Simple concrete mixing
Being able to mix small amounts of concrete is very handy for repairs to walls and paths in the garden, driveway patches and other areas of hard-standing. You can use it to fix fence posts in place and even patch internal concrete floors without having to employ contractors.
The real skill with concrete is knowing which components to use, which percentages of sand, cement and other aggregates to use, then where and how to control the setting, particularly over large areas and in different weather conditions. But mixing up a small batch for a repair job is something that should be within the capabilities of most DIY beginners, although you are encouraged to practice first.
We aren't going to attempt to turn you into a master of concrete in this
article, that would be foolhardy. So we will restrict ourselves to hand mixing of small amounts to use around the garden and home. There won’t be any need for a mixer either.
Sand and Cement
Get hold of your materials first. We will forget about any added aggregates and stick to a simple sand and cement mix. Six parts of sand to one of cement is a good general purpose mix for a mortar for laying bricks or blocks, but you need to go as high as four to one for an area that will be permanently wet, like a pond liner. You'll need a supply of water as well, of course.
A thick sheet of plastic or tarpaulin over a wooden board makes a good platform for mixing. You need the wood to give a hard surface to shovel against and the sheet helps to keep everything together and uncontaminated. Put the sand and concrete on the tarpaulin and mix it all together thoroughly with a spade or shovel.
Preparing the Water
Shape the dry mix into a hummock and make a well in the centre. This is where you will add the water, but that needs preparation first. You need to add a plasticiser which will help the mix remain malleable while you work it into whatever you are repairing. A few drops of washing up liquid in a bucket will work, or you can buy a commercial plasticiser.
Get a bucketful of water and mix the plasticiser in, then pour some into the middle of your hummock. Then gradually draw the cement and sand mix into the well, mixing thoroughly as you work your way round. Add water slowly and keep the mortar mix on the dry side initially. It's much easier to add some more water than it is to mix up a new dry sand and cement load to add if you've already made it too damp.
Getting the mortar to the right consistency is something that comes from experience. You need to be able to modify the amount of water you add depending on all sorts of factors -- how dry the materials are to start with, whether there is more or less water in the atmosphere, and of course the job you are doing. But generally you should be aiming for a consistency that will pour slowly. Then apply it to the job in hand.