Crimp Curving

Crimp curving is applicable to all profiles, but it is most suited to asymmetrical sections that cannot be rolled or drape curved.

Crimp curving is produced by pressing a small crimp in either the tops of the ribs or the pans of the sheeting. The profile is progressively shortened at these points causing it to bend. The radius can be altered by the spacing of and the number of crimps.

Some machines are capable of forming high-strength steel by a combination of compression and tension in the die design, and some machines require the use of strippable film as a lubricant to avoid coating damage. Where sheets are to be end lapped and different strength materials are used together, machine adjustment is required to ensure an acceptable fit because their profiles are not usually consistent.

Fitting curved sheeting requires considerable care to ensure a satisfactory and aesthetically pleasing job. Setting out requires first checking that the materials delivered on site are within specified tolerances, and before commencing work the building should be checked for squareness.

The curving process can cause dimensional changes, which can lead to misalignment, so the sheets should be kept square with the building. Some minor saw-toothing at the gutter end is to be expected when fitting curved sheeting. When multiple curves are required that cannot be provided on one sheet, the sheets should be fixed in the order shown in Fixing Order: Curved Sheets.

Fixing Order: Curved Sheets

Fixing Order Curved Sheets

 

All transverse laps of crimped curved roof cladding must be mechanically fixed and sealed.

Some paint checking and microcracking is likely to occur at the crimps on metallic-coated steel cladding and these may show a white bloom. This is more readily seen in unwashed areas, such as when crimp curved sheets are unlined as a canopy or over a walkway roof. This area is required to be washed regularly under the maintenance provisions of the supplier's warranty.

The underside of colour-coated roof cladding is provided with a primer and backer coat only and if this is exposed in an unwashed area and can be seen, it should be post-painted with two coats of Acrylic paint. These areas are subject to maintenance as an unwashed area. (See Overpainting) Because the top of crimped sheeting is also subject to the collection of dirt and debris, particularly in the low-pitched area, it is subject to maintenance requirements.

All side laps of crimped curved sheets below the minimum pitch for the profile must be mechanically fixed and sealed.