Types of Floor Screeds
Underfloor heating screed floors are normally sand-cement screed floors. These are traditional screeds and are suitable for all applications provided they are specified correctly. The biggest drawback is the drying time; BS 8203 estimates the drying time for a sand cement screed as one day for each millimetre of screed thickness up to 50mm thick. There are now available special additives which enhance the strength of the screed and reduce the drying times. The manufacturers can provide further guidance on drying times.
Screed Floors – Calcium sulphate pumpable, self-leveling screeds
A common use these days is for a levelling screed to be used to accommodate underfloor heating. The liquid nature allows the screed to “wrap” around the pipes giving a better thermal transmission to the screed floor.
These screeds can be laid as bonded or un-bonded. They can be laid in much larger areas than cement sand screeds, around 2000m2/day. However, they must not be used with reinforcement because the calcium sulphate is corrosive to steel. These screeds are also generally not suitable for use in damp conditions or where wetting can occur. These screeds are all proprietary products and therefore vary from one supplier to another. The guidance given here is therefore generic and the manufacturer should be consulted before specifying. If they are intended to be used as a wearing (structural) screed then the manufacturer should be consulted.