Cavity Wall Tie Failure

Cavity Wall Ties Failure due to Corrosion

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Cavity Wall Tie Types

The original cavity wall ties are often either thin mild steel ties, sometimes coated in bitumen to protect them. Then there are thicker ties know as fishtails due to their forked ends embedded in the mortar, these are often coated in zinc for their protection. Different regions around Manchester have varied wall ties as construction methods developed and standards unified.

Today we have stainless steel wall ties that will last the life of the property.

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The Problem

Since construction over decades these cavity wall ties are subject to weaterh on the outerleaf and their coatings start to fail and rust away.

The thin steel ties of metal stri[p or butterfly wall ties often show not evidence of this corrosion until the cavity wall begins to move as the restraint effect of the cavity wall ties diminishes. The thin wall ties tend to rust away at the external elevation point of contact to nothing more that a discolouration of the mortar. In extreme cases ther is no cavity wall tie in the outerleaf ( See the picture to the right).

The thicker fishtail wall ties (so called due to their forked fish tail like ends) have more density and as the rusting process starts they expand slowly causing horizontal cracking in the mortar beds, This type of cavity wall tie can expand up to ten times their original size and this effect can usually be seen as a horizontal crack to the brickwork as the expansion increases it may cause bowing of the wall as the wall expands in height.

How to cure the problem

In both cases the need for remedial installation of new remedail cavity wall ties is essential to keep the building cavity brickwork stable.

In the case of fish tail cavity wall ties the isolation from the brick work or complete removal is an additional requirement to complete a successful repair.

Where the brickwork has moved significantly additional rebuilding may be required. In the case of significant movement this is often decided by a structural engineer.

The Solution

The property where the corrosion is seen in the picture above had remedial wall ties installed previously, these were poorly installed and the roof spread was also having an effect, remedial work involved significant rebuilding of the rear elevation, triangulation of the roof timbers (strengthening works) and stainless steel remedial cavity wall ties to supplement the shortfall of the original remedial cavity wall tie installation.

New remedail cavity wall ties are availbe in many forms from resin/resin fixng to double mechanical and variations in between, all are not made from stainless steel with stainless neopreen expansion points.

Prevention

To discover if the wall ties are corroded a boroscope can be used to examine the exisitng cavity wall ties to ensure they are in good condition or if corrosion has started. Ifthe cavity has had cavity wall insulation it will be necessary to expose the end of the wall tie in themortar bed or remove a brick to exxamine the tie in detail.