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For further information please contact SLE Cladding Ltd. Tel.
01948 666 321. Fax. 01948 66 55 32
PROFILED GALVANISED STEEL ROOFING & CLADDING SHEETS |
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Corrugated Galvanised Roofing Sheets have been available for well over 100 years. With the introduction of Plastisol and Polyester and other coatings for which galvanised sheets are the base material, the box profile took the dominant position in roofing & cladding, yet it has failed to displace the corrugation as the preferred profile for galvanised sheets, who still retain their position as the most popular of low cost basic cladding materials. Treated sensibly and properly erected in un-polluted atmospheric areas and given an occasional coat of paint at the appropriate time, they have the ability to last many years like Polyester coated steel. At the other end of the scale, erected unpainted in the corrosive atmosphere over a blacksmiths forge or over an enclosed farm slurry pit their life span can be as little as 18 months. Overlap : The side overlap should be at least one corrugation, two in exposed areas. Ensure that the overlap faces away from the direction of the prevailing wind. End overlap varies according to the roof pitch. - 150mm (6") = 15º pitch, 225mm (9") = 10º pitch, or 300mm (12") = 5º pitch. Fixing Sheets : The British Standard states that sheets should be nailed at every valley at the sheet ends or at a join or lap and every other valley on intermediate purlins (bearers). This advice is not always adhered to. For corrugated sheets fix at the top of every other corrugation at sheet ends and joins/laps and every third corrugation on intermediate purlins. Side Lap Fixing. Side laps can also be stitched together. This is particularly recommended for exposed areas. This is done with Self drill & Tap Seam Stitchers (Teks). Most roofers fix at 18" centres, but this can be varied to suit locations.
CURVED GALVANISED SHEETS SLE Cladding Ltd can supply 0.7mm curved corrugated galvanised sheets in a 10 x 3" corr. With curved sheets it is standard practice to double side lap the sheets for a better seal, this reduces the effective coverwidth of a 10 x 3" corrugated sheet to 2ft 3" (625mm) The tightest radius that sheets can be curved to is :- Prime Quality a 3 ft radius and up to 16ft long. Superior Seconds Quality a 10 ft radius and up to 12 ft long. CLICK HERE to visit our page on CURVED SHEETS. WARNING BEWARE OF WHITE VAN MAN BEARING GALV SHEETS. These seemingly very cheap sheets (bought for cash) are usually of a quality that SLE Cladding Ltd or other reputable companies do not trade in. They may have their uses as shuttering for concrete, fencing off building sites or protecting windows and doors on redundant buildings. or other very short term uses. Extreme caution should be taken in purchasing them for any longer term use. STACKING When stacking sheets, place one sheet on top of another. DO NOT slide one sheet down the profile or corrugation of another, as this will scar the galvanising.
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SLE Cladding Ltd can supply sheets cut to length from stock or to order as per below
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to see profiles Fixings Suitable fixings for Corrugated Galv Sheets are Spring Head Nails with Black Poly Washer or Drive Screws with a Galvanised Diamond Curved Washer with a diamond felt washer underneath. For Box Profile Sheets, use Tek Screws in the valley. Note. Some roofers are now using a longer type AB TEK Screw on corrugated sheets. This is mainly a question is of appearance. Do you find the Tek Screw riding high on top of the corrugation unsightly? BARRIER . For a quality long lasting roof it is advisable to place a barrier between the sheets and the purlins on which they rest to prevent any corrosion of the sheets from the purlins. This is most important where livestock are being housed. It applies equally to both metal and timber purlins as timber purlins are often tanalised (pressure treated with chemicals to prevent rot) In the case of existing metal purlins remove any build up of rust. The barrier can be a liberal coating of bitumen paint or plastic tape.
PAINTING
Bright
shiny new galvanised sheets should be left up to 12 months for the
surface to go dull before painting, otherwise in very hot weather
the paint is liable to peel off.
If
leaving the sheets this length of time before painting is not an
option due to aesthetic considerations. The surface may be
treated with a Mordant etching solution to remove the shine and provide a
purchase for the paint. Wash off the etching fluid and allow to
dry before applying paint.
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for page on MORDANT SOLUTION
FAQ's (Frequently asked question) Why doesn't a galvanised sheet rust at the edges or when holes are drilled into it? The answer taken from a British Steel ( Now Corus) information leaflet is:- The corrosion rate of Zinc in most UK atmospheric environments is known to be only 1/10th to 1/30th the rate of mild steel. Furthermore if the surface is painted. then the protective effect of the duplex coating is synergistic (i.e. whereas, in a given environment the zinc coating might last six years and the paint coating on mild steel around 2 years then the life of the painted zinc would be not eight but more like 11 to 13 years) Galvanic protection across small bare areas (cut edges) also occurs. This happens when two dissimilar metals are in electrical contact in the presence of a conducting medium (moisture). Galvanic corrosion of one takes place whilst the other is protected. The most reactive of the two metals will become the anode in a natural electrical cell and if the anode does not form an insoluble high resistance oxide film (and zinc does not) it will oxidise and produce electrical current to protect the cathode from corrosion. Zinc protects steel by galvanic action because it is anodic to steel at normal ambient temperatures.
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