How to Install PHOMI MCM Tiles: A Step-by-Step Guide

PHOMI MCM flexible stone goes up faster and with far less weight than conventional tile or stone, but it is not forgiving of a rushed bond. Almost every complaint we see comes down to two things: air trapped behind the panel, or too much adhesive letting the panel slide. This guide gives the actual figures rather than general advice.

Tools you need

• Notched trowel, 4 mm notch
• Smooth trowel for the substrate coat
• Pressure roller, for bedding the panels. This is not optional
• Angle grinder with a diamond disc, or a sharp utility knife for thin panels
• Spirit level, tape measure, chalk line or string
• Joint spacers, grout bag or pointing gun, pointing iron, sealant gun
• Low speed mixer, clean buckets, sponge, soft brush, wide brush for wetting

Step 1: Prepare the substrate

The substrate must be flat, sound, clean and dry, with no hollow areas, loose material, dust, oil or efflorescence. Repair cracks and hollow spots with polymer cement mortar before any panel goes on.

• Concrete, render, brickwork: clean off dust and laitance, repair defects, prime if highly absorbent
• Existing tile, stone or mosaic: remove loose or damaged areas, fill, then apply an interface agent over the whole surface
• Painted surfaces: strip loose, flaking or powdery paint. Remove non water resistant filler completely
• Metal and aluminium composite: lightly abrade, then apply an interface agent
• Timber: interior can be bonded directly, exterior needs waterproofing first
• External insulation: panels bond to the reinforced base coat only, never to bare insulation

Step 2: Use a C2TE S1 adhesive

The manufacturer requires a C2TE S1 adhesive, classified to EN 12004 and EN 12002. Do not substitute a lower class. Every letter in that code is doing a job on this material:

• C2, cementitious with improved adhesion of at least 1,0 N/mm2. Carries the panel on a facade through freeze and thaw cycling
• T, reduced slip. Stops a large thin panel sliding down the wall before the adhesive grabs
• E, extended open time. Gives you time to place, adjust and roll the panel before the bed skins over
• S1, deformable, transverse deformation from 2,5 to under 5 mm. Absorbs differential movement between substrate and panel, which is what prevents edge lifting and cracked joints

Within that class, choose a low alkali formulation. Panel faces are mineral and porous, and a high alkali bed can push efflorescence and lime bloom through to the surface. Never bed panels on plain sand and cement mortar: only a classified, polymer modified adhesive is acceptable. Polymer cement mortar remains the correct material for repairing and levelling the substrate beforehand.

Bond test a small area of the real substrate first, especially over paint, metal or old tile. Mix mechanically with a low speed mixer, only as much as you can use within the pot life, and never retemper with extra water.

Step 3: Set out

Order 10 to 15 percent extra for cutting, breakage and colour selection, and use panels from one production batch on any one elevation, because shade varies between batches. Mark out the rows with a level and a string line, and start from openings and corners so cuts finish where they are least visible. With no pattern given by the designer, set out like brickwork with staggered joints.

Step 4: Bond the panels, and roll them

This is the step that decides whether the job lasts.

1. Dampen an absorbent substrate with water using a wide brush. Damp, not wet.
2. Apply adhesive with the smooth side of the trowel, then comb it through with the 4 mm notched trowel in continuous unbroken ribs. Only cover the area you can panel before the adhesive skins over.
3. Back butter the panel with a thin, even coat across the whole back.
4. Place the panel and move it back and forth across the ribs to collapse them, then press home.
5. Roll the panel with a pressure roller, working from the centre outwards. This expels trapped air and closes the voids between the ribs. Rolling is what turns combed adhesive into genuine full contact.
6. Check alignment with the level each row, and keep adhesive off the face. Clean any that lands there immediately, not later.

Why the roller matters. Too much adhesive makes the panel slide down the wall before it grabs. Too little pressure leaves air pockets behind it, which show up later as hollow spots, lifting edges and, outdoors, frost damage. The 4 mm notch plus the roller is the combination that avoids both.

Step 5: Joints and corners

• Jointed laying outdoors: 5 to 8 mm
• Close jointed laying outdoors: about 1 mm, never fully butted
• Interior flat panels: natural joint under 0,5 mm
• External corners: 45 degree chamfer on both panels, or a purpose made corner element
• Internal corners: butt and seal with matching caulk
• Junction with window and door frames: polymer based sealant, never cement grout
• Never bridge a structural movement joint with panels. Carry the joint through the finish

Step 6: Cut to fit

An angle grinder with a diamond disc gives the cleanest edge and is what we recommend. A sharp utility knife works on thinner panels. Cut face up and support the panel so it cannot flex at the cut line.

Step 7: Joint the work, with the right material in the right place

Two different materials, in two different places, and they are not interchangeable.

Across the wall, cement based jointing mortar. Use a cement based jointing mortar between the panels, in a class suited to the exposure. Do not joint a facade with an interior decorative filler, and do not leave joints unfilled outdoors.

Around openings, polymer based sealant. At every junction with a window or door frame, a sill, a flashing or any other dissimilar material, use a polymer based sealant, not grout. These joints move, because the frame and the facade expand at different rates. A cement mortar there will crack within the first season and let water in behind the finish.

Working the cement joints:

• Rake and clean the joints to an even depth before filling. Uneven depth dries unevenly and leaves patchy colour
• Dampen the joints first, but no standing water at the moment of filling
• Fill with a grout bag or pointing gun. For semi dry grouts, two passes wet on wet, then compact with a pointing iron
• Dress the joint, let it go off briefly, then brush clean with a soft brush
• Keep water dosing, joint depth and joint width identical across the elevation, and use grout from one batch. Do a test area and approve the colour before committing

Step 8: Curing and protection

• Joint only once the adhesive has set. Follow the adhesive data sheet. On a cement based system over external insulation, allow up to 7 days at 20 degrees C
• Protect finished outdoor work from rain for at least 48 hours
• Protect fresh joints from rapid drying, direct sun and strong wind for at least 5 days
• No traffic on floors until adhesive and grout are fully cured

Weather and temperature limits

• Substrate and air between 5 and 40 degrees C during installation and for 24 hours afterwards
• No work in rain or snow, or on a surface still wet from rain
• No work above 90 percent relative humidity
• No work in wind above force 5, roughly 10 m per second
• Avoid direct sun on the working face above about 27 degrees C in the shade, and screen the scaffold

Storage and aftercare

Store flat, dry and under cover, out of direct sun, and never stand pallets on edge. Carry panels flat: they are flexible, but a sharp fold marks the face permanently. Clean finished surfaces with water and a soft brush or sponge, never with aggressive solvents or acids, and remove adhesive or grout residue while it is still fresh.

These figures are general guidance for MCM flexible stone. Where the project specification or the data sheet of the adhesive, grout and sealant you are using says something different, that document takes precedence.

Need the full installation guide as a PDF, or advice on a specific substrate? Get in touch and we will send it. Ready to order? Browse the full range of PHOMI MCM tiles.