Tiles used to be laid in a thick bed of cement, a time-consuming process called a mud set. The jobs were solid and durable because tiles were embedded in a supporting slab of masonry. Before the tiles or grouted seams could break, the entire floor had to break.

Spreading adhesive in ribs with a notched trowel, called a thin set, has replaced that system. It’s faster and less expensive, but not necessarily better because houses move. Building materials can swell and shrink seasonally. Wall studs can shift. Floors can flex—all more than enough to crack joints and buckle tiles.

Good tile contractors know that the floor—or wall or kitchen counter—has to be rock solid. They may even spend more time preparing a strong surface than laying tile. But that’s only one of many factors determining job quality. The surprisingly large number of negative ratings and comments we receive from consumers indicate that many area tile installers should be avoided.

To get your money’s worth, and a job that looks good and lasts, here are 15 tips on tiling—from finding a good contractor to checking the finishing details.

  • Look for experienced contractors with satisfied customers. Tiling work is often a do-it-yourself job, so how hard can it be? But we put this tip first for a reason. A good contractor can turn shaky floors and other problems into a successful, good-looking project, while a bad contractor can turn the best raw materials into a disaster. Begin by asking friends, neighbors, and colleagues for recommendations. Here at Checkbook.org, we’ve done some homework for you. Our ratings tables for tile installers list customer reviews on tile installers. You might also get referrals from sales staff at tile suppliers.
  • Get several prices, avoiding apples and oranges. We found big price differences when our undercover shoppers got bids for a simple bathroom-floor tiling job from a number of installers—from $600 to $1,600—with the customer supplying exactly the same tile for each installer. The lesson: get at least three or four bids. When contractors check the site, provide each one with the same details. Decide ahead of time about the type of tile you want. Specify the manufacturer, size, color, grade (thinner for walls or thicker for floors), and the color and type of grout for the seams. If you want a porous tile like sun-baked terracotta versus a ceramic tile with a baked-on glaze, ask about the products and procedures for sealing. If a contractor suggests other possibilities, such as a special pattern or edging, ask for a price to your specs and also a price for the alternatives. For you to compare prices accurately, every bid must be based on the same specifications.
  • Question details. While the contractor checks the site and takes measurements, ask how he or she has handled other projects like yours. Laying the main field of tile is the easy part, so concentrate on the edges. Will there be a wooden saddle where the tile meets a wood floor at the bathroom door, or a marble saddle, called a sanitary sill? Ask each contractor to include specs for any prep work required, like a plywood underlayment for floor tile, or cement board backing for shower tile. Tell them you’ll want firm starting and completion dates, plus proof of insurance and a contractor’s license, where required. If a contractor can’t come through with these details on a proposal, who knows what may happen on the job.
  • Compare work proposals. Confirm that the basics about materials and square footage are the same in each bid; then look carefully to see if there are any differences. Single out thorough proposals that follow through on your request to price alternatives separately; check the specifics on plywood underlayment or cement board, and on the type, size, and installation of each component. Details should be part of the proposal, not extras once the job is underway. For example, self-rimming sinks will have to be removed temporarily while counters are tiled, then reconnected and reset in a bead of silicone caulk. A contractor who thinks through the project in detail—and commits the particulars to paper—is most likely to follow through on site.
  • Make a contract. Don’t rely on estimates—ask companies to provide you with a written, fixed price for the work. Most tile projects call for a basic letter of agreement instead of a multi-page contract with fine print. The contract should include details from the proposal about the tile, grout, prep, and finishing work—in addition to names and addresses, insurance information, licenses, and a payment schedule. Try to get payment terms that allow you to withhold all or most of the cost of the job until completion.
  • Plan a layout. Tiles look best centered on the floor or wall with equal partial pieces around the edges. But there are exceptions. Most require a judgment call, based mainly on what you see when you enter the room, or the view from the place or places where you usually sit. If there is one prominent, open wall, and another mostly concealed by furniture, consider using full tiles on the open wall and burying cut pieces under chairs and bookcases. In kitchens and baths, you might use full tiles along the most visible wall, and relegate cut pieces to the recessed toe-space below cabinets. When walls aren’t square, partial tiles along a skewed wall will be uneven—each one slightly bigger than the next. The wall you see most should get the square pieces. The wall you see least should get the irregular pieces. Once you have tiles on site, it’s wise to test different options with a dry layout using spacers that allow for grout seams. Cut lines should be straight and clean in any case, as pros use water saws that cut tile the way circular saws cut lumber.
  • Checks for prep work. Tile needs a smooth, rigid surface for support. And in most houses, standard wood joists covered with half-inch plywood isn’t rigid enough. There are two fixes. One is to beef up the framing (if it’s exposed in the basement, for instance), by gluing and screwing additional joists to existing timbers. The more common solution is to add another layer of plywood. Those sheets should lap over existing seams and be screwed down. Step on a tile set over a popped nail head, and the tile cracks. On walls, the best underlayment is cement board (common brand names include WonderBoard and Durock). The heavy, masonry, waterproof panels should be set with corrosion-resistant screws, and the seams covered with fiberglass mesh tape in thin-set mortar.
  • Checks for floor jobs. A typical job should start by creating a smooth surface that’s as rigid as a concrete slab. The next step is an application of adhesive with a notched trowel that forms uniform ribs. (Tile manufacturers specify the type of adhesive and rib size.) Then tiles are nestled into the adhesive and aligned with temporary plastic spacers, though many tiles have nubs on the edges that automatically create even seams. After the adhesive hardens (usually overnight) grout is forced into the joints with a float trowel. When the grout hardens, the haze on tile surfaces is wiped clean.
  • Checks for wall jobs. Wall tiles should be supported with spacers or nubs during installation; otherwise, some tiles can sag under their own weight before the adhesive sets.
  • Checks for countertop jobs. A typical job should start with a layer of cement board that’s glued with construction adhesive and screwed to the plywood countertop and cabinet framing. Careful contractors may sweep the surface with a metal trowel to make sure that no screw heads protrude. Then joints are buried under fiberglass mesh tape and thin-set mortar. The weak link is the seam between the counter and backsplash. If backsplash tile is attached to the wall, and countertop tile is attached to the cabinets, the seam can work open because the two anchoring surfaces don’t move as one. The better installation is to assemble the plywood counter and backsplash as a unit, adding silicone to the joint, and then screwing together the two pieces of plywood. When both are covered with cement board and tiled, the crucial seam won’t crack, even when the countertop is stressed enough to shift.
  • Checks for shower jobs. Building tile showers is exponentially more difficult than laying tile floors. The contractor has to create a slightly sloped floor that is strong enough to stand on without flexing, that remains waterproof despite regular soaking—and that has a hole in it for the drain. Tilers used to install a lead pan, and slope the mud-set floor to the drain by eye. Modern materials include a supporting form with the proper slope built in, and backup protection with a rubberized sheet under the floor that wraps several inches up the walls. Fully-tiled showers require many cuts that DIYers often make with a nipper, snapping off pieces of tile to create access for plumbing lines. Pros should use a hole saw to make neat circular cuts that are easier to waterproof than jagged edges. If the job isn’t watertight, the tile, wood subfloors, and joists underneath can require extensive and expensive rebuilding.
  • Checks for grout. Color is your choice. But ask the contractor for a recommendation about the type of grout: Portland cement, sanded or unsanded, epoxy? The most common is sanded Portland cement, used on most tiles with joints over 1/8-inch wide. It takes about 24 hours to dry, becomes hard like concrete, but remains porous unless sealed, even with latex additives. Some manufacturers add anti-fungal and mildew resistance agents, which can help in wet areas. Non-sanded grout is generally used for joints under 1/8-inch wide, and on easily scratched tiles such as polished marble (sanded grout swept across the floor will scratch and dull its surface). Epoxy resin, which doesn’t need sealing, is the best grout, but not often used. It contains epoxy resins and a hardener, which makes it highly resistant to stains, mildew, and water. But epoxy is expensive and difficult to install.
  • Seal the grout. It’s an extra step, but worth the time to reduce future maintenance. Most sealers are liquid silicone, and applied with an artist’s brush or a small, roll-on applicator that only coats the seams. (Silicone on the tiles would make them too slick to walk on safely.)
  • Caulk the tub seam. All seams should be grouted—except the joint where wall tiles meet a tub because the wall of tiles stays put while the tub below them moves slightly when it’s filled with water. The shifting is due to weight—the tub plus 320 pounds for 40 gallons of water plus your weight. It’s enough to make a tub shift and eventually break open the connecting seam to a row of tiles. Once that happens, water can seep into the wall. The solution is to caulk the connecting seam with silicone. It’s flexible enough to withstand the stress without cracking like grout.
  • Buy extras. Save a few extra tiles and some of the powdered grout mix, particularly if you’re using exotic materials or unusual sizes and patterns. Tile is rugged. But if someone drops a bowling ball on your indestructible floor—no problem: you’ll have replacements.