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Unread 10-28-2003, 12:28 AM   #1
hipdeepinmud
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what kind of fasteners?

In our last episode, (http://johnbridge.com/vbulletin/show...?threadid=8073)
I was helping a friend provide additional support to his sub-floor. This weekend my friend's son is arriving to tile, and I had a quick question.

The sub-floor is 1/2" plywood, and 1/4" Hardibacker is going on top. Using the quadratic equation, that's 3/4". Since the Hardibacker is not supposed to be screwed or nailed to the joists, what would be the best fastener to use over the joists? 3/4" roofing nails? CBU screws (do they come in 3/4"?)? Some other kind of screw?

In the areas not over the joists, I'll use the 1 1/4" screws or nails. But the idea of using little 3/4" roofing nails so the joists are not penetrated concerns me. Will there be sufficient holding power?

Thanks for any help on this. It may be academic, as the person doing the work probably won't listen to any suggestions and will just use drywall screws to fasten the Hardibacker through the plywood and joists. If this happens, how much will this increase the chance of cracks in the grout/tile?

Much appreciated,

Steve
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Unread 10-28-2003, 06:21 AM   #2
bbcamp
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Steve, don't worry about using different size screws or nails, adjust the spacing to clear the joists. The spacing pattern is a maximum, there is no minimum. Tests have shown that installing the CBU into the joists will cause cracking tiles or grout down the road.

BTW, you need 1/2" CBU over 5/8" plywood. What you have planned is insufficient. (Yes, I do remember the friend's son. )

Bob
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Unread 10-28-2003, 08:22 AM   #3
stullis
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If it was sufficiently blocked up from underneath then the 1/4" cbu will be fine.
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Unread 10-28-2003, 08:26 AM   #4
Bill Vincent
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I'm assuming there's 3/4" sheathing or some other kind of subfloor under the 1/2" plywood, in which case 1 1/4" screws every 6" will do just fine, and you don't have to worry about missing the joists. If, however, all you have is that 1/2" plywood and 1/4" CBU, you might want to add some more subfloor before the CBU goes in, or screwing into the joists will be the least of your worries.
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Unread 10-28-2003, 10:15 AM   #5
hipdeepinmud
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Sistered joists

I appreciate the replies. The subfloor is just 1/2", but we added plywood, sistered joists, and added blocking underneath. The thing is, with all that added, there's not much area that ISN'T lying over a joist. The entire perimeter of the room, the 16" oc original joists, the sistered joists on both sides of the originals, the blocking- if these areas are avoided, there's not much area that will be screwed into.

Because of this, would it be better fasten the Hardibacker over the joists with 3/4" nails or screws? Or will screws in the field of the Hardibacker suffice?

Thanks for helping me make the best of the cards I've been dealt. I realize that this is not the way to do quality work. Bill, I saw the photos on your website and was very impressed, and realized the standard I'm shooting for.

Steve
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Unread 10-28-2003, 12:09 PM   #6
cx
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Wish you'd kept this on your original post, Steve, easier for everybody to keep up with the background on the project. Yeah, I know you posted a link, but sometimes folks miss that or just elect not to go look at it. Maybe one of the moderators will put them together for us - I don't think we're done with this project yet.

I think your situation is already sufficiently non-standard that your fastner schedule isn't gonna be as important as it might have been. I'd suggest you just get some 1 1/4 or 1 1/2 nails or screws and just nail it down to whatever's under there, following the CBU manufacturer's recommended use of thinset and spacing of fastners - if you can get Junior to do it that way, of course.

I think you've done all you can to provide structure for the installation, just hafta wait and see how it all holds up. Hell, it might work out fine. Or it might not. That's just a guess.

My opinion; worth price charged.
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Unread 10-28-2003, 12:49 PM   #7
hipdeepinmud
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Hi cx,

Sorry about the split posts. In the future I'll add it to the original post.

When you say "just nail it down to whatever's under there", you don't mean fasten it to the joists, do you? Or are you saying that at this point, it might not really matter, with the way nothing has really been done correctly?

I'm sure I've taxed everyone's patience on this, and I'm very appreciative of the time people have taken to respond.

Steve
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Unread 10-28-2003, 04:37 PM   #8
cx
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Quote:
Or are you saying that at this point, it might not really matter, with the way nothing has really been done correctly?
Yep, that's pretty much what I meant, Steve. If you shored up that subfloor from underneath as we discussed, most everything under that half inch ply is more like joist than subfloor. I wouldn't worry about trying to miss or hit anything in particular. Just install the CBU and "tile on" is what I'm suggesting at this juncture. Others may have different advice. Keep in mind that I'm not a tile expert, I'm just a guy who builds stuff. Sometimes really nice stuff, though.

My opinion; worth price charged.
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Unread 10-28-2003, 05:54 PM   #9
hipdeepinmud
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o.k., I think I got it cx. Maybe it's like not using insulation or double-paned windows, then worrying about whether drapes or blinds would keep out the cold better. I'll advise my friend to let things be and hope for the best.

I really like the way you approach the various questions that get raised on this forum. And I'll bet you're one great builder.

Cheers,

Steve
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