A 1620 × 3240 mm Laminam panel weighs about 165 lb at 6 mm and over 320 lb at 12 mm. It is too large to wave into place and too unforgiving to rescue once the mortar grabs. The install order has to be decided before the crate is opened. This is the field walkthrough we use on Brickell, Coral Gables, and Key Biscayne projects when the spec calls for true large-format porcelain — nine steps, with the numbers we measure to at each one. Read it alongside the work.

How to install large-format porcelain slab in nine steps

To install large-format porcelain slab, you survey and correct the substrate to ± 1.5 mm over 10 ft, prime and waterproof in wet zones, dry-fit the panels, mix LATICRETE 254 Platinum or equivalent ANSI A118.4/A118.15 mortar, trowel and back-butter for ≥ 95% mortar coverage, lift each panel with a vacuum frame, set with leveling clips at 1.5 mm joints, beat in and verify lippage under 0.5 mm, then grout or fill the dry joint after the mortar has cured. Each step has its own tolerance. Skipping one shows up two weeks later as a hollow panel, a lipped seam, or a cracked corner.

The nine steps below are the order our crews work in on every slab job, whether the panel is a Laminam Calacatta vanity wall in Coral Gables or a Neolith floor running through a Brickell foyer. The full pillar context — elevator clearances, dry-joint layout, cut planning — lives in our large-format porcelain installation in Miami guide. This post is the field method.

Why Miami changes the install

Miami slabs move. The concrete deck of a Brickell condo expands and contracts with the day-night swing, the AC duty cycle, and the salt-laden humidity that lives in every west wall. A porcelain slab amplifies whatever the substrate does. On a 24-inch tile, a 2 mm bow becomes a manageable spacer adjustment. On a 3240 mm panel, the same 2 mm over the same span becomes a visible lip in raking light.

That is why the spec for large format is tighter than the spec for standard tile. The TCNA Handbook calls for ± 1/8 inch in 10 ft for tile with any side longer than 15 inches — that is roughly ± 3.2 mm. We hold our slab substrates to ± 1.5 mm over 10 ft because the eye reads the seam between two 3240 mm panels long before the substrate reaches TCNA-minimum tolerance. The same is true for moisture: condo slabs read above the 75% RH threshold more often than people expect, and that needs to be measured before mortar mixes.

Step 1 — Survey the substrate

Before anything is unloaded, the substrate gets mapped. Floor jobs get a laser datum at finished-floor height, a chalk grid at 24-inch centers, and rod-and-read measurements at every grid intersection. Walls get a plumb-line drop and a 10 ft straightedge swept across the field.

We document hollow spots, cracks, soft patches, framing movement, and any prior leveling work. The deliverable from this step is a marked-up floor or wall plan that tells the leveling crew exactly where to add height, where to grind, and where the substrate is already in tolerance. Our floor leveling in Miami guide details the rod-and-read method in full, and our flatness tolerances for large-format tile post explains why ± 1.5 mm over 10 ft is the slab number, not the TCNA tile minimum.

Step 2 — Test moisture and correct flatness

Concrete moisture is measured per ASTM F2170 with in-situ relative humidity probes. We will not mortar a slab over a substrate above 75% RH unless the manufacturer’s tech data sheet permits it with a vapor-mitigation primer. On condo decks the reading is often the deciding factor in scheduling — we do not bend the threshold to hit a calendar. The full method is in our moisture testing for condo slabs in Miami post.

Flatness correction is phased. High points get ground; low areas get filled with a polymer-modified patch up to about 12 mm; broader corrections use a self-leveling underlayment over a primed deck. A second laser sweep verifies the pour landed in tolerance before any tile work continues. If the substrate cannot be brought into tolerance, the spec changes — that is not negotiable on slab work.

Step 3 — Prime and waterproof in wet zones

Once the substrate is flat, dry, and clean, primer goes down per the bonding mortar manufacturer’s tech data sheet. Wet zones — shower walls, shower pans, tub decks, curbless transitions — get a bonded waterproofing membrane on top of the primer. We use Schluter Kerdi as our default; the membrane and the band detail at every change of plane are what actually protect the home.

The membrane is flood-tested for 24 hours before any tile sets. Skipping the test is the single most common failure we see in re-do jobs we are called in to fix. The full assembly — corners, drains, niches, penetrations — is documented in Schluter Kerdi vs sheet membranes for Miami baths, and the curbless detail lives in curbless shower in a Miami condo. For the service surface, see Schluter Kerdi shower waterproofing.

Step 4 — Dry-fit and lock the layout

Every panel is dry-fit before any mortar is mixed. We pull the cut sheet, mark the panel orientation, and lay the panels flat on protective foam in the staging area. Bookmatch pairs get oriented; vein continuity is verified panel-to-panel; the cuts at outlets, niches, drains, and returns are scribed and confirmed against the actual rough-ins, not the as-drawn rough-ins.

Layout decisions get locked here. The vanity wall is centered. The shower niche is sighted to the eye line. The floor and wall joints are aligned where the design calls for it. Thin cuts are pushed to the corner the eye does not land on. On a Coral Gables hallway, we will often re-balance a 28 ft run by 6–10 mm at one end to keep both end cuts above 200 mm — that is a layout call, not a cut call, and it has to happen before the first panel is back-buttered.

Step 5 — Mix the mortar to spec

Large-format porcelain is set in an ANSI A118.4 or A118.15 polymer-modified large-and-heavy-tile mortar. Our default is LATICRETE 254 Platinum, thinned to slump per the printed tech data sheet. The water ratio is measured, not eyeballed. Pot life is tracked with a kitchen timer; mortar past pot life goes in the waste bin, not on the substrate.

We mix small batches. A panel that takes 12 minutes to back-butter and set should not be reaching for mortar that was mixed 35 minutes ago. The mortar’s open time on a Miami summer afternoon is shorter than the spec sheet number — we work in the shade and time it accordingly.

Step 6 — Trowel and back-butter for full coverage

ANSI A108.5 requires at least 95% mortar coverage for tile installed in dry interior areas and full (95%–100%) coverage in wet areas and exterior. Large-format porcelain hits that number only with a two-direction, two-surface method:

A 1/2 inch x 1/2 inch U-notch or square-notch trowel combs the substrate in one direction, parallel to the short panel edge.
A 3/16 inch flat skim is back-buttered onto the back of the panel.
The panel is set, slid 1–2 inches across the trowel ridges to collapse them, then beat in.

We verify coverage on the first panel of every wall and every fifth panel after by lifting and looking. If coverage is below 95%, the trowel size goes up or the mortar slump comes down. The number is checked, not assumed.

Step 7 — Lift with a vacuum frame

Any panel over 1 m² is lifted with a vacuum frame. A 1620 × 3240 mm panel is 5.25 m² — it is not lifted by hand. Our crews use 6- or 8-cup frames matched to the panel weight, with a tested vacuum gauge, dual-circuit redundancy, and a strap backup on every lift over a vanity or fixed glass.

The lift path is rehearsed. We carry the panel in the orientation it will set, with a clear walking lane to the wall or floor. On condo jobs the elevator clearance and the apartment-door swing are measured before the crate is loaded — a 3240 mm panel does not turn a corner that a 3050 mm panel does. The handling discipline is what keeps the panel intact from the staging area to the wall.

Step 8 — Set, level, and verify

The panel is landed on the trowel ridges, slid across them to collapse the lines, and beat in with a wood-faced rubber float and a deadblow mallet. Edges are leveled with a tile-leveling clip system — we use a Cortag or Raimondi RLS at 1.5 mm joint width as the default. Clips go on every edge intersection and every 12–18 inches along long seams.

After the panel is beat in, we read lippage with a digital caliper or a lippage gauge across every seam. The target is under 0.5 mm. Above that, the mortar bed gets adjusted before it skins — adding mortar under the low edge or working the high edge down with the mallet. Once a clip system has set, the time window to fix lippage is gone. The same discipline applies to porcelain bath walls — see porcelain slab bathroom walls for the wall-specific detail.

Step 9 — Cure, joint, and inspect

Mortar cures undisturbed for the time on the tech data sheet — typically 24 hours before clip removal, 14–28 days before heavy traffic on floors. Clips are tapped off parallel to the joint, never across it. The 1.5 mm joint is then either grouted with an unsanded cement grout or filled with a color-matched epoxy or silicone, depending on the wall-vs-floor and wet-vs-dry classification per TCNA Handbook EJ171.

The dry-joint walls in many of our slab baths are color-matched silicone at the changes of plane and 1.5 mm joints filled with a flexible polymer between panels. The choice is made at the layout meeting, not at the grout bucket. Final inspection is a panel-by-panel walk: lippage, joint, edge, cut, alignment, hollow-sound check. Anything that does not pass gets fixed before the next trade enters the room.

The numbers we measure to

The nine steps above hold up because the tolerances are explicit. If a spec is silent on a number, the field will choose its own — and that is where slab jobs go wrong.

Step	Measurement	Tolerance / target
Substrate flatness	10 ft straightedge or laser, rod-and-read	± 1.5 mm over 10 ft
Concrete moisture	ASTM F2170 in-situ RH probe	≤ 75% RH (or per TDS)
Bonded membrane	24 h flood test	No drop in pan level
Mortar standard	ANSI A118.4 or A118.15	LATICRETE 254 Platinum (default)
Mortar coverage	ANSI A108.5 lift-and-look	≥ 95% (interior dry)
Mortar coverage (wet)	ANSI A108.5 lift-and-look	95%–100%
Panel handling	Vacuum frame, gauge-verified	Any panel > 1 m²
Joint width	Tile-leveling clip system (Cortag, Raimondi RLS)	1.5 mm
Lippage at seam	Lippage gauge / digital caliper	< 0.5 mm
Cure before traffic	Per mortar TDS	24 h light, 14–28 d heavy

Numbers like these are also what a designer or architect’s spec sheet should call out — see the large-format porcelain spec sheet for architects for the full callout template.

Common mistakes — what we are called in to fix

Most slab failures we re-do trace back to one of these four:

Substrate left in tile-tolerance, not slab-tolerance. TCNA’s ± 3.2 mm over 10 ft is fine for 12-inch tile. It will read as a lipped seam under a 3240 mm panel. The substrate has to come down to ± 1.5 mm.
Mortar coverage assumed, not verified. Without lift-and-look on the first panel and every fifth panel, coverage drifts. Hollow corners follow.
Hand-lifting a panel over 1 m². Cracks on slab jobs almost always start in transit, not at install. The vacuum frame is not optional.
Grouting before mortar has cured. Tapping clips out early or grouting at 12 hours instead of 24 telegraphs hairline cracks at the joint.

The other failure mode is comparing materials by max size and forgetting the rest of the spec. Laminam, Neolith, and Dekton handle differently in the field — thickness, weight, cut method, and recommended mortar are not interchangeable. Our Laminam vs Neolith vs Dekton breakdown covers the field-relevant differences.

When The Miami Floors is the right fit

We install large-format porcelain slab — Laminam, Neolith, Dekton, and equivalents up to 1620 × 3240 mm — across Miami-Dade and Broward, with most of our work in Brickell, Coral Gables, Key Biscayne, Miami Beach, and Pinecrest. The firm is led by Ivan Herrera; he personally walks every slab project before sign-off. The Miami Floors is Schluter certified, and structured around the substrate-first method described above.

If you are speccing or building a slab project, start at the service surface — large-format porcelain slab installation — or read the cluster pillar at large-format porcelain installation in Miami. For projects where the slab meets a stone counter or hearth, see stone and marble installation. The finished panel is only as good as the nine steps behind it.

Reviewed by Ivan Herrera, April 2026.

Sources and references:

TCNA Handbook for Ceramic, Glass, and Stone Tile Installation (2025) — §EJ171 movement joints, §F125 large-format and heavy tile.
ANSI A108.5 — Installation of Ceramic Tile with Dry-Set Cement Mortar or Latex-Portland Cement Mortar — mortar coverage requirements.
LATICRETE 254 Platinum technical data sheet — ANSI A118.4 and A118.15 polymer-modified mortar spec.

How to Install Large-Format Porcelain Slab: 9 Field Steps