# sub floor seam, tile overlap



## ONE DAY DECKS (May 24, 2009)

Putting down 18in tile, but in one spot it only overlaps the seam in sub floor by 2in. 
Will this be a problem?

Thanks Craig


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## angus242 (Oct 20, 2007)

What is the tile underlayment?


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## ChimneyHill (Apr 10, 2011)

What does the sub floor consist of? What did you use for an underlayment? Gonna need some more info


eta: beat to the punch


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## ONE DAY DECKS (May 24, 2009)

1/4in Hardibaker over 5/8 ex plywood over 1x12 on a 45 on 2x10s at 16oc


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## angus242 (Oct 20, 2007)

As long as your CBU is installed correctly and the tile stays on top of it, you should be fine.

I assume you meant 2x12.


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## ONE DAY DECKS (May 24, 2009)

angus242 said:


> As long as your CBU is installed correctly and the tile stays on top of it, you should be fine.
> 
> I assume you meant 2x12.



1x12 on a 45 on 2x10s at 16oc


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## angus242 (Oct 20, 2007)

Plank subfloor?


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## bloop (May 17, 2012)

yes. He has 2 x10 joists.
on top of them is space sheating with 1x 12 on 45 degree
on top of that is plywood
on top of that is 1/4 hardie


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## ohiohomedoctor (Dec 26, 2010)

Just dont do this.


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## angus242 (Oct 20, 2007)

<---- Slow :blink:


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## ohiohomedoctor (Dec 26, 2010)

But happy


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## ONE DAY DECKS (May 24, 2009)

Should I use 3/8 notch to help with leveling of the 18in tiles?


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## angus242 (Oct 20, 2007)

I use a 1/2" with 18".


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## Evan1968 (Dec 5, 2010)

For 18" tile the floor needs to be pretty flat to begin with....like really flat. Your dealing with 18"s. Unforgiving creatures they are.

You dont level with thinset as you go. Homeowners,that don't know any better, and hacks do that.That's what they make SLC for. Flatten the floor before you set. 

A 3/8" notch aint going to cut it. 1/2" is what you need. I'm sure you will be back buttering/keying the tile as all good setters do when setting 18"s.

I already know you have thinset under the Hardie and will be taping and mudding the seams cause i read the same question you posted on that "other" forum.:whistling

Not sure if you are looking for a different answer to the same question.:no:


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## RareRenovations (May 26, 2012)

I'm a full service contractor but I did my apprenticeship as a carpenter. I worked for a tile setter on the side over the years and I bring in a subcontractor to do tile work on some projects depending on the size, my work load, and the level of detail. I'll post some pics of my most recent bathroom tile project with a fair amount of detail, a heated floor, and quite a few imperfections in the existing walls that needed to be compensated for. I'm offering my opinion from experience, my understanding of the question, and how I would address the issue if it was my own project.

My first concern when setting 18x18 tiles is their unforgiving nature. I know that it is expensive, but I find that a few buckets of level quick after damming off the perimeter with spray foam goes a long way when setting larger tiles. A 3/8" notched trowel will not get it done and back buttering, setting, then pulling up and buttering again to handle low spots can kill your productivity. It's even more fun when you hit a previously unnoticed high spot that you can't span without elevating the surrounding tiles. Old plank style 1x subfloor is notoriously uneven with cupping and offset elevations at butt joints. The plywood will ease those imperfections but they will still be telegraphed to the surface. The 1/4" hardi board does nothing to ease the undulating surfaces beneath it. This set up sounds like a prime candidate for a few bags of leveling compound over a properly primed surface with spray foam or fiberglass insulation tucked around the perimeter. Mix it up super loose and help it out with a bull float or at least a cheap deck brush on a long pole. You will know right away if you need more bags when the product either spreads across a wide area or creates a shallow pool right where you dump it out. The mechanics on this board who do this more often than I do may add a mat or membrane but 2x10's, 1x's, plywood, and hardi board seems pretty resistant to deflection if it's all installed properly. I always include PL Premium between subfloor layers when I'm doing the building so that the surfaces move in unison and are resistant to creaking in the future. 

Sorry for running on. A 2" offset from the tile joint and backer board joint should not be any cause for concern if it is installed properly, gapped a hair for a nice mud bed, and taped to reinforce the joint.


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## Evan1968 (Dec 5, 2010)

Let's clear a few things up as we don't want suspect info going out to the masses.



> The plywood will ease those imperfections


Plywood will not ease anything when it comes to a non-flat floor



> Mix it up super loose and help it out with a bull float or at least a cheap deck brush on a long pole.


Follow the directions and mix it like the bag say's to mix it. Too much water will weaken the final product. You don't "help it out"...its called self leveling compound for a reason. Find the low spots on the floor with a straight edge first and start there.



> 2x10's, 1x's, plywood, and hardi board seems pretty resistant to deflection


 There is a calculation for deflection for subfloors that needs to always be used. Those 2x10 joists would need to have a pretty short unsupported span to meet L/360 which is the minimum for ceramic tile. Read this.. http://www.contractortalk.com/f74/deflection-l-360-l-720-what-does-mean-how-you-calculated-90976/



> I always include PL Premium between subfloor layers


 Never under CBU.



> so that the surfaces move in unison


No,no and no



> A 2" offset from the tile joint and backer board joint should not be any cause for concern if it is installed properly, gapped a hair for a nice mud bed, and taped to reinforce the joint.


 Got one!:thumbup:


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## RareRenovations (May 26, 2012)

Plywood will absolutely ease imperfections in 1x plank subfloor. An 1/8" difference in elevation between 2 runs of planking may not be represented on the surface of the plywood. Depending on the width of the planks and the thickness of the plywood, the low point may be totally spanned over a small area and the plywood can not be made to follow that profile. It will not eliminate differences in elevation over larger areas or sweeping highs and lows but it will address minor imperfections.

Houses are designed to the L/360 standard. #2 Hem-fir 2x10's have a clear span of 16-17' depending on the dead load calculation but the higher span is using the most common live/dead load calculation for residential living areas. That is not a relatively short span and within the range of every properly constructed home.

For someone mixing leveling compound for the first time, the consistency of the product may seem way thinner than anything they are used to. I'm not suggesting anything other than the directions on the bag. I probably expressed it the wrong way but nice and loose is how it's supposed to be. I guess you've never seen a self leveling roller to spread out compound before it sets. In smaller areas, another tool will do the trick as long as you know the window you have to move the product around a bit. Self leveling compound is still susceptible to that terrible tendency of water to bead up or maintain a humped leading edge caused by surface tension. If you want to get into corners and the like, spreading out that leading edge breaks the surface tension and allows the product to seek out level unimpeded.

I'm aware of the methods for fastening backer board to the subfloor. Perhaps I expressed that the wrong way as well but for the subfloor layers, ideally joists to the first layer, then the first layer to the plywood layer, I would use adhesive. There is more that one school of thought on the matter but based on the advise of a structural engineer, properly gluing wood subfloors to joists allows the whole system to act in a way that further reduces deflection.

The masses are lucky to have such a champion for truth.


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## RareRenovations (May 26, 2012)

And on the one issue I was unsure of, the addition of a mat or membrane to further distribute load as some are designed to do, I deferred to installers who know more about the subject.


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## RareRenovations (May 26, 2012)

Evan, my name is Shawn. I see a fair amount of hackery around here and also some very sound advice. Clarifying or challenging some of what I proposed is cool. I might have been unclear, or I may have just been wrong and in that case, I would appreciate the education. I would anticipate a full scale dismissal of my post if I suggested using an old flip flop in place of a grout float or mixing some pea gravel in with the thinset to handle those pesky low spots but it seems like you made a real effort to categorically invalidate my post going as far as providing bad info about clear span and deflection suggesting that an uncommonly short span is the only way to stay within a widely known and accepted tolerance. I freely admitted my poor choice of words and missing clarification about gluing the backer but to insinuate that self leveling compound is 100% self leveling and does not require any spreading or breaking of surface tension to properly address the condition it's designed to alleviate leaves me questioning if your motive was passing on the right information or seeing who can pee farther. I stand with you in elevating us all to a higher standard in the construction industry, but competitions of trajectory, length, and duration of streams are better settled at summer camp.


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## Evan1968 (Dec 5, 2010)

RareRenovations said:


> Evan, my name is Shawn. I see a fair amount of hackery around here and also some very sound advice. Clarifying or challenging some of what I proposed is cool. I might have been unclear, or I may have just been wrong and in that case, I would appreciate the education. I would anticipate a full scale dismissal of my post if I suggested using an old flip flop in place of a grout float or mixing some pea gravel in with the thinset to handle those pesky low spots but it seems like you made a real effort to categorically invalidate my post going as far as providing bad info about clear span and deflection suggesting that an uncommonly short span is the only way to stay within a widely known and accepted tolerance. I freely admitted my poor choice of words and missing clarification about gluing the backer but to insinuate that self leveling compound is 100% self leveling and does not require any spreading or breaking of surface tension to properly address the condition it's designed to alleviate leaves me questioning if your motive was passing on the right information or seeing who can pee farther. I stand with you in elevating us all to a higher standard in the construction industry, but competitions of trajectory, length, and duration of streams are better settled at summer camp.


Lighten up...it was clarification, not invalidation and it didn't take much effort.You hit on good subjects.I just went a bit more indepth. Re-read your post like you know nothing about tile. It needed a bit of clarifying.


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## RareRenovations (May 26, 2012)

It's all good. The goal is to build a good resource for people of varying skill levels. It's easy to lose sight of the fact that you may be assuming everything you say will be taken in context without clarification. Sometimes I draw blank stares and head nodding which are good indicators to stop assuming but they don't come through in this medium.


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## Evan1968 (Dec 5, 2010)

No issues my friend.:thumbsup:
The keyboard should have a "context" key. Im working on a sarcasm key.


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## RareRenovations (May 26, 2012)

I'm working on a petition where we all pledge to limit our use of emoticons to one per week.


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## CO762 (Feb 22, 2010)

Evan1968 said:


> Let's clear a few things up as we don't want suspect info going out to the masses.


Well there goes more than half of my posts.....


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## Evan1968 (Dec 5, 2010)

co762 said:


> well there goes more than half of my posts.....


lol...


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