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-   -   What size screws for underlayment (https://www.johnbridge.com/vbulletin/showthread.php?t=115593)

Motordoctor 02-28-2015 09:02 AM


Originally Posted by Hardibacker cement board installation guide
determine layout of HardieBacker cement board

•Stagger all HardieBacker ® cement board joints. Do not align with subfloor joints.

•Never allow all four corners of boards to meet at one point.

•We recommend an 1/8” gap between board edges.

•Keep sheet edges 1/8” back from walls and cabinet bases

Sorry about that, the first quote was from their guide, but wrong section. It was the vinyl flooring section. I hate trying to read online PDFs, being an old geezer I prefer books. I watched their instructional videos and they showed laying down the CBU perpendicular to the plywood. Too bad, putting it perpendicular to the joists would have been easier since the room is 10ft wide.

cx 02-28-2015 09:08 AM

Gotta admit I don't read the installation instructions for the other flooring types when I'm on those manufacturers' websites. Hell, I have plenty trouble keeping the tile information straight in my little pea brain.

Glad you got it sorted out, though, and that it's just like we thought it should be. :)

Motordoctor 03-02-2015 11:22 PM

Another odd ball question here. Since I've never worked with mortar before I'm not familiar with its characteristics. When I put down the CBU, I'm going to use a 3/8" trowel to help even out the subfloor deviation. So I set the CBU on the mortar, move it around to seat it and check the X-Y axis for level/flatness. Assuming it comes out level and most importantly flat, will putting the screws to it at this point change that? Meaning does the mortar squish out when you apply a clamping force or does the stuff stay put? Sorry for the dopey questions but I'm sitting around twiddling my thumbs waiting for the Mortar I ordered to show up.

cx 03-03-2015 09:37 AM

Dan, you do not want to try to level or flatten your subfloor while installing your CBU. You must install the CBU according to the manufacturer's instructions, which will usually include a trowel size and material type.

You can flatten a subfloor at the joist tops or you can flatten the floor on top of the CBU, but you don't try to flatten between subfloor and CBU. You'll get a little flattening just by installing the CBU, just as you might when installing a second layer of subflooring, but you must attach the CBU directly onto the subfloor as instructed.

My opinion; worth price charged.

Motordoctor 03-08-2015 09:28 PM

I finally got my mortar today so putting down the CBU starts tomorrow. After I put down the mortar and put the screws to it I'm assuming that walking on it is a bad thing? The reason I ask is this: don't want to put myself into a corner so if walking on it before the mortar sets is bad, I will have to do it in a couple of steps so I have an escape route. Thanks

cx 03-08-2015 09:32 PM

I know of no CBU manufacturer who prohibits walking or tiling on newly (and correctly) installed panels on floors.

Motordoctor 03-09-2015 07:45 AM

Ok. Couple of actual tile questions now ;)
  • Are the 18x18 tiles prone to "lippage"? Meaning do I need a leveling system? When the mortar sets will that move the tile's plane?
  • To keep the mortar out of the plywood joints and out of the wall spacing what works? I've heard of just using tape, and also caulking.

Houston Remodeler 03-09-2015 09:38 AM

Lippage has a few factors;

1- How flat are the tiles to themselves ? Lay one upside down on the other facing upwards. Try to give it a spin or to rock the upper tile. Look at the gap between the edges.

2- How flat is the substrate?

3- Troweling / setting skill level

4- Mising the thinset too loose will cause sinking tiles

5- Too little thinset will cause sinking problems

Motordoctor 03-09-2015 04:52 PM

2 Attachment(s)
Well, I got half the CBU down, used one bag so far. Have to say, that's hard work. Mixed it a little on the stiff side and that really gives your forearms a workout. I didn't know how fast the bucket would set up so I was going flat out for about 2 1/2 hours. Gave me a couple of nice trowel blisters, didn't have time to stop and put a piece of padding in there. Putting down the mortar didn't take long, it was putting all those screws in that burned up the time. The pot life was outstanding, I had to pick the wife up at work, then come back and the mix was still good so I put down one last sheet and used up all the mortar.
You tile guys are studs, that's all I can say. Probably give my back a day to rest and back at it again on Wednesday. Hopefully by the weekend I might actually put a tile down :clap1:

cx 03-09-2015 06:11 PM

That's why you'll find a lot of pros switching to roll-up sheet membranes for their tile underlayment, Dan.

Motordoctor 03-09-2015 06:31 PM

1 Attachment(s)
I can see why, it's one hell of a lot lighter than the CBU and no screws. I just couldn't bring myself to spend that much money. When somebody else is paying though, I can see it. Bottom line, on a job, time=money. I had a few tiles in the garage from the previous owner so I put them down on a piece of CBU. Now I'm not a tile virgin anymore, I set two tiles :dunce:

cx 03-09-2015 06:37 PM

Good time to pry them up and check your coverage, Dan. Very important step, 'specially when you're too new at the game to have developed your technique to get consistant coverage at the level required for the application.

Motordoctor 03-10-2015 06:39 AM

That's what I figured. How long should I let it dry? Although it's been about 15 hours now.

davem 03-10-2015 06:46 AM

The easiest time to check coverage is right after you set it. I'm sure you could still pop them off now and have a look though. :)

cx 03-10-2015 08:11 AM

Do it now, Dan.

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