 Kioran, moioran, whaka alofa atu, konna Māori, Māloni, talofa, girei. This video has been made for the course Working with Concrete. Watch it as you work through the course. It'll show you some ways to mix and lay concrete and build with concrete blocks. First, let's look at concrete itself. Concrete is made of cement, sand and rock, and water mixed together. Most cement you're likely to use comes from places like Papua New Guinea, Fiji, Australia or New Zealand. It's a fine grey powder that makes the concrete set hard. It usually comes in bags like these. There are different grades of cement for special purposes, but use general purpose or GP grade for most jobs. This is GP cement from Australia. It's important to keep the cement bags dry. Store them off the ground and keep them covered. Sand and stone. This is sometimes called aggregate. Most places use a mixture of sand and small stones or rock, like this. For most jobs there are two portions of sand to three portions of stones. Here on Tarawa they use crushed coral rock to do the same job. Whatever you use, make sure it's clean and free from rubbish, leaves, grass or roots. Water must also be reasonably clean. Don't use sea water. It may stop the concrete from hardening properly, and it can make any steel reinforcing rust or corrode. Once everything's been mixed together, the concrete will start to harden. It could be hard enough to walk on carefully after a few hours. But it can take days to get to a useful strength. It'll then keep getting stronger for months or even years. What is concrete used for? Concrete is used to make paths, roads, houses, blocks and to hold posts in the ground. Your workbook will help you work out the size, shape and thickness of concrete you need so that your job is strong enough and fits in with your local conditions and building requirements. This video can only give you a very general guide. Laying concrete. To make a good job of laying concrete you need to follow some basic steps. Get your site ready, mix the concrete, pour and compact, level and finish and finally cure. Your tutor and your workbook will take you through each of these stages in detail, using the tools and materials you have locally. This video will show you some of the main points. Let's look at each step. First, getting your site ready. Before you mix any concrete, you need to get everything ready to put it in the place you want it. Decide exactly where it should go and how thick it needs to be. Dig out the ground as deep as you need it and make sure the bottom is level and firm. Formwork. Make a wooden framework to hold the wet concrete while it sits. This is called the formwork. Some people call it boxing or shuttering. A thin concrete path only needs a simple timber frame with pegs like this. For thicker concrete, the formwork needs to be much stronger and really well made to hold the weight of the wet concrete. This is even more important than soft soil like this wall foundation in Kiribati. See how the sides are made from thick plywood with a strong timber frame and braced supports. The top of your formwork will be the top of your concrete, so make sure it's level and exactly where you want it. Here the pink string line has been used to get everything set out right. The black polythene sheet in these pictures will stop the loose sand underneath from mixing with the wet concrete as it's poured. It will also help to stop the concrete drying out too quickly. This is another type of formwork. It's the concrete base for a water tank on Tarawa. The formwork is a concrete block wall. It's filled with a rubble of old bits of concrete and blocks, then covered in sand and compacted down level. Concrete will be poured in the top to make a large solid base. Reinforcing. Steel reinforcing in concrete makes it stronger and holds it together under load. For a simple path or a small slab on firm ground you probably don't need any. For thicker work like roads, house bases, foundations and high block walls, you will need reinforcing mesh or steel rods. You must get expert help to work out how much steel you need and where to put it in the concrete. See, the steel bars here are wired together and the spacer blocks underneath keep it off the bottom. These steel rods for the block wall are also joined to the foundation steel. Here is some steel running along inside a block wall. OK, your site is ready. The formwork is done and any reinforcing is in place. You're nearly ready to start mixing your concrete. Remember these safety points. Your finished concrete needs to be thick enough for the job. Formwork needs to be strong enough to hold all the wet concrete without moving. Correct reinforcing in the right place is vital for safety in structural jobs. Get expert advice and help. Mixing concrete. You can mix concrete by hand. This is good for small jobs but it takes a long time and it's very hard work if you have a lot to do. Or you can mix in a concrete mixer. This is easier on your back and arms. It's quicker and used properly. It does a better job because it mixes more thoroughly. Whichever way you mix your concrete you must use the right amounts of cement, sand, rock and water for the job you're doing. Use a bucket to measure. Your workbook has a table showing the different amounts to put in a mix for various jobs. Here's a good general 3-2-1 mix ready to go. Mixing by hand. Here students and teachers from the Banuatu Institute of Technology in Port Vila show you how they mix concrete. They're mixing on a concrete floor but you could use a large piece of board or any flat surface that you can clean off afterwards. Measure out your dry materials. Using a bucket to measure the sand, stones and cement makes sure you get the right amount. It's much better than using a shovel. Now mix thoroughly. Two people working like this makes things much easier but you could do it on your own. Turn and mix it at least three times, like this, to make sure it's properly mixed. It should all be the same colour when done. Collect it all in a mound and make a hollow in the middle. Add water and carefully start to mix in. Then keep mixing and turning until it's all the same consistency. These workers in Samoa are mixing a really big batch in one go. They need to take extra care to mix it properly and they'll have to use it all quickly before it starts to go off. OK, shovel it into a wheelbarrow and off you go. If that was your last batch don't forget to clean up the tools and work surface before it dries. Mixing in a concrete mixer. A concrete mixer does the same job as mixing by hand but it does all the turning and mixing for you. Mixers come in different sizes and are usually powered by electric motors or small petrol or diesel engines. Get your tutor to show you how to safely operate and look after the one that you have. You can use a mixer on your own but it's a lot easier with a group of helpers. These workers on Tarawa are working as a team to mix batches quickly. As you can see they have a long way to go. First they put in about half to two thirds of the water then the aggregate. Here they're using a mixture of crushed coral rock as the aggregate so they don't need to measure sand and rock separately. Add the cement. Note again that they're using buckets to get an accurate measure. Mix together adding the rest of the water to get a mix that is workable but not too sloppy. Keep mixing for at least two minutes. Pour out and away you go. While the team starts on the next batch. When you've finished remember to clean the mixer before the concrete sets. Remember these safety points. It's difficult sometimes but try not to make clouds of cement dust like this and avoid breathing it. The dust can harm your lungs and it can crack or burn your skin as well. Most mixers are driven by belts from the motor. Keep your hands and loose clothes away from all the moving parts. Water, wet concrete and electricity are dangerous together. If you use an electric mixer follow the safety instructions very carefully. Pouring and finishing. As each load of concrete is mixed pour it into your formwork. This is a continuous process that needs to keep going before the concrete sets. Start at one end and fill up to the top of the formwork. Add each load onto the edge of the wet concrete. Compact the concrete as you work along. Push it down with a shovel or a rake. Make the concrete fill up all the gaps and spaces. If you're lucky enough to have a vibrating compactor like this one it makes things easy, especially with all that steel work. But a piece of wood or a rake can do a good job too. Level the surface as you fill the formwork. This is often called screeding. Use a straight piece of timber across the formwork or a large float to level and compact the surface. That should leave a surface like this, which is perfectly good for a wall foundation like this one. Meanwhile keep adding more concrete on the wet edge compacting and levelling as you go until the job is finished. If you have to stop put a piece of timber across the formwork and finish off neatly like this. And fill, compact and level right up to the timber. Leave it all to set and harden. If you need a smoother surface finish polish the surface again later when the concrete has set but it's not quite hard. Use a finishing float like this. Here's another concreting job. This one is for a thin floor slab. Start pouring at one end. Settle and compact. This time using a float and finish. Notice how they're using string lines from the formwork to help keep the level and the right height. Concrete must be kept damp for a few days while it hardens properly. This is called curing. If it dries too quickly it will be weak and may crack easily. When the surface has set hard enough to walk on start the curing process. Regular sprinkling with water like this will work well. Or you could use a hose. Large construction sites often cover the wet concrete with big polythene sheets to keep the moisture in or use special chemical sprays that seal the surface. Once the concrete has set hard you can take away the formwork. Remember these safety points. Wet concrete can crack and burn your skin so avoid as much skin contact as you can. Wear boots if you can get them. Getting covered in cement or stepping in wet concrete is not a good idea. There we are. A good job well finished. Those steel uprights will hold and reinforce the block wall. And it's blocks we will look at next. Concrete blocks. Concrete blocks come in all sorts of shapes and sizes. Most building blocks are hollow like these. They are used to make walls, buildings, supports, decoration. These blocks laid on their sides will eventually have plants growing through from the garden box behind. Blocks are made of cement mixed with a fine aggregate of sand and small stones or rock. They use a very dry mixture compared to the concrete mixes we use to pour slabs and foundations. Here's a hand mould being filled. Weck, compacted by dropping it. Then compacted and levelled by hand. Taken to storage, turned over and the mould is removed straight away. That's why the mix needs to be so dry. Here's a block making machine at work on tarawa in Kiribati. Aggregut and cement go in the hopper which tips it all into a big mixer. Pour in just the right amount of water and mix and mix. Down a conveyor belt and load it into the mould by hand. The mould vibrates and then compresses the mix. And three more blocks ready to go. They're stored in the open and sprayed regularly with water to help them cure. Mixing mortar Making mortar for block laying is very similar to making concrete by hand but on a smaller scale. Your workbook has details of the amounts of sand and cement you need to use. Put the sand and cement onto a piece of board. Turn from side to side with a trowel to mix thoroughly. It should all be the same colour when ready. Collect it into a mound and make a hollow in the middle. Add water and mix in carefully like this. Mix thoroughly again adding more water if needed. It should be a smooth soft paste like this. Make only the amount you can use in about 30 minutes work. If you make too much it will go off before you can use it. Laying blocks Before you start you need a solid foundation blocks for the job mortar tools trowel levels gauges a string line. Put down an even bedding layer of mortar. Start at one end of the wall and put the first block in place. Tap the block down into the mortar. Check its level across the block. Here on Tarawa they're using a string line to keep things straight and the right height. Lay the next block. Mortar the edge place and check alignment. Now do the same for the next layer. The first block goes on the end or corner. See how it's facing round the corner so that the blocks are staggered but the cores are in line. Place the block and tap down. Check the height. Check its level and in line. Trim off the excess mortar. This special steel set square can be used to check that corners are right. This chap really knows what he's doing. Trowel on the mortar mortar the block mortar the block end Place the block tap down and check alignment with the string line. Trim the spare mortar. He makes it look so easy. Notice the steel reinforcing running inside the blocks along this long wall. Keep checking all the way. As you go up make sure the blocks are upright and not bulging or leaning or sagging. Before the mortar fully sets finish off the joints neatly. Scrape off flat like this or for a better finish use a tool like this. It also helps to push the mortar into any gaps. Filling blocks. If you need to you can fill the blocks with concrete. It makes the wall stronger and fixes any steel reinforcing. Only do this when the mortar has fully set. Pour in the concrete and push it down to fill all the spaces. It's just like compacting a concrete slab. Then leave it to set. In this decorative garden wall on Tarawa they're filling a gap and fixing that post into place. They use some simple formwork put in some stiff concrete push down and compact tap the sides to settle things and level the top. It's a simple and clever idea but don't use it for anything that needs to be really strong. Cutting blocks. You may need to cut blocks for half blocks for the ends of a wall or for blocks to fill gaps. If you have one you can use a concrete saw like this. Mark the block then cut along the line. These machines can be very dangerous if they slip or jump out of the cut. Don't use one until your tutor has shown you how to use it safely and correctly. That dust comes out in clouds and clouds. It's not good for your lungs so avoid breathing it. Cover your mouth and nose with a mask or a cloth. Water can help to stop some of the dust. You can also cut blocks with a heavy hammer and a special chisel called a bolster like this. Mark the block, put it on a flat surface or a bed of sand and work around the marks with the chisel until the block breaks. You'll probably need to clean up the ends afterwards. You must wear eye protection when cutting blocks. Chips of concrete will fly about and can damage your eyes. Working with concrete can be interesting and rewarding. You can make things that are useful and long lasting. Your workbook tells you a lot more about laying concrete and building with blocks. It helps you work out the sizes and quantities you need. It also tells you about other tools and techniques. We hope you enjoy working with concrete. It takes a good bit of practice to do a really good job so keep practising. And remember, get expert advice and help with your plans for those large or important jobs. Plan and work safely at all times.