Poultice
A poultice is a paste-like cleaning compound applied to a porous surface — natural stone, unsealed concrete, brick, limestone — to draw a stain out of the pores through capillary action. The paste is spread roughly a quarter-inch thick over the stain, covered with plastic, and left to dwell for 24-48 hours. As the poultice slowly dries, it pulls the dissolved stain out of the substrate into itself, where it can be scraped off and discarded.
In depth
Poultices are the only effective method for removing deep-set oil, grease, wine, rust, and organic stains from travertine, limestone, granite countertops, unsealed bluestone, and similar porous materials that would be destroyed by aggressive scrubbing or acid. The base (usually diatomaceous earth or a specialty clay) is blended with a solvent or chemistry matched to the stain — hydrogen peroxide for organics, mineral spirits for oil, acid chelators for rust. Patience and matching the chemistry to the stain are everything.
How this shows up on our jobs
For deep-set oil stains on limestone steps or high-end travertine patios in Madison-area homes, we mix a poultice on-site and return the next day to remove it.
Services where this matters
Related terms
Efflorescence
Efflorescence is the white, chalky, powdery deposit that forms on the surface of brick, concrete, stone, stucco, and block masonry when water dissolves mineral salts inside the material and carries them to the surface. As the water evaporates, the salts are left behind as a crystalline residue. It is cosmetic — not structural — but it is frustratingly persistent because every rain cycle can push more salts to the surface.
Chelating Agent
A chelating agent is a chemical that grabs onto metal ions — calcium, iron, copper, magnesium — and holds them in solution so they can be rinsed away instead of bonding to a surface. The word comes from the Greek chele ("claw") because the molecule literally clamps onto the metal ion like a lobster claw. Common chelators include EDTA, oxalic acid, and citric acid.
Organic vs. Inorganic Stain
Organic stains are caused by living or once-living things: algae, mold, mildew, lichen, tannins from leaves, berry drip, insect excretion, pet urine, and so on. They contain carbon and respond to oxidizing chemistry — sodium hypochlorite or hydrogen peroxide (percarbonate) — which breaks the carbon bonds and destroys the stain at the molecular level. Inorganic stains are mineral-based: rust, hard-water deposits, efflorescence, metallic irrigation over-spray, fertilizer streaks, and the like. They contain no carbon and will not respond to bleach at all — you need an acid or a chelating agent to dissolve the metal or mineral and carry it away.
Dwell Time
Dwell time is the interval between applying a cleaning chemistry to a surface and rinsing it off. It is the single most misunderstood variable in exterior cleaning. Chemistry does not clean instantly; it needs time to break chemical bonds, kill organisms, or dissolve minerals. Too little dwell and the chemistry is wasted. Too much dwell — especially in direct sun — and the chemistry can damage the surface, bleach landscaping, or drive the stain deeper.
Polymer Sealer
A polymer sealer is a protective coating applied to a cleaned and dried surface — glass, concrete, wood, metal, brick — that forms a long-molecule chain on the surface to repel water, dirt, and staining. In window cleaning, glass-specific polymer sealers (often silicon-dioxide based, sometimes called "glass coats" or "hydrophobic treatments") cause rain to bead and sheet off, which keeps windows cleaner 2-3x longer between professional cleanings. On concrete, acrylic or urethane sealers protect against oil, rust, and de-icing salt.