I was asked this week to inspect a low rise flat development in Oxford as cracking has been noted on the corner of the building at roof level. The development was built in the 1960’s with cavity walls and a flat roof with a low parapet around the edge of the roof.
Prior to my inspection I had asked for the cavity to be opened up because the Managing Agent thought there may be a cavity wall tie problem. It was immediately clear that the cracking was not associated with cavity wall tie failure or missing cavity ties. Indeed the metal ties are in very good condition although many are bridged with mortar droppings from top to bottom of the wall.
Each flat has a patio door which has a railing across it. The railings had been removed prior to my visit and whilst there, the builder opened up the brickwork at the sides of the patio door opening. The balcony rails were fairly typical for a 1960’s flat with a painted metal frame and hardwood handrail. The steel of the balcony rail was built into the brickwork on either side of the door opening. It looked in good condition although there were signs of surface rusting where the paint finish was peeling off.
The frame was made up of flat bar or T shaped steel 5-6mm thick. Where the steel had been cut off adjacent the brickwork of the patio door it was clean and in good condition. When the wall was opened up it soon became clear that where it was built into brickwork of the wall, the 6mm thick steel had reduced to just 2mm and could be easily bent and twisted with a hammer. The steel had rusted. The rusting process had caused expansion of the steel whereby it had doubled in width so that the 5mm wide bar had grown to 15mm wide; that expansion causing the brickwork to crack and move.
Prior to my inspection I had asked for the cavity to be opened up because the Managing Agent thought there may be a cavity wall tie problem. It was immediately clear that the cracking was not associated with cavity wall tie failure or missing cavity ties. Indeed the metal ties are in very good condition although many are bridged with mortar droppings from top to bottom of the wall.
Each flat has a patio door which has a railing across it. The railings had been removed prior to my visit and whilst there, the builder opened up the brickwork at the sides of the patio door opening. The balcony rails were fairly typical for a 1960’s flat with a painted metal frame and hardwood handrail. The steel of the balcony rail was built into the brickwork on either side of the door opening. It looked in good condition although there were signs of surface rusting where the paint finish was peeling off.
The frame was made up of flat bar or T shaped steel 5-6mm thick. Where the steel had been cut off adjacent the brickwork of the patio door it was clean and in good condition. When the wall was opened up it soon became clear that where it was built into brickwork of the wall, the 6mm thick steel had reduced to just 2mm and could be easily bent and twisted with a hammer. The steel had rusted. The rusting process had caused expansion of the steel whereby it had doubled in width so that the 5mm wide bar had grown to 15mm wide; that expansion causing the brickwork to crack and move.
The exposed steel had been painted and protected against rusting but the short length of rail that was built into the wall did not have any rust protection and over the 40 years since the rail had been installed the rail had rusted, that rusting process had lead to expansion and in at least one case almost failure of the steel
A check of the other rails of the other flats showed that similar cracking was present on virtually all other balconies. It is a good example of the energy involved in the rusting process of steel.
