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Unread 01-18-2002, 11:13 PM   #1
BoiseXJ
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Question

We're installing tile in a 30x11 room and I'm having issues. The subfloor is 1 1/4" particle board on 4x8 joists... my issue is that the joists are 32" on center. The joist supports are 7 feet apart. I want to do a good job and from what I hear, that is unacceptable. So, I crawled under the house and mounted about 35 cross braces using joist hangers (on the seams of the subfloor, every 4 feet). I'm going to shim them tonite (to ensure solid contact with the subfloor, but I still seem to have floor bounce. I don't really know what is 'too much' bounce in the floor though. What should I be doing? Should I add MORE cross bracing? Or have I added enough?
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Unread 01-19-2002, 02:24 AM   #2
chip
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Boise,

You have a problem indeed.

I hope you haven't already bought some special order tile.

The others will be along to help with the substructure soon.

I can tell you that any bounce is bad! Tile is what you might call rigid. The mortar that bonds it, is rigid. Bouncing is a no-no!!!

OSB is not a suitable substrate for the installation of ceramic tile. You will want to add a layer of cement backer board, which of course will add more weight to the floor,as will you setting material and tile.

You would be better off to hire a structural engineer to help you through this.

But our "En-gen-eers will be along shortly with all the help you will need, I'm sure.

Listen close and follow directions. Please!

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Unread 01-19-2002, 08:35 AM   #3
John Bridge
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Go morning, Boise,

Chip has pretty much laid it on the line for you. From the way you describe it, your floor will not support a ceramic tile installation unless you completely re-build it. Putting blocking across the span does next to nothing. It doesn't increase the longetudinal stability of the structure at all. What you would need would be more, and larger, joists. The general rule is 2x10 joists set 16 inches on center (14-1/2 in. apart). There can be exceptions, but you are nowhere near the minimum.

Particle board is not only unacceptible for ceramic tile; it is a no no for other types of flooring as well. This is because it has a propensity for expansion (swelling) when moisture contacts it. OSB (oriented strand board) is a little better but still not as good as plywood. So once again, you are not even close.

My advice: Unless you are prepared for some major tear-out, I would consider some type of flooring that will have a better chance of survival over your subfloor -- carpet or linoleum, perhaps.

Others may have differing opinions here. Mine is certainly not final. I get over-rulled all the time.
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Unread 01-19-2002, 01:12 PM   #4
Rob Z
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Boise


Ditto on everything said so far. If this floor MUST have ceramic, my first instinct is to say to rip out the particle board, install joists between the existing joists (and end up with 16" centers), and install 3/4 T&G plywood with either backer board, a mud bed, or Ditra on top.

It would be quite and undertaking for my small company.
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Unread 01-19-2002, 09:05 PM   #5
BoiseXJ
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This is very upsetting... I was foolish enough not to check the board before I began working today. I had talked to a local contractor, a friend of ours, and he had said I was good to go. But now, checking on here, you say it won't work. I spent the day cutting my 1/2" Durock to fit.

I don't know what to do. I've spent $300 on Durock, which I can't return now.

Just to verify what you all are saying:

1 1/4" particle board (that is what the large chips glued together are called, right?) is bad?
32" on center joists are unacceptable? Even with cross braces?
Durock will not make the floor any more durable?

What will happen if I go ahead and put tile down?

What would you do? It sounds like my only option is to pull the durock out, throw it away, and put linoleum in. Is that right? This stinks.

Are there ANY other solutions?????
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Unread 01-19-2002, 10:37 PM   #6
Bud Cline
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The large chips glued together are OSB (orienred strand board).

John were is the photo illustration I put up here showing the swollen partucle board? I don't know where to look for it.

Thought Boise might like to see it.
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Unread 01-19-2002, 11:11 PM   #7
Jaz
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Boise,

Sounds like you have OSB. Which is a little better than particleboard. But man, who the heck built that floor? How did it pass inspection? I've installed over 3/4 ply and Durock on 24 " on center, was very nervous. Told customer they may have some cracks.

Durock would make it much stiffer...but I don't think stiff enough. Actually I'm possitive! I wouldn't even recommend vinyl, unless it was the 12' wide perimeter glued type.

Regardless what you end up installing on top, make sure you have a vapor barrier on the ground, the proper landscape slope away from building and enough cross ventilation vents to keep it dry. I'm assuming you have a crawl space?

By the way..to you people posting questions..It would be helpful if you also told us WHERE your project is. It sometimes makes a dif. if its in Texas as apposed to Ohio. The building custom and mainly the weather will often influence our answer to you.

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Unread 01-20-2002, 12:53 AM   #8
Bud Cline
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The "joist supports" you mention, what size are they?

Where's CX? Maybe he could check in here and suggest something.
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Unread 01-20-2002, 08:24 AM   #9
cx
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Well, Bud, you know I ain't s'posed to be givin' advice over here on accounta I ain't no tile man, but I almost posted last night anyway.

As I understand the situation, he's spanning 29" by 46 1/2" with 1 1/4" Beaver Barf over what should be a solid structure (4x8s on 7 foot post centers). The added joists across the 32" spacing, shimmed under the sub-floor is what I'm looking at for the span I'm seeing.

For a customer, no way. But if it were my own house and I really wanted tile and didn't wanna tear out the existing subfloor, I'd tile it as he is planning.

I'd also disavow all knowledge of this advice when the cracks start to appear, but then again, It'd be my house.

My opinion; worth price charged.


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Unread 01-20-2002, 09:03 AM   #10
BoiseXJ
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Moisture barrier? For moisture that soaks thru the grout, thinset, durock and another layer of thinset?

I need you guys to speak in idiot terms, cuz I'm no tile expert.

So what you're saying is that despite the fact that this OSB is 1 1/4 inch thick, it's no better (or actually it's worse) than 3/4 inch plywood?

Could I put cement or stone pads in the crawlspace and put joist supports up into my cross bracing?

On another note, if I return the tile will linoleum stick to durock? Or do I need to tear out the durock? And if I do keep it with linoleum, do I still need to thinset it to the floor, or just screw it down?
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Unread 01-20-2002, 09:33 AM   #11
John Bridge
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Hey Jaz, I'm assuming Boise is in Boise, as in Idaho. I could be wrong, though.

Boise,

I think we may be able to salvage the situation here, and I'll ask CX to comment again when I'm finished. I think if you remove the cross pieces you've installed and install additional joists instead, you will stiffen the floor considerably. Your joists are set 32 in. on center. If you insert a new one in the middle of each space, you'll have 16 in. centers, which gets us closer to the minimum recommendation on joists.

The minimum joist size is 2x10, but since you'll have 4x8s with the new 2x8s between them, and since your spans are only 7 feet between supports, you should be in good shape. Certainly, you'll be in much better shape than you are now.

You can cut up the cross pieces you remove to make solid blocking midway between the supports. This will stiffen the structure somewhat -- not a lot, but you have the material on hand, and I'm assuming you will take the time. Putting props on blocks laid on the ground will not get you past the first frost cycle in your neck of the woods, if it even gets you that far.

The moisture barrier Jaz is referring to is laid on the ground and goes all the way tight against the foundation wall. (You do have a foundation wall? If not it will go against the perimeter skirting. You do have skirting? )

I think the moisture barrier can be something like 6 mil poly, but I'm not really qualified to state that. CX? Jaz? Anybody?

That along with adequate crawl space ventilation will help keep your osb from swelling on the underside.

Bud,

You expect ME to find YOUR picture? I'll try, man, but that was a long time ago. You didn't mail it to me, so it must be on your site, no?

[Edited by John Bridge on 01-20-2002 at 10:39 AM]
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Unread 01-20-2002, 11:29 AM   #12
Jaz
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Boise, John and All,

Most people use poly as a moisture barrier on the ground, it's cheaper. But it's not the best because in wet areas it'll trap water. I think the best barrier is a landscape fabric. It is usually black and allows moisture to pass and evaporate.

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Unread 01-20-2002, 04:06 PM   #13
BoiseXJ
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This is Idaho, so it's VERY dry here... I don't see the moisture barrier as a concern. I don't know if I made it clear before but this is a pre-existing home. (12 year home) My contractor friend says that the 1 1/8 inch OSB I have is better than plywood and has a span capability of up to 48 inches (compared to 24 for 3/4 inch plywood). He is saying that will the cross bracing I should be fine. He wants me to verify by checking in my crawlspace while my wife stands/hops/moves around on the subfloor and I measure the floor to see if it drops at all. He said this type of floor should have no more give than any other type of subfloor.

As for the 'adding joists' idea, this is impossible. The only way I can add joists is to tear up my subfloor and put them in. (ie, not going to happen).

I didn't understand your comment about 'when the first frost cycle hits' causing the added joist supports to fail?

Here's the joists:
[img]http://communities.msn.com/_Secure/0MQAAAIER*7Ba2Tz1!ZrEAggCTM3x7h*uuXwc5CWHfOI3sbvkO7xYmJ!Lws18SajexCzMpFMwz!GNeXeBwT2klA/joists.jpg[/img]

[Edited by BoiseXJ on 01-20-2002 at 05:31 PM]
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Unread 01-20-2002, 05:06 PM   #14
Bud Cline
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John forget finding the picture. I thought you might remember the context but it'snot important now. It wouldn't matter anyway.

Something tells me this is going to be a short lived thread.
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Unread 01-20-2002, 05:39 PM   #15
John Bridge
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Boise,

We are all of us here, contractors. Anyone who says osb has twice the rating of 3/4 ply worries me. The floor won't make it for a tile installation. There's not much more we can add to that.

It already appears that the underside of your osb has begun to swell and delaminate. Idaho is apparently not as dry as you think. At least not under your house.

Any support placed directly on the ground will "heave" out of place with the first freeze/thaw cycle.

Sorry.
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