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Old 03-01-2011, 06:44 AM   #1
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yet another subfloor build up Q


Tiling Bathroom (just a bit over 4x8 total space) & Entryway (just a bit over 4x10 w/ small closet). The tiles are 12x12 glazed porcelain for entryway and 6x6 porcelain for the bathroom.

Joists are 2x10, 16 OC. Subfloor in the entry way is 1x12 planks laid perpendicular to the joists and running "the long way" through the space. In the bathroom the subfloor was the 1x12 planks, but all but ~6sqft at the doorway has been replaced by 3/4" "dryply" to deal with a rot issue.

I'm trying to keepthe surface level w/ adjacent strip hardwood flooring.

Based on searching and book reading, laying the hardi directly on the planks is a mistake.

My plan was to lay 3/8" sheathing over the planks, then mortar + 1/2" hardi.

The questions I have are:

1) Is 3/8" sheating + 1/2" hardi the best way to go?
2) Or, would 1/2" sheathing + 1/4" hardi be better?

3) What rating/grade should the ply be? I went to the orange big box, explained what it was for, and was pointed to some 3/8" ply, it seemed OK at the store, but I didn't pay much attention because I needed to rent their van and only had about 10 mins before the end of day cut off. It's labeled as Georgia Pacific "3/8 Rated Sheathing". When I got it home I noticed it's got some warp to it, and I also noticed that it "crackles" and flexes an awful lot when moving it--almost as if the plys aren't attached to each other very well? All sheets seem to be about the same, but one seems to be a bit worse. I've laid them out flat on the floor and they do lay flat w/ some weight on them. If the 3/8 ply + 1/2 hardi is OK, then is this particular stuff good enough, or should I make sure that it's got a certain grade/rating?

If it matters, I already have that sheathing, such as it is, and the 1/2" hardi... but if it's not correct I am happy to buy the right stuff if needed.


Last edited by bubbler; 03-01-2011 at 07:41 AM. Reason: clarity
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Old 03-01-2011, 07:25 AM   #2
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yet another subfloor build up Q


Edited original for clarity, please disregard or delete this post


Last edited by bubbler; 03-01-2011 at 07:36 AM. Reason: delete
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Old 03-01-2011, 11:25 AM   #3
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yet another subfloor build up Q


OK, we're glad you supposedly found the right answer. I'm gonna answer anyway for those who have a similar situation.

The joists and their spacing sounds ok, but you didn't mention what the span of the joists is. That's very important, along with the species and grade.

You also didn't say if the 1x12 planks are t&g or not, makes a big difference. I will assume they're not t&g. 3/8" underlayment grade is not thick enough. 1/2" might not even do it if the planks are cupped or bowed at all. You'd have to tell us that.

Quote:
Based on searching and book reading, laying the hardi directly on the planks is a mistake.
That's right, shouldn't do that, you need the ply.

Quote:
1) Is 3/8" sheating + 1/2" hardi the best way to go?
Again, this method would be way bad. BTW, sheathing is not for floors. Sheathing is a cheap grade of ply used for the exterior side of walls to be covered with siding or (?).

Quote:
2) Or, would 1/2" sheathing + 1/4" hardi be better?
Yes, this adds strength. Remember Hardie adds nothing except a tile friendly substrate.

Quote:
3) What rating/grade should the ply be?
Officially C/C or better ext. glue, but may be hard to find. B/C or one labeled underlayment grade is good.

Quote:
I'm trying to keepthe surface level w/ adjacent strip hardwood flooring.
That should be your least priority unless you have a commercial building. In which case you should install the same type of flooring through out.

Jaz
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Old 03-01-2011, 12:58 PM   #4
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yet another subfloor build up Q


Quote:
Originally Posted by JazMan View Post
The joists and their spacing sounds ok, but you didn't mention what the span of the joists is. That's very important, along with the species and grade.
Span is 13' from foundation wall to a main center beam which itself rests on a concrete block wall at this location.

I don't know what species, but I do know that nailing/drilling into it is far more difficult than new lumber I buy. It also feels about 50% heavier

Quote:
Originally Posted by JazMan View Post
You also didn't say if the 1x12 planks are t&g or not, makes a big difference. I will assume they're not t&g.
Not T&G, just planks, they are separated from each other by approx. 1/2" or so gap. They are butted up over the joists and nailed down.

Quote:
Originally Posted by JazMan View Post
3/8" underlayment grade is not thick enough. 1/2" might not even do it if the planks are cupped or bowed at all. You'd have to tell us that.
...
BTW, sheathing is not for floors. Sheathing is a cheap grade of ply used for the exterior side of walls to be covered with siding or (?).
...
Officially C/C or better ext. glue, but may be hard to find. B/C or one labeled underlayment grade is good.
The planks are "mostly" level with each other, but some, particularly around the main beam or exterior wall appear slightly raised vs. the others around them

I would say that they aren't cupped, they don't seem to be bowed--but I haven't held a straight edge against them yet.

I'll plan to find a 1/2" - 3/4" underlayment or exterior grade plywood to use, perhaps just another layer of the 3/4" dry ply I'm already using, but then I'm back to my woes over height (which I know, shouldn't be the top concern)

Quote:
Originally Posted by JazMan View Post
Remember Hardie adds nothing except a tile friendly substrate.
Given this fact, and that I'm trying to minimize the height... is Ditra a better choice than 1/4" hardi? I suppose adding 5/8" or 3/4" exterior ply wouldn't be so bad if I could get the thickness of the substrate as low as possible.


Thanks Jaz!
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Old 03-01-2011, 04:34 PM   #5
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yet another subfloor build up Q


A 13' span is better than minimum building code for regular flooring. It's probably ok for ceramic, depending on the species and grade. I would say you're right at the borderline if the joists were installed right and in good condition.

However, the deflection between the joists is more crucial, so add as thick a plywood as you can. I highly recommend Ditra, it's better than CBU and only adds 1/8" total.

Jaz
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Old 03-01-2011, 04:54 PM   #6
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yet another subfloor build up Q


Quote:
Originally Posted by JazMan View Post
A 13' span is better than minimum building code for regular flooring. It's probably ok for ceramic, depending on the species and grade. I would say you're right at the borderline if the joists were installed right and in good condition.

However, the deflection between the joists is more crucial, so add as thick a plywood as you can. I highly recommend Ditra, it's better than CBU and only adds 1/8" total.

Jaz
Actually, I need make a correction somewhat...



My 13' span is from main beam to exterior walls...

The bathroom (marked by the red rectangle) is actually only about 4' of space which begins at the main beam. The joists under there were damaged, so they are all doubled up (8' 2x10' positioned over the main beam and secured to the existing joists). I'd say there are about 5-joists under there, maybe 2 were what I'd consider to be actually compromised, the others were OK... but we sistered them all to be safe.

The entryway is actually a bump out of the house situated over a crawl-space of sorts, I don't think of it as one because it's completely open to the basement and does not have a dirt floor. The house foundation is basically a box all around with a typical conditioned but unfinished basement, then there is this bump out (part of original house, not added on) which has a foundation which is the same make up, but only ~3' deep. There is a cement floor in there, and the access to it is through a "window" sized opening in the main foundation. So I guess the joists there actually only span about 4-5' maximum. The joists are continuous from the far fall of the bump out back to the main beam in the center of the house.


I'm thinking probably none of this really changes the advice, but wanted to note it just in case.

I have virtually no hands on experience with CBU, and even less with Ditra, so I guess I will do some research on that before moving forward... but at the moment we have no functioning bathroom, and the only thing standing in the way between this moment and having a toilet is me tiling that floor

Last edited by bubbler; 03-01-2011 at 04:56 PM.
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Old 03-02-2011, 07:52 PM   #7
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yet another subfloor build up Q


So, no working bathroom and no basement to make a temporary shower either. Huh.

Jaz
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Old 03-02-2011, 07:58 PM   #8
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yet another subfloor build up Q


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So, no working bathroom and no basement to make a temporary shower either. Huh.
Jaz
We have the basement, it's the entryway that has the crawlspace...

Fortunately the lease on our rental apartment is through the end of the month
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Old 03-02-2011, 08:17 PM   #9
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yet another subfloor build up Q


OK, so, do you have a full height basement at this location? Not a crawl space. OK, got it. Have you made a temporary shower down there? Or are you showering elsewhere? It's done all the time if you have a floor drain and a laundry tub or (?) nearby.

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Old 03-02-2011, 08:43 PM   #10
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yet another subfloor build up Q


Quote:
Originally Posted by JazMan View Post
OK, so, do you have a full height basement at this location? Not a crawl space. OK, got it. Have you made a temporary shower down there? Or are you showering elsewhere? It's done all the time if you have a floor drain and a laundry tub or (?) nearby.

Jaz
The house is vacant while we're doing and having work done... We've done a huge amount of work to the house so far, the tile has been what scares me the most and certainly has been the one I'm timid about

I plan to do some write-ups of the various things we've done once I have more free time

- Tore down partition wall between kitchen & dining room
- Pulled down exterior wall plaster in kitchen to insulate and re-wire
- Pulled up hardwood in hallway and back bedroom for replacement
- Laid 600sq-ft of laminate on the 2nd floor (over asbestos tile)
- Gutted the bathroom, sistered the joists and replaced the rotten sub-floor
- Removed wallpaper from several spots
- Replaced all interior doors
- Painted every surface
- Replaced all windows

We've had a contractor in to install new kitchen tile floor (poorly done by this forum's standards) and cabinets. A hardwood contractor will be in reinstalling new wood and refinishing the rest (hopefully in a week! wood was supposed to be delivered today for acclimation)

Before we move in I'll be working w/ a carpenter friend to replace the front and rear doors with new pre-hung replacements.

This spring the same carpenter friend I will be tearing down the completely unsafe rear deck (one corner is completely unsupported, the beams have totally rotted away) and building a new one...

...but now that we're down to the wire (3 weeks till move in), I need to get the tiling done by this weekend so that the plumber can be in next week
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Old 03-06-2011, 08:16 PM   #11
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yet another subfloor build up Q


So I had some soft boards in the entry way...

This particular spot was 26" between joists, but it's only a 4' span and has 2x8 joists (I was mistaken earlier when I said the 2x10s continue in the crawl space)

Anyway, long story short, I put down some 3/4" dryply to replace the planks, then put some 15/32" BC ply on top. Next step will be mortar + 1/4" hardi and then the tiles. I can't wait for this to just be done!!

I stuck my head into the crawl space window from the basement (shop-vac'd for about 20 mins first to removal all the spiders and dead house centipedes... yuck!!). I added some new 2x6's as cleats, plus I put a cross brace (right) in to support the edge of the ply and the existing plank:



This is the view from above... so basically I sistered the existing joist and the band joint(?), I also added a cleat on the left (had to notch the heck out of it for the heating pipes) and added the cross brace on right):



The 3/4" dry ply is down:




First sheet of 15/32" is in... it's a single sheet that I cut slices out of... I figured it's best to have as few sheets as possible:



The second (and last) sheet is in. I left a very small gap between the two sheets:



There will be new hardwood in the hallway, that's going to about about 3/4" give or take after sanding/finishing. My tile floor is going to end up being about 3/8"-1/2" higher. The HW installer suggested re-screwing all the planks into the joists, then laying 1/2" hardi and tile (no add'l ply) which would allow the two floors to meet w/o a transition piece... I sort of liked the idea, but at the same time I'm OK with a threshold here because it will hopefully minimize the migration of dirt/moisture from the entryway to the hall way.

The pics aren't very interesting, but I always like to see them in other posts

I took the day off tomorrow, so hopefully you'll get some finished tile shots

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