Tile over a concreat slab [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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07-04-2001, 05:52 PM

BTW....Nice web site. We just bought a house down in Friendswood. It is 32 years old and has a concreat slab. We need to put in about 1500 sq feet of tile.
My question(s) is this:

1. Do we need to lay anything on top of the slab before we lay the tile? Do you lay the tile with straight portland cement? It seems that would take a lot of problems out of leveling and cracks in the slab. Is that correct?

2. Do you think 16 or 18 inch tile looks good in large areas? Or should we stick with 12 inch tile?

3. How long do you think it would take a couple of newbies to lay 1500 sq feet of tile?

Thanks in advance for the help.

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07-04-2001, 06:49 PM
Well, I'm probably a poor substitute for the "master", but John's evidently out drinking a Lone Star and holding a sparkler so heres my 2-cents. 1500 sf of tile for some "newbies". You won't be "newbies" after this. How long will it take? I'll assume your not talking one big square room (if you are, call me, I'll take the job). With a multi-room, halls, closets, nooks, and crannies layout, you will be making a few cuts here and there. As a novice, if you can set 100 - 150 sf/day (in a mult-room layout with many cuts) you'll be making a very good showing.

Stay with the 12x12 tiles. The larger format tiles require special consideration in terms of coverage on the backs of the tile and leveling in relation to each other.

The setting material you want to use is comprehensively referred to as "thinset". It comes prepackaged in 50lb bags that you mix with water or a latex/acrylic liquid additive. For simplicity, get a "modified or multi-purpose" thinset which already has this ingredient in dry form in the bag, so all you add is water.

Slab preparation is difficult to recommend without seeing. Hairline cracks in a slab this old shouldn't pose much of a problem. (settling cracks, same level side-to-side) Custom manufactures a thinset called Flexbond that they say allows you to set tile over small cracks without these cracks transmitting through to the tile. Personally, I prefer to treat visible cracks of the nature describe with an isolation membrane of some type.

The more "specifics" you can provide, the better advice you can glean from this "international forum". Good Luck, and call back as the project progresses.

John Bridge
07-05-2001, 06:23 AM
Hi Pilot, Welcome aboard!

I was out drinking Miller's, not Lone Star. LD's over in the San Antonio/Canyon Lake area. I guess nobody's trucked any decent beer that far out in the boonies yet.

I'll concur on everything else, though. I've often said that bonding ceramic tiles directly to a concrete slab is not the best thing in the world someone can do. But in an existing house, it's usually the only feasible thing to do, so go for it.

There are crack isolation systems of all types that can be applied to the entire floor. For 1500 feet the cheapest would increase your material cost by about $1500. And none of these systems will prevent cracking if there is vertical movement down the road. I have yet to sell a complete system.

What we do instead is treat the cracks that look like they could develop into trouble spots, and then we go about out business assuming that nothing else will develop. If something does occur in the future, it can be dealt with then.

I would not talk you out of the larger tiles. They are certainly more work, and you have to be extra careful to get them supported properly, but it's really a design dicision. And guess what. We have a design board right here. So hop over there and Ask Marla and Susan their thoughts on the matter. They're sitting there awaiting your arrival.

And then tune back in here, because there are a few other folks who will also post their opinions. Between us, we are perfectly willing to shepherd you through the entire project.

(Friendswood is a bedroom community south of Houston, about halfway to Galveston.)

Rob Z
07-05-2001, 06:46 AM
Hello Project Pilot, John, and Latney

This is an easy moderator job today-I concur with John and Latney. 1500 sq. ft. would be a big job for my helper and me, so if you're new to tiling I'm sure it will take you quite a while. It is hard to make reccomendations about your slab with out seeing it. The larger the tile, the flatter the slab needs to be.

There are standards that attempt to quantify just how flat a floor should be. The TCA used to say a floor needed to be flat and level to within 1/8" in 10 feet. Now they have relaxed the standard to 1/4" in 10 feet. I don't think I have ever encountered a floor that was to that standard (except a floor that had been mudded).

Try to get some straight edges and check to see if there are any big crowns or low spots in the slab. Let us know what some of the worst offenders are, if any. For example, I just worked on a concrete floor that had a crown that dropped off 5/8" in two feet, and had other high spots that were easily measured.

Get back to us with some info like this, and we can make specific recommendations for you.


07-05-2001, 01:00 PM
Thanks for all the advice guys. I am sure we will have a lot more questions before we are done and we look forward to chatting as the project goes alone.

BTW...do you guys know of any good contractors in the Houston/Friendswood area? I need to remove a load-bearing wall before I start our tile job.

See ya

07-07-2001, 10:03 PM
For what it's worth I just finished setting 1500 sq ft of 18X18 tiles in a new home. This is a big project that took me the better part of 6 days to complete. Keep in mind this is only setting the tiles...Grouting remains.

I was the only one doing the job so a helper would definitely speed things up. The larger tiles will go faster than the 12"s.

My advice is use the larger tile ; I like the reduced number of grout lines. The trade off is the likelihood of more complex cuts around doorways and other obstructions.

If you decide to go with the larger tiles, make sure you have a wet saw that will handle your size tile.

From one rookie to another... best of luck


07-09-2001, 05:28 AM
Will your slab readily absorb moisture?

Put a few droplets on the slab and see if they will absorb in a few seconds.

If so you can use thinset. If not you may have to go an alternate route.

Let us know.