Opinion on Contractor recommendation

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Old 08-02-20, 04:22 PM
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Opinion on Contractor recommendation

I've been reading a lot about plank sub floors and tile installation on this forum but I haven't been able to find the answer to my question. Mostly because most people who ask about plank sub floors say that it's an old house, my house was built in 1987 and has plank sub floor.

The plank sub floor is 1/2 inch x 8 inch pine and their spaced about 3/8th inch apart. I ripped up the old sub floor to install new tile. My contractor tells me what he wants to do, and what will work, is screwing in a 1/4 luan underlayment to the plank sub floor and then on top of that he is going to screw and mortar 1/2 inch cement board to the underlayment and tile on top of the cement board. I'm guessing he knows what he's doing but that doesn't sound right to me.

The plank sub floor is in good shape and by all accounts still solid.

Is 1/4 underlayment and 1/2 inch cement board a suitable installation?
 
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Old 08-02-20, 06:40 PM
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NO!
And if that's what he suggest I would not let him back in the house!
What you have now is to weak and there's going to be cupping, 1/4" would just mirror all the flaws.
And Luan is full of voids in the ply's, and can cause adhesion issues.
The only way I would do this is cut out the old sub floor, check the floor joist to make sure there all even, and use Advantech sub flooring, or at least go over what you have now with 1/2" A/C plywood, but before installing I'd add ceramic 2-1/2" decking screws to the old sub floor.
You also would want to make sure any ring shanked nails or screws used do not go into the floor joist.

 
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Old 08-02-20, 07:12 PM
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Thanks for confirming my suspicions. Unfortunately funds are low for me right now so I have to do the demolishing myself and cutting out the old plank sub floor isn't something I have the time to do. Since I can't cut out the old sub floor.... You're suggesting I can screw the old sub floor to the joists. Then it's OK, albeit not the best option, to screw a 1/2 " A/C plywood to the existing plank sub floor, but do not hit any joists when screwing it to the old plank sub floor? Then would a contractor still need to add a 1/4 cement board to the AC Plywood before tile?
 
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Old 08-02-20, 08:54 PM
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Tile is a one shot deal, done wrong it it will fail.
1/4" under layment would be useless!
There is no need for 1/2" cement board on a floor, it adds 0 strength!
When I'm faced with what your dealing with I cut out the old sub flooring with a Toe Kick saw, you can buy a cheap one at Harbor Freight or rent one at Home Depot.
By removing that old flooring and replacing with Advantech you'll have 1/2" less height to deal with at the threshold and have a rock solid flat floor.
Once that's done you lay 1/4" cement board in a bed of thinset spread with a 1/2" toothed trowel.
 
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Old 08-02-20, 11:37 PM
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Do you have the room for 3/4" plywood? Granted the plank floor is not the best but ripping out is a tough option, the more sub floor the better!

 
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Old 08-03-20, 04:23 AM
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Do you have the room for 3/4" plywood? Granted the plank floor is not the best but ripping out is a tough option, the more sub floor the better
Yes, there is. In fact, the floor I'm ripping out of the kitchen now was installed with 3/4 " plywood on top of the plank sub floor and the tile was laid directly on the plywood. The tile is the original tile but it's ugly, which is why I'm replacing it. Originally I was going to do 3/4 again but there wouldn't be any room for any kind of cement board, the tile would need to be laid directly on the plywood - as it was originally. What I'm hearing though is that cement board adds no strength and seems it's just used because it's easier to work with. I was always under the impression it added strength as a second sub floor.

By removing that old flooring and replacing with Advantech you'll have 1/2" less height to deal with at the threshold and have a rock solid flat floor.
I appreciate you letting me know the best way to do this but ripping out the old plank flooring isn't an option for me.


 
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Old 08-09-20, 03:24 PM
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I'm now considering taking out the plank subfloor and using Advantech as you suggested. However, when I look at the plank sub floor, the joists aren't lining up where I would be cutting away the planks (with the toe kick saw) how do I support the Advantech sub floor if there is no joist to secure the wood too? When I get to the end of the room, if I cut away the plank subfloor there is just an empty space where the wall would meet the Advantech. Do I have to add a joist in the basement?
 
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Old 08-09-20, 06:57 PM
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Use joist hangers and scab in boards across the ends.
 
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Old 08-12-20, 06:42 PM
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That makes sense, not sure why I didn't think of that. Another issue with taking out the old plank subfloor. I have some cabinets low to the floor so short of removing all the cabinets there isn't a way to get under the cabinets to remove the planks. There would be about 2 feet of plank subfloorr that I wouldn't be able to remove along one wall. Would it be OK to leave that section.as plank subfloor and the rest plywood or is that not a good idea?
 
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Old 08-12-20, 06:56 PM
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Use a toe kick saw... cut around wall edges, cabinet edges, and add blocking between joists as needed to support cut ends of old plank subfloor, or walls that rest between joists on top of that subfloor. Put down new 3/4" subfloor. Use an uncoupling membrane if you don't want the added height of cement board.

Luan has no place being used as an underlayment, imo. And 1/2" planks arent suitable for tile.
 
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Old 08-14-20, 09:57 AM
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You don't need to remove the planks. You can go over the planks with 5/8" or thicker exterior grade plywood, bc or better. If height is a concern you don't need to use cement board over the plywood. You can use ditra. It's better than cement board anyway.
 
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Old 08-25-20, 11:37 AM
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Oddly enough I had another tile Installation company come out today and told me the same thing. He can go right over the plank subfloor with mud and then add a 1/2 inch Hardibacker directly onto the planks, no other plywood at all, just Hardibacker. He said he does it all the time and guarantees it wont crack. I personally don't like that idea as I said in earlier posts but I did find it interesting that he suggested the same thing as the 1st guy. I don't know, maybe it's a Massachusetts thing? LOL

However, this same guy said he can also do the Kerdi Membrane over the existing plywood if I prefer, said he would charge me the same price for either option. I think I'll go with the membrane and plywood.

 
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Old 08-25-20, 11:49 AM
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That's not right. He can't go over 1/2" planks without adding more plywood. 5/8" would be the minimum. Hardi isn't structural and will add no strength to the floor. 1/2" hardi is no better than 1/4" and 1/4" is all that is needed over the plywood. If you want that floor rock solid, use 3/4" plywood over the planks, then ditra. FYI Kerdi is a waterproofing membrane for wet applications like showers. It isn't an uncoupling membrane, but ditra is. I'd run away fast from this contractor.
 
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Old 08-25-20, 12:12 PM
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FYI Kerdi is a waterproofing membrane for wet applications like showers
He didn't mention the type, he just said he could us a membrane on top of the plywood and I asked if it uncouples the tile from the floor and he said yes, so it's probably Ditra. I definitely don't like the idea of no other plywood just the planks, I'm only sharing because I would never do that yet 2 contractors have suggested it.

Thanks for chiming in, it seems Ditra over plywood is the superior application for tile installation and it's what I'll go with, assuming the quote is in the ballpark of what I'm looking at. It's 400 sq ft. I'm assuming under 5k to install? Will a Ditra install cost more than that, it's just ditra and tile install, no underlayment work.
 
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Old 08-25-20, 01:11 PM
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He can't go over 1/2" planks without adding more plywood. 5/8" would be the minimum.
The reason HeresJohnny says that is because there are industry standards. Any Tom, Dick, or Harry can "say" he can do it, or has done it a certain way. However the fact is that what he is suggesting does not meet industry standards for subfloor deflection. What's he going to do if/when your grout fails or your tile cracks? You want to bet on it? Will he even answer his phone when you call to complain?

Industry standard when you run into 1/2" subfloor is to add a minimum of 5/8 ply... and 3/4 would be better.

And you havent mentioned anything about the size and span of your joists, which is also a factor. Yours may be fine, but you wouldnt believe the people who think they can tile successfully on top of overspanned, or undersized floor joists.

Not trying to cause alarm, but if you have had 2 contractors tell you the same thing, they are both giving you bad advice. They want to get the job, which I understand. They need to give you a low price in order to beat out the next guy. The only way to do that is to cut corners, and that's what they are doing. You need to find a tile layer that will tell you the truth about what the minimum subfloor thickness should be.
 
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Old 08-25-20, 01:17 PM
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I agree, it's extremely difficult to get contractors to call you back in this area, even more difficult to get them over to your house. Which is why more times than not I end up doing things myself. I called 8 tile contractors, only 4 called me back and only 3 offered to come to the house. I have the 3rd coming later today, we'll see what he says and I thank you all for the advice, there's no way I will have anyone tile the floor who isn't going to add a minimum of 5/8 inch subfloor to the planks.
 
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Old 08-26-20, 06:27 AM
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The quote came in for a Ditra install and it's reasonable so I think I'm going to go with that. Can I tighten up the old subfloor and clean it up as much as possible to install the Ditra over it, or when installing Ditra does the plywood need to be new and clean? The subfloor now is solid but it's ripped up a bit and has some thinset remnants on it from the old tile I ripped up.

BTW - my joists are 16' apart with a span of about 11 feet, a little less.
 
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Old 08-27-20, 11:15 AM
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What are the floor joists, 2x8's, 2x10's? You need minimum 5/8" exterior glue bc plugged or better grade plywood over your existing planks. If you already have that, make sure the ply is in good condition, not delaminating, not all gauged up, clean and flat. Thinset will have to bond to it. If the ply isn't in good condition it should be replaced.
 
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