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Prepare the Subfloor
Marble floor tile (and all floor tile) requires a smooth, flat, water-resistant base for installation. If your existing subfloor is wood, cover it with a layer of cement board to add both stiffness and moisture-resistance to the floor. Cement board doesn't stop moisture from passing through it — it's not a vapor or moisture barrier — but it won't be damaged by moisture like wood is. Cement board also bonds really well with thin set mortar, which you will use to install your marble tile.
To instal...l cement board, spread thin set over the wood subfloor, using a 1/4" notched trowel. Lay the cement board sheets into the thin set and fasten them to the subflooring with 1 1/4" cement board screws. Leave about 1/8" of space at all seams and where the cement board meets the walls.
Apply cement board joint tape (a special alkali-resistant mesh tape) over the seams between the cement board panels, then cover the tape with a thin layer of thin set, using a 6" drywall knife. Make sure the seams are smooth and flat and flush with the panel faces.
Continue to 2 of 13 below.
- Marble tile
- Thinset mortar (tile adhesive)
- 1/4" notched trowel
- Cement board
- 1 1/4” cement board screws
- Cement board joint tape
- 6" drywall knife
- Tape measure
- Chalk line
- T square
- Tile spacers
- Straight 2x4 board
- Rubber mallet
- Wet saw (or custom-cut tile pieces)
- Marble tile and grout sealer
- Foam brush
- Work gloves
- Grout float
- Grout sponge
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Create Reference Lines
It looks best if the tiles radiate outward from the center of the room, rather than starting abruptly from one of the walls. In order to achieve this effect, you need to create reference lines on the surface of the cement board underlayment.
Find the center of two opposing walls and use a line chalk to mark a path in between them, dividing the room in half. Then, measure to the center of that line, and use a T-square to draw a perpendicular line at the mark, using a pencil. Snap a chalk line... across the floor using the pencil line as a guide, dividing the floor into four equal quadrants.
Check your layout by dry-laying (no mortar) full tiles along both reference lines from wall to wall. If the last tile that is against any of the walls is less than a few inches wide, adjust your chalk line grid as needed so that the tiles along the walls are an acceptable width, based on your preference. This usually means that a tile, rather than a grout line, will be at the very center of the floor, but there's really no drawback to this.Continue to 3 of 13 below.
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Mix and Spread the Mortar
Mix thin-set mortar according to the manufacturer's instructions. Mix only a little bit at a time, and make more when necessary. Using a notched trowel, to spread the adhesive onto the floor, starting at one of the corners where your reference lines intersect in the center of the room. As you work, use the notched edge of the trowel to create grooves in the mortar. This will increase the adhesive strength of the bond with the bottom of the marble.
On marble tiles that are 12" square... and smaller, a 1/4" notched trowel will create large enough grooves. However, if you have much larger tiles, or if you are using irregular tumbled or natural cleft materials, use a 1/2" notched trowel to create wider, deeper grooves in the adhesive.Continue to 4 of 13 below.
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Set the First Tile
Spread enough mortar to easily cover the bottom of a single tile, and make sure that its entire surface is notched. Gently press the first tile into place, aligning two of its edges with the chalked lines. As you press it down, twist the tile slightly to ensure that it properly sets in the mortar bed below.Continue to 5 of 13 below.
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Tap With a Rubber Mallet
A rubber mallet is a large hammer with a soft rubber head. This can be used to lightly tap the surface of the marble tile, to press it more firmly into the mortar. However, be careful not to tap too hard, as marble is a relatively soft material and can crack rather easily. You also want to avoid moving the tile as you are setting it.Continue to 6 of 13 below.
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Use Tile Spacers
Continue to spread mortar for each tile, then place the tile before moving on to the next one. Follow the reference line towards the wall, using it as a guide to keep your placement straight. Use tile spacers to maintain consistent spacing between tiles. This helps ensure the grout lines are sharp and uniform.Continue to 7 of 13 below.
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Check the Tile Height
After placing every three or four tiles, use a 2x4 to ensure that they are at an even height. Place the board across the tiles, and tap the board lightly with the rubber mallet. If the marble is polished you may want to cover the front of the wood with a piece of carpet to prevent scratches. You can also do this across multiple rows when you have more tiles installed.
Once you reach the wall with the first row, take note of the gap at the end that may require a custom-cut piece. Then, move back... to the center point of the references lines, and continue to place tiles adjacent to the first row. Take a moment after every few tiles to ensure that all of your lines meet up and the entire floor looks sharp and consistent.
As you work, be careful not to step on any mortared tiles. Typically, marble floor tile should be allowed to set for at least 48 hours after installation. Because of this, you have to be careful not to tile yourself into a corner that you can not escape from. Work on the quadrant that has the door last, and as you set the tiles, be sure to leave a traffic path for yourself.Continue to 8 of 13 below.
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Cut Tiles With a Wet Saw
Use a tile saw or wet saw, to cut tiles as needed. You can buy a small wet saw for under $100 dollars, but most DIYers simply rent them by the day. Smaller, portable saws are able to handle basic straight cuts on tiles up to 12".
A wet saw works by spraying water on the material, as you run it through a spinning table saw blade. The water helps to keep the blade cool and the cuts smooth as it moves through the marble. Because marble is delicate and easy to crack, move very slowly as you cut each... piece. For difficult cuts, or if you prefer not to use a saw, ask your tile supplier if they will cut pieces for you.Continue to 9 of 13 below.
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Remove Excess Mortar
For a strong bond, you want to use enough mortar so that you can create notches in it with the trowel, without seeing bare cement board. You also want to set the tile with enough force that it collapses the ridges created by the trowel, but not so much that it forces the mortar up through the grout lines. If excess adhesive comes up through the gaps, remove it with a paint stick or a utility knife.
When all of the tile has been installed, let the mortar to dry completely, following the... manufacturer's directions. Do not walk on the floor during this time, or you risk moving or depressing a tile.Continue to 10 of 13 below.
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Seal the Marble
Marble may seem like it is a very hard, solid material. It is rock, after all. But in actuality, marble is a very delicate flooring material that needs to be taken care of. Not only is it prone to cracking and chipping, but it is also very porous, and many materials can penetrate the surface of the stone, causing permanent stains. This is why you must seal the tile with a high-quality marble tile sealant. It's important to seal the tile for grouting it because grout can stain the tile,... especially if it is unsealed.
If you have polished marble, use a very thin coat of sealant, and use the foam brush to smooth out any puddles or tiny bubbles that appear on the surface, as they can dry into permanent features. The surface of tumbled and honed marble will be more forgiving, but the same rules apply there as well.Continue to 11 of 13 below.
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Grout the Tile
Mix the grout as directed by the manufacturer. As with the mortar, mix only as much as you can apply in about 15 or 20 minutes when the grout starts to set up. Apply the grout to the joints using a grout float. Try to direct as much of the mix into the grooves as possible, and wipe up any excess that gets on the tiles.Continue to 12 of 13 below.
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Wipe the Tiles Clean
Use a large grout sponge that is slightly damp to gently wipe the surface of the marble tiles clean and remove excess grout. Be careful not to allow any moisture to seep down into the grout lines, as this can cause the mix to become muddy and washed out. Also, avoid inadvertently wiping the grout out as you work with the sponge. Allow the grout to cure as directed.Continue to 13 of 13 below.
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Seal the Grout
Check the manufacturer's recommended waiting time before sealing the grout. A wait of 7 days is not uncommon. Seal the grout with a foam brush as directed. It's also a good idea to seal a marble tile again, perhaps several times, waiting for each coat to dry before applying a new one. This creates a strong protective layer on the surface of the material. You may need to reseal the tile every 6-12 months, depending on how much traffic the room gets.