Bossing, Welding, Jointing, Fixing, Corrosion
Bossing and Welding Methods
Lead sheet should be carefully worked or lead welded/burned so that the lead is not thinned by more than 25% or weakened by creasing or stretching. Bossing and welding/burning lead should be carried out by experienced (preferably registered) lead operatives using the proper tools and equipment.
It is important to check for compatibility when specifying or using certain types of the following materials:-
Joints in leadwork are weathertight but not watertight. Joints in leadwork are designed to keep water out whilst allowing for thermal movement. It is therefore important that the type of joint used is appropriate for the type of application or situation.
Support and Fixing Methods
Lead sheet must be adequately supported on a smooth base sufficient to take the weight and to allow for thermal movement to take place. It may be laid on timber, plywood, concrete or masonry together with a suitable underlay. The lead sheet should be held in position with fixings of a type, strength and position which:
- Support the weight of the lead sheet
- Are resistant to corrosion
- Allow for thermal movement to take place
- Resist wind uplift
Lead sheet is resistant to most forms of corrosion likely to be encountered in a roofing situation, but certain precautions need to be taken against the following:
Mortar: Unprotected lead damp proof courses and cavity trays may corrode in the presence of moisture
Lichen Growth: The acid run-off from lichen or moss on a roof may cause small holes to appear in the lead sheet under the drip-off point from tiles or slates. A sacrificial flashing may be fitted to the lead gutter or roof, or the growth may be treated with a chemical fungicide.
Condensation: In certain conditions the underside of lead sheet may corrode and it is important to design the roof to reduce the risk of condensation and provide adequate ventilation.
For further information, contact the Lead Sheet Association Tel: 01622 872432