What are the types of PAP and their use?

What will you learn from the article?

When used for roofing, roofing felt must meet specific technical requirements, as it will be exposed to significant temperature fluctuations ranging from -30°C in winter to +70 °C in summer, rain and snow, water freezing, and strong winds. Direct sunlight, especially UV radiation, is also conducive to the destruction of the coating.

Less stringent requirements are set for roofing felt used for layer waterproofing, covered with a pressure covering. This is the application of roofing felt forming waterproofing and anti-moisture insulation in the underground parts of the house - laid, for example, on the walls and floor of the basement, on foundations and on the floors of terraces and balconies.

What determines the usable properties of roofing felt?

Roofing felt products have been used in the construction industry for a long time, but the materials produced in the past did not ensure durability and, in addition, were harmful because they contained tar. The currently offered roofing felts are products with a modified structure using modern raw materials, although some traditional varieties are still used for minor purposes.

All roofing felt, regardless of purpose, consists of several layers of materials, and the type of raw materials used to create them determines the purpose and properties of the product.

The following layers of roofing felt are:

1. A topcoat, the task of which is to create a protective and decorative coating, and for this purpose mineral sprinkles of various granulation are mainly used.
2. The layer of coating mass determines the waterproofing properties of the roofing felt and the technological requirements of the covering. It is applied from various types of modified bitumen with fillers.
3. Carcass, i.e. the construction "skeleton" of the roofing felt, embedded on both sides in bituminous mass, which determines its flexibility and mechanical strength. It is made of traditional cardboard, glass fibers or plastics.
4. The protective film is available in heat-weldable and self-adhesive roofing felt. It prevents the rolls from sticking together. It melts during assembly or has to be torn off.

The type of bitumen used and the carcass material have a major impact on the properties of the roofing felt. All currently used coating compounds are bitumen products in the form of modified bitumens.

Oxidized (oxygenated) asphalt is the cheapest product used mainly to saturate roofing felt intended for waterproofing, e.g. underground parts of the house. The main disadvantage of this material is the limited temperature range of use - below -5°C it loses its elasticity and cracks, and above 70°C it melts.

SBS elastomer modified bitumen is currently the most commonly used coating mass, although due to the high cost of elastomer, it is also available in a depleted version as "semi-elastomer". Roofing felt coated with SBS modified asphalt is resistant to extreme weather conditions and easy to lay, as it remains flexible in extremely low temperatures down to -25°C.

Intermediate functional properties have membranes with a coating modified with APP plastomer - they provide a higher flow temperature (approx. 150°C), but they break at -10°C. This plasticizer also has a positive effect on the resistance of the coating to UV radiation and the impact of air pollution.

Currently used coating masses are bitumen products in the form of modified asphalts, photo: peuceta / stock.adobe.com. glass and polyester fibers in various forms. These warps are characterized by very diverse properties and determine the flexibility and strength of roofing felt.

Glass fiber warps have a low (2-8%) elongation under breaking force. Roof felt with such a matrix cannot be used in places where tensile forces may occur, e.g. when connecting horizontal and vertical elements. They also have a relatively low breaking strength of 300-400 N (in different directions).

Glass fabric warps show the highest breaking strength up to 1500/2500 N in the longitudinal and transverse directions, but with low elongation up to approx. 10%. These roofing felts are mainly used as base layers stabilizing the substrate and mechanically fastened.

Carcasses made of polyester non-woven fabric are a universal carrier layer of roofing felt, ensuring very high elongation of up to 50% in combination with SBS modified asphalt. With a standard weight of 200-250 g/m2, they guarantee a tear strength of 800-1000 N and are used especially for covering roofs with a complex surface. These warps are also available in a polyester-glass version with less flexibility and are mainly used for the production of single-layer roofing felt.

Various types of roofing felt and methods of fastening

Individual layers of roofing felt products can be configured in various combinations of base components, which determines their purpose and laying technology. However, detailed information on the parameters of specific roofing felts is included in the technical documentation of the product, attached to the roll of roofing felt or available on the manufacturer's website.

Due to the intended use, roofing felts are offered as underlay, surface or ventilation, as well as with special properties, e.g. resistant to root overgrowth.

Underlay felt is a basic waterproofing product used, for example, for water and moisture protection of foundations, floors on the ground, terraces or balconies, and as a component of multi-layer roofing. They come in many varieties and various combinations of types of asphalt masses and matrices with fine-grained surface topping, protecting against sticking during transport. The topping also facilitates the connection with the next waterproofing layer.

Surface felts are also products with various configurations of layers and often increased thickness to approx. 5.5 mm, containing coarse-grained protective topping, which can be colored, enhancing the aesthetics of the roofing. The durability of the cover is significantly affected by the thickness of the material used, because over time, under the influence of weather conditions, the roofing felt becomes sterile (asphalt "evaporates").

Ventilation roofing felt is a perforated product, and the holes allow moisture to evaporate from the substrate. They are used on renovated roofs as a base for the top covering, in which ventilation chimneys are placed.

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Methods of roofing felt laying

The method of fixing the roofing felt to the substrate is important for the durability of the roofing and the time it takes to install the roofing felt. Traditionally, mechanical fastening is performed on wooden substrates with the joints sealed with adhesive, and on concrete substrates by cold or hot gluing with asphalt mass.

A significant facilitation in the creation of roofing is the use of heat-weldable roofing felt, which in the basic range differs from the usual only in the edge strip without sprinkles, which facilitates welding at the joints, and the protective foil on the bottom of the roofing felt and on the longitudinal strip, which melts during welding.

As a standard, the heat-sealable roofing felt is glued over the entire surface, successively heating the unrolled roll and the substrate using a propane-butane gas burner. Obtaining a good quality cover created in this way requires a lot of experience from the employee, because in changeable weather conditions, the roofing felt can easily be overheated, causing it to burn or insufficiently melt the asphalt, which will reduce the tightness of the connection.

Roofing felt must meet stringent technical requirements, photo: Ultrament.

On smooth and primed substrates, self-adhesive roofing felt can be laid, which, after removing the protective film, is unrolled and pre-pressed, and then activates gluing by surface heating and rolling with a roller.

By Cezary Jankowski

Elaborated by Martyna Nowak-Ciupa

photo. opening: ImageESine / stock.adobe.com