Concrete acid stains react with calcium compounds in cured concrete to create permanent, variegated colour. The result depends on the concrete, so exact uniformity cannot be guaranteed.

Prepare and Test

Concrete must be clean, absorbent and free from coatings, curing compounds, oil, wax and adhesive residue. Previously acid-washed or densified concrete may react poorly.

Apply water to several areas. Beading or slow penetration indicates contamination or inadequate preparation. Complete a representative test area to confirm absorption, reaction and final colour.

Apply the Stain

1. Use an acid-compatible pump sprayer to apply an even mist.
2. Wet the surface without excessive pooling. Typical coverage is 5–15 m²/L, depending on porosity and required colour.
3. Do not brush or roll because application marks may remain visible.
4. For blended colours, allow adjacent wet applications to flow together and soften their edges.
5. Let the concrete dry before deciding whether another application is required.

Why Is the Colour Uneven?

• Pale areas: dense, densified, acid-washed or low-calcium concrete.
• Dark lines: spray overlap or excessive local application.
• Rejected areas: oil, sealer, curing compound or contamination.
• Different repairs: repair materials vary in porosity and chemistry.
• Clouded colour: normal variation from the chemical reaction.

Clean and Protect

After the reaction, wash and mop with cold clean water to remove salts and residue. Fortis Concrete Acid Stain does not require a separate neutralising solution; this instruction may not apply to other acid stains. Allow the floor to dry fully before coating.

The dry colour may appear pale until protected. Use clear Coat 519 for stronger colour enhancement or Coat 526 for a water-based, lower-odour system.

Safety

Wear the PPE specified in the current safety data sheet, protect adjacent surfaces and use acid-resistant application equipment. Do not use metal spray components that may react with the stain.