How to Mix Mortar / Concrete

July 10, 2013 at 7:26 pm
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It’s rare that you’ll be able to complete a hard-landscaping project, or even minor building works and repairs without having to mix mortar or concrete. Although the mixing process is largely the same, there are lots of different ‘end products’, so this guide will show you how to mix mortar or concrete (both by hand and using a mixer) as well as describe the different products and their applications.

We’ll also include a glossary in this how to, as cement, mortar and concrete are in fact totally different things, but are frequently misnamed.

Glossary

  • Cement – a fine, grey dust like powder which is the key ingredient in both mortar and concrete
  • Mortar- a mixture of cement (or lime), sand and water, usually smooth and used to bind bricks or stones together
  • Concrete – a construction material made using sand, gravel, pebbles or similar aggregates, held in a mortar or cement matrix
  • All-in, or ballast sand – a rough sand with pebbles, used as the main aggregate in concrete

Tools/Materials

Water (mortar or concrete)
Sand (sharp sand for mortar, all-in/ballast sand for concrete)
Cement (mortar or concrete)
Tarpaulin/large plastic sheet to protect the area beneath your mixer/mixing area
Shovel
Cement Mixer (cement mixing tray, or large piece of plywood ‘spot board’ to mix on manually)
Bucket

Instructions – CONCRETE

  1. Before you start mixing anything at all, you need to spend a little time planning what type of mix you require.
    TYPES OF CONCRETE MIX: 
    • Foundation Mix – 1 part cement to 5 parts of all-in/ballast sand. This is a relatively weak mix which is suitable only for concrete which is not going to exposed to the weather, making it ideal for a foundation for a wall, securing gate posts or washing lines, or the base of a path which will be covered by another paving material.
    • General Purpose Mix – 1 part cement to 4 parts of all-in/ballast sand. This mix can be used for the majority of jobs, excluding foundations or applications where it will be exposed to the elements. It would be suitable for a slab base, or flooring in a covered area.
    • Paving Mix – 1 part cement to 3.5 parts of all-in/ballast sand. This is a strong mix, ideally suited to exposure to the elements, so can be used for steps, paths and drives.
  2. Next, you’ll need to estimate just how much you’ll need by calculating the coverage in square metres (always work in metric), then multiplying this by the thickness that you’ll lay. Then add 10% to allow for wastage and an uneven base. The thickness of concrete required will depend on its intended purpose.
    CONCRETE THICKNESS: 
    • 75mm for bases for garden outbuildings, and for paths.
    • 100mm thick for patios (although we would recommend whacked down hardcore in all but exceptional circumstances for a patio, as it is much less likely to crack or sink over time).
    • 125mm for garage floors and drives.
    • 150mm for drives that will be expected to cope with commercial vehicles.
  3. Example: A slab base that is 5m wide, by 2m deep, laid to a thickness of 100mm will need 5 x 2 x 0.1 = 1 cubic metre of concrete. Allowing an extra 10%, as described above to account for wastage and an uneven base, would give a final requirement of 1.1 cubic metres of concrete (although it would be sensible to round this up further still).
  4. Lastly, you’ll now need to calculate how much all-in/ballast sand and cement to purchase. You can use the guide below to give you a reasonably accurate idea. 
    CONCRETE RATIOS: 
    • Foundation Mix – 6 bags of cement per cubic metre of all-in/ballast sand.
    • General Purpose Mix – 7 bags of cement per cubic metre of all-in/ballast sand.
    • Paving Mix – 8 bags of cement per cubic metre of all-in/ballast sand.

Instructions – MORTAR

  1. As with concrete, before you start mixing, you need to spend some time planning what type of mix you require.
    TYPES OF MORTAR MIX: 
    • Normal Mortar – 1 part cement to 5 parts of sharp sand. This mix is well suited to bricklaying in normal conditions. Add a small amount of plasticiser and frost proofer (as per manufacturer’s instructions).
    • Strong Mortar – 1 part cement to 4 parts of sharp sand. This mix can be used for bricklaying in exposed conditions. Again, add plasticiser and frost proofer in small amounts, as directed.
  2. Additives aren’t always necessary.
    USING ADDITIVES: 
    • Frost proofer shouldn’t be added as a matter of course. If temperatures are set to fall below 3 degrees C after laying, then use a frost proofer. It’s not recommended to be laying mortar at temperatures of less than 3 degrees C.
    • Plasticiser will reduce the amount of water that you need, so be aware of this when adding water. It also needs to mix properly, so allow at least another 3-5 minutes to mix through once all components are added.
  3. Next, you’ll need to estimate just how much you’ll need by calculating the coverage in square metres (always work in metric), then multiplying this by the thickness that you’ll lay, if you’re taking on a job where this is a suitable measurement such as laying patio slabs on hardcore. Alternatively, you may choose to calculate based on the number of bricks that can be laid. In either scenario add 10% to allow for wastage.
    CALCULATING MORTAR REQUIRED: 
    • 25kg of cement (1 bag) and 100kg of sand mixed at 1:5 (normal mix) would allow approximately 400-450 bricks to be laid.
    • 25kg of cement (1 bag) and 75kg of sand mixed at 1:4 (strong mix) would allow approximately 300-350 bricks to be laid.
  4. Use the quantities described in step 2 to estimate the scale of the job and purchase materials accordingly.

Mixing Mortar or Concrete – Manually

  1. Using consistent shovel loads, mix out a manageable amount of the dry ingredients onto the spot board. Don’t forget that you’ll be adding water and then moving the ingredients around a lot, so a) get as big a spot board as you can, and b) make sure you don’t overfill the board that you do have!
  2. Mix the dry ingredients together on the board, until the colour of the mixture is consistent. Alternate between shovelling from the bottom of the pile and placing it on the top of the pile, with a downward, slicing action with the blade of the shovel to mix thoroughly.
  3. Make a small well in the centre of the dry ingredients and add a small amount of water (and any plasticiser or frost prevention additives). Always underestimate the water, as it’s much easier to keep adding small amounts than it is to try and compensate for over-wetting the mixture.
  4. Working from the edges of the pile, shovel the dry ingredients into the centre to mix them with the water. Keep repeating this, using the same mixing techniques that you used in step 2, constantly adding a little water at a time until the mixture is the right consistency.
  5. Clean up quickly! Tools can be wrecked extremely quickly by mortar or concrete which is allowed to dry on. There’s no excuse either, as wet concrete is very easily removed, simply by hosing down.

Mixing Mortar or Concrete – Using a Mixer

  1. Begin by adding a small amount of water to the mixer. If it is not already, make sure that it is spinning.
  2. Using consistent shovel loads, begin adding the dry ingredients to the spinning mixer. Take care not to catch the shovel on the internal blades as you fill the mixer.
    TIPS: 
    • When adding your dry ingredients to the spinning mixer, add a single ‘gauge’ at a time. For example, your final quantity of Foundation mix may require 25 shovels of aggregates and 5 shovels of cement. Don’t add all the aggregates, then all the cement; add 5 shovels of aggregate, followed by 1 shovel of cement and allow to mix for a while. This will prevent an unevenly mixed load.
    • Always add your aggregates, then follow with cement. This helps ensure that the cement doesn’t lump together in the water, which would prevent an even mix.
    • Add water in small amounts. The amount of water required is deceptively small and it is always much easier to keep adding water than try and extract it!
    • Don’t forget that the amount of water required can vary between loads, as the sand will have differing moisture levels throughout. Therefore, it’s unwise to try and measure the same amount of water each time – keep adding small amounts and adjust as you mix.
    • Try to avoid starting a mixer when full, as it puts a strain on the motor.
    • To get even strength and colour in your mortar (especially important when bricklaying – you don’t want the mortar changing shade as the wall progresses!), it’s advisable to use a small or 5 litre bucket rather than shovel loads to keep the mixes identical.
  3. Tip the mixed product into a barrow or trug and use as required.
  4. Again, clean up quickly. A mixer can be just as easily wrecked as other tools by mortar or concrete which is allowed to stick on. Stuck on lumps of concrete can also flake off when you’re mixing mortar (which must be smooth), making that much harder to work with  as you’ll be picking bits out of it! Add plenty of water to a spinning mixer, along with a few large stones, or broken bricks. Tip out and hose the inside as the mixer is in the pouring position, preferably into a barrow or other device to prevent making a mess.

Product Recommendation

The Belle Mini Mix 150 Concrete Mixer is a common sight on building sites across the UK, and for good reason. In our experience, they mix both concrete and cement very well and are extremely tough to kill. We have a hard-working mixer which is frequently used, but well looked after, which is now well into its 6th year. There are cheaper mixers on the market, but if you’re going to as far as to spend the money on a mixer, aim to spend a little more and get a Belle – you won’t regret it.

For far more occasional use, the heavy duty octagonal trays are designed to protect the ground from whatever you’re mixing. Complete with a lip around the edge, they prevent water from oozing out and will double as a ‘drip-tray’ underneath a mixer if you are using one. We’ve found this Neat Products tray to be tough and robust.