All about concrete
- By Nigel
One of my first jobs was as a construction worker with a concrete team, so I learnt a thing or two about the material. This knowledge came in very handy when we bought our first house and started landscaping. Some people find working with concrete scary, perhaps because if you make a mistake it can be very hard to go back. But there is really not much to it once you know what you are doing.
Laying concrete is very labor intensive, so doing it yourself can save you lots of money.
Before you attempt to lay your own foundations for a shed or retaining wall, you should probably try creating a path or garden edge. Like many things, working with concrete becomes easier with practice. As you confidence grows, you will find yourself attempting more difficult projects.
"Like many things, working with concrete
becomes easier with practice. As your
confidence grows, you will find yourself
attempting more difficult projects."
Here are some essential things beginners should bear in mind when working with concrete:
Add water slowly: Making your concrete too runny will weaken it. It should be wet throughout and only just runny enough to work with. Add small amounts of water, mix, then add a little more. Do not cut corners here by trying to guess how much water you will need (even if it says how much you should need on the bag).
Avoid rapid set concrete if possible: Unless you really need rapid set concrete, try to avoid it. Rapid set mixes tend to be weaker than traditional cement and they give you less time to lay your concrete and work up a finish.
Get the right tools: It pays to have at least a float and a corner float handy before you start. These are essentially flat pieces of metal with a handle (the corner float has a bend on one end) that you use to work up the surface.
If you are laying a path or larger areas, having a piece of "two by four" handy is a good idea. Working this piece of timber backwards and forwards across the surface helps to get your path or slab level.
Use the right ingredients: If you are using instant mix or ready mix, you can't really go wrong. But most people mix their own from bagged cement, and builders mix (also called aggregate).
You can make your own builders mix by combining good quality builders sand with gravel. We recommend a mix of approximately 2/3 gravel to 1/3 sand by volume. Ideally the gravel should be a mix of smaller and larger stones (up to 1.5cm or 1/2 inch diameter).
So ultimately, however you choose to go about it, cement will be a mixture of :
Wear gloves: Cement is a chemical formulation and is really hard on even the toughest hands.
Concrete is set by a chemical reaction, so to say it "dries" is actually misleading. On the contrary, letting concrete dry out too quickly will give you weak or cracked concrete. You need to keep it wet while it cures.
Don't lay concrete on a hot day unless you can keep it moist. The best way to keep concrete from drying out is cover it with a tarpaulin or wet it ever few hours with a hose (or a combination of both). Wait at least an hour before wetting it, and go easy for the first few hours, or you will damage the finish.
Step by step:
Step one: Prepare your site. it should be 100% ready to go before you start mixing the concrete. This step will usually involve buying some cheap, untreated timber to use as boxing. Non-load bearing concrete (path, shed floor etc) should be at least 50mm thick (2 inches). If laying a slab for a shed you should dig down another 50mm around the edges to support the weight of the shed.
Step two: Work out how much concrete you will need by multiplying the height, width and depth of your prepared site. Most cement comes with a guide as to what volume a certain amount of cement will make.
Step three: Mix dry ingredients as per instructions on the bag. A typical mix is one part cement to five parts builders mix (or approximately two parts sand and three parts gravel).
Add water slowly while mixing as outlined above. If you are lucky enough to have a cement mixer, great. Other wise use a wheel barrow and fold the water into the dry mixture with a shovel.
This is no easy job without a cement mixer, expect to work up a sweat!
Step three: Pour into your prepared site and work into the corners. Screen using a length of timber if you are laying a large surface area. Rest the timber on the top of the boxing and work backwards and forwards.
Warning, concrete is very heavy. Dropping a wheelbarrow load on your lawn can be a pain to clean up.
Step four: Work up the surface with your tools until you get a smooth finish. You can come back 30m later and brush it up if you want a rough look.