need advice on finishing my tile project

[rookietjx2]

I'm laying tile in my kitchen. 1/2 sub floor (don't ask because I have no idea why) with 3/4 OSB over the sub floor, and 1/4 inch hardibacker with thin set and screws. I noticed in one section that I've got a high spot about 1/8 to 1/4 inch high, about eight inches wide and six feet long. Belt sander?

[Houston Remodeler]

Sounds like a joist was crowned.

Shouldah handled this one before the plywood went down. No good way to fix it without cutting successively smaller rectangles into the layers to get down to the joist to plane the top of it. The purpose of cutting smaller rectangles is not to have the seams of the layers right above each other.

[rookietjx2]

The high spot is perpendicular to the joists, about eight inches wide, spanning five or six joists.

[Houston Remodeler]

Over a beam?

[rookietjx2]

Nope. On a hardibacker seam....

I think my daughter got a little too excited and ran the screws too deep which caused them to drill through the hardibacker instead of holding it down.

[Houston Remodeler]

That's an easy fix by;

Cutting out a rectangle of CBU, grinding down the thinset and re-setting the CBU.

[rookietjx2]

CBU = hardibacker?

[Houston Remodeler]

yes,

All Hardie backer is CBU, not all CBU is hardiebacker.

CBU = cementitious backer unit in tile parlance.

[rookietjx2]

Thank you.

[cx]

While we treat Hardibacker as a CBU in most applications, Joe, it's technically a fiber-cement board. In case someone should axe you, eh?

[rookietjx2]

So, why not use a belt sander? It would be faster, but what issues would I be potentially causing?

[Houston Remodeler]

The cbu would be nearly gone and that would be purpose defeating.

[cx]

You do what you want, Joe, but the Hardibacker is made in layers and it remains structurally sound when all the layers are intact. What you're proposing, if you can make it work, will remove half or all the layers in some places, leaving you with not much of a CBU installation at all, eh?

If you do try to sand off that much Hardibacker, I very strongly encourage you to wear serious breathing protection, keep your daughter, and everyone else, out of the area, and to shut down any HCAC system that might otherwise be running. The dust from that CBU is nasty.

But not to fear, you won't get much of it sanded off anyway.

Then you can cut out a section and re-do it.

My opinion; worth price charged.

[rookietjx2]

Lol, I love the response. "you can try it, then you can end up doing it the right way". I was curious why sanding would be a bad idea. I knew about the dust (in momma's kitchen) but I didn't think about it being layered. That's why I asked before I tried. Thanks again.

[rookietjx2]

I'm halfway through my kitchen tile project and I've run into an issue. My floor is nice and flat and level (2x12 joists, 16 on center, 14 foot span, 1 1/4 sub floor, 1/4 Hardi backer) until hit about seven feet to the opposite wall. Then it drops 5/8-3/4 inch, so I'm wondering what the best option is to level. I'm using 6x24 tile in a herringbone pattern, so I can't fudge where it drops.

I think I'm left with two options...

1. Remove decking, level with sister joists, replace decking.
2. SLC.

Option one is my worry since I screwed the crap out of the decking, and finding the screws under the Hardi backer and mortar will be a chore. My thinking is, pull the Hardi backer to where it drops (it's a straight line all the way across the kitchen) and pour SLC.

Yes? No? Better options?

Thanks in advance.