This cement won't stick to anything!!!

[chip]

In the post entitled Ditra, Bri made a statement that cement doesn't stick to cement very well.

Joe Tarver, Executive director of the National Tile Contractors Association. ( with a title like that, you know this guy has 20/20 vision if not better!) John, you really opened a can of worms.

Back to Joe Tarver, at Sikes tile in West Palm Beach,Fl. in December of last year, he made a statement and I quote
"Cement has absolutely no adhesive qualities what so ever"

Now all of you have seen, heard, believe, know and can show all of us examples of cement sticking to cement. I mean there are jobs that have lasted the ages.

How can a man with such vision ( 20/20) make such a statement.

I do understand, do you?

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[Bri]

Hi
Well, as I stated in the Ditra post...if you don't rough up cement and use a slurry to bond the two together, then there's a pretty good chance the the two layers of cement will separate(which I guess the Schluter guy was saying about a cold joint). Even when doing a mud job, the first scratch coat has to be left as rough as possible to get a good bond(and so it doesn't fall down). Try it..make a handfull of cement and throw it on a concrete floor...after it drys you kick it a few times and it comes off clean as a whistle.

[John Bridge]

Then why can't I get those splatters off my street that the redi-mix truck dribbled 17 years ago?

[Rob Z]

Flattile

I need some clarification. Are you refering to portland cement itself, or cement containing products?

Thanks for the emails. I will check out the Bonsal products we discussed at Conestoga Tile soon.

I sent an enmail to the Bonsal folks asking for Propan Propaganda , I mean literature. All they sent me was the Proform pamphlet that I already have (curbs, slope, niches, etc). I'd like to use my inside connection (you) to get the right stuff. Can you help?

Rob

[chip]

I will leave a voice mail as soon as I pull up your profile.

Thanks for your patience and understanding.

I'll also contact david roever again.

Now about cement not sticking,I'm talking about pure cement.

Does anyone out there realize how it sticks(bonds)?



Art

[Edited by flatile on 06-03-2001 at 03:12 PM]

[Rob Z]

Art

My wife's uncle is a chemist, and served for some time as advisor to the Portland Cement Association. He has taught me quite a bit about the chemistry of grouts, concrete, mortars, latex additives, etc.

From my very basic understanding of what he has discussed with me, I'll venture this guess as an answer to your question.

Portland cement is a complex mix of compounds that react chemically when hydrated with a liquid. The liquid doesn't have to be water. Part of the chemical reactions include compounds that form and "lock" together in bigger and more complex molecules as the reaction progresses.

The strength in concrete, mortar, grout, thinset, and so forth comes from the inert aggregate that is encapsulated by the matrix of chemically bonding molecules. Uncle Art can, of course, rattle off the names of these compounds like he's reciting his address; I can't remember the names of this stuff for two minutes.

And the longer the portland cement compound stays under optimum curing conditions, the stronger it gets due to those little molecules moving around and bonding.

One advantage the use of latex additives provides is the retention of moisture that enables the chemical reactions to keep on keepin' on.

You may have seen a fresh bed of mud (mixed with water only) that has been covered with plastic and left for several days-water is condensed on the underside of the plastic, the bed of mud is still "damp" looking, and it will be a much harder bed, sturdier substrate. This is due to the retetention of water in the reacting mortar.

So my guess is that Portland cement won't stick to portland cement because there is no aggregate involved. Portland cement by itself it weak, but mixed with something to form a chemical matrix around?-- Very strong.

Think of the cement slurry that John describes in his book to bond a mud bed over concrete. The nooks and crannies on the microscale offer the cement something to bond into, and the aggregate in the mortar a fraction of a inch above offer bondable surface, as well.

Try bonding a tile to concrete with a slurry of Portland. It probably won't stick very well at all.

Well, let's see what the others have to say.

Rob Z





[Edited by Rob Zschoche on 06-03-2001 at 09:40 PM]

[John Bridge]

Very good, Rob. Only one comment.

Before thin set, all tile was bonded with portland cement. The tiles were soaked and drained beforehand. It wasn't a perfect system, just the only system they had.

Gotta get to the job.

[chip]

You get an A+ and now I can see why John has moved you to the head of the class and the head of this forum.

Ole' Uncle Art, could never had answered that so eloquently.

For cement to "stick" to anything it must 1st be able to absorb into it and or wrap around it and hydrate until hard.

It is in a sense surounding the particles within the item that it is adhereing to.

As John mentioned the old way was to soak the tiles and while the mud bed was still plastic (wet), neat portland cement was sprinkled on to it and the tiles were placed and beat in to the bed.

So you had the plastic bed and the soaked tiles absorbing this neat cement into them and the cement when cured had in fact wrapped around the particles of sand cementing it in place.

In the area that I am currently employed, South Florida, the vast majority of tile being set is done with basic floor thin set. Sand and cement.

Slab on grade, clay body tiles, cement absorbing into each.

My god you say, how can they do that and get away with it. I would never do that you say, they must be nuts.

It's been done this way, not thin set, but cement absorbing into materials and mechanically bonding for centuries.

[Rob Z]

The old wet setting method was hit or miss. I have demo'd hundreds of installations, and see all the time where tiles were held in by nothing more than the grout. The indentations on the back of the tiles are right there in the mud, but no adhesion at all.

Of course, when it worked, it worked great. Two solid inches of wall tile, levelling coat and scratch coat, stuck to the lath. Comes out in sections that takes the two of us to carry. Not big, just very heavy!

Rob