I use for mastic and grout


First of all understand that "_mastic_" is a term used for a particular tile adhesive but you absolutely _WOULD NOT use mastic_ in this application. So forget the word "mastic".

The tile adhesive YOU WILL want to use is "*thinset mortar*".

As far as *grout*, any of the Portland cement-based tile grouts will work fine for your application.



> The original floor was ½ plywood with carpet, I tore the carpet up and installed ½ plywood running the opposite way for more strength,


Excellent move! Your on your way.



> should I install another ½ cement board for strength


Let's clear up another misnomer. Cement board is an excellent "tooth" for tile adhesives but in no way does it ad any strength. You get no structural benefit from cement board.

So in this case 1/4" cement board will work fine. The cost of 1/4" and 1/2" is basically the same so use what you want but 1/4" will work.



> The plan is to redguard the whole floor for protection against moisture.


That'll work!

Now some things you haven't mentioned.

The plywood used must be exterior-grade Exposure 1 plywood, but _*NOT treated plywood*_ of any kind.

The tile must be "porcelain tile".

The thinset should be unmodified (dryset) that you will mix with an additive, _*NO WATER*, use only the proper additive_.

OK, now it's your turn.

_



2 threads on same issue merged

Click to expand...

Not following that!_


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## matt7125 (Dec 2, 2009)

Thanks for the reply!!

_The plywood is exterior grade not sure if it's exposure 1, It's not treated._ I had planned to use porcelain tile, I've read many horror stories and issues with using ceramic. I appreciate the advice on the thinset I'll have to check out what additives are needed.


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## Bud Cline (Mar 12, 2006)

The horror stories come from people doing stupid things without investigating beforehand. Before the Internet it was easy to be stupid, now with Internet help there is no excuse for it.

I've been doing tile about thirty-four years or so and I am not aware of a single failure of any of my outdoor installations. I have done plenty in both the Midwest and North Texas climates. Not all installers can say that. My success has come from being anal and not doing anything without first investigating the possibilities to the inth degree. And that was before the Internet. Hell it's really easy now to do things right.

I will tell you that if you use porcelain tile and if you use Mapei's Kerabond thinset mixed with Mapei's Keralastic additive that tile installation will easily out-live us all.

The preparation is adequate for what you want to do.


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## matt7125 (Dec 2, 2009)

Excellent!!! Thanks again!


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## matt7125 (Dec 2, 2009)

Do I use Mapei's Kerabond thinset mixed with Mapei's Keralastic additive if I'm tile over 1/4in cement board? I've read where it's a good rule of thumb to use this thinset over plywood but if I've laying down cement board is this still needed? Just curious? Also does Home Depot carry this stuff?


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## Bud Cline (Mar 12, 2006)

> Do I use Mapei's Kerabond thinset mixed with Mapei's Keralastic additive if I'm tile over 1/4in cement board?


Yes. I would never apply tile directly to plywood, even tho it can be done it is also a problematic installation.

The Mapei concoction is first class stuff and is used as much for freeze/thaw cycling attributes as it is for bonding to a substrate.



> Also does Home Depot carry this stuff?


Nope, this is "quality" stuff. Menard's carries Mapei products and can special order it. You won't likely find the Keralastic on a big box shelf but you might. Go to a "real tile store" and order it.


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## matt7125 (Dec 2, 2009)

What would be a better underlayment to the tile for my application? Wonderboard or Hardiback board? They're both priced about the same. Thanks again.


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## Bud Cline (Mar 12, 2006)

Better read up on the manufacturer's website.

*Hardie has LIMITATIONS.*
Not the least of which is it *can not* be used exterior.

Just depends on how you define your situation.

How about PermaBase?


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## matt7125 (Dec 2, 2009)

Ok wonderboard (Cement Board) is it then. I've used permabase before and it's great but they only make it in 1/2in that I've seen. I really want to use 1/4in since I already have 1in of plywood already down.


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## matt7125 (Dec 2, 2009)

When I install the wonderboard would it be ok to just use regular thinset mortar or flexibond thinset under the wonderboard and then screw it down or can I just screw it down. The plan is to use 1/4 wonderboard (cement board). I would use the Mapei concoction for setting the tile but for use under the cement board i would go with something premixed from a big box store. Any suggestions would be much appreciated.


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## Bud Cline (Mar 12, 2006)

> When I install the wonderboard would it be ok to just use regular thinset mortar or flexibond thinset under the wonderboard and then screw it down or can I just screw it down.


Does the manufacturer say it is OK to "just screw it down"? Or, do they want you to use thinset mortart under their product? Check it out!



> would it be ok to just use regular thinset mortar


What does the manufacturer say? Check it out!



> I would use the Mapei concoction for setting the tile but for use under the cement board *i would go with something premixed from a big box store*.


And you would be shooting yourself in the foot for no good reason. What does the manufacturer have to say about using premixed anything under cement board?

All manufacturers of tile-stuff have websites with all the information anyone would need to do a proper installation. All of those websites are searchable to make it easier


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## rcorwon (Apr 22, 2011)

Good Morning, I have nearly the exact same environment and saw these recommendations which look great and I plan to follow them precisely. My question is - Can I use slate tile instead of porcelain? Does slate have any negatives like ceramic? Any special considerations?


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