Laying Concrete Flooring
You might be in the process of extending your house by adding a new bedroom or building a bigger garage or just wanting to spruce out the garden by laying a concrete pavement or walkway. For any DIY, this task would prove to be easy as long as you have the basic knowledge in masonry and carpentry.
One of the least expensive materials to use for flooring or pavement is concrete. When laying a concrete floor you must first consider the following points.
How big is the floor to be concreted?
It is important to know the actual dimension of the area to be concreted so you can compute for the volume of the concrete that you will need. If you are planning to lay concrete on a simple project such as a garage, then here is a simple method to follow for you to be able to estimate the materials needed. If you plan on building a 4 meters by 6 meters garage, then the floor area is 24 square meters. To get the volume of the concrete multiply the area by the assumed thickness of the slab, let us say at about 6 inches or 0.15 meter. Multiply the 0.15 meter by 24 square meters and you get a concrete volume of 3.6 cubic meters. The amount of cement, sand and gravel that you will need depends on the class of mixture that you prefer. For a C7.5 .P mix, the ratio would be 1:3:6 where 1 is cement, 3 is sand and 6 is gravel. Here is a simple method to compute the materials.
- For a 1:3:6 cement mixture, multiply the volume (in this case 3.6 cu.m) by 7.5 to get the resulting number of 40 kg. Bags of cement. Therefore 3.6 cu.m X 5.5 = 20 bags of 40 kg. cement. For sand multiply the volume by 0.44 to get 1.6 cubic meter of sand. For the gravel multiply the volume by 0.88 to get 3.1 cubic meter of gravel.
- Therefore for your 4 meters by 6 meters by 0.15 meter garage flooring you would need 20 bags of 40 kg. cement, 1.6 cubic meter of sand and 3.1 cubic meter of gravel. It is standard to add 10% to the amount of materials because of:
- Inaccurate volume delivery of aggregates
- Scattered aggregates in the site
- Inaccurate measurements of materials especially when hand or power mixing
- Cement bags breakage
- Screening of aggregates reduces usable volume
What kind of concrete will you use, plain or reinforced?
Now that you know the volume of your concrete mix, decide on whether you need to pour plain concrete slab or reinforced concrete slab.
Concrete is an artificial stone resulting from the mixture of cement, sand and gravel, crushed stone or other inert materials. A conglomeration of these aggregates producing a solid mass s called plain concrete.
On the other hand, reinforced concrete is concrete with reinforcement embedded in such a manner that the two materials act together in resisting forces. Concrete is compressive while reinforcement is tensile. You can economize by placing large stones in the concrete in the process of pouring thereby reducing the volume of cement, sand and gravel.
Assuming that you want a slab with tensile strength that only reinforcement bars could give, it is better to lay out a wire mesh or a 10 mm deformed bars set at 60 mm both ways. Again, this is assuming that you are pouring concrete on a ground as pouring concrete on a second floor extension takes a lot more of actual structural computation. If this is the case, get professional help.
Hand mixed or Ready-mixed Concrete?
Hand mixed is alright for a concrete floor that is not more than 1 cubic meter. If the need is more than 1 cubic meter, then consider using ready-mixed concrete. However if you are only paving a garden walk, or any ground level slab work, then it's alright to hand mixed a batch since the pouring concrete could be staggered. If you plan to hand mixed be sure to measure each materials carefully. Note that a 40 kg. bag of cement is considered as 1 cubic foot. Sand and gravel are measured in cubic foot too. For a 1:2:4 cement ratio this would mean 1 bag of cement, 2 cubic feet of sand and 4 cubic feet of gravel. The water content should be the minimum necessary to produce concrete workability. The concrete mix must be in plastic form in order to produce top quality concrete.
Rent a mixing machine for the thorough mixing of the cement and the aggregates. You cannot expect to hand mix batches and batches of cement and its aggregates without literally breaking you back. Mixing a batch by power mixer would ensure a well-mixed batch thereby increasing the strength of concrete and its workability. Care should be observed to prevent the particles of sand and gravel from being separated from the paste.
Prepare the ground for the concrete pouring.
Stake the ground that you plan to cement. Make sure that the ground has been tampered, levelled and has its first coarse aggregate lain out. If you are using reinforcements, lay out the re-bars or wire mesh on the designated area. If plumbing and electrical pipes are to be embedded on the concrete flooring too, set them up before concrete pouring. Make sure that all pipe openings are corked up to prevent cement from blocking the openings.
Enclose the area with 6 inches to 8 inches cut plywood nailed to the stakes. Measure the thickness of the slab and see to it to slope the slab for surface draining. If you are mixing by batches, limit the area where you intend to pour as you cannot possibly finish the concrete pouring in a day if you hand mix or power mix.
Make sure that you follow the rules and regulations set forth by the local building officials to avoid delays. Get the necessary permit for the construction.
"I do not understand how it can take 3.1 cubic metres of gravel, plus 1.6 cubic meters of sand, plus the cement and the water to make about 3.6 cubic metres of concrete. Please send explanation to firstname.lastname@example.org"