Ask Me Help Desk - Marble flooring

We are building a new house and we are using 18 inch carerra marble tiles in the foyer and living room. What is the best way to lay the tiles down in order to create a seemless groutless appearance with little to no visible lines? Should we use beveled versus flat versus microbeveled tiles? What is the best type of grout to use? THanks so much in advance.

I hope you won't have a lot of traffic on this floor.. hopefully no kids.. marble is nice but not a great choice when it comes to traffic=(
microbevel is my preference but it is your choice

Micro bevel will provide just enough edge protection. You will want a grout joint, 1/32 to 1/16".

Your question...

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What is the best way to lay the tiles down in order to create a seemless groutless appearance with little to no visible lines?

Stone this size will need to be mud set. It's the only way to really ensure the flatness you need. You could go with cement board then a pour over top of self leveling cement but nothing will exceed a mud set installation.

If this is a slab, you will want an unbonded mud bed to protect the installation from any formed shrinkage cracks as well as to enable the installation of the stone prior to the 28 day minimu cure time for direct bond to the slab.

If it is going on a slab, you could also pour self leveling cement on the slab after the 28 day cure time, then use an antifracture membrane, then set the stone on that.

Normal standards allow for a variance in the plane of the floor to be out of plane, 1/4" in 10' of floor span. You will never set stone so close and so flat without the floor being dead flat to start.

An unbonded mud bed or self leveling cement with an antifracture membrane will give you the flatness you need and protect the stone from any shrinkage cracking as the slab cures and ages.

A wood framed structure changes things significantly.

If this is over a basement or crawl space, if it was not specifically designed for a stone installation, it would not have been designed for the required strength. Due to the fault lines in stone, the structure needs twice the rigidity as what is required for ceramic which is also double the required rigidity for code compliance. Code requires that the floor structure meets a deflection of L/360, meaning that the floor cannot deflect under load, more than 1/360th of an inch for ever inch of unsupported span, using 40/10 live and dead load ratings. For stone, you need a rating of L/720.

The requirement of a double layer of plywood, doubled up joists, reduced joist span by additional post and beam support, etc, all is easy to figure during the design phase but more difficult once work has begun.

Once again, the tolerance for the floors construction (1/4" in 10') will not be acceptable for the stone either and to bring it up to acceptablility, you could install cement board over your double layer plywood floor and then pour self leveling cement over the area or an mud job over felt and lath will make for a dead flat floor. The weight consideration placed upon the wood structure is quite significant. a 1" thick mud bed, without considering the weight of the stone, can be up to 12 lbs/sf. A layer of 1/4" cement board with 1/4" of self leveling cement at the deepest part will weigh up to 9 lbs/sf before any stone goes on it. Without this weight added into the design phase when calculating the dead and live load requirements, your flooring structure can fatigue under the weight, even though it calculated at L/720 using 40/10, you have already added over 10 lbs of dead weight per sf with the stone prior to adding any shared loading of the weight of the home.

The next consideration is movement joints. These are required every 20-24 feet interior or every 8-12 feet when exposed to significant periods of direct sunlight. These should be spelled out by the architect. If this is a slab, they should also be taken into consideration when placing any saw cut control joints into the slab so that the movement joint will fall over a saw cut joint.

Post again with any other questions. ;)

Wow! Thanks for the great information... I really appreciate it.

Unless you are experienced in flooring installations, do not attempt to install your marble flooring yourself to save on the cost. You could end up with a number of broken tiles and an uneven floor surface. Also, your marble floor can get cracked at a later time.

It must also be noted that the tiles are not factory manufactured, and therefore each tile naturally looks different. An experienced installer knows how to make the required markings and lay tile after tile patiently to form a uniform pattern across the floor.

Here is a link that might be useful:
<a href="http://www.helpful-kitchen-tips.com/kitchen-blog/2010/01/11/marble-flooring-review-marble-tile-floor-ideas/">Marble Flooring | Cost | Buying Tips | Installation | Maintenance</a>

Unless you are experienced in flooring installations, do not attempt to install your marble flooring yourself to save on the cost. You could end up with a number of broken tiles and an uneven floor surface. Also, your marble floor can get cracked at a later time.

It must also be noted that the tiles are not factory manufactured, and therefore each tile naturally looks different. An experienced installer knows how to make the required markings and lay tile after tile patiently to form a uniform pattern across the floor.

Here is a link that might be useful:
Marble Flooring | Cost | Buying Tips | Installation | Maintenance