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Unread 05-23-2017, 05:59 PM   #1
itserich
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grab bars - Plywood or 2x12 blocking under tile backer?

This is for a diy bathroom renovation.

I would like to allow for future attachment of grab bars to the wall. From what I have read, grab bars should be attached to some sort of blocking (2x12 fastened to studs) or plywood.

So I would attach to the studs, and then cover with tile backer, either:

1) Plywood, such as 5/8 inch
2) 2x12 block of wood
3) both - blocking, then plywood?

It seems plywood would allow grab bars to be installed anywhere on the wall, but blocks would have more depth and be stronger.

Just curious what is normal? I have a bunch of books, but none of them discuss strengthening the wall frame before installing the tile backer.
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Unread 05-23-2017, 06:15 PM   #2
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Probably the better way to do this is to install blocking, and then, assuming you're using something like cbu, that would get screwed into the blocking. You'd want to try to maybe make a template or a good picture of where the screws are so you don't hit one when later trying to mount your bar as you won't be able to see the screws behind the tile and the backer screws are quite hard.

An alternative, and maybe the only way to safely get a bar installed later on when it wasn't prepped prior, is to use one of the www.wingits.com fasteners. I've used two different versions of these and both work quite well. They're a bit pricier than blocking, but great for an afterthought. These specifically cannot be installed into blocking, so you have to make sure you're not going to hit a stud so it will work, but they are ADA rated safety bar anchors. I've used both this one http://wingits.com/products/wingits_...bar_fastener_4 and this one http://wingits.com/products/wingits_...bar_fastener_5 . This second one, I think, is a little more forgiving in placement, but both need you to be pretty accurate in installation as there isn't a lot of tolerance when screwing on the bar to the fastener. If you're lucky, you can catch one end of a bar into a stud, and only need one of these. For whatever reason, most bars are not designed to hit typical US 16" OC studs, and blocking or one of these fasteners is the only way to anchor one end.
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Unread 05-24-2017, 07:27 AM   #3
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WingIts / Toggle Bolts and Foam Tile Backer

Thanks, I figured the other option is some sort of toggle bolt type product.

The WingIts specifications state they can be used with drywall.

I am planning to use a foam product such as Go Board - which is 1/2 inch of foam - on the walls.

Are WingIts and other toggle products regularly used with foam tile backer boards? Just curious.
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Unread 05-24-2017, 11:47 AM   #4
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I sure wouldn't, but I don't know if they've done any testing on such foam boards.
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Unread 05-24-2017, 01:59 PM   #5
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I seriously doubt any type of toggle bolt or a WingIts like design would provide adequate strength when using a foam backer board...they need something relatively incompressible and then work by having a large footprint that spreads the load out over a large area and relies on the rigid tile on the front to provide additional stiffness. When you tighten one of those down with foam...it would just end up compressing and digging into the foam after it broke through the skin. FWIW, drywall is a lot denser and the paper covering is also thicker.

Schluter has some videos where they show how to install a faucet in the foam board when it is used as a countertop base, then tiled. They also have one that shows how to reinforce things where you might need to add a screw. IN that situation, they route a pocket in the foam, then take a suitably thick acrylic cutting board, and thinset it into that recessed pocket. That, again, spread the load and being both a rigid material and able to hold a screw, once bonded in place, can work. It might not work great on a thinner board. When on a counter...the route a pocket and then install a recessed layer of additional tile. On eth bottom, the cut out the remaing foam around the shank large enough so you can tighten the nut down...it ends up sandwiched between two layers of tile...no foam. It would just continue to loosen up if it was tightened down on foam and not have much strength.
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Unread 05-24-2017, 05:08 PM   #6
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blocking + plywood

Thanks.

I plan to use a wall mounted sink, and for that I will want to install blocking.

I will also install blocking for future possible wall mounted fixtures such as grab bars, but to be extra sure 1/2 of plywood under the tile backer would make adding almost any wall fixture possible, I think.
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Unread 05-25-2017, 04:58 PM   #7
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FWIW, 1/2" ply doesn't have the greatest screw holding ability. It will have fine shear strength, but the tension/pull strength isn't fantastic. This is why solid blocking is most often recommended.
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Unread 05-26-2017, 01:10 PM   #8
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I agree with Jim and would use good quality 3/4" ply at a minimum.

I also agree with making a drawing, template, or taking a picture with a tape measure included along the wall for reference. You need to know where your ply or blocking is years down the road when it's time to use. Put the drawing or photo in a freezer bag that's stapled to the inside carcass of your vanity cabinet and it will never get misplaced.

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Unread 05-26-2017, 01:27 PM   #9
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If you're going to go with plywood for grab bars, I'd specify 3/4" baltic birch, cabinet-grade plywood. Standard plywood allows significant voids in the middle that will reduce the strength of the plywood and screws. Be warned - it's expensive. Much cheaper to use 2x12 blocks.
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Unread 07-03-2017, 08:04 PM   #10
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Plywood Subfloor Movement Joints - Fill with Silicone?

I am working on a small 5 x 7 foot bathroom.

The plywood subfloor is two layers: 3/4 tongue and groove plywood attached to the studs, and 5/8 inch BCX plywood above that.

I have been following guidelines for installing the subfloor using the Ditra installation handbook.

https://s3.amazonaws.com/scclegacy/m...ndbook_eng.pdf

I am confused about what I think Ditra calls “movement joints” on pages 17 - 19. The Ditra handbook does call for gaps between the plywood, and mentions using some sort of tape to cover the gap, such as Kerdi Band or Kerdi Flex, but I don’t think it makes any mention of filling them with silicone caulk, while other sources do seem to recommend that, though I could be confused.

So, my question is, should the gaps be filled, or not? I use a lot of silicone in other projects and there is a small bit of flexibility, but not much. It seems it would restrict movement of the plywood.

This photo show 3 “movement joints.” First is a gap between the top plywood of the subfloor. This will be under a shower base, so the cleavage membrane will cover it, preventing mud deck from filling it.

Second, around the perimeter, is about 1/4 inch gap. Third, I installed plywood on one of the walls, and left around 1/4 inch gap between the subfloor and the plywood wall. I do plan to install foam tile backer GoBoard on the walls, so that should also prevent thin set / mud deck from entering those gaps, but maybe not.

I am confused about this, so if there is any literature, please let me know. Thank you.
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Unread 07-03-2017, 08:21 PM   #11
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If you read the plywood industry's guidelines, an UNDERLAYMENT layer (not the original subfloor) can be installed without any gaps. Their reasoning for that is that the original subfloor is likely to be installed on somewhat wet wood, and sit in the open before things are closed in, so the moisture level will vary radically as it gets rained on and then hit with the sun maybe multiple times - IOW, it needs that gap to prevent buckling of the panels. By the time you are ready to install the underlayment for say tile, the house has been sitting enclosed for awhile, and it's not likely to get rained on, as it is being heated, and maybe air conditioned...so, since ply is pretty stable by itself, in an enclosed building, the gaps are not needed. If the ply has not been stored outside and got rained on, it should be fine.

I wouldn't worry about doing anything special...spread the thinset, embed the Ditra.
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Unread 07-03-2017, 09:57 PM   #12
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Erich, I've combined you with your previous thread on this bathroom project for continuity so folks can see what you're working on and what's been previously asked and answered. We can give it a more generic title any time you'd like to suggest one.

What you're dealing with there is a second layer of plywood and not an underlayment. A little nit-picky, perhaps, but I wish our industry would stop using that term when the material involved is not in fact being used as an underlayment. If you were planning to install your tiles directly to your top layer of plywood, it would, in fact, be an underlayment. You're not, so it's not, it's a second layer of subflooring and always a good thing to have under a ceramic tile installation as far as I'm concerned.

But given your description of what you're planning to do, I'd agree with Jim that you can pretend those joints are not there. If you want to protect them under the portion of the floor that will receive Ditra, you can use a "bond-breaker" tape over the joints. If you can't find any such tape, 3/4" masking tape would suffice if covering them makes you more comfortable.

My opinion; worth price charged.
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Unread 07-04-2017, 07:55 AM   #13
itserich
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blocking and gaps

Thanks CX, about the terms I agree, it gets confusing. My understanding is both pieces of plywood form the subfloor.

I left the gap only because of Ditra's instructions. I had read that may apply only to new construction, but it gets so confusing, so followed Ditra's recommendation.

Some sort of tape sounds good, and much easier than Kerdi Bond or Kerdi Flex.

As to the blocking discussion, I ended up using plywood on this wall because it is the exterior wall. It is filled with foam board insulation between the studs, so the only way to attach anything to it will be to either hit the stud with a screw or use wing it type screws through the plywood. (Several layers of foam, which is why the "studs" are horizontal, not vertical.)

Here is a photo of the blocking on another wall and the foam before it was covered. The blocking, except for the sink, is the same height. Grab bars apparently are installed about 36 inches above the floor.

Thanks for all the advice.
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Unread 07-04-2017, 09:09 AM   #14
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If you intend to tile the wall in question, I would much rather see you install the blocking pictured rather than plywood sheathing. The plywood is much more apt to cause enough movement to result in a failure of the tile installation.

My opinion; worth price charged.
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Unread 07-04-2017, 06:45 PM   #15
itserich
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The plywood wall would be covered with foam tile backer (GoBoard), and then tile.

I thought the backer would uncouple the tile from the plywood.

Is plywood / tile backer / tile on the wall, more problematic than the same setup on a floor? (I am using Ditra for the floor in this case, not foam tile backer).

My reasons for plywood on the wall is to add rigidity, and to be able to attach things to the wall.
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