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FAQ's
01. How can you cure concrete in cold weather? Is it ok for concrete to get frost?
In cold weather it is important to prevent heat loss from the freshly placed concrete, therefore water curing is not recommended. It is advisable to leave the formwork in place or cover the concrete with plastic and insulate it.
Strength development is slower in cold weather therefore curing times are extended. If concrete is exposed to frost before it has reached 3 to 5 MPA damage can be caused to the surface. It is recommended to only place concrete in cold conditions between 10:00 and 14:00.
02. How quick can you demould using RHC and OPC?
Typically the day after casting, however this depends on the mould and the method of manufacture. It is important to demould the concrete carefully and then to cure it.
03. How do you make concrete waterproof?
A commercially available waterproofing additive can be added to either the concrete, plaster or mortar.
04. What does 1:3:3 mean?
The volume of each component of the concrete per batch (or mix) i.e. one bucket of cement to three buckets of sand and three buckets of stone.
05. Why does plaster crack in full sun or wind?
The plaster shrinks due to excessive loss of water from the plaster either from evaporation or absorption. If possible do not plaster in direct sun, if this is unavoidable, pay particular attention to curing.
If plastering on to clay bricks, they should be wet before plastering. This is not the case with cement bricks or blocks.
06. How is concrete strength measured?
Concrete strength is measure in MPa (Mega Pascal). Concrete mixes vary according to the final strength required. The higher the MPa the stronger the concrete.
07. What cement can you use for a braai that will be ok with heat?
PPC SureBuild is suitable for the mortar in a mix ration of 1 part cement to 5 sand. Well-burnt clay bricks should be used for the braai.
08. What is the difference between a 32.5 and a 42.5 cement?
This is the standard that specifies strength as set out in SANS 50197-1. The 42.5 class and 32.5R class cement has a minimum strength at 2,7 days and a minimum and maximum strength at 28 days.
The 32.5N class cement has a minimum 7-day strength and a minimum and maximum 28-day strength.