How to Sand and Cement Render?

Use plastering sand to cement render. 4 sand-1 of cement (4-1) for scratch coat with a combined waterproofer/plasticiser added. If the blockwork has a good enough key, you wont need to use PVA on the wall or in the mix. Just give the blockwork a wet down as you go, and apply the first coat to the wall say 6 or 7 mm thick, and then scratch it, ( an old 6" paint brush handle with "small" nails hammered in along the top works fine), scratch just deep enough to provide a key, but not right through to the blocks. There is no set thickness for the overall render, but the two coats combined would be around 15mm give or take the odd ml. The top coat, applied a day or two after the scratch coat has set and cured, would be a mix of 5 plastering sand, 1 of cement and 1 of lime (5-1-1). A waterproofer/plasticiser would be added to the water prior to mixing. Again, wet the wall before you top coat it.To "float off" using a wooden float, is to close up the render surface after being screeded/straightened off with the straight edge or darby. Floating is a process that is ongoing, and involves going over the same area of wall with the float a few times as the render goes through the stages of going off. When the render is at the final stage of "floating off", it is then sponged over (sponge finish)to give it more closer finish, and an even, slightly sanded texture.. There is a lot of work involved in cement rendering and if you're without experience, you have a daunting task ahead of you, but good luck to you anyway. A good dry day with not too much sun is perfect, you don' want it to dry out too quickly.

Roughcaster.