A John Bridge-Tile Your World Review

- John P. Bridge (October 2007)

Ditra-Set Mortar (courtesy Bostik.com)

Thin set mortar, made from portland cement, is the “glue” that holds the modern tile industry together. A product of the 1950s, thin set, then known officially as “dry set mortar,” ended the eons-long practice of bonding tile and stone to substrates with pure cement, a process which was time consuming and tedious. Henry M. Rothberg, founder of the Laticrete company, is credited with pioneering the switch from pure portland cement to thin set mortar. Nowadays, the old process is rarely used in developed countries. There are presently thin sets for everything, and some of them will stick to everything.

“Modified” thin sets contain latex or plastic polymers that give them more flexibility and glue-like qualities. There are thin sets that bond very well to glass, for example.

And then there are un-modified thin sets that are now called “dry set mortars.” There are various brands and grades of dry set. At the John Bridge Forums we urge people to use the best dry set they can obtain. Never buy the builders’ grade product, the price leader on the shelf. Go “top of the line” for only a few dollars more. Your project deserves it.

Several years ago Schluter Systems®, the maker of the Ditra and Kerdi tile setting membranes, announced that the company would no longer support the use of modified mortars in the bonding of tile and stone to its membrane products. Only un-modified dry set mortar could be used. The mortars used to bond the membranes to substrates would remain “appropriate to the substrate,” meaning that modified mortar would continue to be used in bonding Ditra to plywood, for example.

A wave of controversy and misunderstanding developed as a result of that announcement. Most tiles are made from porcelain today, and for years thin set manufacturers and the tile industry in general have insisted that porcelain tiles be bonded with modified mortars. And here is Schluter stating flatly that you should bond all tile and stone with dry set mortar when using Kerdi and Ditra. So who should you listen to, the person who makes thin set or the one who makes the membrane?

Since some modified mortars need air to dry, Schluter is concerned that trapped between two impervious surfaces, say Kerdi and porcelain tile, the mortar might never fully set. And since Schluter does in fact make its own products, the company certainly has the right to decide which adhesives can be used in their installation.

Quite a dilemma indeed. Wouldn’t it be great if Schluter were to come out with its own brand of dry-set mortar and guarantee it to work with Schluter products? Well, the next best thing has happened. Schluter Systems has licensed the Bostik company to use the Schluter name on a product specially developed for use with Ditra and Kerdi. The product is called Ditra-set, and it’s a humdinger.

I have used Ditra-set twice, both times when doing Kerdi showers. When the product was first developed in 2006, my friends at Schluter asked Bostik to send me a couple sacks to try out. I used the material on a Kerdi shower I had in progress, and while I was at it I bonded a couple scraps of porcelain tile together as a test.

Bonded Fragments

Fragments of large impervious porcelain tiles were bonded together at 3:00 in the afternoon. Arriving on the job the next morning I attempted to pry the pieces of tile apart with my margin trowel. It’s not unusual for thin set to remain somewhat pliable after only 16 hours, especially when it’s between two pieces of impervious tile (or between impervious tile and a waterproof membrane such as Kerdi). I had no luck with the margin trowel no matter how hard I pushed, so I got out my trusty masonry chisel.

Fragments Broken Apart

Tile fragments were broken apart with hammer and chisel. Dry set mortar isn’t supposed to stick to porcelain tile, is it? That’s what I’ve been told for years, even though years ago I spent a lot of time bonding porcelain tiles to concrete floors in bank buildings all over Texas, Arkansas, and Mississippi with dry set mortar.

I’m here to tell you porcelain tiles can indeed be bonded with dry set, especially with Ditra-set. You can see that when the pieces were separated a good amount of thin set remained on each piece — the bond broke somewhere in the middle of the material; it didn’t cleave off one piece or the other. That’s called good thin set transfer.

Ditra-Set/Kerdi Shower Test

18×18 porcelain were tiles used in the test. A year has gone by since that test. During that period the folks at Bostik have been busy getting Ditra-set into their distribution chain. Until recently I wasn’t able to buy it in Texas. That’s no longer the case. Interceramic, one of my major suppliers, is now handling Ditra-set. I’m working on another Kerdi shower, and I’ve done another test with a different porcelain tile.

Masonry Chisel Used In The First Test

That’s the same old masonry chisel used in the first test. I knew better than to bother with the margin trowel. The conditions of the first test apply to the second. I cemented the pieces together in the afternoon and chopped them apart the following morning. Same result as the first time. Plenty of mortar remaining on both pieces.

Mortar Remaining On Both Pieces

The result was really no surprise. Although more mortar pulled away from one piece than the other, an ample amount remained on both. Perhaps I burned the material into one scrap better than the other. It doesn’t matter, though. That is an excellent bond.

Ditra-Set/Kerdi Shower In Progress

The current shower in progress. Both the Kerdi membrane and the tiles are attached with Ditra-set.

Ditra-set is priced right. It costs about the same as the VersaBond® I use for a lot of applications. VersaBond, a lightly modified mortar, is made by Custom Building Products. Both products currently cost about $15. I don’t believe you can buy a decent thin set for much less than that. I recommend Ditra-set not only for Schluter products, but for any other application where dry set mortar is called for.

Would I use Ditra-set for everything? No, certainly not. There are other thin sets that do a better job in different applications. My friend Dave Gobis of the Ceramic Tile Education Foundation is fond of saying “one size doesn’t fit all.” Choose your products based on the conditions that apply. When it’s Schluter Ditra or Schluter Kerdi, make that product Ditra-set. I certainly intend to from here on out.

Ditra-Set Mortar (courtesy Bostik.com)

A Cautionary Note:

A Tile Product Review

- John P. Bridge (December 2007)

Custom Prism Grout

After a false start in 2005, Custom Building Products, of Seal Beach, California, has re-released Prism SureColor Grout.According to Custom:

“Prism offers consistent color with no shading regardless of tile type, temperature or humidity. And it will not effloresce. Prism’s dense joints provide more resistance to stains than standard cement grouts . . . .”

Prism grout is much lighter than standard sanded grout. What would normally be a 25-pound sack weighs only 17 pounds, however, Prism will provide the same coverage as the standard grout.

Several members of the John Bridge Ceramic Tile Forums were selected to field test the new grout. I’m fortunate to have been one of them.

I tested Prism “Haystack,” one of Custom’s most popular colors, on a Kerdi shower in a new home being built in the Texas Hill Country west of Houston. Weather conditions were mild, but humidity was a bit above the seasonal norm. The shower included walls, floor and ceiling — dense porcelain tile throughout.

I’m not a newcomer to Prism grout, having used the original Prism on a Houston patio in 2005. Although I thought highly of the product, others apparently had problems with it, and it was ultimately withdrawn from the market.

• The Process

The first thing you’ll notice about the new Prism grout (aside from its light weight) is its ease of mixing. Prism doesn’t clump up as does standard sanded grout. Put a little water in the bucket, dump in some grout and give it a stir with a margin trowel. Before you know it, you’ve got a smooth even paste. Let it slake 10 minutes and then re-stir.

Mixing Prism Grout

It’s easy to whip Prism to a uniform paste with only a margin trowel.

So mixing was the easy part, but now it was time to get the grout into the joints, and lucky me, I had a ceiling to break in on. Most of the first effort ended up on the floor. I soon found that Prism grout just plain doesn’t like to be squeezed into joints. And it’s not particularly fond of adhering to tile surfaces. As I attempted to push the grout in it seemed to pull right back out with the trailing edge of the grout float. At this point I was using a soft rubber float with a neoprene face. I had to constantly scrape grout from the side of the float, as that was the only place the grout actually wanted to stick.

In talking to some of the others who tested Prism, I found I was not alone. Everyone complained of the difficulty in getting the grout into the joints and keeping it there. Be prepared to spend about twice as much time as usual in filling and smoothing the joints.

Prism Grout On The Ceiling

It is, of course, easier to slap the grout on the wall and then push it up onto the ceiling. I finally resorted to grouting one joint at a time. After several joints I would try to get as much of the excess off as possible with the edge of the float.

I switched to a fairly hard epoxy float, and that seemed to help considerably. By grouting one joint at a time and then going back over it with the end of the float I was able to get most of the grout to hang in the joints. With a feeling that approached utter joy I finally finished the ceiling and upper walls and began washing.

You’ll be happy to know that Prism grout is not hard to wash. Wring your sponge tightly. Don’t slop any excess water onto the surface. I went over the surface once and got the bulk of the material off while making sure all the joints were full. At this point the grout in the joints was still a bit loose, even though the surface area was completely dry. I didn’t time it, but I think about 30 minutes elapsed between beginning to smear the grout and the start of the wash cycle. I would not want to let it go any longer than that.

When washing Prism, water seems to stay on the surface of the joints, and even after rinsing with the sponge tightly wrung I noticed small beads of water in many of the joints. I was sure this would cause discoloration, but there wasn’t much I could do except to let the grout dry. As I said earlier, it was a humid day, but humidity would not have caused the phenomenon in standard grout.

Water Bleeding Out Of The Joints

You can see water beading out of the joints. I attempted several times to sponge the joints, but nothing seemed to improve the condition.

After the grout had partially dried I was able to clean up the joints a bit with the sponge. I did the best I could and continued on to the lower walls and shower floor, which is tiled with 3-inch porcelain tiles.

The floor went much better, of course. Gravity is your friend here. I was able to get the joints looking good with comparatively little effort. The grout still pulled out of the joints, but the process was much smoother. You force the grout into the joints and then go back a time or two to try to get it smooth and even. Then move on. Don’t continue to toy with the grout. Let it set up, and then wash. Whereas getting the grout applied is a bit of a challenge, washing is a breeze. It’s not difficult to remove all the residue from the surface of the tiles.

Water On The Joint Surface

You can see water on the surface of the joints. I found no way to remove it completely. Leaving standard sanded grout like this would definitely result in a splotched grout job. Surprisingly, the grout job looked good when dried. And when Prism grout decides to dry it does so rather quickly. I did have to touch up a few joints on the walls, but the floor appeared to be perfect. All in all, I was not displeased with the result.

Wall Joints Are Almost Dry

Wall joints are almost dry. Throughout the drying process the grout shading was even.

Walls And Ceiling Looking Good

The walls and ceiling are looking good.

Floor Joints Look Perfect

The floor joints look perfect.

Wall And Floor Joints Drying Evenly

Both wall and floor joints were drying evenly, and at this point it was time to go home.

Returning the following morning I expected to find some discoloration, considering the amount of water that had lingered in the joints during the drying process. But to my surprise I couldn’t find even one discolored joint. The color was true, and there was no shading whatever. (At least one other tester reported that a couple of the lighter Prism colors were not true to the original Custom colors.)

Color Uniformity In The Floor

You can best see the color uniformity in the floor. I don’t think I’ve ever seen a better grout job.

• Conclusions

1. I think I might have had the grout mixed a little loose. I tried to keep it as stiff as possible, but I had such difficulty getting it to cling to the ceiling and walls that I loosened it up a bit. I still had a pasty consistency, but next time I’ll keep it a little stiffer.

2. There is no way to easily get the grout into the joints and get it smooth the first time over, but I think the result is worth the effort. Prism is good grout.

3. Next time I’ll try to wait for a day with less humidity. High humidity and the fact that it wasn’t warm enough to run the air conditioner worked against me. Had I run the air, I think the grout would have dried more readily. Also, my test shower was tiled over the Schluter Kerdi® membrane, which is impervious, so no moisture was absorbed by the substrate.The grout will work better over more porous backings, and Prism will certainly perform better in summer in every part of the country.

Finally, although Prism grout will tax your patience while installing it, washing is not difficult, and the end result is worth the effort. I truly have never seen a better looking grout job using portland cement grout. Using the product is a learning experience, and I think experience will speed the process. It is possible to abuse Prism grout and still come out with an outstanding looking job. I can’t say that about any other grout. Although my fellow product testers might not agree, I’ll use Prism grout whenever I can.

By the way, they sent me ten bags of Haystack. I used most of two. I don’t think the folks at Custom know I’m “retard.”