Old bricks carry decades of character, but that same weathering makes them easier to damage with the wrong cleaning method. Acid, high-pressure water and metal brushes can all strip the patina that makes reclaimed brick worth using in the first place and in some cases weaken the brick itself. This guide covers how to clean old bricks safely for a modern build, what to avoid, and when a repair (rather than a clean) is what’s actually needed.
Before You Start: Inspect, Don’t Just Scrub
Not every old brick is worth cleaning. Sort your stock before you start:
- Hairline cracks — generally fine to clean and reuse.
- Deep splits or spalling (surface flaking) — these need repair, not cleaning. See our guide to fixing crumbling or damaged bricks if this applies to your stock.
- Heavy mortar residue — normal on reclaimed brick and safely removable; see the method below.
How to Clean Old Bricks Safely
1. Dry brush first
Remove loose dust, dirt and mortar fragments with a stiff-bristled (not wire or metal) brush before introducing any water. This alone often lifts a surprising amount of surface grime.
2. Chip off mortar with a chisel, not a grinder
For thicker mortar residue, use a cold chisel and gently tap from the edges of the residue toward the centre. Wetting stubborn mortar for a few minutes softens it before chiselling. Avoid angle grinders on reclaimed brick — they cut into the brick face as easily as the mortar.
3. Wash with water and a mild, pH-neutral detergent
A soft-bristle brush with water and mild detergent is enough for most reclaimed brick. Work in small sections and rinse thoroughly so no soap residue remains, which can cause efflorescence (white salt staining) later.
4. Dry fully before laying or sealing
Let bricks air-dry for a day or two in a well-ventilated area before use. Laying or sealing damp bricks can trap moisture and lead to efflorescence or mortar bond issues.
What to Avoid
- Acid cleaners — acid washing can etch the brick surface and strip the natural patina, and isn’t reversible.
- High-pressure water — reclaimed and heritage brick is softer than modern brick and can be eroded or have mortar joints damaged by pressure levels safe for new masonry.
- Metal brushes, grit blasting or power tools — these remove the surface texture along with the dirt.
This aligns with Heritage NSW’s standard exemption conditions for cleaning heritage items, which cap water pressure at 500 kPa (72 psi) and require pH-neutral detergents for any significant masonry fabric — a useful benchmark even if your project isn’t heritage-listed. South Australia’s heritage guidance on early brickwork goes further, recommending against metal brushes, abrasives or power tools on any brick masonry, not just listed buildings.
Cleaning Heritage and Sandstock Bricks
Sandstock bricks are softer and more fragile than machine-made brick, so the gentlest method that works is the right one start with dry brushing and plain water before reaching for detergent. If you’re restoring a heritage-listed property, check whether routine cleaning falls under a standard exemption or needs approval before you start; our sandstock brick guide covers grading and heritage matching in more detail.
When to Call a Professional Instead
If cleaning reveals structural cracks, spalling, or bricks that crumble under light pressure, the issue is repair, not cleaning. Our step-by-step guide to fixing crumbling or damaged bricks covers diagnosis and repair, including when to bring in our brick matching service for an exact colour and texture match. For load-bearing work such as a retaining wall, always confirm structural suitability before reusing cleaned brick.
Frequently Asked Questions
Does cleaning weaken old bricks?
Gentle methods (dry brushing, low-pressure water, mild detergent) don’t weaken sound brick. Acid, high pressure and abrasive tools can, which is why they’re avoided regardless of the brick’s age.
Can I acid wash reclaimed bricks?
It’s not recommended. Acid can strip the patina that gives reclaimed brick its character and etch the surface permanently. Stick to water-based, pH-neutral cleaning methods.
How long should bricks dry before I use them?
Allow one to two days in a well-ventilated area, longer in humid conditions. Laying or sealing damp brick risks trapped moisture and efflorescence.
Sourcing Pre-Cleaned Bricks
If you’d rather skip the cleaning process altogether, The Brick Pit supplies bricks that are already cleaned, sorted and graded. Browse our full range of recycled brick products or get in touch if you’d like advice on your specific batch.
