Zinc coatings

COMMON CONDITIONS:

Refers to the coating of sloping roofs in zinc.

CHARACTERISTICS:

A zinc roof is made up of two elements:
– the roof is made of zinc plate.
– the drainage membrane with bubbles.

The pitted drainage membrane prevents contact between the zinc sheet and incompatible supports, thus facilitating the evacuation of condensation water that may appear on the inside of the zinc thanks to the presence of bubbles that create a breathing space in the roof.

Beware of Zinc Sheets:

Despite its excellent resistance, Zinc must be handled with certain precautions, in particular:
– avoid throwing the sheets on the ground
– avoid letting them or sliding them over surfaces with protrusions.

Impacts can cause wrinkling or denting in one or more parts of the sheets, and some years later some breakage may appear in these places. Deep scratches can lead to breakages during bending or even afterwards, due to the effect of expansion.

Sheets and reels must be transported and stored in conditions that preserve them from moisture.

The sheets must be stored on a clean, non-roughened surface (preferably on a pallet). Coils must be placed vertically under the same conditions.

Tracing and transformation:
The traces must be made in pencil.
Zinc has good malleability. However, it is necessary to take into account the rolling direction for the execution of closed works.
The most resistant bends are those made perpendicularly to the rolling direction.
However, the gutters and covering plates can be cut and bent according to the length of the sheet.
In cold weather (temperatures below 7°C) the zinc should be slightly heated before working.

Dilation and contraction:

The expansion under the effect of heat causes a zinc elongation of 0.022 mm/m°C in the longitudinal direction of the rolling mill and 0.016 mm/m°C in the transverse direction.
The contraction is the inverse phenomenon caused by the drop in temperature.

All works in zinc must leave the metal free to expand and contract or compensate for this effect by applying specific expansion joints (vulcanized or mechanical).

Given our thermal amplitudes, we must have a maximum oscillation of 1 mm/m.

Welding:

Welding is carried out with the help of a filler metal made of a lead-tin alloy: tin gives the alloy fluidity and lowers its melting point.
It is recommended to use an alloy with » = 33 % tin . The use of an alloy with 40% tin makes it possible to obtain an optimal filling of the high-resistance joint.
The quality of a weld does not depend on the amount of filler metal used, but on its capillary penetration between the parts in contact. and its adherence to these. It is then necessary that the areas to be welded are degreased and clean; hydrochloric acid diluted in water is the most used paint stripper.

Feel free to ask questions and leave your comments!