PVC film — theory and method

PVC foil (isogenopak cladding/isotop) is available in thicknesses of 0.25 mm, 0.35 mm and 0.5 mm and in rolls of 12.5 m or 25 m. The foil comes in grey, white (off-white), black and with a silver coating. Note that PVC foil is not suitable for outdoor use, as UV radiation degrades the material's properties.

Before installation, ensure that the foil is used within the tested temperature range of minus 15 to plus 75 degrees Celsius. The foil is impact-resistant and suitable for use in e.g. freezer rooms, but should not be used outdoors in frosty weather.

Make sure the insulation under the PVC film is correctly and precisely installed before the covering is applied. The PVC film is smooth and will clearly reveal any unevenness or faults in the underlying insulation work.

For pipes of very small dimensions, the small rolls are recommended, as these have a smaller inner diameter and therefore automatically wrap more tightly around the pipe than film taken from the outside of a large 25-metre roll.

The foil can be cut from the roll with a sharp knife while the roll stands upright on the floor — although this takes some experience. A more precise and user-friendly alternative is a foil cutter fitted with a small cutting wheel that runs in a rail and delivers a very neat, clean cut.

PVC foil is mainly secured with gutter adhesive, which is effective but contains volatile and harmful substances. As a less harmful alternative there is a special PVC adhesive based on the solvent NMP, which can be mixed with water in any ratio. Note, however, that this adhesive is water-soluble and may release liquid at joints and leave white streaks.

Rivets are supplied in endless strips and fitted with a maximum spacing of 150 mm. They are designed so the pointed end can be pushed straight through both layers of isotop. If the film is the thickest variant (0.5 mm), you can pre-pierce the hole with an awl so the rivet penetrates more easily.

At the ends of pipe installations, end/lamella bands are used, which are available in the relevant insulation dimensions. Remember that the lamella band is approx. 2 mm narrower than the insulation thickness — e.g. 28 mm band for 30 mm insulation — to avoid a thermal bridge through the insulation.

The lamella band must be approx. 2 mm narrower than the insulation thickness.

V and W bends have a small bend radius (tight curve) and are best used on threaded fittings or press clamps. S and 3S bends have a larger bend radius and are suitable for welded bends. Bends are available in angles from 11 through 22.5, 30, 45 and 60 to 90 degrees. Avoid cutting bends down if possible, as this gives a poorer result and removes the internal end finishes.

Clamp bends and tees have a small flange that makes them difficult to insulate over with ordinary insulation. These components are therefore supplied pre-filled with PU foam and fitted with PVC cladding on the outside. According to DS-452, it is permitted to reduce the insulation thickness by a certain percentage on such small fittings, though not by larger amounts.

Use insulated supports rather than traditional ones, as these reduce heat loss significantly. The traditional support draws 15 per cent more energy out of the pipes. By using insulated supports you can save up to 35 per cent of the insulation thickness. The insulated supports have a PU core with a hard inner core and a PVC covering on the outside so the foil can easily be glued to them afterwards.

For working with PVC film we recommend: a folding rule and square for marking out, dividers ground at the points for cutting holes, an awl for marking fold lines (press gently so as not to crack the material), a craft knife with replaceable blade for precise cuts, and tailor's scissors for small cut-outs.

To ensure accurate fitting, the whole assembly must be positioned correctly before the glue is applied. Temporarily hold the foil in place with a wire with one loose end. When the glue is dry, remove the wire by pulling the loose end. Wires that are to stay permanently — e.g. on finishing bands — must be of a non-corroding material such as copper or stainless steel.

When finishing bands are secured with copper wire, the knots must be kept as small as possible. Twist the wire one and a half to two times around itself and then twist it off — this gives a small and presentable knot.

Tape must not be used as a substitute for adhesive or rivets. When tape is applied, it is stretched lengthways, and over time it will try to return to its original shape, causing it to come away from the surface. Tape is purely a cosmetic and temporary solution.

Tape is only cosmetic and temporary — never a substitute for adhesive or rivets.