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Waterproofing Membrane

It is essential to waterproof some joints, particularly those that are used in the external envelope of a structure where driven rain and pooling of water are likely.

Expansion joints that are used externally and those that are likely to be subjected to ‘wet wash-down’ such as in manufacturing facilities should be waterproofed.


Some ranges of joints contained in Vexcolt’s handbook such as AquAtec, FlexAtec & OmegAtec provide excellent waterproofing performance; however other expansion joints such as mechanical systems may require a secondary waterproofing membrane to ensure the watertight integrity of the expansion gap.

Vexcolt’s Epiflex Vapour Barrier comprises a >1.0mm thick EPDM membrane which is epoxy bonded to the arrises of the slab either side of the expansion gap.


Epiflex is a single ply, fully cured geo-membrane designed to meet or exceed the minimum requirements set forth by ASTM D-7465 for Type I Non-reinforced EPDM Geo-membranes.

Alternatively, and subject to the approval of the designer:

a) Either a self-adhesive or torch-applied sheet membrane (by others) may be used. Ideally a membrane that can be bonded and cross-linked to the structural waterproofing should be selected as this will provide a fully watertight solution – or –


b) A layer of suitable geotextile may be used to span the expansion gap. A flexible, rapid set, two-part Polyurea spray may be applied on top of the geotextile to forma waterproof, flexible seal.

Membranes, when used, should be draped into the expansion gap such that they provide sufficient slack to move in response to structural deflection. 


Provisions should be made for the drainage of the membrane at the design stage. The membrane should be laid on top of any levelling bed being used and span all gaps and extend at least 100mm  beyond gap arises. Membranes should be carried up all upstands and risers and intersections should be formed carefully and tested to ensure watertightness before expansion joints are installed. All joints installed on top of membranes should be affixed with resin anchors to ensure that the waterproofing integrity of the membrane is restored.

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