How to Mix Your Own Concrete for Internal Flooring
Anatomy of Floors
Floors are used every day with little thought given to how they are constructed.
To some degree their design will be determined by the building codes and regulations in force at the time the house was built and the materials that were available. Within these parameters, however, there is substantial scope for variation in construction to satisfy different purposes and functions, while the preferences of the architect and the relationship of the building to its surroundings will also have an impact. This section on flooring identifies and examines the main types of floor construction.
Concrete Floor Construction
Most people think of concrete floors as having a rather industrial feel and consider them second-rate compared to a traditional suspended timber floor, so that they should only really be used for basements or garages. Yet concrete has many advantages and now more than ever before concrete floors are being laid for the main living areas in homes. In particular they are perfect for heavy load-bearing applications and provide an ideal subfloor for many types of floor covering.
Concrete floors can fulfil several different functions. If the house is built on a concrete raft then the ground floor will form part of this foundation and will be part of the overall structure of the property. Concrete floors often form part of a slab that supports walls for the upper storeys, while at the same time providing a smooth level subfloor over which a screed is often laid. If a timber floor has been stripped out and replaced with concrete then this will not obviously have any structural reference to the house. Concrete is most often used at ground level, although it is not unheard of to find concrete floors at higher levels.
When laid correctly concrete has an almost indefinite life span making it a cost-effective replacement for a rotten ground floor. Some older concrete floors can be damp but this is often due to defective damp-proofing and not directly due to the breakdown of the concrete. Newly laid concrete must be allowed to dry out before any flooring material may be fitted. This will take anything from three weeks to several months, depending upon the thickness of the screed.
Concrete serves as an excellent subfloor for many different floor coverings. It is not subject to movement like timber and is capable of handling heavy loads, making it suitable for kitchens and utility rooms where heavy appliances might otherwise damage a timber floor.
Ingredients for Making a Concrete Floor
Concrete is a mixture of coarse and fine aggregates — stones up to around 20mm (3/4in) in diameter with smaller stones and coarse sand — that is bound together into a solid matrix by cement. You can buy the ingredients separately from builders’ suppliers and mix them yourself, buy dry ready-mixed bags of cement and aggregate (ideal for small jobs) or order ready-mixed concrete (best for large areas).
Ready-mixed concrete may be delivered by a large truck mixer with its familiar slowly turning drum, or by a smaller vehicle that carries dry cement, aggregates plus a cement mixer and can mix the amount you need on the spot. Truck mixers can deliver up to about 6cu m (200cu ft) of concrete from their chutes directly to the site. Smaller vehicles mix by the barrowload, which you then have to move from truck to site.
The ingredients of a concrete mix depend on the use to which the material will be put. The ideal mix for laying a concrete floor is 1 part ordinary Portland cement, 1 part building sand and 3 parts aggregate. All-in aggregate is a mixture of sharp sand and 20mm (3/4in) aggregate. Always mix ingredients by volume, using separate buckets or similar containers of the same size for cement and aggregate. Mix batches based on 1 bucket of cement plus the relevant numbers of buckets of sand and aggregate. Be careful when mixing not to splash cement on your skin and eyes — wash it off immediately if you do.
Mixing Your Own Concrete
Tools for the Job
- mixing board
- clean bucket
- hired cement mixer
Measure out the sand and aggregate into a compact heap. Form a crater in the centre with a shovel and add the cement. Mix the ingredients dry until the pile is uniform in colour and texture. If you are using dry ready-mixed concrete, tip out the sack and mix thoroughly. Form a crater in the centre of the heap and add water.
The aggregate will contain some water already, so the amount you need to add will be trial and error to begin with. After two or three batches, you will be better able to gauge how much to add. Turn dry material from the edge of the heap into the central crater. Keep on mixing and adding a little more water in turn until the mix reaches the right consistency — it should retain ridges formed in it with the shovel. If it is too sloppy, add dry ingredients, correctly proportioned as before, to stiffen it up again.
With a mixer
If you are using a cement mixer, set it up on its stand and check that it is secure. Put some aggregate and water in the drum and start it turning.
Add most of the cement and sand, then water and solid material alternately, to ensure thorough mixing. Run the mixer for two minutes once al the ingredients are in, then tip out some of the contents into a wheelbarrow. The mix should fall cleanly off the mixer blades.
Special paints made specifically for colouring concrete can be applied once the floor has been poured and allowed to cure, or pigments can be added to wet concrete while it is being mixed. The advantage of using pigments is that they are longer-lasting and the concrete will retain its colour regardless of wear on the floor.