Slab prep and questions [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


View Full Version : Slab prep and questions

07-13-2001, 05:38 PM
Hi guys,

I have a couple of questions if you have time. The project is setting 1500 sq. feet of 18-inch tile on a 30-year-old slab.

The slab has several high spots. Some places are to 3/8 inch high. A friend told me that it was possible to sand down the high spots. Can you do that? Or should we just float-in the low spots? What is the best stuff to use if I need to float the high spots in? How level do I need to get the slab before I start laying tile?

What is the difference between thin-set and multi-flex? What do they cost per square feet? How thick should the thin-set or multi-flex be?

What is the difference between grout and portland cement?

Does anyone know the best place in south Houston to buy multi-flex and grout? Or for that case, who has the best prices on ceramic tile in south Houston?

Thanks in advance for the help.

Sponsored Links

John Bridge
07-13-2001, 06:00 PM
Hi Pilot,

You've asked some pretty basic questions.

Portland cement is simply cement (construction cement). It's sold in 94 lb. bags and makes things like mortar, concrete, and it goes into thin set, too.

Multi-flex is someone's description of latex/polymer modified thin set -- good stuff.

If you can get a straight-edge about 8 ft. long or so and move it around your floor on edge, you'll soon see what needs to be done. It's much easier to fill in the low spots than it is to grind off the high spots.

You can use thin set or self-leveling mix. I would use thin set and mix it soupy -- rake it off with a straight-edge.

You can't get an existing floor completely flat. You can make the best of an imperfect situation.

[Edited by John Bridge on 07-13-2001 at 08:24 PM]

07-13-2001, 08:25 PM
Multi-Flex is a latex modified thinset made by C-Cure.Derek&Jaqui can tell you about Multi-Flex Strata.They use it quite alot.It is an extremely strong thinset.

Bud Cline
07-13-2001, 10:05 PM

When you use thinset to level with the soupier you make it the easier it is to work with, unfortunately the soupier it is installed the more it will shrink. More than one application may be necessary to achieve the desired results.

07-14-2001, 05:58 AM
Boy I'm sure glad they didn't make the mix of concrete for the bridges I drove over in the Florida keys yesterday, soupy.

Water, too much or too little is the biggest enemy to cement. If you are going to over water thin set it will never have the strength it was desingned to have.

Then you put the same thin set, properly mixed on top of it and expect the soupy substrate to be as strong? It ain't going to happen fella's.

You have just become your own worst enemy.


Your on.

What happens when you over water your products? Does it effect their strength?


John Bridge
07-14-2001, 07:42 AM
Of course, you're right again, Art, but we're talking about a material that is stronger than the concrete it's going to be applied to to begin with. A little extra water won't affect the final outcome.

07-14-2001, 08:03 AM
You know me devil's advocate and all.

What is soupy to projectpilot and what is soupy to you is no doubt different as what is soupy to me.

So in a general forum, to recomend a generic term such as that could spell disaster.

I've got to get your book, is there a recipe for this soup in it?

Personally I like lots of crackers in mine.


Rob Z
07-14-2001, 10:38 AM
Hi Pilot

One thing that you can do is use a feather edge compound like Ardex (there are others, that's just the one I use) to fill in low spots.

Yes, it's more expensive than using thinset as filler material, and it won't rely on your ability to interpret what John means by "soupy". If you have done any drywall finishing, the troweling techniques are similar.

Art's company (Bonsal) make feather edge compounds, but since they don't have them at my supplier I can't try them and tell you how they work.

Art, how about a complimentary bag, eh buddy?


John Bridge
07-14-2001, 12:57 PM
Art, if you send Rob a freebie, you have to send us all a freebie. You know how that works.


Jim Buckley (Flatfloor) manufactures a self-leveling cement. You probably can't get it, but you can look at the web site.

You can't get any of Art's products either. Bonsal hasn't seen fit to market in Texas.

But you can go down to Home Depot and get Custom self-leveling cement. None of it is cheap.

I don't know anybody around here who sells Ardex.

Everybody but Art knows that "soupy" means runny. :-)

Bud Cline
07-14-2001, 01:25 PM

Your soup whether it is "onion (French) soup" or "split pea" ("ich") won't matter in your case unless you are driving your forklift into the shower with you.

Art worries too much. Art, go sit with Daisey for a fifteen minute "time out".

07-14-2001, 03:39 PM
Hi Pilot
One thing that you should try, to install 18" tile,is while you are setting skim the back of the tiles with flat trowel, then install them in your combed bed.This method ensures good adhesion on both the tile and the substrate.

07-14-2001, 04:26 PM
Thanks John, really why fool around with what defines soupy , when with an slc you add an exact amount of water and get the proper consistency and you can take your forklift into the shower. (seems kinky tho)

07-14-2001, 04:50 PM
I don't want to be a party pooper here..but it seems to me that mr pilot is going to try install 1500 ft of 18x18 tile as a beginer....sorry...but do you have any experience setting tile at all? 18x18's are tough when you're a pro..just curious.


07-14-2001, 05:00 PM
A 1500 s/f shower with 18 x 18 tiles should be done right and not randomly with any thing from chicken broth to cream of mushroom to a good thick Clam chowder.

Now get off that damn fork lift and wash behind your ears, or none of Sonnie's pop corn for you tonight.

Remember Soupy Sales? Now if you had said the consistancy of a custard pie, you would have gotten no complaints from me.


07-14-2001, 05:19 PM
Well we just went to HD. They have this stuff called "Versabond". I am assuming this is some kind of thin-set? Should we use regular thin-set or versabond? The slab is 30 years old and has a lot of hair line cracks and has had a lot of other flooring on top of it over the years.

One other question: Can we install the tile over Linoleum?

John Bridge
07-14-2001, 05:38 PM
First things first. Custard ain't "soupy."


Versa Bond is one of the thin sets I use all the time. It is a modified thin set (meaning it contains latex or plastic polymers), and a modified is what you should use on your slab.

No, do not install tile over linoleum.

The cracks are going to be a judgement call on your part, since none of us can see them. If you think they've been there forever and are not going to move in the future, go over them with the Versa Bond and forget them. If the edges are flaked off, or if one side of the crack is higher than the other, treat them with an anti-fracture membrane (See Frank Mazzola's post).

1500 feet is a very large job, even for us. You will have to factor in some movement joints.

07-14-2001, 05:57 PM
Bri, if you were asking moi if I had any experience laying tile, answer is no. Do I have any experience leveling floors? yes:)

Art, sorry, didn't mean to ignore an excellent rhetorical question the obvious answer ; absolutely it weakens the strength of the mix and will affect bonding.

[Edited by flatfloor on 07-14-2001 at 08:10 PM]

07-14-2001, 06:09 PM
Gosh no Jim...I was asking Mr John already stated..1500 ft is a lot..even with experience. Sorry for the confusion..( it was the beer)


07-14-2001, 06:13 PM
I don't have any beer and I'm still confused. But it's a cool idea see ya!