Sealers, coatings and the Australian UV problem

A sealer is asked to do too many jobs in Australian concrete: keep the wine out, keep the oil out, keep the colour in, make the slab look wet on a Tuesday, and survive a ultraviolet climate that eats thinner polymers for breakfast. Some of those jobs are compatible. Many are not. The honest conversation is about classes of chemistry and about which surface you are actually trying to protect — a kitchen, a polished house floor, a west-facing driveway — not about a miracle in a drum.

This journal names families, not products. If a contractor will only talk in catalogue titles, ask them which family they mean.

Penetrating versus film-forming

The first fork in the road is simple.

A penetrating sealer is carried into the pore structure. Silanes, siloxanes and some silicate or siliconate treatments live here. They reduce water uptake and, to varying degrees, staining. They do not build a plastic skin. The concrete still looks like itself: dry when it is dry, darker when it is raining. Wear is slower to see because there is no gloss to lose. Recoating, when it happens, is a refresh of a treatment, not a strip-and-start.

A film-forming sealer sits on the face. Acrylics, polyurethanes, epoxies and various hybrids live here. They can deepen colour, add sheen, and act as a sacrificial layer against acid and tyre marks. They can also peel, whiten, scratch and chalk. You have added a coating. The maintenance is now coating maintenance.

Neither family is virtuous. A penetrating sealer on a thirsty, poorly cured decorative slab will not invent density. A film on a slab that is still damp, or that was finished with a curing compound nobody named, will not invent adhesion. Curing is not a sealer. Confusing the two is how a Sunday compound becomes a Monday bond-breaker.

Wet-look is a lighting effect, not a durability upgrade. If you need the slab to look wet to look finished, the mix or the finish may not have been what you wanted.

Classes, not brands

Acrylic, silane, polyurethane, epoxy

Acrylics are common on Australian driveways and stamped work because they are familiar, relatively cheap, and they deliver the darkening people were shown on a sample. In our ultraviolet light they are also the class most likely to chalk — a dry, pale dusting as the binder gives up — and to wear to a patchy map in wheel paths. Recoating is possible if the old film is sound and clean. It is miserable if the film is peeling.

Silanes and siloxanes are penetrating water-repellents used on facades, some pavements and masonry. They generally leave appearance closer to untreated concrete. They are poor at “enriching” colour, which is a disappointment only if enrichment was the brief. They are a better brief for a wall you want to keep looking like a wall.

Polyurethanes — aliphatic ones, when ultraviolet stability matters — build a tougher film than a basic acrylic. They are used on interiors, on some furniture, and on outdoor work when someone is prepared to pay for a coating and to recoat it as a coating. They can yellow if the chemistry is wrong for the sun. They can look like a plastic tablecloth if the gloss is high and the slab is large.

Epoxies are interior animals. They amber in sunlight. They are coatings for garages and some commercial floors, not for a north terrace. If an outdoor decorative slab has an epoxy story, ask why.

Silicates and densifiers sit in a neighbouring conversation, especially on polished floors. They react with the paste and harden the skin. They are not stain-proofers on their own, and they are not a substitute for a later guard or a change in household habits.

Hybrids exist and multiply the number of drums. The question remains: does it penetrate, or does it film? What happens to that film after two summers?

The Australian ultraviolet problem

Ultraviolet light here is not a footnote to a European data sheet. A north or west driveway, a roof terrace in Brisbane, a pale pool surround in Perth — these are outdoor laboratories. Binders that survive a mild temperate year will chalk, fade and embrittle faster when the dose is higher and the slab temperature is higher.

Chalking is the polite word for the binder turning to dust. You see it as a light, dry film on the hand, and as a colour that has gone from “wet stone” to “tired pavement”. The aggregate starts to read more. People then apply another coat, often a different coat, and trap dust in a new film. The driveway becomes archaeology.

Colour fade is a mix problem as much as a sealer problem. Oxide in the paste is more stable than a tint in a thin acrylic. If the colour you bought lives only in the sealer, the sun will take it back. Specify colour in the mix. Use the sealer to protect, not to paint.

Heat works with the light. A dark sealed slab can be hot enough to soften a soft film and to take the imprint of a car mat. That is not mysterious chemistry. It is a black object in an Australian afternoon.

Wet-look disappointment

Many decorative jobs are sold on a photograph of a freshly sealed, darkened slab. The client then lives with two disappointments: the slab dries to a lesser colour, and the sheen wears first where they walk.

The useful preview is a sample that has been sealed, left in the weather, and walked on. Compare it wet, dry, and three weeks later. If you still want the wet look, budget for recoating as you would budget for painting a deck. If you do not want that hobby, choose a penetrating treatment and a mix whose dry colour you can like.

Interiors are a different disappointment. A high-gloss film on a living-room slab will show every swirl of the applicator and every scratch from grit. A satin or a penetrating guard on a honed or polished interior floor is usually the more adult choice. Kitchens add acid. A film that is a sacrificial layer against lemon is defensible if someone will refresh it. A film that was sold as permanent is a story.

Recoating, interiors and driveways

Recoating is the test of whether the first sealer was a system.

On a driveway:

• Wash, degrease, and remove loose film before you add more
• Do not pile a new family of chemistry on an old one without a trial
• Expect wheel paths and the letterbox walk to need more care than the edges
• Accept that a penetrating refresh looks like almost nothing, and a film refresh looks like a paint day

On an interior floor, the grit is incoming sand, not only ultraviolet light. Mats, a vacuum that does not grind grit across the room, and a guard that can be maintained without closing the house for a week — these are the specification. A garage epoxy and a living-room densified floor are not the same maintenance leaflet.

Furniture and benchtops sit closer to joinery. They take oils and acids in small, intense doses. Recoating a table is a workshop job. Recoating a driveway is a weather window. Do not let one conversation borrow the other’s promises.

When a sealer fails badly — peeling in sheets, whitening in a bloom, a slippery wet film — the repair may be mechanical. Grinding back to a face you trust is kinder than another drum. That is already a repair essay. The sealer lesson is earlier: choose a class that can fail in a way you can live with.

A sealer specification that this journal respects names the family, the sheen, the interior or exterior duty, the compatibility with the curing compound, and the recoat interval in Australian sun. It does not name a feeling. The slab will provide the feeling, whether you asked it to or not.