Intro

On most jobs, the failure starts before the first tile is set. Don’t make this mistake in tile installation: skipping real surface prep and flatness checks. This is the number-one reason for lippage, hollow spots, cracked grout, and callbacks. In this guide, we’ll show you what to check, the exact tolerances to hit, and simple steps that save time. You’ll see how to test flatness in minutes, when to use self-leveler, and how to get proper mortar coverage. Keep it simple. Follow the numbers. Prevent problems before they happen.

Quick Answer

Don’t make this mistake in tile installation: setting over an uneven, dirty, or weak substrate. Hit flatness first—1/4 inch in 10 feet for small tile, 1/8 inch in 10 feet for large format. Clean, prime, level, and verify 95% coverage in wet areas (80% dry). Use movement joints and follow cure times.

Table of Contents

• The Real Mistake: Unprepared Surfaces Cause Most Failures
• Check Flatness Fast (And Know the Numbers)
• Prep That Works: Clean, Bond, Prime, Level
• Layout, Joints, and Movement
• Mortar, Trowels, and Coverage
• Wet Areas, Transitions, and Edges
• Document It in Your Proposal
• Key Takeaways
• FAQ
• Conclusion

The Real Mistake: Unprepared Surfaces Cause Most Failures

Most tile issues come from poor prep. Not the tile. Not the grout. The base. If the floor isn’t flat and sound, you fight lippage, you waste thinset, and you own the callback. Don’t make this mistake in tile installation—treat prep as part of install, not an optional step.

What “unprepared” looks like:

• A dip of 3/8 inch across a doorway.
• Paint, dust, or cutback residue blocking bond.
• Cracked plywood or loose OSB panels.
• Old thinset ridges left proud.

What “ready” looks like:

• Flat to the correct tolerance.
• Clean and primed as needed.
• Movement planned at perimeters and changes of plane.
• Proper underlayment secured per spec.

Check Flatness Fast And Know the Numbers

Don’t make this mistake in tile installation: guessing flatness by eye. Use a straightedge and write it down.

Numbers that matter (common standards used by pros):

• Tile edges under 15 inches: max 1/4 inch variation in 10 feet; 1/16 inch in 12 inches.
• Tile edges 15 inches or longer (large format): max 1/8 inch in 10 feet; 1/16 inch in 24 inches.
• Concrete cure (new slabs): allow 28 days before most bonded systems, unless the product says otherwise.

How to check in 5 steps:

1. Lay a 10-foot straightedge in 4 directions (N-S, E-W, both diagonals).
2. Mark gaps over the limit with a wax pencil.
3. Note humps too; humps cause lippage fast.
4. Measure the worst spots (e.g., 5/16 inch dip at 7 feet).
5. Decide: grind humps, patch dips, or pour self-leveler.

Tip: On walls, use a 6-foot level or a long aluminum straightedge. Check vertical and horizontal.

Prep That Works: Clean, Bond, Prime, Level

Don’t make this mistake in tile installation: trying to “fix” the floor with extra thinset. Thinset is not a patch. It’s for bonding, not flattening.

Simple sequence:

1. Clean: Vacuum twice. Remove paint, dust, and old adhesive. Scarify smooth concrete.
2. Secure: Re-screw subfloors every 6-8 inches along joists. Fix squeaks now.
3. Prime: Use the manufacturer’s primer for self-leveler or patch. Follow the label.
4. Level/patch: Use self-leveling underlayment for wide areas (1/8–1 inch). Use patch for small spots (up to 1/4 inch per pass).
5. Grind: Knock down humps with a grinder and shroud. Wear PPE.
6. Underlayment: Install cement board or foam backer per spec (thinset under, fasteners every 8 inches, tape seams).

Timeframes to plan:

• Self-leveler walkable: commonly 2–4 hours. Tile in 4–16 hours (check bag).
• Primers: typically 1–3 hours to dry.
• Patches: often 30–90 minutes per layer.

Layout, Joints, and Movement

Don’t make this mistake in tile installation: tight layouts with no room to move. Tile needs joints.

Layout basics:

• Snap control lines from the true center or a focal edge.
• Aim for at least 1/3 offset on large planks to reduce lippage.
• Keep grout joints consistent: 1/16–3/16 inch are common. Use spacers or leveling clips.

Movement joints (simple rules many pros follow):

• Perimeter joints: 1/4 inch at all walls and columns. Always.
• Interior fields: soft joints every 20–25 feet in each direction.
• Sun/exterior areas: soft joints tighter, around 8–12 feet.
• Changes of plane: caulk, don’t grout.

These small gaps stop tenting and cracked grout. Add them to the scope so clients know what to expect.

Mortar, Trowels, and Coverage

Don’t make this mistake in tile installation: poor mortar coverage. Voids lead to cracks and loose tiles.

Follow these checks:

1. Trowel size: Match notch to tile. Example: 1/2 x 1/2 inch for big planks; 1/4 x 3/8 inch for standard 12x24.
2. Key-in coat: Burn a thin layer into the substrate with the flat side first.
3. Straight ridges: Comb in one direction. No swirls. Helps air escape.
4. Back-butter: Back-butter large format tiles and stone.
5. Coverage targets: 80% minimum interior dry; 95% in wet, exterior, or stone. Aim for 100% at corners and edges.
6. Minimum thickness: About 3/32 inch after tile is bedded.

Timing matters:

• Pot life: Usually 2–4 hours.
• Open time: Often 10–15 minutes. Touch test—if it skins, re-trowel.
• Grout time: Commonly after 24 hours.

Pull a tile every 10–12 pieces. Check coverage. Adjust if low.

Wet Areas, Transitions, and Edges

Don’t make this mistake in tile installation: skipping waterproofing in showers and wet rooms.

Wet area checklist:

• Slope: 1/4 inch per foot to drain, minimum.
• Waterproof: Use sheet membrane or liquid-applied per spec. No pinholes.
• Cure: Many membranes need 12–24 hours before flood testing.
• Penetrations: Seal valves and niches carefully.

Transitions and edges:

• Plan finished height. Avoid trip lips larger than 1/4 inch without a beveled transition.
• Use trims on outside corners for protection.
• Caulk changes of plane and perimeters with a matching sealant.

Document It in Your Proposal

Don’t make this mistake in tile installation: assuming the client understands floor prep. Put it in writing.

What to include in your proposal:

• Flatness standard you’ll meet (e.g., 1/8 inch in 10 feet for large format).
• Allowance for self-leveler or patch (e.g., up to 2 bags included, more is extra).
• Movement joints and perimeter gaps.
• Waterproofing scope and cure times.
• Access limits: “No traffic for 24 hours after set, grout next day.”

Pro tip: Capture site photos and voice notes during the walk-through. Tools like Donizo let you record details with voice, text, and photos, then turn them into a clean, branded proposal fast. When the client hits e-sign, you’re covered.

Related internal linking ideas to pair with this post:

• Link “professional proposals” to your proposals guide.
• Link “project timelines” to your scheduling article.
• Link “invoice templates” to your billing resources.
• Link “change orders” to your margin protection post.

Key Takeaways

• Flatness first: 1/4 inch in 10 feet (small tile), 1/8 inch (large format).
• Thinset bonds; it doesn’t fix dips. Use patch or self-leveler.
• Coverage counts: 80% dry areas, 95% wet/exterior. Back-butter big tiles.
• Movement joints stop cracks: perimeter 1/4 inch; field joints as needed.
• Document prep, joints, and cure times in your proposal and get it e-signed.

FAQ

What is the biggest mistake in tile installation?

The biggest mistake is setting tile over an uneven or dirty substrate. Fix flatness first, clean and prime when needed, and use patch or self-leveler. This prevents lippage, hollow spots, and cracked grout.

How flat does a floor need to be for large format tile?

For tiles 15 inches or longer on any edge, aim for no more than 1/8 inch variation in 10 feet and 1/16 inch in 24 inches. Grind humps, patch dips, or pour self-leveler to meet this.

Can I use thinset to level the floor?

No. Thinset is made to bond tile, not to level large areas. Use patch compounds for small spots and self-leveling underlayment for wider areas. You’ll get better coverage and fewer callbacks.

How much mortar coverage do I need?

Common targets are 80% coverage for interior dry areas and 95% for wet zones, exterior, and natural stone. Pull a tile to verify. If coverage is low, change trowel size, back-butter, or adjust your technique.

Do I really need movement joints indoors?

Yes. Perimeter joints and soft joints in large fields prevent tenting and cracked grout. Keep a 1/4 inch gap at walls and add field joints as needed, especially in sunlit or heated areas.

Conclusion

Don’t make this mistake in tile installation: ignoring prep and flatness. Get the surface right, plan movement, and hit coverage. You’ll avoid lippage and costly callbacks. Next steps: 1) Check flatness with a 10-foot straightedge. 2) Plan your patch or self-leveler. 3) Pull tiles to verify coverage. If you want faster, cleaner proposals with site photos and voice notes, try platforms such as Donizo. Build trust, set clear expectations, and deliver solid work every time.