The Effects of Salt Deterioration on Buildings
Many buildings in Sydney, particularly those near the coastal area, are affected by varying degrees of salt deterioration. This is particularly relevant to many buildings which are over 50 years old but can also be relevant to buildings of a lesser age. The main, or common, problems associated with salt deterioration of buildings include the following:-
Mortar To Brickwork And Deterioration Of Bricks
The softer lime mortar used in external brickwork prior to the 1960's can be substantially affected by salt deterioration. This is more prevalent in the exposed location but also buildings located 2-3 kilometres from the sea can also be affected over a longer period. The salt has caused disintegration of the mortar and will result in the mortar being a soft powder form.
The salt deterioration can extend through the brickwork either partially or to the full width of the external course of brickwork.
In extreme cases, the mortar will disintegrate and allow downwards stacking of the bricks and eventually collapse of the external walls.
External surface repointing or cement rendering of the building will be structurally inadequate as in the majority of cases the deterioration of the mortar extends all the way through the bricks. Cement rendering will not remedy the problem, as the render will only be inserted into the brickwork to the depth of 10mm maximum and not the full width.
Many of the bricks used during 1960, 70's and 80's are not salt tolerant and can be subject to surface delamination. This occurs as the salt crystals adhere to the brickwork and are absorbed into the bricks. During rain the crystal will expand and then push the outer surface of the brickwork away and cause surface deterioration. Once the harden surface of the brickwork is lost, then the rate of deterioration of brickwork will accelerate. It is not possible to prevent the surface delamination of bricks and would require replacement of the affected bricks on an individual or whole basis.
Rusting and Deteriorated Wall Ties
The third concern with the wall construction is the rusting and deterioration of the wall ties, which secure the external skin of brickwork to the main building. With complete rusting of the wall ties, this will allow the external brickwork to bow out as it is unrestrained and in extreme cases can cause complete collapse of the external skin of brickwork.
If the brickwork is not bowed, then specialised stainless steel screw fixing can be inserted through the brick walls and can secure the brickwork to the main building. This would only be undertaken if the mortar is in a sound condition. Should the mortar of the brickwork be in a deteriorated condition, and the wall ties known to be rusted, then the only remedy is to scaffold the building and remove the bricks on an individual basis, clean the bricks, relay and reinstall. Specialised stainless steel wall ties will need to be inserted within the brickwork to secure the relayed brickwork to the main building. The extent of deterioration of the mortar and ties can only be determined by an expert in this field.
The presence, or otherwise, of rusted wall ties can only be determined by experts and may involve some part removal of external bricks on an individual basis to examine the condition of not only the mortar but the wall ties which secure the brickwork. The assessment of the deterioration of the mortar to the bricks and rusted wall ties relies upon specialised expertise as well as some investigative site inspections.
Terracotta roof tiles are not salt tolerant particularly those manufactured after 1950. The earlier type of roof tiles, that being prior to 1914 or between 1914 and 1950, vary in their type of construction and have varying salt tolerances. It is the later type of roof tile that is stronger but is less salt tolerant. Where terracotta tiles have been installed near the sea, they will be subject to varying degrees to salt deterioration. This deterioration is mainly evident to the underneath side mainly at the top. In extreme cases, water entry will occur through the holes that are created from the salt deterioration. It is not possible to prevent salt deterioration to terracotta roof tiles. Should an inspection reveal only some partial affected roof tiles, then the affected tiles can be replaced on an individual basis. If the degree of deterioration is extensive then it is more economical to remove and replace the whole of the affected areas using new tiles.
Various structural timbers, particularly the Oregon and pine, will be subject to delignification if located near the sea. We have seen in some situations where no deterioration exists to Oregon timbers in some buildings while others nearby have significant delignification. For this reason an inspection on an individual basis is required. Delignification is a breakdown of the cells which results in a substantial furry finish to the outside of the affected timbers. Where delignification is considered minor then it is not a structural issue but mainly visual. In extreme cases, over a prolonged period, this can result in significant structural lose of strength and can cause collapse of a roof.
Shopfront awnings are usually of two types. One being the older style hanging type that usually has a steel truss framework, or similar. A later cantilevered type has the more modern look. Many of the awnings have framework added so that decorative metal or flat sheet fibro can be added to cover the structural framework. The enclosure of the structural framework prevents periodical inspection of the structural framework for rust to the structural members. Usually the structural framework, particularly in older buildings, is not galvanised and therefore prone to rust. Inspections for the condition is limited, but concern would exist when substantial rust is evident to the perimeter structural beam and soffit cladding.
Where rusting of surface patch overlinings exist, then it would be reasonable that the structural soundness of the framework would be in doubt.
Many unit buildings constructed prior to 1985 had insufficient “cover” or thickness of concrete over the structural steel reinforcing within a concrete slab. This allowed salt laden air to penetrate the concrete and cause concrete cancer (spalling) to many buildings, particularly balconies. If left untreated, balcony failure can occur. We are now seeing only a few situations where balcony collapse occurs, but reinforces the need for adequate and timely remedial works.
David Hall Building Appraisals
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