Your bricks might get all the attention, but the mortar holding them together decides whether the wall lasts. Get the mix wrong and you end up with joints you can scrape out with a key, stains bleeding through the face of the bricks, or cracks that never stop growing.
You won't be mixing it yourself, but you can check your bricklayer is. Here's what you need to know.
C11 - Enclosed Stage Inspection Checklist
$119.00 AUD
Last updated 28 Oct 2026 · Revision 6 · Free updates for life
Checklist Type: Major (Enclosed Stage)
Form Factor: Fillable, print-ready PDF (A4, 42 pages)
When to use: Enclosed (lock-up) stage: brickwork and external cladding
A 152-point enclosed stage checklist for brick veneer and fibre cement, weatherboard or foam cladding. Check the cavity, ties, flashings, windows and lintels before the linings hide them.
What mortar does
Mortar is the glue and the cushion between bricks. It bonds the units together, takes up small differences in brick size, seals the joints against weather and lets the wall move a little without cracking the bricks themselves.
It's made of four things:
- Cement, the binder that gives strength.
- Lime, which makes the mix workable, holds water so it cures properly, and keeps the mortar a little flexible.
- Sand, the bulk of the mix. Bricklayers use a fine, clean "brickies' sand".
- Water, added gradually until the mix is soft enough to spread but stands up on the trowel.
The right mix for most homes
Australian masonry is designed under AS 3700 and the NCC Housing Provisions. For most brick veneer homes the standard is M3 mortar: 1 part cement, 1 part lime, 6 parts sand by volume.
Close to the coast it's a different story. M3 is generally fine more than about 1 km from a surf coast or 100 m from a river or estuary. Inside those distances, salt attack is a real risk and a stronger, denser M4 mortar is normally required, typically 1 part cement, half a part lime and 4.5 parts sand, along with exposure-grade bricks and more corrosion-resistant wall ties. If you're building near the water, check that your plans or engineer's notes actually specify M4 and that's what turns up on site.
Why the ratio matters
The balance between ingredients is where things go wrong:
- Too much sand makes weak, crumbly joints that wear out of the wall.
- Too much cement makes a hard, rigid mortar that cracks instead of moving with the bricks. Mortar should be weaker than the bricks, so if anything cracks it's the joint, which is easy to repair.
- No lime makes the mix harsh, hard to work and quick to dry out, which weakens the bond.
- Too much water on site washes out strength and stains the brick face.
A straight 3 sand to 1 cement mix, which you'll still see recommended online, is too strong and stiff for normal brickwork. Stick with the specified class.
Additives: what's fine and what isn't
Proper mortar plasticisers are made for the job and help workability. Bottled lime-replacement products should only be used as the manufacturer directs.
Two things should not be going into your mortar:
- Dishwashing detergent. It's a common site shortcut to make the mix "fatter", but it puts too much air into the mortar and weakens it. If you see a detergent bottle next to the mixer, ask questions.
- Calcium chloride accelerators. They speed up setting but corrode wall ties and steel in the wall. They have no place in house brickwork.
What to check on site
You don't need to be a bricklayer to spot most mortar problems. When the brickwork goes up, look for:
- Lime bags on site, or a proper mortar additive, not just cement and sand.
- A consistent colour across the walls. Patchy colour usually means the batches weren't measured the same way.
- Firm joints once cured. If you can rub mortar out with your thumb or scrape it easily with a key, it's weak.
- Joints properly filled and ironed, with no gaps or holes, especially around windows and at the base of the wall.
- Mortar smears and stains cleaned off the face of the bricks.
- White powdery deposits (efflorescence) appearing soon after laying, which can point to too much water or salts in the mix or bricks.
Our C11 Enclosed Stage checklist covers brickwork and mortar checks step by step, so you can walk the site with something in your hand rather than relying on memory.
Further reading
These two guides go into much more detail on mortar mixes if you want the technical side.
The bottom line
For most homes, the answer is simple: M3, 1:1:6, measured properly, with real lime and no detergent. Near the coast, expect M4. Ask your builder what's specified, then check what's actually being mixed. It's a cheap question that can save you a very expensive wall.
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