However, there are some good reasons for keeping an original lath and plaster ceiling. Sometimes this failure can be disastrous, the collapse at the Apollo theatre in 2014 injuring 88 people during a performance was caused by water ingress weakening the lath and plaster ceiling. Where sagging is evident the ceiling will move if gently pushed or make a hollow sound if tapped. If this spreads across the ceiling even the horsehair can’t support the weight and the ceiling, or sections of it, will sag and then may collapse. This weak point is usually at the lugs that wrap around the laths. Plaster is brittle by nature and will crack at its weakest point under vibration or through water ingress. If there are lots of small timber laths with creamy lugs of plaster in between, the ceiling is original. In older properties you can check the type of ceiling by looking under the loft insulation, or lifting a bedroom floorboard. Interested? Browse our "My dad told me about them!" articles How to check for lath and plaster It was usually applied in two or three layers to a thickness of around 25mm. The lime improves workability and breathability of the plaster. The plaster was usually made from lime mixed with sand and cement and included horse hair to act as a natural reinforcement and effective bonding key. Plaster was then applied to the underside of the laths, held in place by being squeezed through the gaps to create a ‘key’ or lug. Laths are thin strips of wood (around 25-38mm wide and 3-8mm thick) spaced around 5mm apart and nailed to the ceiling joists above. Picture courtesy of Malone Associates Ltd What is lath and plaster? Most pre-1930s houses will have traditional lath and plaster ceilings.
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