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

Kman 02-19-2015 06:04 PM

Quote:

Originally Posted by Dan
I'm planning on using Loctite PL Premium construction adhesive under the plywood. Only thing HD had in the large tube size. That OK?

I'd recommend you not use any adhesive in your application. Lines of adhesive can create tiny voids which will allow for vertical movement. You don't want that.

Motordoctor 02-19-2015 07:00 PM

Quote:

Home Depot sells CustomBlend thinset mortar, the lowest rung on their product ladder, and bedding CBU in floor installations is one of the few applications for which most of us would ever recommend it.
WOW, that stuff is cheap, only $7/bag.

Do you think I need to fill in the low spots with some patching compound or is that just wasting time? I was looking at this stuff but I don't know if it will take having screws run through it. HENRY® 547 UniPro Universal Patch & Skimcoat.

cx 02-19-2015 08:35 PM

Dan, if you'll visit our FAQ you'll find a brief tutorial showing how to properly attribute quotes you post here on the forums. Very simple once you see it. :)
Quote:

Originally Posted by Dan
WOW, that stuff is cheap, only $7/bag.

And worth ever dime.

When using CBU as your tiling substrate you fasten it to whatever subfloor you have. If your floor is not sufficiently flat after the CBU is installed, you fix it at that level. You can't do any flattening or leveling between the Subfloor and the CBU.

My opinion; worth price charged.

Motordoctor 02-19-2015 08:53 PM

Quote:

Originally Posted by CX
When using CBU as your tiling substrate you fasten it to whatever subfloor you have. If your floor is not sufficiently flat after the CBU is installed, you fix it at that level. You can't do any flattening or leveling between the Subfloor and the CBU.

Excellent. Thanks as always for your help. I got some heavy duty commercial floor jacks to crank the floor up but they are not needed. Just have to put some reinforcement at the midpoint on the joists and I think I'm in business.

Motordoctor 02-20-2015 07:19 PM

Well, I got my answer to the question "does the subfloor lack of flatness transfer to the plywood underlayment." That answer is Yes it does. Put down one sheet and checked it. Not so good. Like a teeter totter that floor. So I either have to grind down the high spots or shim up the low spots.

Have a theory about how to fix it, thought I would put it out there. How about leaving the subfloor/plywood as is, and float the CBU on top of about 1/2" of medium bed thinset. The CBU would rest on the top of the high spots and the thinset would take up the low areas. The only fly in the ointment that I can see is putting screws though hard thinset, since you can't screw it down until it is set up.

The other two options are rent a drum sander from HD and take about 1/4 off the floor or rip all the subfloor up and just put down 3/4 Sturd-I-Floor plywood. It would take about $200 worth of plywood to do it plus ripping all the old stuff off. Probably why I was considering sanding it.

Thanks again for all your help here.

cx 02-20-2015 07:27 PM

See post #33, Dan. Don't think I can make it any more clear.

Up to you what you wanna do, of course.

cpad007 02-20-2015 07:38 PM

I say remove the solid wood planks, fix the joists, and lay down 3/4"...all nice 'n flat and likely level.

Now you have a good foundation to do whatever you want on. :)

Kman 02-20-2015 09:23 PM

Dan, it's important that you find out exactly what is causing the floor to be out of plane. Is it a joist that's high or low, or is the subfloor sagging between the joists? If the plumbing is not in the way, you may be able to check the joists from below with a straight edge or a string. If there's just one or two low joists, you might be able to push them up from below. If the subfloor is sagging in between joists, you could remove a section and replace it.

Motordoctor 02-20-2015 11:14 PM

Quote:

Originally Posted by KMAN
it's important that you find out exactly what is causing the floor to be out of plane. Is it a joist that's high or low, or is the subfloor sagging between the joists?

Looks like I have one joist that's higher than the rest. Of course it would be the joist that I can't get to from the bottom easily (furnace is in the way). So replacing the subfloor probably wouldn't change anything. OY what a pain :wtf:

cpad007 02-22-2015 12:52 PM

If by "replacing the subfloor" you mean removing your solid wood planks, I would think you'd have all the access you need.

Short of shaving down the high joist (not recommended unless you can possibly sister up something next to it for most of its length), you can add to the rest of the joists to bring things to flat and/or level.

Kman 02-22-2015 03:19 PM

Unless it's pushed up very high, there's no reason you can't shave off a little to get it in line with the others. Of course, that will require removal of a good part of the subfloor to get it to it.

Motordoctor 02-24-2015 07:48 PM

The never ending kitchen floor saga.
 
I thought I would try getting the subfloor a little closer to being flat so it didn't "telegraph" through the plywood. Dug out the belt sander and had at the high area on the one joist. After 4 hours and 4 belts I got about halfway in a 2ftx4ft area. That's going to be way too slow.

Decided I need more power, at that rate it would take a month of sanding to get the job done. So drove to Home Depot and rented the big bad drum sander. Truthfully I was underwhelmed by the stock removal rate of it even with 24 grit sanding belts. Sanded the entire floor but it's still not as flat as I would have liked. Spent about 5 hours on it, probably took about 1/4" off the high area around the one joist. I guess it's as good as it's going to get, can't make love to it forever. There are low areas, little more than 1/8" in a lot of spots but I've wasted entirely too much time on this now. At least the plywood won't have a big hump in it right over the joist anymore :)

Weird place to be high, it's on the third joist over from the door about 3/4 span near the resting point for the joists. So it's not like I could jack the other low ones up since I would think that spot would be in the middle and not near one of the ends. It is what it is. Can't rebuild the whole house just so I can put in $130 worth of tile.

I hope setting the tile goes easier than this ;)

cpad007 02-25-2015 11:59 AM

Wood moves. When that joist started drying out, it released some tension and caused a hump. I betcha there's a decent knot in the area where you found this hump...or there may be nothing visual at all. Gotta love wood!! :D

Motordoctor 02-27-2015 11:00 PM

Quote:

Originally Posted by HardiBacker Installation guide
• Install smooth side up.

Install HardieBacker boards perpendicular to subfloor panels.

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

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

•Lightly butt the board joints. Do not leave a gap or force edges together.

•Join factory-cut edges together in the body of the floor.

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

Dumb question here, does this mean I should put down the CBU parallel to the floor joists? Since the plywood underlayment is perpendicular to them.

cx 02-27-2015 11:39 PM

Dan, structurally it matters not a whit which direction any of the CBU panels fall with reference to the joists. I noticed that part in the Hardibacker installation instructions about orienting the panels opposite the plywood panels very recently and don't recall ever having seen it before. But if that's the way James Hardie wants you should install them, then that's the way we'll recommend you install them.

I think the part about not gapping the panels is relatively new as well. Seems to me they usta call for a 1/8th" gap. But, again, if that's now the way they want'em installed, I recommend you install'em that way.

My opinion; worth price charged.


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