Ceramic Tile Advice Forums - John Bridge Ceramic Tile

Welcome to John Bridge / Tile Your World, the friendliest DIY Forum on the Internet


Advertiser Directory
JohnBridge.com Home
Buy John Bridge's Books

Go Back   Ceramic Tile Advice Forums - John Bridge Ceramic Tile > Tile & Stone Forums > Professionals' Hangout

Sponsors


Reply
 
Thread Tools Search this Thread
Old 03-01-2002, 09:59 PM   #1
John Bridge
Mudmeister
 
Join Date: Mar 2001
Location: Houston, Texas
Posts: 66,617
Send a message via AIM to John Bridge
Kicked out of the Advice forum by Rob Z.

Paul brought up something about mortar sticking to mortar, this as a result of something I said about scratch coats and re-coats.

Here's the deal, Paul. Cement forms a mechanical bond. It oozes into tiny pores and crevices and hardens. The little fingers/tentacles hook in and won't let go.

When you introduce additives into the mix, you do it for one of two reasons (or maybe both): You either want to improve the elasticity of the product, and hence improve its tensile strength; or you want to form a "chemical bond."

The chemical bond, of course, has nothing to do with the abilities of the cement to "cling."
John Bridge is online now   Reply With Quote
Sponsored Links
Old 03-02-2002, 08:36 AM   #2
chip
Travelin' Salesman
 
Join Date: May 2001
Posts: 1,088
Joe Tarver

The Top Man at the National Tile Contractors Association, says it best!!

Cement has absolutely no adhesive qualities, what so ever.

If It can't absorb into the substate and or the tile, it isn't going to stick.

In the days when "MUD BEDS" were the only way to set tile (now they are just "THE BEST WAY"),they used to soak the tile, and sprinkle cement on the still plastic mortar, and set the soaked tile on the cement and it would be absorbed into the tile and the mud bed and harden. This creates exactly what John is talking about.

Chip
__________________
Never did it, just know what I read or was told.
chip is offline   Reply With Quote
Old 03-02-2002, 09:34 AM   #3
Derek & Jacqui
Registered User
 
Join Date: Jun 2001
Location: Obion, TN
Posts: 635
Send a message via MSN to Derek & Jacqui
Chip
Not all tiles need to be soaked
__________________
DEREK & JACQUI

NULLI SECONDUS
IMPOSSIBLE DONE IMMEDIATELY, MIRACLES TAKE A LITTLE LONGER
Derek & Jacqui is offline   Reply With Quote
Old 03-02-2002, 12:59 PM   #4
Paul D.
Engineer/Grammarian - Austin
 
Join Date: Jan 2002
Location: Austin, Texas
Posts: 376
John and Chip

Ok, think I understand the description of how tiles were set years ago directly in a mortar bed without thinset adhesives.

I think I don't understand what a scratch coat is. Is it an initial layer that is roughed up in some what to give a surface to grab on to?

Is the only reason we are instructed to use a thinset layer when applying more mortar to a mortar surface that the base mortar is finished smooth?

__________________
Paul Despres, Austin
"Nothing to it, once you know how..."
Paul D. is offline   Reply With Quote
Old 03-02-2002, 02:32 PM   #5
John Bridge
Mudmeister
 
Join Date: Mar 2001
Location: Houston, Texas
Posts: 66,617
Send a message via AIM to John Bridge
Yes and yes. The scratch coat is "scratched" with a comb-like tool or a piece of metal lath to make the surface course. The next layer of mortar, the flush coat or "brown coat," hooks into the scratch. The scratch coat system is used when there is no backing behind the mortar. The lath is strung over a moisture barrier and attached directly to the studs. It is not uncommon to end up with an inch-and-a-half of mortar behind the tiles. Tearing a typical installation out takes some doing.

It is overkill in a residence to everyone except Dave G.

I use thinset to bond mud to mud when the existing mud is smooth. When building showers, for instance, I don't usually float the top of the curb until I've tiled its sides and leveled them. I can then use the tiled sides as screeds to float out the top. I smear a little thin set before adding the mud for the top if I have forgotten to scratch the first laid mortar (which happens quite often).
John Bridge is online now   Reply With Quote
Old 03-03-2002, 08:49 AM   #6
chip
Travelin' Salesman
 
Join Date: May 2001
Posts: 1,088
John,

Didn't they used to soak all the tiles?

So the "neat cement" (where did that term come from, and what does it mean?)would be drawn into the moist tile, and dilute, dry and harden?

Does anyone soak tiles anymore? For thin set?

Chippster
__________________
Never did it, just know what I read or was told.
chip is offline   Reply With Quote
Old 03-03-2002, 08:59 AM   #7
John Bridge
Mudmeister
 
Join Date: Mar 2001
Location: Houston, Texas
Posts: 66,617
Send a message via AIM to John Bridge
Hi Chippy,

The term "neat cement" originated in England and is used in Australia and New Zealand as well. In the States it's always been referred to as "pure cement" or just "pure."

Tiles were soaked back before my time (but not before Derek's time ). All wall tiles made from slip (4-1/4, etc.) and other soft clay tiles were soaked. Harder quarry tiles and porcelains (mosaics) were not. If you soak hard tiles they form what we used to call a "water bond." When the water dries up, so does the bond. Likewise if the softer tiles were not allowed to stand after being soaked or sprinkled, you would get a water bond also.

The only tiles I soak when using thin set are Saltillo tiles and raw terracottas.

Old Dave Gobis, being older than dirt, can add something here also.
John Bridge is online now   Reply With Quote
Old 03-03-2002, 09:16 AM   #8
chip
Travelin' Salesman
 
Join Date: May 2001
Posts: 1,088
John,

If you didn't soak the harder tiles, how did the "pure cement" make the bond?

I've been told, that even marble was soaked.

Hey, curious minds do in fact want to know!!

Chip
__________________
Never did it, just know what I read or was told.
chip is offline   Reply With Quote
Old 03-03-2002, 09:21 AM   #9
Rob Z
Guest
 
Posts: n/a
Chip

I just looked up "neat" in the dictionary.

"...not diluted or mixed with other substances. Refers particularly to liqours."

I think I remember my grandfather refering to his martini as being "neat". Once I learned how little vermouth he had in his glass, I made the mistake one time of saying "Grandpa, that's not a martini, that's just a glass of gin". He got a bit upset when I mentioned this.



  Reply With Quote
Old 03-03-2002, 09:27 AM   #10
Rob Z
Guest
 
Posts: n/a
Chippy

The porcelains and the quarry tiles that I have demo'd from houses whose vintage preceeds the development of thinset....have almost no bond at all. The tiles were beat down into the mud and the cement and sand oozed up into the joints. The grout was pushed down into joints, and bonded to the sand/cement from below. Entire floors were held down from the grout alone. At the same time, they were totally supported by the mud below, because each tile was pressed into a cavity in the mud.

Almost 100 % coverage, almost 0% bond

  Reply With Quote
Old 03-03-2002, 10:48 AM   #11
John Bridge
Mudmeister
 
Join Date: Mar 2001
Location: Houston, Texas
Posts: 66,617
Send a message via AIM to John Bridge
The pure cement was mixed into a pure cement slurry.
John Bridge is online now   Reply With Quote
Old 03-03-2002, 10:59 AM   #12
John Bridge
Mudmeister
 
Join Date: Mar 2001
Location: Houston, Texas
Posts: 66,617
Send a message via AIM to John Bridge
Rob beat me to the draw by about a second, but anyway, he's right. There was something of a bond, but not much. The success of the method depended on the mud bed, which acted not only as a firm support but as an uncoupler as well. The mud and grout combo locked the tiles in, as Rob has stated. It would not have been practicle to set tile directly to a concrete or wood substrate. Everything had to be floated. Everything.

As an aside, the success (superiority) of modern mud jobs still rests on the fact that the mortar uncouples the tile field from what's under the mortar. Most of us have run into bonded mortar beds over concrete slabs that have become mostly hollow. The mud has broken its original bond with the concrete, but the tiled field remains unbroken.

This is one reason why Ditra is superior to some of the other membranes. It uncouples to a greater degree because of its higher profile and unique design.

(Hey Schluter, When do I get my first check?)
John Bridge is online now   Reply With Quote
Old 03-03-2002, 10:12 PM   #13
Paul D.
Engineer/Grammarian - Austin
 
Join Date: Jan 2002
Location: Austin, Texas
Posts: 376
Wow. Excellent stuff. Good coverage on "neat," Rob. As I see from my new spiffy handle , it would likely have been my place to fill in the definition, had I not been out taking in all the sunshine and cool weather .

So John, a modern mud job properly done will resist cracks to a high degree? Just like one big monolithic chunk of concrete apart from the framing? It seems marginal then to use CBU, unless you can be responsible for the framing as well. Do you caulk all your joints at the change of plane, or do you find you can get away with grouting the corners?
__________________
Paul Despres, Austin
"Nothing to it, once you know how..."
Paul D. is offline   Reply With Quote
Reply

Stonetooling.com   Tile-Assn.com   National Gypsum Permabase


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 10:58 AM.


Sponsors

Powered by vBulletin® Version 3.7.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Copyright 2014 John Bridge & Associates, LLC