Cement, sand, wooden molds, measuring can, trowel and water
1. Measure the materials using the measuring can.
2. Mix 4 parts sand with 4 parts cement thoroughly.
3. Form a mound and make a circular hole in the middle of the mixture.
4. Pour about ½ of a measure of water into the hole. Allow the water to seep into the mixture. Mix well. Add more water if needed. The mixture must not be too dry or too wet.
5. Place the mold in an upright position on a level surface. Put the mixture in the mold until half-full. Pack the mold. Scrape the surface.
6. Invert the mold carefully and pull the mold upward.
7. Sprinkle daily with water for a curing period of 28 days.
8. Test for compression strength by successively loading heavy objects. Record the total mass [kilograms] of the objects when the block cracks. The will tell you how much your hollow blocks can hold. – Bato Balani
Visual source: cmsb