Outdoor tiles cover everything from a porcelain alfresco floor to a sandstone-look travertine pool surround, and the right cleaning method depends entirely on which you have.
Get it wrong on natural stone and the damage is permanent.
Identify the tile first
Porcelain — dense, usually a consistent colour through the body, water does not soak in. Very durable and chemically tolerant. Most modern alfresco tiling.
Natural stone — travertine, limestone, sandstone, bluestone. Variable markings between pieces, water darkens it. Acid sensitive if it is carbonate stone, which travertine, limestone and marble all are.
Glazed ceramic — glossy surface, lighter body visible at a chipped edge.
Terracotta or quarry tile — porous, earthy, usually sealed.
Quick test: put a drop of water on an inconspicuous spot. If it darkens the tile, it is porous. If it beads, it is dense or sealed.
Porcelain and glazed ceramic
The easy case. Warm water with a mild alkaline detergent, a brush, rinse. Mould and algae come off with dilute hypochlorite.
Tolerates moderate pressure well. The limit is the grout, not the tile — pressure cuts grout out of the joints.
Stubborn mineral deposits on porcelain will take a mild acid without harm to the tile, but keep it off any adjacent natural stone and off the grout, which it will erode.
Natural stone
No acid. Not vinegar, not lemon, not tile and grout cleaner, not pool acid, not hydrochloric brick cleaner. On carbonate stone each of those etches the surface permanently.
Use pH-neutral stone cleaner for routine work, mildly alkaline degreaser for oil and sunscreen, dilute hypochlorite for growth.
Low pressure only. High pressure erodes the softer bands and opens the surface so it absorbs more and re-soils faster.
Detail by stone type: limestone, travertine, bluestone, sandstone.
The grout is usually the problem
Nine times out of ten the tiles are fine and the grout has gone dark.
Grout sits below the tile surface, so water and dirt collect in it, and cement grout is porous enough to hold both. Outdoors it also grows mould before the tile does.
Dilute hypochlorite and a narrow grout brush does most of it. An oxygen bleach paste left to dwell works on stubborn areas without the fume.
Avoid acid grout cleaners on cement grout — they dissolve it and you end up re-grouting. And keep any acid well away if the tiles are natural stone.
More in why the joints fail before the tile does.
Specific stains
Mould and algae on the shaded side. Hypochlorite, dwell, rinse. Prevention is light and airflow.
Oil and barbecue grease. Alkaline degreaser; a poultice for anything that has soaked into stone.
Rust from furniture feet. pH-neutral rust remover on stone, standard oxalic product on porcelain — here.
Efflorescence in the joints. Brush off dry. Recurring bloom means water beneath the tiles.
Hard water marks from sprinklers. Covered separately.
Tannin from leaf litter or an overhanging deck — pH-neutral tannin remover on stone.
Slip
An outdoor tile that has gone slippery is almost always carrying a biofilm, and killing it is what restores grip. Scrubbing the visible growth off leaves the film behind.
Relevant anywhere there are steps or a pool — slip resistance and who is liable.
Then sealing
Porcelain needs none; the grout may. Natural stone benefits from a breathable impregnator. The decision is in outdoor tile sealer: which type for which tile.
For a professional clean, see tile and grout cleaning.
