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Grind-in-place Installation of Marble, Granite, and Other Stones Floors
Many readers may not have heard of the grind-in-place technique of marble, granite, or other stone installation because they are starting their career as stone restoration professionals. But the main reason is that people of this country install stone floors in an unorthodox fashion. It is the most ancient and famous technique of installing marble floors in most parts of the world. Secondly, such stone floors have superior quality to other stone floors installed with pre-finished marble, granite, or other stone tiles. Let us learn more about the grind-in-place technique and why it is better than factory-finished installation.
What Is A Grind-In-Place Installation Technique?
The term is self-explanatory. But it is an unusual method in this region and calls for a little explanation. We first need to understand how the finished product will perform and how to prevent potential problems.
The Best Formula for A Grind-In-Place Installation
The installer lays down a 0.75-1.50-inch layer of mud over the sub-floor, ensuring that it levels the entire surface. The mud formula varies widely as per the installer's personal preferences. It ultimately refers to the proportion of sand and PLC (Portland cement), ranging from 9:1 to 6:4, but my favorite is 4:1 as I have already installed more than 400 floors, mostly marble.
Mud Bed Preparation
The installer thoroughly mixes both cement and sand and then slightly dampens it with water. You got to ensure that mud is loose and fluffy. The "mud" is also popularly referred to as "dry-pack." Installers mostly use the edge of some wooden boards for leveling. Sometimes, they also use a comb to improve the fluffiness before leveling. The comb is typically a wooden stick with several teeth. The installer lays the mud in sections for comfortable working and avoiding that nobody steps on it.
Then he lays stone components on this freshly laid mud. He butters the first component with about one-eighth-inch cement on its underside, which comes into contact with the "mud bed." Then he pounds that component into the mud by using a flat, heavy rubber mallet. After buttering the next piece with cement, he also wipes its edges with the same PLC cement and butt-joins with the previous component. He then pounds it and continues with the process. After he completes one section, he lays down another area and repeats the same process.
The Mud Serves Two Purposes
- It levels the floor
- It prevents floor cracking due to any movement of the sub-floor. The mud bed absorbs any potential cracking in the sub-floor and does not transmit it to the stone floor
The modern method of doing it is slightly different. Here, the installer lays down mud on the entire-sub floor and leaves it for curing. The installer then installs the components using a thin-set and wipes the edges with a sandless grout with a matching color. The installer accordingly adjusts the sand and cement proportions. The standard curing time for the mud bed is a minimum of two days. The floor installation begins after the curing completes.
The Stone Pieces
The stone pieces consist of 2cm or about 0.75 inches, and they may have several different shapes. Moreover, there is no finishing on the faces or edges, unlike pre-finished marble tiles. The faces are rough due to the usage of a modular saw or gang saw.
The Standard Italian Installation
The standard Italian installation requires 50x25cm or about 20x10 inch tiles. The installer installs them in a brick-layer pattern. The installer may also create many other designs like a medallion or some intricate pattern as per the designer's imagination.
Role of Grout
Although the installer butt-joints the floor components, grout is still an essential part of the installation. The installer applies grout on the tile edges before joining with other pieces because the butt-joint method does not leave any gaps for grouting later on. It seals the floor completely. Remember that here we are not talking about the impregnating sealer. The installer packs the floor with grout to ensure that water does not go under the components like tiles or stones because the grinding and honing phase involves a large amount of water.
Moreover, grout also prevents chipping of floor components, especially in the case of limestone or marble.
Grinding and Honing
After the stone or tile components settle on the entire floor, the whole project requires a curing period of a couple of days. After that, the team grinds on the whole floor, making it look like a seamless, monolithic, and super-flat floor without any lips or grout groves. The honing follows after the grinding cuts. It removes persistent scratch patterns left by coarse grinding elements. At this point, the floor is generally complete. You may go for a low-hone finish for commercial heavy-traffic use and may prefer a medium-hone finish (aka satin finish) for residential installations.
Suitable for Commercial Spaces Only
The said grind-in-place installation is a traditional formula. People use it in countries typically where they build houses with bricks and concrete, unlike wood-frame dwellings. Hence, you can use the original recipe in this country in commercial spaces only.
Human Resource Issues
The human resource availability and their training is another issue for stone setting. Many setters know how to lay mud beds but are not familiar with the complete grind-in-pace installation process. Typically, they complete the mud job followed by pre-finished tiles because that is the only material available. If you talk about customized stone pieces in 2cm (about 0.75 inches) slabs, they come pre-finished on their faces. Hence, they are unaware of the subsequent process of grinding and honing. In this country, the setter installs the floor components as the final phase of the project. They usually set the pieces using thin-set material followed by grout filling (hopefully) and cleaning. That is the end of the job to them.
Not Suitable for Residential Spaces
Although it is possible to use the traditional grind-in-place technique in commercial buildings, you should not use it for residential places. In this country, most house structures use wood frames that are usually unstable compared to brick and concrete buildings and prone to large settlement movements. That is why I will not suggest using the traditional grind-in-place installation technique.
The Way Out: Process Modification
It does not imply that you should forget about the possibility of using the grind-in-place installation technique. You may modify the traditional formula a little to ensure that you get the same result while withstanding potential settlements. You can also use the existing human resources without the need for any specialized training.
In this country, two different contractors usually complete such a project. The first type does the job of laying the mud bed and setting floor components. The second type refers to stone restoration professionals who grind, hone, and optionally polish the entire floor.
Recommended Modifications to The Traditional Method
Use of Joists for A Rigid Structure
The beginners should consider the heavy and rigid nature of the stone floor. They have to use oversized joists and keep them close enough to get a flex rate of a minimum of L720. Using steel joists will be a much better idea. Please ensure to use plywood sheets of a minimum of 0.75 inches. I recommend using two layers of plywood which you may glue and screw to one another. It leads to a rigid structure which is the prerequisite for a stone floor.
Mud Bed Vs. Cement Boards
The next step is to lay a mud bed. Some contractors prefer using 0.25- to 0.75-inch-thick cement boards by gluing and screwing to the plywood as an alternative to the mud bed. Although it is acceptable, in my opinion, you should prefer a mud bed. In some cases, the cement board seams become quite troublesome, especially on large floors.
Hence, we assume that you will lay the mud bed. You may set the stone tiles or stone pieces with a white thin set after curing of mud bed. Please ensure to keep a 1/16" gap between all floor components to allow enough grouting. After the floor setting, you have to use sandless grout and ensure that you push it deep in between the floor components that you initially left all over the floor. Fill the grout in such a way that it slightly mounds at the grout lines.
Grinding, Honing, And Polishing
After a couple of days, the stone restoration contractor will begin his grinding work, followed by honing and optional polishing.
Why 1/16" Grout Gap
Why did we leave a 1/16" grout gap instead of wiping the edges and then butt-joining of traditional method?
The reasoning is simple. Irrespective of the mud bed thickness and sub-floor structure's strength, there is a possibility of large settlement movement transmitting to the floor surface, especially in large floors or in earthquake-prone zones. If the floor cracks due to such settlement movements, it will be challenging to replace the cracked pieces without damaging the adjacent ones. Moreover, it will be technically impossible to reinstall by butt-jointing. The new component will also need some space for installation. Even if you fill the gaps with grout, it will stand out over the rest of the floor, which is butt-jointed and may look awkward.
The 1/16" grout gap in the design phase can resolve this issue. You can quickly remove the damaged pieces without damaging any of the adjacent components. Moreover, you can reinstall the new parts by keeping a 1/16" uniform gap across the floor.