Acid washing concrete, bricks and aluminium with a sprayer

Short answer: diluted acid needs an acid resistant sprayer. Acid attacks the seals, valves and nozzles in sprayers that aren't built for it. An alkaline sprayer with EPDM seals is the wrong choice too. The sprayer leaks, loses pressure and can drip acid where you don't want it.

This guide covers choosing the right sprayer and using it safely.

What acid washing is used for

Diluted acid products are used for:

Every product is different, so the label and safety data sheet (SDS) are your guide to strength, contact time and rinsing.

Choosing the sprayer

Use a sprayer sold as acid resistant. Acid resistant sprayers have seals and parts made for diluted acids, and some have an acid resistant trigger valve and nozzle as well.

Check the acid and the strength. Our acid resistant pump sprayer suits diluted acids, including hydrochloric acid up to 25%. Look at section 3 of the SDS to see which acid your product contains. If it's an acid we haven't listed, or you aren't sure, check with us before use.

Never use an alkaline sprayer for acid. Sprayers with EPDM seals are made for alkaline chemicals, not acids.

Keep it for acid only. Use one sprayer for acid and label it, so it never gets mixed up with your degreaser or other cleaners. Colour coding collars make this easy.

Fit the right seal kit. Acid and alkaline seal kits are different. Only fit the kit made for your acid sprayer model. Our guide to VITON, EPDM and NBR seals explains why.

Step by step

Always follow the product label. It overrides any general advice here.

  1. Read the label and SDS first. Check the mixing directions, contact time, rinsing and the protective gear it calls for.
  2. Protect what's nearby. Cover or wet down plants, metal, glass and painted surfaces close to the work area.
  3. Prepare the surface as the label directs. Many products say to wet the surface with water first.
  4. Mix exactly as the label directs, then fill the sprayer and pump it up.
  5. Test a small patch in an out of the way spot.
  6. Spray an even coat and work in small sections.
  7. Don't let it dry on the surface. Scrub if the label says to.
  8. Rinse well, and neutralise if the label says to.

Concrete and pavers

Acid products are used both to clean concrete and to prepare it before sealing. The label tells you which job a product is made for and how to use it. Work in small sections so the product doesn't dry before you rinse.

Bricks

Acid products are often used to clean mortar residue off new brickwork. Some bricks can stain, so check with the brick maker before you acid wash.

Aluminium brightener

Aluminium brightener is a diluted acid, so it needs an acid resistant sprayer. Check section 3 of the SDS. If it lists an acid we haven't covered here, check with us before use.

After the job

Release the pressure, rinse the sprayer with clean water and spray some through the nozzle. Store it empty and out of the sun. Replace the seals with the right kit when it starts to weep or lose pressure. Our guide on how to use and look after a pump up sprayer covers this.

Safety

Questions

Can I use a garden sprayer for acid wash?
Only if it's sold as acid resistant. Acid damages the seals and parts of sprayers that aren't built for it.

What sprayer do I need for brick acid?
An acid resistant sprayer. Check the SDS for the acid it contains. If it's hydrochloric acid, our acid resistant sprayer suits it up to 25%.

Can one sprayer do acid and degreaser?
No. Acids and petroleum solvents need different sprayers. Use one for each and label them. See our chemical guide.

How strong can the acid be?
Always mix to the strength on the label. Our acid resistant sprayer suits hydrochloric acid up to 25%. For anything else, check with us before use.