Mastering Mortar Mixing: A Comprehensive Guide for Masonry Contractors

Mortar is an important building material used in masonry construction. Yet mixing it properly is an art that takes years of experience to master. Masons need the correct mortar mix for strong structures and good-looking jobs like garden paving or brick walls. This article explores mixing and provides tips for achieving optimal workability, bond strength and colour consistency. 

From lime putty to Portland cement ingredients, perfecting mortar mixing begins with understanding the fundamentals. Each component is important in proper mixing techniques and how weather and cure times impact the process. By breaking down the task of mixing, you will gain the knowledge to achieve long-lasting results.

What is the difference between mortar, concrete and cement?

Though they share some common ingredients, mortar, concrete and cement each serve unique purposes in masonry construction. 

Mortar

Mortar consists of cement, lime, sand, and water in varying ratios. It possesses weak strength and people use it to stick bricks, blocks, and stones together. Plus, it allows some flexibility of movement.

Concrete

Concrete contains cement, sand, aggregate rock and water. It possesses high compressive strength and people use it to construct projects like a reinforced slab, walls and foundations. 

Cement

Cement is the binding agent in both mortar and concrete. A fine powder that acts as glue when mixed with other materials and water. Portland cement is the most common type of cement. People use it to attach tiles to floors and plasterboard.

Different types of mortar mixes

For masonry mortar, one size does not fit all. Getting the mortar mix right for the specific job is key to achieving compressive strength, flexibility and water resistance. Here is an overview of 4 common mixed mortar types and their best uses.

Hand mixing vs machine mixing: Which is best?

You can mix mortar by hand or with a mechanical mixer. Both methods have pros and cons to consider when choosing tools and techniques.

Hand mixing

Advantages

Lower cost: You only need basic tools like a hoe, shovel, and mortar box or tub to lower the cost. This is a low-cost mixing method requiring minimal tools. 

Useful for small batches: Hand mixing works well when dealing with small project volumes that would not overload the mason. Batches for small DIY mortar repair jobs can be easily hand-mixed.

Easier to gauge water amounts: You can visually assess its consistency and adjust water amounts as needed during mixing.

Disadvantages

Very labour intensive: Hand mixing requires significant physical labour to blend ingredients. This can lead to fatigue over many batches.

Difficult for consistent mixes: Mixes by hand can vary in proportions, thoroughness, and moisture content, making consistency difficult. Achieving the ideal consistent mortar properties is challenging.

Not practical for large projects: Mixing mortar by hand for large-scale masonry projects is difficult and time-consuming, making it impractical. 

Machine mixing

Advantages

Fast mixing: Mechanical mixers can rapidly combine all ingredients into a smooth, homogenous mixture. Most types can produce a batch in just a few minutes.

Consistent batches: Machine mixing ensures each batch has the same proportions, mixing time and dispersion of ingredients. This helps with quality control.

Manageable for large volumes: Contractors can produce large amounts of consistently mixed mortar needed for substantial masonry projects.

Less physically demanding: With automated mixing, you avoid the significant physical exertion of hand mixing many batches.

Disadvantages

High equipment cost: Good quality mechanical mixers have a high initial cost to buy or rent. This investment may not make sense for small jobs.

Can overmix if not careful: Extended mixing times can destroy air entrainment and make mortar overly smooth. You must monitor mix cycles.

Extra water for consistency: High-speed mixing tends to stiffen it as it rapidly hydrates cement. With this in mind, you may need additional water.

Tops tips on how to mix mortar

Mixing mortar correctly is important for achieving maximum strength, whether you use a ready mix mortar or make it yourself. Here are some tips for choosing the right ingredients, tools, and mixing methods to keep each batch consistent. 

Type N

• Use fresh mortar within 2 ½ hours of mixing to prevent stiffness and poor bond strength. Mortar will begin to harden past its ideal state the longer it sits after initial mixing. Using mortar more than 2 ½ hours old will make application difficult. It could result in adhesion issues between masonry units.
• Do not retemper black or coloured mortar because it will lose its vibrancy. Coloured and black mortar using mortar dye contains pigments that will oxidise and fade with repeated remixing. 
• Dampen brick or stone slightly to prevent excess water absorption from the mortar. Some masonry units are porous and will suck moisture from fresh mortar, preventing proper curing. Lightly dampen units before laying to limit water loss from the mortar.

Type S

• Use coarse, angular sand for better compressive strength. Sharp, coarse sand particles provide mechanical locking of the mortar matrix, increasing strength. Rounded, fine sand will weaken the mix.
• Let mortar sit for 10 minutes after initial mixing to fully hydrate the cement. Allowing the cement paste to become fully hydrated improves overall performance. You should not add extra water during this time.
• Limit retempering to avoid decreased strength. Do not retemper after 2 ½ hours. Overmixing releases entrained air, and stale mortar will lose strength. 
• Proper tooling forces paste to the surface, creating a weather-tight bond and attractive profiled finish. Allow it to firm up past the thumbprint stage before tooling.

Type M

• Maintain a consistent mix for uniform colour and workability. Variations in sand quantities or moisture content can alter its performance from batch to batch. Be sure to follow the mix proportions precisely.
• Properly cure in moist conditions for 7 days to gain full strength. Proper curing locks in moisture to fully hydrate cement particles. Cure with damp woven burlap for one week.
• Flush out the mixer between batches to avoid contaminating the new mortar. Leftovers will alter the properties of fresh mixes. Thoroughly clean all tools and mixers between batches.

Type O

• Use lime putty rather than hydrated lime for better workability and plasticity. Lime putty provides superior smoothness and curing strength compared to hydrated lime.
• Dampen porous historic bricks before laying to prevent excess water absorption. Old bricks will draw water from it, affecting bond and cure. Pre-wetting controls suction.
• Do not overwork it when tooling joints or it will lose bond strength. Low-strength Type O requires careful, minimal tooling to avoid damaging integrity.
• Allow for a slow 28-day cure to achieve moderate strength. Full carbonation cure and strength development can take up to 28 days. Protect from freezing during cure.

Should you use a mortar plasticiser?

When used properly in recommended amounts, plasticisers provide significant benefits. However, despite the benefits, there are a few drawbacks you need to consider.

Plasticiser advantages 

Plasticiser disadvantages