Day 17: Lintel, Padstones and Engineering Bricks
Today the walls were completed. Padstones and engineering bricks were added to provide the supports for the roof’s steel frame which is due to arrive tomorrow. The lintel went up too which supports the brickwork and roof above the patio windows / doors.
The lintel is like an inverted T. It allows a row of bricks on the outside and a row of blocks on the inside. There is also a gap in the steel that is filled with insulation so the cavity wall insulation is constant across the wall.
The padstones are simple reinforced blocks. They are extremely tough, designed to bear the weight of the steel girders which support the whole roof. If padstones were not used in time the blocks would crack and disintegrate and destabilise the whole roof.
The size of the padstone should always be specified by the architect’s engineering drawings because they need to be strong enough to support the weight of the roof.
A traditional padstone was a simple stone used to keep wooden supports off the ground. Staddle stones is the name given to the mushroom shaped stones that support old barns. These were designed mostly to keep mice out of the bars, but they also kept the wood dry and providing a solid base for the building.
Padstones can be made on site but for small jobs a builder will often purchase some ready made ones.
Engineering bricks are like small padstones. The builders remove some of the old bricks in the wall and replace them with 3 engineering bricks, stacked on on top of two, to support the end of a steel beam.
Engineering bricks are the size of a standard brick but provide extra strength and also low water porosity.
There are two grades in the UK. Class A are blue and the strongest bricks with a strength of 125N/mm². The blueness is because they are fired at a much higher temperature. Class B are usually red and have a strength greater than 75N/mm².
Engineering bricks can be used to create a damp proof layer, but this is a very expensive alternative. This method will eliminate the risk of brickwork slipping on a damp proof later when the mortar is still wet.
Accrington bricks were famous engineering bricks. They were made from 1887 until 2008 and used for the foundations of the Blackpool Tower and the Empire State Building, both of which are still standing!