Thinset coverage

[ranger481vs]

I started to lay 12 x 24 porcelain tile in a bathroom. I'm using a 1/2" square notch trowel with LFT thinset. After laying a few tiles, I pulled one up and I'm not sure my coverage is good enough, as I could still see a lot of trowel lines. See pic. Is that considered poor coverage? I also back butter each tile before setting.

I only lightly wiggled the tile and pressed it into the mortar fairly lightly too. Is this my problem? Could someone help explain how much wiggling and pressure I should apply to the tile?

[Kman]

Welcome to the forum, Matt.

I'm not sure that the amount of pressure you're using is the issue, but maybe the condition of the thinset mortar. It looks to be a little dry.

When it's mixed properly, thinset should be sticky enough that touching it would cause a bit of transfer to your finger. If that doesn't happen, it's too dry. Same thing with the tile, if it doesn't transfer to the tile, it's too dry.

That could be caused by mixing the thinset too dry, having it spread on the floor too long before covering it, or the substrate drawing moisture from the tile. Or any combination of those three.

Originally Posted by Matt

I also back butter each tile before setting.

Explain what you're doing there. Typically, if you've combed thinset on the floor, you would put a thin coat on the back of the tile with the flat side of your trowel immediately before setting it. Are you doing something different?

[rmckee84]

Always trowel parallel to the short side of the tile.
You'll need to put a decent amount of downward pressure, then slide the tile perpendicular to the notches you combed out in the thinset.

Your coverage looks pretty poor, 20% maybe. You're looking for a minimum of 80% in a dry area.

[ranger481vs]

Thanks for all the replies. This is helpful.
I realized the photo I posted is hard to see what's going on. I pulled these tiles up a few hours after setting them so the thinset was already pretty dry. In the pic, 1 tile was just pulled up and flipped upside down, so you can see the amount of coverage on the floor and what's on the back of the tile. The trowel lines are squished, but they have not blended together completely.

I think my main issue was not putting enough pressure on the tile.

As for back buttering, yes just skimming the tile with the flat side of the trowel. However, I would back butter, then trowel the floor, then put the tile down

[Kman]

What are you tiling over, Matt? Looks like wood of some sort right next to the tile, but obviously I can't see what was under the tile. The color of the picture makes it difficult to make out certain things.

[ranger481vs]

I'm tiling on cement board that was adhered with thin set and screws. I calculated the deflection rating before starting anything, so no concerns there.

P.S. The part in the pic that looks like wood, is a 12 x 24 tile.
So, in the pic this is the order of what you are seeing from top to bottom:
1. Wood grain tile right side up
2. Troweled thinset area after tile was removed (this is after 3 hr dry time)
3. Tile that I removed is flipped over.

[jadnashua]

You have 288sqin on that large tile. Say you weighed 288# and pressed straight down, that's only 1psi...you really need to push the tile back and forth to smush the thinset notches down and spread them evenly across the back of the tile. This is one reason why many Europeans tend to use a slant-notch tile...the slanted 'towers' of thinset fall over onto themselves after combing, and you have a flatter surface so it's easier to embed the tile with good coverage. IOW, probably nobody setting tile can get good results on that size tile just by pressing down...you MUST move it back and forth to spread that thinset evenly after using a traditional trowel. Just pressure can work with smaller tile, but pushing back and forth across the notches is still better and less work.

[ranger481vs]

Thanks. I think I should be OK going forward. When I set my first tile, I'll do a little practicing make sure I get the technique rights. So, I will pull up a Tile and check the coverage, and when it's good, then I'll send it again for good.

Great forum, And excellent help. I've been a lurker, and learn quite a bit by reading other posts. So, this site has been very helpful will beyond this particular thread that I started.

[tatumjonj]

I know it's been stated, but that thinset looks really dry. It either skinned over or you mixed it too stiff.

[ranger481vs]

Yes, as I noted, the thinset you are seeing in the pic has at least 3 hrs dry time already. It is not freshly set tile that I pulled up.

My thinset mixture is much creamier when I'm actually laying the tile, somewhere between mayonnaise and peanut butter consistency.