0.4mm Grout Haze Removed from Polished Porcelain with a Fila Deterdek Wash

What the grey film is

Grout haze on polished porcelain is a thin cementitious deposit, usually around 0.2mm to 0.5mm, left as grout water rises through the joint and evaporates across the tile face. The remaining calcium and silica do not behave like loose dust. They key into the micro-porosity of the fired glaze, so dry buffing only polishes the film and moves the loose residue around.

Matte and textured tiles hide the same deposit more easily. A polished 60x60cm slab under raking light does the opposite: the whole floor takes on a grey bloom, especially where downlights or low winter light skim the surface. With grey cementitious grout, the colour of the haze can look like a wash intentionally spread over every tile.

Fila Deterdek is the product many European tile fixers use for this job. The formula is a buffered descaler based on phosphoric and other organic acids; hydrochloric acid is absent. Builders-merchant muriatic acid at full strength can attack coloured grout pigment and burn a polished face, while Deterdek at 1:5 in cold water dissolves cement residue on fully vitrified porcelain and leaves the tile body untouched. The buffering also makes indoor use possible without a respirator on your face, provided the room is ventilated.

Washing with Deterdek

Start with clean water on the floor before the acid mix goes down. A cementitious joint that is only 48 hours old is still thirsty. If concentrated acid is allowed to soak into that dry line, it can weaken the grout core and leave a soft, crumbling joint months later.

Pre-wetting changes the way the wash behaves. The joint fills with plain water first, so the diluted descaler stays mainly on the surface film. The work then happens where the haze sits, across the tile face and the upper edge of the joint.

For a normal polished porcelain haze, mix one litre of Deterdek with five litres of cold water. A floor that has sat for a fortnight with a heavier cement deposit can justify 1:3 on fully vitrified porcelain. Marble, Carrara-look natural stone, and any acid-sensitive stone are outside that stronger wash because acid damages the surface.

Spread the solution with a stiff nylon brush or a single-disc machine fitted with a white pad. Give it three to five minutes of dwell time. A faint fizz is normal as carbonate residue reacts, but the liquid must stay wet during that dwell.

Agitate the surface before extraction. The machine pad or brush loosens the softened mineral film, and a wet vacuum removes the suspended residue before it settles back into the pores. Leaving the slurry on the floor turns a cleaning step into another deposit.

Rinse twice with clean water. The rinse is functional, since acid salts left behind can dry into a fresh film and make the floor look hazy again. On a 20 square metre kitchen floor, the wash, extraction, and two rinses usually take about 90 minutes.

Marble is outside the method

The same acid that removes cement haze from vitrified porcelain will attack marble and Carrara-look natural stone. A label that says porcelain still deserves checking if the surface imitates stone closely enough to make the material uncertain.

What an anhydrite screed changes

Anhydrite screeds are calcium-sulfate based and are common under new-build wet rooms and heated floors in Germany, France, and the UK. They cannot be tiled onto raw. The laitance on the surface has to be sanded back, then the slab has to be sealed with an anhydrite screed primer such as Mapei Primer G or Ardex P51 before adhesive is applied.

Without that primer, gypsum in the screed reacts with moisture and cement in the tile adhesive. The reaction forms ettringite, a crystalline compound that expands and lifts the tile. A floor with that weakness cannot be cleaned aggressively, even if the polished porcelain surface itself would tolerate the descaler.

Acid wash water can travel through grout joints. On an unprimed anhydrite screed, it can reach the unstable gypsum-cement interface and speed up debonding that already began under the tile. The visible haze may be removable, but the safe amount of agitation and water is limited by the condition of the layer below.

Schluter Ditra Heat adds another variable. It is a polyethylene uncoupling membrane with a studded profile that isolates the tile from substrate movement and holds heating cable in the channels between studs. If that embedded heating was run warm during grouting, the grout cures faster and drives more mineral residue to the surface, so haze on a Ditra Heat installation can be heavier than on an unheated slab.

The membrane also changes rinsing. Flooding the floor during an acid wash can leave water in the studded void and in the air space that lets the tile move independently. A standard mortar bed can slowly release wash water, while alkaline moisture trapped around the membrane may push salts back through the joints for weeks. Use a wet vacuum for the two dry rinses; a mop leaves too much water behind.

Lippage, clips, cut edges, and dust

Tile levelling clips such as Raimondi systems or RLS wedge-and-clip systems hold adjacent tiles in one plane as the adhesive cures. On large-format slabs of 60cm and up, lippage of even 1mm casts a visible shadow line. That small step also catches grout film where a pad cannot make flat contact.

A good clip installation leaves a continuous polished plane, so the acid wash can remove the haze in one even pass. Failed clips, poor tightening, or setting by eye alone leave micro-steps along the joints. Residue then gathers at the low side of each joint, and those lines often need hand-detailing with a nylon pad and Deterdek on a cloth, because the machine rides over the lower tile while the film remains in the shadow of the higher edge.

Cutting introduces another hiding place. A 120x60cm porcelain slab cut with a rail-guided scoring tool such as a Montolit, or with a wet bridge saw, has a raw fired edge that is more porous than the polished face. After grouting, that edge holds mineral residue more tightly than the top surface and is often where haze reappears after a poor rinse.

Dry-cutting with a diamond blade leaves very fine porcelain dust. If that dust settles into a wet grout joint before curing, it becomes part of the film that later has to be removed. The reliable sequence is cut, vacuum every cut edge and the tile face, then grout. Fixers who grout over cutting dust can wash three times and still see a bloom under LED downlights.

Epoxy residue and films that return

Epoxy grout haze does not respond to Deterdek. Phosphoric acid dissolves cementitious residue, while cured two-part epoxy such as Mapei Kerapoxy needs a dedicated epoxy grout haze remover within the first 24 to 36 hours, before the resin fully hardens.

Clean removal at 1:5 is a useful clue that the grout was cementitious and the porcelain was genuinely vitrified. Streaking, resistance, or a bloom that returns after rinsing can come from an unsealed substrate or from a polished face that is less impervious than its label claimed. On some floors, the visible film is easier to identify than the condition of the adhesive and screed interface.