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Cannot See the Caviweep?

18 Feb 2019

When choosing the best cavity weep to suit a project, one should consider the exposure and the finish of the elevation. Choosing a weep that offers sufficient outflow to service the masonry absorption area is essential, whilst aesthetically the appearance of the building should not be adversely affected.

Brickwork and stonework can normally accommodate weeps within the perp joints, and selection of an appropriate weep colour (or a weep manufactured in suitably translucent material) can result in the outlet merging with the mortar shade. Rendered surfaces are another matter - does one omit weeps in the hope and anticipation the render will prevent penetration of all water, or does one make some provision - so a discharge route is in place should it be required during the life of the building?

Whilst render may be water resistant when new, during the life of a building all rendered surfaces are susceptible to fissures and cracks. These can occur anywhere throughout the rendered area, as well as at junctions with alternative finishes and window/door openings. Therefore building-in a means for water to escape always makes sense, with the accompanying caveat they should ideally be unnoticeable!

Water penetrating a rendered surface can initiate five major deficiencies:

1)        Damp banding and patching will manifest where arrested water pools on the DPC tray / lintel. It is trapped and cannot escape other than forwardly.

2)        Wet substrate and any substrate affected by internal pooling will deteriorate. Water is feeding the collection area behind the render coat – it cannot dissipate in the normal manner.

3)        Freezing temperatures and wet retention will initiate delamination / spalling.

4)        Portland cement materials are susceptible to attack from soluble sulphates within walls where water is prevented from evacuating and the masonry skin cannot dry out.

5)        Rendered elevations will be affected aesthetically and painted render can suffer film detachment and film ballooning.

Cavity Trays of Yeovil manufactures a range of discreet Caviweeps that are barely visible once installed. They remain in place ready to function whenever water permeates the structure. They provide a passive means of escape that is always in place – from when a masonry skin is new and thereafter.

One such Caviweep - the discreet Small Adjustable Caviweep can be opened and closed like a telescope, making it compatible with a wide range of skin thicknesses. It also has small louvres to guard against the ingress of wind-driven rain and insects, as identified in the NHBC Guidance and Good Practice (Tech Extra 17).

An alternative to the beneficial small louvred outlet is available with a sister weep called the Beak Weep. The Beak Weep offers weathering protection not enjoyed with elevation open outlet styles of weep.  The discreet ‘beak’ shields a downward discharge outlet. With a range of colours including a popular translucent option, merging with the surface finish is easily accomplished.

Draining the cavity wall can be executed in many ways, and a modern version of the masonry bleed straw is offered in the form of the Pyramid weep. Its’ shape permits it to be incorporated within small mortar beds / Ashlar walling applications and service masonry features unable to accommodate conventional cavity weeps.

The above three examples are from a range of six Caviweep types offered by Cavity Trays Ltd. All versions are specifically designed to merge with brickwork, stonework and rendered finishes and promote best practice

Cavity Trays Ltd of Yeovil

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