Tile Sealer: Which Tiles Need It and Which Type to Buy

A tile sealer is a liquid that soaks into, or sits on top of, a porous tile so that water, oil and dirt cannot get into the body of the tile and stain it. The catch is that most tiles fitted in UK homes today do not need one at all, and putting sealer on a tile that cannot absorb it is the most common way people end up with a sticky, hazy floor. This page sets out which tiles need sealing, which of the four types of sealer to buy, how much you need, and how to fix a sealer job that has gone wrong.

It is written by the team at Bromley Tilers, who seal natural stone, terracotta and encaustic floors across Bromley and south east London. If you want the step-by-step for grout lines in a bathroom, see our separate page on how to seal grout and tiles.

Which tiles need a tile sealer?

The question to ask is not “what kind of tile is it?” but “will it drink water?”. A tile that absorbs liquid will also absorb tea, red wine, cooking oil and the pigment in coloured grout, and a sealer is what stops that.

Glazed ceramic wall and floor tiles: no. The glaze is the seal. Sealer cannot penetrate it and will only leave a film.
Glazed porcelain: no. Porcelain is classed under BS EN 14411 as having water absorption below 0.5%, and the glaze closes the surface completely.
Unglazed matt porcelain: usually not, but check the manufacturer’s sheet. Some cheaper through-body porcelains absorb more than the standard suggests.
Polished porcelain: often yes. Polishing opens microscopic pores in the surface, which is why polished porcelain can pick up grout stains and greasy footprints. Many are factory sealed, but that treatment wears off.
Natural stone (limestone, travertine, marble, slate, sandstone): yes, almost always, and often before grouting as well as after. Our page on sealing natural stone before grouting covers that sequence.
Terracotta and handmade clay tiles: yes. They are among the thirstiest tiles you can buy.
Quarry tiles: usually yes in kitchens and hallways, where grease and grit get trodden in.
Encaustic and cement tiles: yes, and they need it before grouting, because the pigment layer stains easily. See our encaustic tiles page.
Terrazzo: real cement or resin terrazzo, yes; terrazzo-effect porcelain, no.

Cement-based grout is porous whatever tile it sits between, so it is often worth sealing grout even where the tile itself needs nothing. Epoxy grout does not need sealing.

The water drop test

If you are not sure, test it. On a clean, dry tile (or an offcut), drip a few drops of water and watch for five minutes.

The drops stay beaded and the tile underneath does not change colour: the tile is not absorbent, so do not seal it.
The tile darkens slowly around the drops: low porosity. One or two coats of an impregnating sealer.
The water disappears within a minute or two: high porosity. Expect three or more coats, applied generously.

Repeat the test after sealing. When the water beads on a stone or terracotta tile that used to soak it up, the job is done. Repeat it again once a year to know when to reseal.

The four types of tile sealer

Walk into a tile shop and you will see a shelf of bottles with similar names. They fall into four groups.

Large grey natural stone floor slabs with fine joints — Grey natural stone floor slabs in the National Bank of Denmark, Copenhagen. Stone like this is usually protected with an impregnating sealer. | arne jacobsen, national bank, copenhagen, 1961-1978. by seier+seier (CC BY 2.0), via Flickr, https://www.flickr.com/photos/94852245@N00/2443176025

1. Impregnating (penetrating) sealer

This is the default for natural stone, terracotta and unglazed tiles. It soaks into the pores and lines them with a water and oil repellent, leaving nothing on the surface. The tile looks and feels the same and still lets moisture vapour out, which matters on ground floors and in showers. A typical example is LTP Mattstone, which the maker describes as a natural matt finish impregnating sealer for natural stone, unglazed porcelain, terracotta, quarry, brick and concrete.

2. Colour enhancing sealer

An impregnator with an added “wet look” effect. It deepens the colour of slate, limestone and riven stone so it looks as it does when damp, without leaving a gloss. It is a permanent change, so always try it on a spare tile first.

3. Surface (topical) sealer

These form a film on top of the tile, from a soft satin to a high gloss. They are traditional on terracotta and quarry floors and are sometimes used over an impregnator on rough, riven surfaces. The film wears in walkways and needs topping up, it can make some floors more slippery when wet, and it should never go on a tile that does not absorb, because it has nothing to grip.

4. Grout sealer

A lighter impregnator for cement grout lines, usually brushed on or sprayed from an aerosol. It keeps grout from turning grey in floors and from taking up mould spores in showers. It is not a substitute for a tile sealer on stone.

You will also see solvent-based and water-based versions of the same product. Solvent-based sealers tend to penetrate dense stone better, but they smell strongly, are flammable and need good ventilation. Water-based sealers are low odour and easier to use in a small bathroom. Either works if you follow the data sheet.

How much tile sealer do you need?

Coverage depends almost entirely on how porous the tile is, which is why the label gives a range. LTP’s data sheet for Mattstone gives roughly 1 to 2 litres per 10m² for lower porosity floors and 3 to 4 litres per 10m² for higher porosity floors. A honed limestone kitchen floor sits near the low end; reclaimed terracotta can go past the top.

Buy for the high end. Running out between coats means the last coat goes on a day later than the first, and patchy absorption shows up as patchy colour on enhancers.

How to apply a tile sealer

Make sure the floor is fully dry. A newly laid floor holds water in the adhesive and grout. Sealing too early traps it, which can show as white bloom later. Follow the grout maker’s minimum cure time before the final coat.
Clean it properly. Any grout residue, dust or old wax gets sealed in for good. Use a pH-neutral cleaner and let the floor dry again.
Check the temperature. Most sealers have a working window. The Mattstone data sheet says not under 5°C or over 25°C and not in direct sunlight, which rules out a cold garage floor in January and a conservatory floor at midday in July.
Apply thinly and evenly with a lint-free cloth, a soft brush or an applicator pad, working into the tile rather than flooding it.
Buff off the excess. This is the step people skip. The LTP sheet says to rub over the surface with a soft cloth after an hour; any impregnator left standing on the surface turns into a sticky film.
Wait between coats. At least two hours for Mattstone; check your product.
Keep it dry while it cures. The same data sheet says the floor dries in about two hours but needs a further three days to become fully resistant, and should not get wet in that time. Plan a bathroom floor around that.

When sealer goes wrong: haze, sticky patches and white bloom

Most callouts we get for “tile sealer problems” are one of three things.

A sticky or hazy film: too much impregnator, not buffed off, or sealer applied to a tile that could not absorb it (polished porcelain that was already factory sealed is a common culprit). It can often be lifted by re-wetting with the same sealer and buffing straight away, or with the manufacturer’s recommended remover. Do not reach for an acid cleaner on stone.
White patches under the sealer: moisture trapped by sealing too soon, or efflorescence (salts) coming up from a new screed. The cause has to dry out first; resealing over it locks it in.
Dark, blotchy colour: uneven coats of a colour enhancer. It evens out only with more coats of the same product, so test first.

How often should you reseal tiles?

There is no fixed interval, because it depends on traffic and cleaning. A shower wall in limestone may need a top-up coat every year or two; a hallway in terracotta every few years; a guest bathroom floor longer. The water drop test tells you: when water stops beading and starts darkening the tile, reseal. Harsh cleaners strip impregnators faster, so a pH-neutral stone cleaner extends the life of the seal. If you are planning a new stone or terracotta floor, the trade body The Tile Association lists member tilers who can advise on the right treatment for a particular tile.

Frequently asked questions

Do porcelain tiles need sealing?

Glazed porcelain does not, and sealer on it will only leave a smeary film. Polished porcelain often benefits from sealing because polishing opens tiny pores in the surface. Unglazed matt porcelain usually does not, but check the manufacturer’s guidance or do the water drop test.

Is tile sealer the same as tile sealant?

No. A tile sealer is a liquid that protects the tile and grout surface. A tile sealant is a flexible bead, usually silicone, that fills movement joints such as the line between a bath and the wall. Most bathrooms need sealant; only some need sealer.

Does sealing make tiles waterproof?

It makes them water repellent, so spills bead up and can be wiped away. It does not waterproof a shower or wet room. That job belongs to the tanking membrane under the tiles.

Can you seal tiles that are already laid and grouted?

Yes. Deep clean the floor, let it dry fully, then apply an impregnating sealer over tiles and grout together. On porous stone and encaustic tiles it is still better to seal before grouting as well, to stop grout pigment staining the surface.

Will a tile sealer make my floor slippery?

An impregnating sealer leaves nothing on the surface, so it should not change the grip of the tile. A gloss surface sealer can make a floor more slippery when wet. If grip matters, ask for an impregnator or a product sold as anti-slip, and see our page on whether porcelain tiles are slippery.

What is tile primer, and do I need it as well?

Primer is a different product altogether. It goes on the wall or floor before the adhesive, to stop a dusty or absorbent surface such as plaster or anhydrite screed sucking water out of the adhesive. It never goes on the face of a tile.

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contact@bromleytilers.co.uk