WHY CHOOSE DISTILLED POLYMER-BITUMEN MEMBRANES

 

WHY CHOOSE DISTILLED POLYMER-BITUMEN MEMBRANES ?

Producers of synthetic roofing and covering products/systems often compare them with products that are generically defined “bituminous”, without however specifying whether they are conventional bituminous sheets of oxidised bitumen or bitumen modified also with polymer additives but in a concentration that does not affect the physical structure of the mix, hence the characteristics of the bitumen remain preponderant. Polymer-bitumen membranes (PBM) are on the other hand made up of a polymer-bitumen amalgam, where the continuous phase (the matrix) is the polymer in which the bitumen is dispersed and the physical/chemical properties of the latter, and consequently of the membrane, are mainly determined by the polymeric matrix; the mechanical properties of the sheet, on the other hand, are mainly determined by the reinforcement with which the membrane is produced. A special feature of the polymer-bitumen membranes is in fact that they can be produced with varying levels of mechanical resistance, which can be adapted to the requirements of the various fields of use by strengthening them with increasingly resistant reinforcements.
Non-woven polyester fabrics are the most commonly used type of reinforcement, because they are able to associate an efficient mechanical resistance with a high ultimate elongation of around 35-60% (higher than that normally found in polyester fabrics, which is around 15%). They are mainly able to guarantee a higher and more uniformly distributed resistance to impact and static loading than normal fabrics, used mainly as reinforcements in synthetic sheets, which tend to snag when subjected to point loads. This reaction is comprehensible considering the fact that the fibres of non-woven fabrics are tightly distributed in all directions of the space, even vertically through the depth of the product, whereas the fibres of other fabrics are more or less tightly mesh-woven (warp and weft) and arranged just on the plane. That’s not all, more modern reinforcements made of composite non-woven fabric associated with fibreglass confer a dimensional stability to the membrane of less than 0.25% on a non-bonded sheet and half the dimensional shrinkage as opposed to that of synthetic membranes reinforced with polyester meshing, whose stability is around 0.50%. This feature is of course important for a synthetic sheet that has to be laid loose or partially fixed, but is much less so for a polymer-bitumen membrane that can be completely bonded in total adherence and, in such case, the dimensional shrinkage drops to around 0.02-0.05%.
Another important feature that distinguishes the polymer-bitumen membranes is their thickness, which is no less than 4 mm for the single-layer membranes, and this is definitely more compatible with building requirements, where the unit of measurement is not the tenth of a millimetre; this aspect also affects the fact that the covering, both after application and during laying on-site, can withstand foot traffic of operators wearing normal shoes, without having to wear light sports shoes, which are generally imposed by the producers of synthetic coverings right from the initial on-site laying phases.
Aesthetic performance neither is a handicap for the polymer-bitumen membranes with self-protection; they are produced with the upper face protected with mineral flakes or granules that are incorporated hot in the upper part of the mix while it is still in the melted state to guarantee irreversible adhesion. This, together with the possibility to use mineral grit coloured in the oven at high temperatures, for light colours (grit with high saturation and luminosity “MINERAL REFLEX WHITE” is also used) resolves the problem of absorbing sunrays and determines a lower temperature in summer. The slate-coated surface, on the contrary to synthetic sheets, can be painted over and creates an ideal substrate to ensure a long service life of the paint; the reflectance of the roofing can be further boosted using the special WHITE REFLEX paint, consequently cooling the roof and/or saving in conditioning expenses in summer. The mineral protection, combined with the resistance to point loads of the non-woven polyester reinforcement fabric, in addition to the thickness of the material and the flexible properties of the rubber-bitumen amalgam, determine greater resistance to hailstone, which is decreed also by legal standards; in fact, for the membranes in polymer-bitumen, the applicable European standard states that the reinforced membranes are scarcely affected by hailstone, to such an extent that no specific test is requested, which, on the contrary is indeed requested for synthetic sheets.
The laying technique for polymer-bitumen membranes, even though it still requires a certain degree of training, is much more intuitive and easier than that used for synthetic sheets in general, plus there is no need for costly accessories and fixing devices; the latter are indeed often calculated separately in the metric estimation of synthetic coverings and have a significant economic impact on the cost of the roof, especially those with fractioned elements and/or with numerous skylights. The special feature of the polymer-bitumen membranes lies in the fact that the membrane itself becomes adhesive by heating it with the torch so that it can be bonded to the laying surface without using adhesives or other additional materials; this property minimises water seepage, even if the waterproof covering is pierced; in other words, it avoids the “funnel effect” that forms when the parts downstream from the completely loose or partially fixed coverings are pierced, as in the case of synthetic coverings. This principle has also been exploited for waterproof coverings on motorway bridges where the risk of piercing is significant, considering that road asphalt is laid and rolled with a roller compressor directly over the polymer-bitumen membranes bonded in total-adherence to the bridging deck. The possibility to bond in total adherence of the polymer-bitumen membranes limits water seepage in the case of leaks and facilitates traceability. The same technique is used to seal the overlaps and, by torch bonding both ends, a secure autogenic seal is obtained; considering such outstanding operational simplicity, which cannot be said for sealing synthetic sheets, no further inspections are necessarily required afterwards, as is the typical case for the operational techniques on synthetic membranes because they do not offer any obvious and definite signs of efficient execution right from the laying phase; when sealing polymer-bitumen membranes, a clear continuous trickle of melted mix can be seen approximately 10 mm outside the overlap, thus guiding the operator efficiently throughout the job and confirming that the seal is correct, just like you would see when welding metals.
Again thanks to the fact that the membranes are torch-bonded, which is not the case for synthetic sheets, old polymer-bitumen coverings can easily be repaired without any special preparation in advance, if not a quick brushing to remove dirt that may have settled on the coverings, even those protected with mineral granules where the application methods are the same as those used to seal the ends of the new coverings (in the case of repair work on old coverings made up of synthetic membranes on the other hand, the latter have to be cleaned in advance with special solutions and in many cases combined with strenuous mechanical brushing work).
Another just as important advantage that distinguishes the polymer-bitumen membranes from synthetic membranes is yet again determined by the thermo-plastic characteristics of the material and by how simple patch repair work can be done just as easily without using adhesives. A covering can also be completely renewed simply by laying a new layer on top of the old one, bonding it using a torch in total adherence, consequently avoiding demolition expenses and transport costs to the tip.
The result will not just be a new single-layer covering (which is what happens necessarily when renewing a synthetic covering where the new one cannot be bonded on top of the old one), because when the new polymer-bitumen membrane is bonded onto the old one, any imperfections will melt and merge together, actually creating a new multilayer covering, which also exploits the old reinforcement because it is incorporated in the new layer.
On the contrary to what one may think, polymer-bitumen membranes are not so sensitive to fire as other types of synthetic sheets actually are, such as Polyolefin (TPO) sheets; because the latter are not chlorinated, they are naturally not resistant to fire, as in the case of PVC and CPE, which they aim at substituting; additionally, unless they are appropriately supplemented with special additives, they cause the flame to spread very quickly, since they are not bonded to the laying surface, but are loose and the flame is able to work its way also underneath. Fireproofing additives in synthetic sheets also trigger additional problems of toxicity of the fumes.
As for the service life of the coverings with SBS-modified polymer-bitumen membranes, rather more interesting than the insurance policies of the manufactures are the statistic surveys carried out by independent institutes; on this topic, you can refer to the Swiss survey carried out on the service life and defects of the waterproof coverings of flat roofs, which reveal that the expected service life of a roof with visible covering in polymer-bitumen (in Switzerland, just the SBS-modified membranes are produced) is 25 years and with few defects, as opposed to the 15-20 years of the PVC sheets, which also have a higher level of defectiveness.
In 1994, the Swiss French waterproofers, complained about technical problems on the synthetic sheets in PVC in a letter addressed to the manufacturers and project designers. One should recall that Switzerland is the traditional district of PVC covering producers and, at the beginning of the 90’s, was one of the first European countries to produce sheets in TPO; this proves that innovation should always be confirmed by long-term experience and cannot always be replaced by a simple test in a laboratory. Such experience on polymer-bitumen membranes already exists because they have been produced since the 60’s.
The special feature of the polymer-bitumen membranes is the fact that they are laid over the old covering with which they merge solidly thus they have a unique ability, in terms of prefabricated membranes, of renewing an old covering simply by bonding a new membrane to it in total adherence and thus extending the service life of the new layered arrangement, which becomes even more efficient than the previous one because it is thicker. This property of the polymer-bitumen membranes meets the criteria of sustainable building and adds a new concept of service life, which is no longer mere durability but rather the “typical service life” of the system; the coverings can indeed be renewed by laying the new membranes over the old covering with which they merge solidly without producing demolition waste up to 1÷2 times; based on the overlying protection system applied, the service life of the layered arrangement is 60÷90 years.