Controlled chemistry

Acid Washing

Acid washing is the standard method for removing cured mortar and cement film from masonry. It is also the fastest way to permanently ruin a wall. The difference is entirely in the preparation.

Think Brick accredited
Fully insured
20+ years experience

Think Brick accredited

Fully insured

20+ years experience

Illawarra to the Highlands

Quick answer

What is acid washing on brickwork?

Acid washing is the application of diluted hydrochloric acid to masonry to dissolve cured mortar smear, cement film and lime deposits. The brick must be saturated with water first so the acid reacts on the surface rather than soaking into the unit, and the wall must be neutralised and rinsed immediately afterwards. Typical working dilutions range from 1:10 to 1:20 depending on brick type and mortar hardness.

At a glance

Active chemistry: Diluted hydrochloric acid
Never use on: Vanadium or manganese-affected brick
Critical step: Full saturation before application
Finish step: Neutralise, then rinse to clear runoff

What acid actually does

Hydrochloric acid reacts with the calcium compounds in Portland cement and lime, breaking the bond between the dried mortar film and the brick face so it can be rinsed away. It is doing chemical work, not mechanical work, which is why pressure is a secondary tool on this job rather than the main one.

That same reaction does not stop at the mortar smear. It will attack the mortar in the joints, the surface of susceptible bricks, aluminium window frames, colorbond, glass, galvanised fixings and anything growing in the garden bed below. Control of where the acid goes and how long it stays there is most of the skill.

When acid is the wrong answer

Plenty of masonry should never see acid, and knowing which is the difference between an accredited cleaner and a bloke with a drum of hydrochloric.

Cream, white and light bricks that may carry vanadium salts — acid converts a removable yellow-green stain into a fixed brown one.
Dark and charcoal bricks coloured with manganese — acid draws the manganese out and streaks it down the wall.
Heritage and hand-made brick with soft lime mortar, where acid erodes the joint faster than it cleans the face.
Certain glazed, engobed and through-coloured ranges where the manufacturer explicitly voids warranty on acid contact.
Sandstone, which reacts badly and can develop iron staining and surface friability.

Concrete and blockwork

Acid washing is also used to etch and clean concrete — removing surface laitance before a coating goes down, lifting cement splatter from a new slab, and opening up the profile of a driveway. Blockwork and besser walls clean the same way as brick but usually need a stronger mechanical component because of the open texture.

Coverage

Where we do acid washing

Illawarra

Wollongong · Shellharbour · Albion Park · Dapto · Kiama · Shell Cove

Shoalhaven

Nowra · Bomaderry · Vincentia · Huskisson · Berry · Culburra Beach · Ulladulla

Southern Highlands

Bowral · Mittagong · Moss Vale · Bundanoon

Sutherland Shire

Helensburgh · Engadine · Sutherland · Cronulla

Based at Warilla. Everything from Helensburgh to Ulladulla and inland to the Southern Highlands is inside our normal working area.

FAQ

Acid Washing — questions we get asked

How strong should the acid be for brick cleaning?

There is no single correct strength. Working dilutions generally sit between 1:10 and 1:20 hydrochloric acid to water, set by the brick type, how hard the mortar has cured and the temperature on the day. Stronger is not faster — it is just more likely to burn.

Why do bricks need to be wet before acid washing?

Dry brick is porous and pulls acid deep into the body of the unit where rinsing cannot reach it. That trapped acid keeps reacting, drawing salts to the surface and causing burn and efflorescence for weeks afterwards. A saturated brick has no capacity to absorb, so the acid stays on the face and rinses off cleanly.

Is acid washing safe around plants and pets?

With the right precautions, yes. Garden beds are soaked before and after so runoff is diluted, plants near the wall are covered, and drainage is directed away from sensitive areas. We ask that pets stay inside while we are on site and until the final rinse is done.

Can I acid wash bricks myself?

You can buy the chemical, which is exactly the problem. The failures we get called to repair are almost all DIY or unaccredited jobs where the wall was not pre-soaked, the mix was too strong, or the acid was used on brick that should never have been acid washed. Remediation costs far more than the original clean.

Keep reading

Need acid washing quoted?

Call 0448 882 780 or send photos through the quote form. We will tell you what the job needs and what it will cost, including when the honest answer is that you do not need us.

0448 882 780 Free quote