One of the first steps when learning how to concrete is to know what the terms are, these are explained in the “Concrete Mix” section so I won’t repeat them here, but I will be referring to them a lot so make sure you check them out.
this will be determined by either vehicle traffic or pedestrians that will be using your concrete slab.
For these specifications, See “Concrete Mix”
LEVELS AND DRAINAGE.
It is very important to consider your levels at this stage, If you are concreting up against the house then there are regulations in regards to how close you are allowed to the damp course, in my area Council have specified 100mm (4”) below, so check with your local Council so you know. You have to think where the water is going to go, and how you are going to deal with that, you can see the Ground Drainage section (coming Soon) for some ideas.
SECURING THE FORMWORK.
Once these decisions have been made and you have excavated the unwanted material, you are ready to place the formwork in position. Don’t be tempted to just use any scrap piece of wood for this, learning how to concrete and this aspect of the work is so important for the finish. The formwork not only creates the shape of your concrete slab but provides you with the edge, which in some cases you will be seeing a lot, so you need it to be precise.
Metal or wooden Pegs are usually hammered in on the outside of the formwork, You can also use bricks, soil, or anything that is heavy enough not to move when the concrete is being placed in. Sometimes you may need to place a peg on the inside to hold the formwork in place or to keep a curve, these can be removed immediately once the concrete has been place in.
THE USE OF PLASTIC.
It is really only necessary to use plastic placed underneath the Concrete slab when you are pouring the likes of a garage, shed or house slab. It is really only to help keep moisture from absorbing into the slab for these areas where you will be standing or living. It is not necessary for patio, paths or driveways.
REINFORCING STEEL MESH.
Your steel mesh is then cut and placed in, overlapping each piece approx. 230mm (9”). It is also important to cut the mesh 50mm (2”) from the inside edge of the formwork. This will prevent any chance of the steal being exposed to the edge.
The steal can be placed on what are called chairs which will support the steal at the recommended height in the concrete which is usually about 25mm (1’) from the surface. It is also Ok to lift the steel as you are placing the concrete in, you just have to make sure that with each barrow load or as the chute from the truck is pouring, THE STEEL DOES GET LIFTED,
Leaving it lying on the ground does nothing for the concrete, so if you are going to learn How to Concrete, please, don’t get into this bad habit.
Although this will be done a bit later on during the process, You will need to pre-determine where these joints will be placed, I prefer to cut the steel for these joints, creating a break in the reinforcing, some concreters will not cut but have the area covered completely with the reinforcing,
But for me the joint is to allow the concrete to expand and contract in different weather conditions so I break up the continual steel bond by cutting the steel 50mm (2”) either side of the joint.
I will place a marker where these gaps are like a different peg or something so when the concrete is in I can then do this work.
For other popular methods see the Expansion Joint section on the Concrete Slab page.
READY TO START POURING THE CONCRETE.
This is when the action starts, NOW BE WARNED, you will not have time to stop work until the concrete is in and prepped, this is where the size of your concrete slab will determine how hard and how long you are going to work before you can sit down for a break. Don’t worry though you may have to have a long break once this is done, waiting for the finishing stage.
Your main job at first is to get the concrete spread along your first edge, If you are up against the house then this would be the first edge. Then down the two sides and leaving the last edge to finish at, sort of like painting a floor in a room.
PLACING IN THE CONCRETE.
Then you can start filling in the middle, ideally you just need enough concrete placed in there to be just above the finished height. That way you will not have too much to keep moving back when you start the screeding. This can be done in stages, edges, middle, edges middle and so on. Tap the formwork boards when the concrete is against them to work the edges.
START THE SCREEDING.
You don’t want to get too far ahead with just placing the concrete in before you will need to start screeding, it will just make this process too difficult. So try and have someone help if the job is of reasonable size so they can continue placing in the concrete and you can start screeding and floating.
If you don’t have a Bull Float then you can work with the steel float and the screed consecutively, first you will screed a portion and then just lightly run the float over it VERY LIGHTLY, this will further aid you in bringing up the slurry.
The screeds have a LEAD edge and a TRAIL edge to them, the lead edge which is the sharper one is the edge that is closer to you, this edge will cut easier into the concrete allowing you to obtain the correct level.
You can slightly roll the screed pulling the handle towards you to push it away from you and work almost like a sideways stretched 8 pattern. Once the whole area has been screeded you will have to do the initial floating, this will create a pad on the inside of your formwork.
If you intend to use the form work to determine the level of concrete, you can achieve this screeding with a good straight piece of timber, which is placed across the formwork and using a sawing motion, work the concrete so the slurry comes to the surface as you move your way along the job. You will need two people involved in this procedure and you will both have to work in synch with each other.
THE INITIAL FLOATING AND EDGEING.
The edges will need to be moulded after the screeding is done, so you work with the float and make sure that you have worked up a bit of slurry then place the edger in the concrete, lifting the leading every time, go backwards and forwards till the moulded round edge has no stones, then float on top again cleaning any marks the edger makes. This cleaning can also be done with a steel trowel.
You may or may not have a bull float but if you do you need to wait a little bit till there is a bit less movement in the slab before you use this tool, if it’s done too soon then you will end up moving the concrete around too much and upset your levels. You just want to seal the surface really and remove any imperfections in your screeding. This will be best achieved if you use this tool in the direction 90 deg. to your screeding.
NOW YOU CAN REST A BIT….
PLAY THE WAITING GAME.
The time to place the finishing touches on your concrete slab is when the surface is still moist enough that some comes off with your fingers when touched but there is no or very little movement in the concrete.
The weather will play a big part of this but also the volume of water in the mix, whether you have poured your concrete slab on plastic or not and wether the sun is shining on the slab. All of these factors will help determine how soon you are able to start finishing your work.
You may have a part of the slab that is ready and another part not, you just have to hope that by starting on the section that is ready, the next bit will be ready when you get there.
There are a variety of finishes described in the Concrete Slab section but whichever one you decide on the timing is critical to the quality of the look. Too soon and you will move the concrete around too much, too late and you will have to work harder and faster to obtain the correct finish. While you are learning how to concrete, it is best to keep testing it every ten minutes or so, this way you won’t have any surprises.