Bonded Screeds need to be laid onto a concrete base, and be bonded using an adhesive such as PVA, SBR or epoxy resin. SBR has approximately the same characteristics as PVA, but it is not water soluble after drying, and so is recommended around wet areas, such as swimming pools.
Un-bonded screeds are not bonded directly onto the concrete base, but are intentionally debonded with the use of a DPM (damp-proof membrane). The advantage is that any cracking from the sub-base is not carried through to the screed, drying times can be reduced by omitting the concrete drying time.
Floating Screeds are laid on insulation to provide an insulated floor area. All walls and pillars must be lined with edging foam or 20mm insulation, this will protect against shrinkage and cracking. This system is the most commonly used in house building, especially with underfloor heating systems.