Mortar staining on brick faces is one of the most frustrating problems in bricklaying — and one of the easiest to prevent if you get your technique and preparation right from the start. A combination of good work habits, the right mortar mix, and prompt cleaning will keep your finished brickwork looking sharp.
Why Mortar Stains Bricks
Mortar contains cement, which is highly alkaline and can bond to the porous surface of bricks if left to harden. Once mortar cures fully, removing it without damaging the brick face becomes difficult and sometimes impossible without acid washing — a messy, hazardous job you really want to avoid. Prevention is far easier than cure.
The main causes of staining are:
- Excess mortar squeezed onto the face during laying
- Mortar dropped from higher courses and smeared when wiped
- Using a mix that is too wet or too stiff
- Leaving mortar smears to dry before cleaning
- Rain washing fresh mortar slurry across the face
Get Your Mortar Mix Right
A mortar that is too wet (sloppy) will squeeze out excessively and run down the brick face. A mix that is too stiff is hard to work and can cause you to press harder, again pushing mortar onto the face. A good general-purpose bricklaying mortar for NZ conditions is typically a 1:1:6 mix (one part cement, one part lime, six parts sand) or a 1:5 mix (cement to sand with a plasticiser). The mix should hold its shape when squeezed but not crumble.
Always use clean, well-graded bricklaying sand — dirty or fine sand produces a weaker, stickier mortar that smears more readily. Check with your local supplier (such as PlaceMakers or Mitre 10) for the right sand grade for your region.
Laying Technique to Minimise Smearing
Good technique is the single biggest factor in keeping brick faces clean.
Apply Mortar Neatly
- Furrow the bed joint down the centre of the mortar bed rather than spreading it right to the face edge. This reduces squeeze-out onto the face when the brick is pressed down.
- Apply mortar to the end (header) of the brick before placing it, not to the course already laid — this gives you more control.
- Use a trowel size suited to your brick so you're not over-loading each joint.
Place Bricks Carefully
- Lower bricks into position rather than sliding them, which smears mortar forward onto the face.
- Use a firm, single downward press to seat the brick to your line — avoid rocking or shuffling.
- Cut off excess mortar from the joint immediately after placing each brick, before it starts to stiffen.
Keep Your Trowel Clean
- Wipe your trowel frequently on a damp rag or sponge. A mortar-caked trowel transfers smears to the brick face every time it touches it.
Protect the Brick Face During the Job
- Bag or cover completed sections with hessian or plastic sheeting at the end of each day to protect against rain washing mortar slurry down the face.
- If rain is forecast while mortar is still green (uncured), cover the work — rain on fresh mortar can carry cement slurry across large areas of brickwork.
- Keep a damp sponge or soft brush handy and wipe any smears off the face immediately — within minutes of them occurring, before any initial set takes place.
- Some bricklayers apply a proprietary brick release agent or masonry sealer to the face of bricks before laying. This creates a temporary barrier that makes mortar easier to remove. Ask your supplier about products suitable for your brick type.
Jointing at the Right Time
Tooling or raking joints at the correct time also reduces smearing. If you tool joints too early (mortar too soft), mortar smears onto the face. Too late, and the mortar crumbles and falls onto lower courses. The right time is when the mortar has stiffened enough to hold a thumb print without sticking — typically 30–60 minutes after laying, depending on temperature and humidity.
After jointing, use a dry, stiff-bristled brush to brush off any loose crumbs before they bond to the face.
Dealing With Smears That Do Occur
Despite best efforts, some smearing is almost inevitable. The golden rule: clean smears while they are still fresh.
| Stage | Cleaning Method |
|---|---|
| Wet/fresh (minutes old) | Damp sponge or soft cloth — wipe gently, don't smear further |
| Partially set (hours old) | Stiff dry brush to crumble off, then damp sponge |
| Fully cured (days old) | May require dilute hydrochloric (muriatic) acid wash — specialist job |
If you do need to acid wash, this is a hazardous task requiring full PPE and careful neutralising. Refer to WorkSafe NZ guidelines and consider engaging a professional cleaner or bricklayer.
NZ Climate Considerations
NZ's variable climate affects mortar behaviour. In hot, dry conditions (common in Canterbury and Hawke's Bay summers), mortar dries faster — keep bricks damp before laying to reduce suction, and work in smaller sections. In cold or wet conditions (common in Southland and Wellington winters), mortar takes longer to set and is more vulnerable to rain damage. BRANZ provides useful guidance on masonry construction in NZ conditions.
When to Call a Professional
If you're tackling a significant brickwork project — a new veneer wall, retaining wall, or structural masonry — it's worth engaging a qualified bricklayer. Structural brickwork may require a building consent under the NZ Building Code, and some work must be carried out or supervised by a Licensed Building Practitioner (LBP). Always check with your local council before starting. For large or complex jobs, or if you've ended up with heavy mortar staining that needs acid cleaning, a professional will have the right tools and experience to get the best result. You can find qualified local bricklayers on tradedirectory.co.nz.
Licensed Building Practitioner (LBP)
