The Chemical Cheat Sheet: Exact Soft Wash Ratios by Material
The Math Behind the Mix
Before we dive into the exact percentages, you must understand what these numbers mean. When professionals talk about a "1% mix", they are referring to the final concentration of Sodium Hypochlorite (SH) hitting the wall - not the strength of the bleach in the bottle.
Commercial pressure washers buy SH in bulk at a strength of 12.5%. To get a 1% house wash mix, they must dilute that 12.5% SH with water at roughly a 10-to-1 ratio (often achieved automatically using a downstream injector or a proportioner manifold).
The Master Material Chart
Different materials hold onto roots and mold differently. Porous surfaces require stronger chemistry because the algae is embedded deep within the material, whereas smooth surfaces clean up quickly with weak mixtures.
Vinyl Siding & Painted Wood
Vinyl is smooth and non-porous. Mold grows exclusively on the surface, making it incredibly easy to kill. Anything stronger than 1.5% risks stripping the factory UV coating off the vinyl or oxidizing the paint on wood.
Stucco & Dryvit
Stucco acts like a sponge. Algae roots grow deep inside the thousands of tiny pockets. A stronger 3% mix ensures the chemical penetrates deeply to achieve a full root kill. High pressure will blow holes in Dryvit instantly.
Brick & Masonry
While the brick itself is hard, the mortar joints between them are incredibly delicate and prone to crumbling under pressure wands. A stronger SH mix protects the mortar by allowing for a gentle, low-pressure rinse.
Concrete Driveways
Up to 6% hot mix
Concrete is heavily textured. After spinning a surface cleaner, pros 'post-treat' the wet concrete with a 3-4% hot mix and leave it to bake in the sun. This bleaches out algae hiding in the physical valleys.
Asphalt Shingle & Tile Roofs
The black streaks on roofs are caused by Gloeocapsa Magma, a notoriously tough bacteria that feeds on limestone. This requires an incredibly 'hot' mix to eradicate entirely without dislodging the protective asphalt granules.
Material | Target SH % | Why? |
|---|---|---|
| Vinyl Siding & Painted Wood | 0.5% - 1.5% | Vinyl is smooth and non-porous. Mold grows exclusively on the surface, making it incredibly easy to kill. Anything stronger than 1.5% risks stripping the factory UV coating off the vinyl or oxidizing the paint on wood. |
| Stucco & Dryvit | 2.0% - 4.0% | Stucco acts like a sponge. Algae roots grow deep inside the thousands of tiny pockets. A stronger 3% mix ensures the chemical penetrates deeply to achieve a full root kill. High pressure will blow holes in Dryvit instantly. |
| Brick & Masonry | 2.0% - 4.0% | While the brick itself is hard, the mortar joints between them are incredibly delicate and prone to crumbling under pressure wands. A stronger SH mix protects the mortar by allowing for a gentle, low-pressure rinse. |
| Concrete Driveways | 3.0% - 4.0% Up to 6% hot mix | Concrete is heavily textured. After spinning a surface cleaner, pros 'post-treat' the wet concrete with a 3-4% hot mix and leave it to bake in the sun. This bleaches out algae hiding in the physical valleys. |
| Asphalt Shingle & Tile Roofs | 4.0% - 6.0% | The black streaks on roofs are caused by Gloeocapsa Magma, a notoriously tough bacteria that feeds on limestone. This requires an incredibly 'hot' mix to eradicate entirely without dislodging the protective asphalt granules. |
The "Never Wash" Warning List
Sodium Hypochlorite is an incredible oxidizer, but it is destructive if applied to the wrong materials. A true professional knows when not to spray.
- Unsealed Natural Wood (Decks & Fences): Never spray strong SH on a wood deck. It will bleach the wood fibers dull gray and destroy the lignin (the natural glue holding the wood together). Wood requires specialized cleaners (Sodium Percarbonate) and chemical brighteners (Oxalic Acid).
- Copper & Bronze Fixtures: High-end light fixtures or architectural accents made of unsealed copper or bronze will instantly flash-oxidize when hit with bleach, turning green/black and requiring intense metal polishing to fix. Always tape these off and cover them with plastic.
- Delicate Textiles: Patio furniture fabrics, awnings, and outdoor rugs should be moved away from the drop zone. Even a 1% overspray mist will permanently bleach spots into colored fabrics.
- Automotive Clear Coats: Never wash a house while cars are in the driveway. While weak SH might not strip the clear coat instantly, it can leave permanent chemical water-spotting on the glass and paint if it dries in the sun.
Precision chemistry separates the professionals from the novices. Always measure your mix, always pre-wet your landscaping, and always respect the power of the chemical.