Liquid Screed – Anhydrite (Preparation)

Preparation Guide

Building should be water tight prior to installation.
Doors and windows should either be installed or the openings made weather proof.

Screed thickness

When preparing floor areas for screeding, consideration must be given
to the recommended screed thickness.

Bonded - 25mm
Unbonded - 30mm
Floating Domestic - 35mm
Floating Commercial - 40mm
Underfloor Heating - 50mm (minimum 30mm cover over the pipe)

High spots in the substrate usually dictate the minimum screed thickness. All systems require perimeter edge strip which should be fixed to the walls in a similar manor to a skirting board and around any columns and pipework.

Bonded System – The substrate must be structurally sound and suitable for application. All loose material must be removed from the substrate leaving the surface dust free. This is now ready for a suitable primer to be applied prior to the screed installation.

Unbonded System – As above the substrate must be structurally sound and suitable for application. All debris and contamination must be removed from the substrate surface and a polythene separating embrane must be installed. If a DPM already exists under the substrate, then a 500 gauge polythene membrane or similar is sufficient. Lap joints should be 100mm and all joints must be taped. The polythene should continue up the face of the walls at least the depth of the screed but we would recommend a further 100mm to protect wall finishes.

Floating System - Any high/low points that could affect the stability of the insulation boards should be removed along with any debris. The insulation boards should be laid flat, tightly butt jointed and preferably with staggered joints. A polythene separating membrane (500 guage or similar) is required and should be installed on top of the insulation boards. Lap joints should be 100mm and all joints must be taped. The polythene should continue up the face of the walls at least the depth of the screed but we would recommend a further 100mm to protect wall finishes.

Underfloor Heating - The preparation is the same as for a floating system with the addition that all heating pipes are to be securely fixed. Warm water systems should be pressure tested and filled prior to the application of screed to reduce the risk of pipes floating.