8 Steps to Mixing Concrete by Hand Without a Cement Mixer
Make Concrete Without a Mixer
A cement mixer does a great job at mixing concrete, thoroughly blending cement, stone and sand to give a consistent result. However it's also possible to mix concrete by hand without a mixer with a little care and some effort. Sometimes the need arises to mix concrete for setting gate, fence posts or a clothes line into the ground. Another possibility is that you have to make a concrete slab to act as a base for something like a fuel bunker. All you need for mixing concrete are the three materials, water and minimal tools: A shovel, a couple of buckets and optionally a sheet of plastic.
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How Do I Mix Concrete? - 8 Easy Steps!
- Spread a plastic sheet on the ground.
- Measure out the materials.
- Place the stone and sand into a pile on the sheet.
- Place the cement on top of the pile of sand and stone.
- Shovel the material in the pile to one side, creating a new pile and repeat three times.
- Make a deep crater in the pile and add water.
- Fold the mix in from the sides.
- Continue to fold inwards and "chop" the pile to distribute water through the mix.
See below for lots more details and photos.
What is Cement?
Cement is a binder, used as an ingredient in combination with sand and stone to make a composite material called concrete. The three constituents on their own have no real strength but when bound together, stones interlock like a 3D jigsaw puzzle and sand and cement fills the gaps. Cement just glues the stones and sand together but it's the stone that gives concrete its shear and compressive strength, not the cement.
There are several different types of cement, two examples are Portland cement and blast furnace slag cement. Portland cement is made by baking limestone in kilns and grinding the clinker produced with a little gypsum to form a fine powder. Blast furnace slag cement is made from the waste products of the steel industry.
Your Options - Pre-mix Concrete or Make Your Own
If you need to mix concrete by hand, there are two options:
- Buy a bag of pre-mixed concrete (drymix). This is available at all good home improvement stores. It has all the ingredients dry mixed together for making concrete, i.e. the cement, sand and stone. All you have to do is put it into a bucket, wheelbarrow or on a piece of plastic on the ground, add water and spend a few minutes mixing it. Usually the product comes in 2 to 4 stone bags ( 10 kg to 25 kg) with varied setting times. Quick setting concrete is available for fixing posts into the ground so that they don't have to be stayed.
- Premixed products from stores tend to work out more expensive if you're going to need several wheelbarrows of concrete. The alternative is to mix your own. All you need is cement, sand and stone (20 mm). Instead of sand and stone you can use ballast or gravel, which is a mixture containing varying sizes of particles ranging from sand to stone. Gravel contains rounded stone and was deposited in gravel pits as a result of the ice age and other geological activity. Gravel or ballast can have a varying proportion of sand/stone, so you may need to judge whether you need to add additional sand, if any.
Crushed stone is produced in quarries by crushing blasted rock and then the result is graded by being passed through a succession of sieves. In theory, this should make better concrete than rounded stone from gravel pits, because of the sharp angular edges.
Concrete Mixing Ratios
A C20 mix consists of:
- 1 part cement
- 2 parts sand
- 4 parts stone (aggregate)
Alternatively a mix of sharp sand and stone, sometimes called ballast, can be used, and this is mixed 6 to 1 with the cement.
A stronger, more hard wearing C30 mix, suitable for thinner and narrower concrete slabs, e.g. pavements, consists of:
- 1 part cement
- 2 parts sand
- 3 parts stone (aggregate)
As in the case of the C20 mix, if you're using ballast (sand and stone), mix it 5 to 1 with the cement.
Ideally stone should be 15 to 20 mm in size (9/16 to 13/16 inches).
Sharp sand should be used, graded from 0 to 5mm. Don't use fine stuff which is really for mortar/plastering.
The quality of hand-mixed concrete can be variable because of incomplete mixing. Therefore don't rely on it for structural applications such as building foundations.
How Much Water Do I Need For Making Concrete?
The max amount of water that should be added is 0.55 times the weight of cement. So for a 25 kg bag:
25 x 0.55 = 13.75 kg or 13.75 litres
This is approximately the volume of a 3 gallon (Imperial) bucket.
The mix shouldn't be overly sloppy and should be able to self support itself without slumping.
What Does C20 Mix Concrete Mean?
It means the concrete can withstand a compressive force (or more correctly pressure) of 20 newtons per square millimetre (20 MPa) without crushing. So in theory, for a 10 cm x 10 cm square (about 4 inches x 4 inches):
Area = 100mm x 100mm = 10,000 square millimetres
So total compressive force that the concrete can withstand without crushing is:
Force = pressure x area = 20 N/mm2 x 10,000 mm2 = 200,000 newtons.
A newton is equivalent to a weight of about 0.1 kg so:
200,000 newtons = 200,000 x 0.1 = 20,000 kg weight or 20 metric tonnes on a 10 cm by 10 cm square.
In reality a concrete slab would probably crack or sink with much less than this magnitude of load. This is because the underside of the slab would be spanning the individual stones of the sub base foundation and not supported underneath at every point over its full extent. These figures really refer to the compressive strength of a 150 mm concrete cube as measured on a test jig.
Tools and Equipment For Mixing Concrete
- Builders shovel. (The pointy type one)
- Ideally three, 3 gallon buckets. One for water, one for cement and one for sand/stone. If the sand or stone is wet and you use this bucket afterwards for measuring cement, it will stick to the sides and bottom.
- Polythene sheeting. A sheet of polythene helps to prevent mess and contamination of the concrete by pebbles, leaves, soil and other debris. It also makes it easier to scrape up all the leftovers with no wastage. I use 1200 gauge polythene (the heavy stuff used as a damp proof membrane under concrete) and this is widely available in hardware stores. You can of course mix concrete in a wheel barrow or bucket, but there's more room to mix on a sheet.
- Wheelbarrow or buckets. For transporting the concrete to its final destination. Alternatively you can mix in situ.
For laying concrete, you can use a garden rake or a 1 x 4 board nailed or screwed onto a length of 1 1/2 x 2 for spreading.
Do I Need to Wear Personal Protective Equipment (PPE) When Mixing Concrete?
- A dust mask will help to prevent the inhalation of fine cement dust while measuring out and loading the mixer.
- Gloves to protect hands. Cement is somewhat caustic when dry, so if you have sensitive hands, these will give protection.
- Safety glasses stop cement dust or splashes of concrete from getting into your eyes
- Steel toe-capped boots. Optional. You may end up standing in or close to concrete while mixing/laying. Steel toe-caps protect your toes from dropped bricks, blocks or rocks. They normally also have a steel insole to protect feet from nails, glass or other objects that penetrate the outer sole.
Cement is generally available in 25kg bags. In the US it is sold in 47 or 94 pound bags
Mixing Concrete: Sand, Cement, Gravel, and Water
When mixing by hand, it is essential to thoroughly mix the concrete to get consistency throughout the mixture.
If you need to mix a small amount, for instance half a bucket, place the stone and sand and finally the cement into the bucket. This needs to be thoroughly dry mixed with a garden or block layers trowel. Water is then added, say half a pint at a time and mixed throughout the bucket. More water can be added until the concrete is at the required consistency. If the mixture becomes too sloppy, add more cement. If you are filling a hole in the ground e.g. around a post, the mixture can be a bit more sloppy so that it flows easier.
Larger quantities of concrete can be mixed on a flat surface on the ground
You can measure the proportions of the mix by counting shovels. However I find it easier to use buckets. If you go for a C20 mix, a single mix using buckets ( which totals 7 buckets of material) is enough to produce a wheelbarrow of concrete.
So remember you need:
- 1 bucket of cement
- 2 buckets of sand
- 4 buckets of stone
- If you're using polythene sheet, spread it on the ground and weigh it down with blocks/bricks or whatever at the edges in windy weather
- Place the stone onto the ground followed by the sand. Alternatively you may have gravel which is a composite mix of large and small stone and sand. If there isn't much sand in the gravel, you can add some more
- Place the cement evenly onto the top of the pile. If you have someone to help you mix, it will be easier. Start at the edge of the pile with the other person facing you. The aim is for both people to keep shovelling the pile to one side to create a new pile adjacent to the old pile. Repeat this three times so that's four mixes in total.
- Now it's time to add the water. Make a crater in the top of the pile about half its diameter so that it looks like a volcano. Again, it's important that the pile doesn't have slopes that are too steep so when you add the water it breaks through the crater and runs down the slope! Add half the water, the amount depends on the amount of dry mix you have created.
- Now with the shovel, go around the edges of the crater and keep sliding the mix into the center. Then use a chopping motion with the edge of the shovel to mix the water with the dry mixture. Continue to shovel the dry mixture from the edges of the pile towards the center. Eventually the mixture will become easier to control as the water becomes more distributed. Then keep sliding the shovel under the mixture and turn it over bit by bit and use a chopping motion with the edge of the shovel to thoroughly mix the concrete.
- Continue adding water until the concrete is of a consistency that doesn't slump and can support itself in a pile.
Don't forget to wash your shovel when finished before the concrete sets on it!
Should Concrete be Sloppy or Stiff?
Ideally concrete should be able to stand up in a pile on a shovel and not slump.
How to Mix Concrete
Steps 1 to 8
Step 1: Spread a Plastic Sheet on the Ground
Cement is alkaline and caustic and can burn sensitive skin or cause eye damage. Wear safety glasses and gloves
Step 2: Measure Out the Materials
Things can go wrong fast when mixing concrete and you only have about half an hour before it starts setting. If you're working alone, it's important that everything is ready. Make sure all your tools are to hand, a mixer has a full fill of fuel and is running properly.
Fill a barrel with water if you need to do lots of mixes.
Step 3: Place the Stone and Sand on the Sheet
Step 4: Place the Cement on Top of the Sand and Stone
Step 5: Shovel to One Side From the Edge of the Pile and Repeat Three Times
Concrete shouldn't be sloppy. Don't add too much water initially. The consistency is right when a pile pulled to one side with a shovel stays put and doesn't slump. Add more water or cement as necessary.
Step 6: Make a Deep Crater and Add Water
Step 7: Fold the Mix in From the Sides
Step 8: Continue to Fold Inwards and "Chop" the Pile to Distribute Water Through the Mix
How to Mix Concrete in a Mixer
A cement mixer allows you to mix concrete quicker and get more consistent results. However things can go quickly wrong if you don't control the amount of water in the mix. However here are some tips to get the best results.
- A UK builders bucket will typically hold 3 UK gallons or 13.5 litres. These are convenient for measuring out quantities of materials before mixing commences.
- A small Belle mixer such as the Minimix 130 or Minimix 150 will mix about 90 litres of concrete, so if you do a C20 mix, i.e. 1 bucket of cement, 2 buckets of sand and 4 buckets of stone, this will produce about a wheelbarrow full of concrete. You can make the mix stronger by reducing the amount of stone to 3 buckets (C30 mix)
- Measure out the stone, sand and cement into 3 separate piles on the ground. Again a sheet of plastic or large wooden board such as a sheet of plywood keeps the ground clean and prevents contamination of the materials by soil and dirt
- It's advisable to use a small barrel or other large container to hold water if you're doing several mixes. You'll need multiple buckets of water and you don't want to have to go off filling a bucket from a tap or hose if a mix begins to stick to the drum.
- Start the mixer
- Shovel some of the stone in first and half a bucket of water. The abrasive nature of stone helps to scour any remaining wet concrete stuck to the drum from an earlier mix session.
- Never put a shovel into a rotating mixer drum. The mixing spoons can catch the shovel and swing it around and hit you in the face
- Next add cement, sand and water alternately, from the piles. As you add cement and sand, watch for a moment to see how the mix is progressing and add water so that the mix is not over sloppy, but at the same time not so dry that it sticks to the drum
- You can add all the materials to the drum first and do a dry mix. However cement will stick to the inside of the drum and the likelihood is that material at the back of the drum won't mix properly and get wetted as you add water. So it's better to add them a bit at a time
- Continue to add the remainder of the cement and sand
- If the mix starts to overflow out of the drum, place the wheelbarrow underneath to catch any spill
- Allow to mix on full speed for about 3 minutes
- Reduce the speed of the engine and commence unloading of the mixer into the barrow
- When the drum is empty, a new mix can be started. Add some water first to rinse off the concrete stuck to the inside of the drum. This slush can be incorporated into the next mix. If you are working alone, stop the mixer so that you can deal with transporting and unloading the barrow
- Don't forget to wash all concrete from your tools before it sets and hose out the drum, ideally while the engine is running and the drum is tipped. Try to avoid getting water from the hose onto the engine. If the mixer is electric, unplug it and relocate the extension lead out of range while hosing
- Use timber boards placed at strategic points to act as ramps and bridges so that you can get your wheelbarrow over uneven terrain and ground at different levels
- Don't try to push a loaded wheelbarrow up a step, it's easier to pull it
- Spread concrete with shovels and a rake after you tip it out of the barrow. You can also make up a makeshift rake using a long length of timber with a board nailed to the end
- If you use a cement mixer, obviously you can empty the concrete directly at the point where you need it, rather than transferring to a wheelbarrow
- When laying concrete floor sections adjacent to each other, feather the edge of the new concrete with a sweeping brush so that it blends with the previously laid section
Laying a Concrete Slab
- If you're laying a concrete slab, tip the mix from the barrow within the formwork (the boards which bound the slab) and furthest from the front. Roughly scrape out the barrow and use a rake to spread the concrete, making sure its pushed into all corners. Use the back of the rake with the handle vertical to compact and pack the concrete, especially around the edges of the formwork.
- Start a new mix
- Continue to build up the level of concrete until it's about 1/2" above the formwork boards.
- If you work fast and alone, you should be able to lay about 3 barrow loads of concrete before a slab needs to be screeded (roughly levelled flush with the forms with a timber board)
Curing of Concrete
During curing or hardening of concrete, a process called hydration occurs where water chemically bonds to cement. So some of the water you added actually never dries out. It is locked to the cement in a bond forever!
Don't allow concrete to dry out in hot weather or if there are strong drying winds. It needs to cure slowly, so ideally cover with plastic to prevent moisture loss
Protecting Concrete in Cold Weather (or Dry Weather)
The best time to make concrete is when the weather is mild. Freezing weather conditions can weaken concrete and hot dry weather can cause water to evaporate too quickly so that there is insufficient water for it to cure properly, resulting in cracking.
Until concrete cures, it should be protected from the weather and never allowed to freeze for the first 24 hours. Minimum curing temperature should be 40 F (4C). In freezing weather conditions, water in concrete expands as it freezes. As ice crystals grow, they push the concrete outwards, breaking bonds between cement, stone and sand. Then when they melt, they leave millions of micro-cavities, so the concrete ends up porous like a sponge, potentially weakening it.
You can cover concrete slabs after laying with blankets/polystyrene/bubble wrap or whatever to help prevent it freezing. If frost is due to set in at night, lay your concrete early in the day so that it firms up, before covering with insulating material (otherwise it'll get marked by the covering).
In hot, dry weather, wait for a few hours until the concrete firms up. Then cover it with polythene to prevent moisture loss and cracking.
How to Make Concrete Stronger
Concrete is only strong in compression, not tension. This means that it'll withstand being squeezed but not bent. So for instance a concrete pillar in a building can withstand tons of weight pushing down on it, but a concrete beam spanning an opening (e.g. a large doorway in a building) would snap under moderate load. To strenghten it, steel bars called reinforcing bar or rebar is inserted when the concrete is wet. Because steel is strong under tension, the resulting composite material becomes strong both under compression and tension.
You can add rebar rods or grid to concrete when laying floor, pads or anywhere you think that it'll be subject to heavy loads and in danger of cracking. It's also a great way of getting rid of any scrap iron you've accumulated.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
What is curing?
It's a chemical reaction in the concrete during which water bonds with calcium compounds. During the curing process, excess water also evaporates and the concrete becomes stronger.Helpful 8
What volume of concrete would your 7 bucket mix make?
About a wheelbarrow. Buckets are 3 imperial gallons or 3 x 4.54 liters. From a quick Google search, a builder's wheelbarrow is 65 to 85 liters in volume.Helpful 7
How long does it take concrete to cure?
Under normal drying conditions, you can usually walk on concrete after 24 hours. A general rule is that it reaches 70% strength after a week and a month to get near full strength. Concrete will continue to strengthen however over months and years. Its best to avoid putting heavy items on it for a week and don't drag things across it which can leave scrape marks.Helpful 7
© 2012 Eugene Brennan