Add a layer of cement plaster to unfinished interior breeze block walls in order to add insulation, create texture or patch damaged areas. A basic plaster is made with a mixture of cement, masonry sand and water; however, different things can be added, depending on how you want the plaster to look. Add animal hair to create texture, as well as strength. Add a cement colouring agent to create a coloured plaster. Hydrated lime can also be optionally added to plasticise the mortar and make it more resistant to cracking. Add lime, especially if you are working with very thin layers of plaster.
Create a slurry. Mix equal parts of cement and sand, and add enough water to make a soupy mix, or slurry. Coat the walls with the slurry before plastering to help ensure adequate bonding of the plaster to the wall.
Paint or trowel a thin layer -- not more than 3 mm (1/8 inch) -- of the slurry onto the wall. If necessary, work in small sections at a time so the slurry won't dry out while applying plaster. If necessary, keep the slurry layer moist by misting it with water.
Create your plaster mix. Mix 3 parts of sand and 1-1/2 parts cement. If using hydrated lime, substitute about 10 per cent of the cement with hydrated lime powder. Mix plaster in a bucket or tub with a drill that has a cement mixer drill bit, in a wheelbarrow with a shovel, or, for larger quantities, in a cement mixer.
Gradually add water until you achieve a thick plaster mixture. If you are adding animal hair or another texturing ingredient, gradually mix that in until you see it evenly distributed throughout the plaster.
Apply your plaster to the wall as desired. Read through a guide to plaster texture techniques (see Resources).
Cover the wall with waterproof insulating blankets (also known as a concrete curing blanket) for 48 hours to incubate the plaster while it cures. Waterproof insulating blankets can be purchased or rented from many hardware supply shops. Simply tack the blankets to the ceiling so they hover just in front of the wall. It is OK if the blankets touch the wall, once the plaster is no longer wet.
An environment that is too hot or too cold can induce improper curing of your plaster. It is best to apply plaster in temperatures between 10 and 20 degrees Celsius (50 and 68 degrees Fahrenheit).