Mapei Planitop Fast 330: Levelling a 12mm Fall Across a 40 Square Metre Kitchen

The 12mm Fall Sets the Bag Count

Start with the measurement that drives the specification: 12mm at the low point, tapering toward zero at the high side of a 40 square metre room. Planitop Fast 330 is rated 3mm to 40mm in one application, so that fall sits inside its range and can be dealt with in a single build. A compound capped at 10mm pushes the job into two pours, and the interface between pours is a common starting point for hollow areas.

Ordering starts with the average depth across the room. Coverage is roughly 1.5kg of powder per square metre per millimetre of thickness. Across 40 square metres at an average of about 6mm once the fall is divided, the dry material comes out near 360kg, which means fifteen 25kg bags with a margin. It is common to see twelve bags ordered, then the low corner takes more material than expected and someone discovers at four that the wholesaler closed at three.

Fast 330 is a calcium sulphate free, cement based compound. It can be pump applied or hand mixed, and it is walkable in around three hours at 20 degrees. That fast return to traffic is the attraction on a kitchen job when fitters want to tile the next morning.

Anhydrite Screed Changes the Preparation

If the existing floor is an anhydrite screed, the job turns on the surface preparation before any levelling compound is mixed. Anhydrite is calcium sulphate. Portland cement in contact with it, with moisture present, can form ettringite at the interface. The bond then fails weeks later as a dusty grey layer. That interface failure is one of the common causes of a poured floor delaminating over a flowing screed.

The repair path starts mechanically. The laitance, the weak skin that forms as an anhydrite screed cures, has to be sanded back with a 40 grit mesh until the aggregate shows. After that, the floor needs vacuuming to a genuinely dust free finish.

Primer choice follows. Mapei Primer G, thinned, can seal the prepared surface. Primer PU100 is used where residual moisture is a concern. The aim is to leave the cementitious compound bonding to a sealed, stable face instead of a friable sulphate skin.

Moisture is the gatekeeper. Anhydrite needs to reach roughly 0.5 percent CM by carbide method before it takes a cement based product above it. A hair hygrometer reading the room air gives no reliable view of moisture in the screed core.

On a 40 square metre flowing screed poured in winter, drying can run six to eight weeks with the heating off. It can run longer when the room is poorly ventilated. Fast 330 poured over a screed still sitting at 1.2 percent can look acceptable at handover and show cracks by spring.

Where the substrate is ordinary sand and cement screed, the preparation is simpler. Primer G neat over a swept, sound surface is enough.

Deflection Still Breaks Tiles

A level surface over a bouncy floor still leaves the tile layer vulnerable. The levelling compound corrects plane and depth; it does not turn a moving substrate into a rigid base.

Large Porcelain Needs a Consistent Bed

Once the floor reads flat, the porcelain sets the next tolerance. A 600 by 1200 tile, now common in kitchens, will show lippage at the joints when the bed varies more than about 3mm over a 2 metre straightedge. Fast 330 can self level well inside that tolerance, which is why it is used to deal with the fall before the adhesive goes down.

The adhesive has to suit the tile format. A standard C1 wall adhesive under a 1.2 metre porcelain plank is a callback waiting to happen. Mapei Keraflex Maxi S1, an S1 deformable class cement adhesive, fits this situation because it holds a 10mm notch bed and has enough deformability to move fractionally with the substrate.

Solid bed coverage matters with large format porcelain. Back butter the tile, comb the floor in one direction, and aim for more than 90 percent contact under a kitchen floor tile. A void under a 1.2 metre plank becomes a crack line as soon as a stool leg lands on that spot.

Grout spacing separates large planks from small splashback tiles. Rectified porcelain planks commonly run on a 2mm to 3mm joint. The flatter the bed, the tighter the joint can be kept without lippage.

Metro tiles on a splashback behave differently. A 2mm joint on a 100 by 200 metro tile is fine because the tile is small enough that plane variation does not accumulate across the face. A 1mm joint on rectified porcelain over a floor that is only nearly flat leaves installers grinding edges late into the job.

Engineered Oak Over the Same Levelled Floor

Suppose half the kitchen takes porcelain and the route into the dining area takes engineered oak. The cured Fast 330 surface can suit both finishes, and the oak brings one extra requirement: an expansion gap. Engineered oak moves seasonally, less than solid oak, yet a 6 metre run still needs a perimeter gap of around 10mm to 12mm, hidden under the skirting or a scotia.

Adhesive squeezed into that perimeter gap, or a tight door architrave trapping the boards, can make the floor buckle in the first humid August. The boards lift into a ridge that can be felt underfoot. The gap gives the whole floor room to move with seasonal moisture change.

Where oak meets porcelain, use a proper expansion profile at the threshold. The profile allows the two finishes to work to their own tolerances across the junction.

Water Areas Need the Membrane Above the Leveller

A kitchen has less exposure than a wet room, yet the area around a dishwasher and sink sees more spillage than any bathroom floor outside the shower. When a client wants the tile to run from the kitchen into an adjoining utility with a floor drain, Schluter Kerdi goes down over the cured, levelled Fast 330 before the tile is fixed.

Kerdi is a polyethylene sheet with a fleece backing. It is bonded with the same S1 adhesive, lapped 50mm at seams, and dressed up the wall behind the units. That placement matters because the membrane needs a sound, flat plane to bond to. Levelling compound poured onto polyethylene has no mechanical key.

Travertine makes the same principle more obvious. The stone is porous and will wick standing water through to the bed. A penetrating Lithofin sealer handles surface staining on the stone; waterproofing still depends on the membrane below the tile assembly.

Running the Pour

Mixing water is the quiet variable in a self levelling floor. Fast 330 takes a specified ratio, near 5.5 litres to a 25kg bag. Every extra half litre added for easier flow reduces strength and invites surface crazing as the excess water bleeds off.

Use a clean bucket and a forced action paddle. After mixing, let the material rest for 60 seconds before pouring.

Work the room from the far corner toward the door in one continuous operation. Keeping a wet edge across 40 square metres is optimistic for one person and realistic for two. A spiked roller pulled through the fresh pour releases entrained air, the bubbles that cure as pinholes across the surface. Spiked shoes let the installer cross the wet material without leaving trowel scars.

The fall is the part that needs control. Fast 330 finds its own level, so a flat kitchen can be poured flat. A designed fall toward a drain has to be formed with a pin gauge and a screed rail because the compound wants to settle level.

On a kitchen and utility layout, the professional fix is to set the flat porcelain field first on the drawings and mark the break line where the drain fall begins. The drain area is then pulled separately with the pin gauge and rail while the material is fresh, keeping the main kitchen plane flat and giving the utility its fall. The unresolved detail is the exact width of that formed transition, because it depends on the room layout, the drain position and the tile module.