Cutting or drilling operations on any metal produce fine metallic filings known as swarf. Steel swarf will rust immediately on reaction with oxygen and water to produce a stain that is very often mistaken for the rusting of the substrate. Such damage to metal cladding and pre-painted steel coatings is avoidable; it is the result of poor fixing practice or the work of other trades.
If swarf is not immediately cleaned from pre-painted steel building products, damage can appear either as localised rust stains or as fine scratches from swarf embedded in shoes. This type of damage will naturally detract from the performance or the appearance of the product. Non- ferrous metals also produce swarf, but as it does not rust it is not so obvious. It should, however, be removed in the same manner as steel swarf.
There are several different types of swarf. The most common swarf left on metal roof sheeting is that left as a result of using self-drilling screws, which consist of helically shaped coils and small chips. This local type of swarf should be regarded as a necessary part of the roofing process and can be easily removed, by regularly sweeping swarf into a receptacle with a nylon brush or using a small magnet.
Swarf can collect under flashings, screw heads, washers and in sheet laps, particularly with the use of horizontal cladding, and staining can arise if swarf is not removed as soon as it is generated.
Extra care should be exercised when fastening sheeting to structural steel because drilling heavy steel can create a large amount of swarf.
Power nibblers provide a clean cut but produce a metal cutout that can become embedded in the soles of footwear of people working on the roof, and it can be detrimental to the roof coatings. Nibling operations should be performed on the ground and this type of swarf should be cleaned up as it is produced.
N.B. — A power shear does not produce swarf.
Swarf produced by friction cutting or abrading equipment consists of fine metal particles, which have a large area of exposed steel, and therefore corrode very readily. It can be distinguished from drilling swarf by the 'sandy' feel of round particles, and the rust marks have a central round spot with a diminishing halo.
The particles generated by hole saws are also as the result of friction and are included in this category. This swarf is produced as hot particles; oxidation is rapid and they are not easily removed because they can embed themselves by melting or burning into the surface of the metal or coating.
Friction cutting equipment by definition produces heat, which destroys the metallic and paint coating in the vicinity of the cut. This method of cutting is unacceptable and material cut in this manner is not covered by any warranty. See 4.17C Friction Cut Edge.
Friction blade or carborundum disc cutting is not permissible on metal roof or wall cladding.
The roofing contractor will safeguard himself from any damage claim if round swarf is discovered, by not using any friction type cutting tools on site. Power shears, guillotines and hand snips do not produce swarf and in skilled hands are capable of cutting any shape required for the installation of metal cladding.
A common cause of swarf complaints arises because other trades have used grinding equipment in the vicinity of a newly completed roof. Wind carried swarf can contaminate large areas. Designers and other contractors should be aware of the likelihood of such damage, and project planning should include scheduling of all cutting or grinding work to be completed before laying the roof cladding.
Failure to do so can result in damage and the necessity for a reroof or repainting. The liability remains with the person who caused the damage and is not the responsibility of the roofing contractor.
Other debris that is created from the roof cladding process, including rivet stems, nails, screws, broken drill bits, tools, and used sealant cartridges left on a roof surface, can all cause rust staining.
All debris should be removed daily from the roof cladding and gutters.