A lintel is a block or plate of concrete used to fill gaps on buildings or during construction work. They are steel-reinforced in order to carry heavy weights and to prevent the concrete plates from breaking during fitting. They are usually bought pre-manufactured, but can be made to measure on site.
Measure the gap you wish to bridge with the lintel and make a note of the exact size.
Create a mold according to your measurements by sawing out one bottom piece from the plywood, adding half an inch on each of the four sides. Saw out four side pieces. The height of the side pieces should be the same as the thickness of your gap.
Nail the side pieces tightly to the bottom with a hammer, creating an open top box. Paint or spray the inside of the box with a treatment to prevent the concrete from sticking to it.
Cut the rebars to the same size as the length of the box and place them inside. Put the spacers between the bars to prevent them from moving. Position the box with the bars on a level surface.
Mix the ballast and the cement in a bucket. Add water and stir the mixture to a muddy consistency. Put on safety glasses.
Pour the concrete mixture into the box on top of the rebars. Fill box up to rim. To ensure an even distribution of the concrete, take a hammer and lightly knock around the edges of the mold. Wait one minute until the concrete is evenly distributed throughout the mold; add more concrete mixture, if needed.
Leave to stand for 24 hours; then remove the mold. Place the concrete plate horizontally on a dry surface and leave for one week. After seven days the lintel is dried throughout and ready for use.