Tips on Tiling
Using tile in RVs, buses, and tiny houses on wheels can be a tricky subject. For spaces that move, tile is at a greater risk of failure than other surfaces. Tile is also heavy, and it usually requires a substantial substrate that's heavy, too.
But tile is a beautiful and versatile finish. It can be an attractive option for creating custom waterproof shower surrounds or bathroom floors. It also makes a beautiful and easy to clean kitchen backsplash.
Tile can be used successfully in structures that move all the time like RVs and buses. If Hofmann Architecture can do it, so can you. (Note: HofArc seems to have taken down a lot of their older resources, so that link points to the Wayback Machine). Using these techniques in structures that don't have conventional foundations but move infrequently (or not at all) can improve the longevity of your tiled surfaces.
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Build on the Right Foundation
A tile foundation needs to be sturdy enough to avoid bending under a load (i.e. resist deflection), but also installed a way that minimizes the transfer of motion to the tile. For tiled walls, it's a good idea to use at least 1/2" thick plywood for sufficient stability. If you can get your hands on some of DUROCK's UltraLight foam tile backer board, you could use it on top of a thinner substrate to build lighter-weight walls. Floors should be at least 3/4" thick plywood with sufficient framing underneath to prevent deflection.
If your structure moves, try to attach the wall to the structure in a way that will hold it firmly in place, but won't transfer motion to the wall in a way that will cause it to flex. You want your tiled wall to be rigid and self-supported—as close to freestanding as possible.
For floors, you need an uncoupling membrane on top of the 3/4" plywood floor like Schluter DITRA, or a layer of Hardiebacker. For electric heated floors under tile, consider using DITRA heat, which integrates the heating coil into the uncoupling membrane.
If you're installing tile in a space that routinely moves like a travel trailer or a THOW that you're taking on tour, consider whether you can avoid laying tile across joints in the plywood subfloor. Subfloor joints will be especially susceptible to shifting, so unless you're going to heroic lengths to prevent transfer of motion, tile should be confined to small areas. Tiling a small bathroom floor is much safer if the entire floor is on a single sheet of plywood. Tiling a shower wall is much safer if each plane is a single sheet of plywood.
Your foundation needs to be flat. If you're tiling a floor that isn't perfectly flat, use a coating of latex floor leveling compound first to achieve a perfectly flat surface.
Waterproof Shower Walls and Pans
For shower enclosures or wet baths, there needs to be a waterproofing membrane behind the tile. Paint-on waterproofing like Red-Guard works well on stationary structures, and might be OK for a mobile application, but a membrane waterproofing system would be less likely to crack due to shifting or vibrations. Schluter's Kerdi membrane system is a good choice for waterproofing shower walls. Be sure to use the pre-formed inside and outside corners where you need them.
Using a prefabricated one-piece shower pan is a good idea since it's less likely to leak if it shifts. But if you need a custom tiled shower pan or wet bath floor, consider using the Kerdi shower kit, which includes a formed pan for easy tile installation. If your shower or wet bath doesn't fit any of the factory options, you can cut the Kerdi shower tray to fit.
If your shower has a horizontal surface like a bench or niche, it must slope toward the drain to prevent water from pooling on top of it. Traditional construction suggests 1/2" per foot of slope, but since mobile spaces are rarely perfectly level, a more aggressive slope might be warranted.
Learn How to Set Tile
Most tile installations that fail, mobile or otherwise, fail because the installer's technique was terrible. Before you attempt to install tiles anywhere, watch this video about proper technique for setting tiles. It's only 6-1/2 minutes, and it will make you a better tile installer than almost any handyman or DIYer you've ever met.
Did you skip the video? Go back and watch it. It's seriously the best 6-1/2 minutes you'll ever invest in your successful tile installation.
Choose the Right Tiles
Larger tiles are more likely to fail in a mobile application. Even if your structure never moves, shifting in a structure without a traditional foundation can cause problems for large format tiles. Instead, use small mosaic tile sheets, which will be much more forgiving when your structure flexes.
Ceramic and glass mosaic tiles are available in 1/4" and 3/8" thick sheets, which weigh significantly less than 1/2" or thicker tiles. For extremely lightweight applications, consider resin mosaic tiles like Flextile.
Ceramic and glass mosaic tiles are unlikely to break when properly installed. But installing natural stone tiles or large format tiles in a space that moves is asking for trouble. If you can break a tile by hand, it's probably too fragile to use in a space that moves.
Use The Right Adhesive and Grout
For applications following our tips to this point, modified thinset and traditional unsanded grout works well for setting tiles in a mobile space. You can use latex admix instead of water to mix your grout, which will improve flexibility and bond strength. If you're using resin mosaic tiles, consult the manufacturer's instructions for the proper adhesive.
For some applications like backsplashes or shower walls on relatively flexible surfaces that won’t be exposed to too much water, a product like MusselBound Adhesive Tile Mats might be a better option than traditional adhesives.
If you're using a waterproof membrane product like Kerdi or Ditra, be sure to be mindful of the role of air exposure for curing, and plan your products accordingly. Read the directions. Kerdi and Ditra don't allow air to pass through, and modified thinset needs exposure to air to cure. These membrane products must be installed with unmodified thinset between the membrane and any large, impervious surface. If you're setting the membrane directly on plywood, you're OK to use modified thinset, since plywood isn't an impervious surface. Since we're using very small tiles, you can use modified thinset to set the tiles, since there's plenty of airflow from the grout lines.
If you are setting a membrane over cement, leveling compound, or any other impervious surface, you should use unmodified thinset instead. If you were using large format tiles (which you shouldn't be for this project), you'd need to use unmodified thinset to set the tiles as well.
Don't Rush Cure Times
Read the directions on your thinset. It may take a week or more before your tiles are fully cured after installation. Don't install tiles at the last minute and then move the structure before the cure is complete.
Mind Your Corners and your Edges
Use aluminum tile trim matched to your tile thickness to finish outside corners and trim edges. Aside from looking better than the raw edge of a tile, the aluminum trim will shield the vulnerable edge tiles from damage.
The grout line at any change of plane (i.e. corners) should be filled with caulk instead of grout, since the edges of the plane are especially prone to shifting. You can purchase color-matched caulk that will look virtually identical to your grout. Tape and the corners first, then grout over top the finished caulk line once it's cured.
Cutting Mosaic Tile
Mosaic tile can be a pain to cut, since it's composed of tons of tiny tiles that need to be cut individually. Your instinct might be to rent a wet saw, but you'll find that it's difficult to keep the individual tiles from shifting when they hit the blade, and the water can often cause the tiles to fall off their mesh backing.
The best tool for cutting mosaic tile is usually a manual tile cutter. Score each individual tile, then press to snap them one-by-one. Alternatively, using a diamond blade on your angle grinder works well, and is especially useful for touching up certain small cuts that the manual cutter is having trouble with.
Avoiding Lines Between Sheets
We've all seen mosaic tile installations where the individual sheets are clearly visible. Even slight imperfections in lining up sheets can be clearly visible in the grout lines of the finished tile.
Stagger your tile sheets so the joints between your sheets don't line up over your entire tiled surface. If all your sheets line up in a perfect grid, even tiny imperfections will be obvious because they'll visually reinforce one another. It's worth the extra effort to trim your sheets so that the edges are staggered.
After placing each couple of sheets, step away from your work and look at it from a distance. It's harder to see when tiles don't perfectly line up if you're looking too closely at your work. Step a few feet back, and the problem areas will pop out at you, so you'll have time to adjust them before the thinset cures. Don't be afraid to pull a sheet off the wall and try again if you need to.
Don't rush. Mix a small amount of thinset at a time, use cold water, and make sure it's not too thick. If your thinset starts to set up on you, don't let it force you to work fast. Dump it, and start a new batch. Use a paint mixer attachment for your drill to mix thinset so you don't get too tired while mixing batch after batch.
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