Expol Styro-drain polystyrene drainage board can be placed hard up against the retaining wall after the water proofing membrane or tanking has been applied, use Expol Construction adhesive to secure the sheets to the wall before back filling. The sheets of Styro-drain are placed on top of IOOmm perforated drain surrounded by drainage gravel situated at the base of the retaining wall. On high reach retaining walls a double thickness of Styro-drain along the base of the wall may be required allow for increased compression and better drainage. Expol Styro-drain should cover all waterproofing membrane and tanking, the sheets of Styro-drain should not be exposed at the top of the wall. Styro-drain has been tested by Opus International Consultants Ltd. OPUS INTERNATIONAL CONSULTANTS Job No. 169402.00 Reference No. 02/402/001 Permeability Tests: EXPOL STYRO-DRAIN Test Methods: Permeability as per "Constant Head Permeability of Aggregate, Based on Soil Laboratory Testing by E.H.Head, Den