- Roll roofing elements
- Choice of materials
- Preparation of the base
- Laying base waterproofing
- Applying a protective layer
For flat and pitched roofs, weld-on roll roofing remains the most preferred material. Its installation is simple and quick, and its performance can be easily enhanced with additional layers. And yet, the device of such a coating requires compliance with a number of rules..
Roll roofing elements
Although the application of bituminous coatings on flat roofs has been practiced for more than a century, this technology has come to civil engineering relatively recently, mainly due to the appearance on the market of modern high quality insulation materials. Unlike the roofs typical of Khrushchev’s panel houses, the current roll roof is not just a layer of bitumen fused onto a concrete base plate. Today, such coatings are distinguished by high manufacturability, many times longer service life and extremely high maintainability..
It is not necessary to use prefabricated and monolithic slabs as a base base for a roll coating; almost any type of solid lathing will do: formal concrete slabs cast on a fixed corrugated formwork, or a frame structure sheathed with sheet materials on top. The base of the roof can be supported by various types of support system: metal or wooden trusses, rafters, beams. Also, any type of roof thermal protection device is allowed in the supporting structure. The only limitation for the use of a soft roof is the slope angle of the slope – no more than 30 °.
The roofing itself has a complex structure. The outer layer is represented by a protective and decorative shell, which is used as roll materials with a high-strength base and a surface sprinkled with mineral chips or covered with a layer of modified bitumen. An elastic layer is located under the protective coating, which serves as the main waterproofing, and in the case of hot application, protects the base material from high temperatures. All this is laid on a base covered with an adhesive layer of bitumen with reinforcement.
Choice of materials
There are two types of roll roofing materials: those with a base, such as cardboard or fiberglass, and baseless. Both varieties have the same high performance, but the specifics of the installation are somewhat different..
Materials with a base are preferable from the point of view that during transportation and installation, their integrity will be guaranteed to be preserved. At the same time, base coatings require more careful handling, and during the installation of the roof, only of them must be independently provided for the outer layers of reinforcement, for example, glass cloth, fiberglass or cardboard.
Reinforcing materials are the most common because of their ease of use. Roofing material is considered the cheapest, in a slightly higher category is waterproofing reinforced with fiberglass. Foil, polyamide or polyester film can be used as additional interlayers. The inclusion of additional layers is carried out mainly in order to increase strength and, accordingly, ensure a long service life. Usually, the main materials are protected with powder or a layer of hard plastic, so they are usually used in the outer layer of the roofing.
Base materials are generally used to increase the overall thickness of roofing and waterproofing. Thus, even if a gap is formed in the protective coating, water will not be able to penetrate the substrate, and the roof will calmly survive until the next repair without intensive development of damage. Not all base coatings are characterized by low strength, the highest quality of them have an impressive thickness and multilayer structure of various types of bitumen, modified with polymer additives and reinforced in bulk with fiber, for example, asbestos or glass.
The third group of materials for soft roofing is adhesive mastics, due to which a strong adhesion of the entire coating to the base and layers is ensured. Mastics can be pre-applied to the back of roll materials, while base coatings are completely cured elastic bitumen, which, in fact, turns into mastic when melted. Mastics are cold and hot, it all depends on the method of application and preparation, which may vary depending on the manufacturer’s recommendations.
Preparation of the base
At the first stage of the installation of a soft roll roof, the base surface is prepared. Depending on the base material, the preparation method may differ.
For concrete slabs, careful alignment is required to eliminate irregularities exceeding 3–5 mm per meter of plane length in any direction. The gaps between the slabs, chips, pits must be sealed with cement mortar; in especially severe cases, a leveling screed is required. After the surface is leveled and dried, it should be dedusted and the adhesion improved with a primer, which can be used as means intended for the preparation of foundations before applying waterproofing. A thin layer of mastic is applied to the primer with a brush, which can be cold or hot, depending on which method of gluing is provided for the remaining layers.
A reinforcing material of low density – up to 150 g / m2 is immediately laid on the not yet hardened mastic. It is important that the reinforcement is done as soon as possible with a freshly applied compound for a high-quality impregnation. If the hot application method is envisaged in the future, the reinforcement is covered with another layer of molten bitumen..
Wood substrates coated with cold-applied materials are prepared in the same way. Often the base itself is represented by two rows of edged boards. The first is laid along the slope line with an indent of 50-60 mm, the boards of the second layer of the sheathing are tightly rallied, while maintaining the direction at an angle of 30-45 ° relative to the lower boards. Also, the second layer of the base can be represented by sheet materials..
In any case, the application of a preparatory layer of mastic is necessary in order to level the strengthening of the base, as well as to ensure high-quality adhesion, which will not be affected by wood shrinkage. If the roof is applied hot, it is advisable to additionally protect the wood from the effects of high temperatures. For these purposes, you can use asbestos fabric, increase the thickness of the preparatory layer, or replace the top layer of a continuous sheathing with heat-resistant materials, for example, DSP or LSU.
Laying base waterproofing
Quite often, the protective and decorative coating of the soft roof is laid immediately on the preparatory layer. When it comes to premium quality materials on roofs with slopes above 20 °, this approach may be acceptable, but usually an under-roof waterproofing device is required. It not only provides additional protection against leaks, but also serves as a reinforcing layer, helping to increase resistance to mechanical damage and compensating for warp vibrations. In this case, roll materials are rolled across the direction of the slope, starting from the bottom, the joints are made with an overlap of at least 10 cm.
As already mentioned, it is customary to use base materials for waterproofing. For slopes with a slope of up to 10 °, it is optimal to apply 3-4 layers, with a slope of 15-20 °, at least two are required, for the steepest roofs one will be enough. The recommended final thickness of waterproofing is determined by snow loads and the predicted melting time of the caps, in the case of arranging an exploited roof, the thickness of the waterproofing is greatest. Usually roll-up waterproofing is applied by hot method, this is the simplest and most efficient installation method. However, if cold mastic was used in the base, its overheating can lead to an irreversible change in the physical and mechanical properties. The general rule is that laying the lower layers hot, and the upper ones cold, is permissible, but not vice versa..
Hot application involves using a gas flare torch connected to a propane cylinder to melt the surface of the adjacent layer materials. Before fusing, the roll is pre-rolled across the roof and positioned in compliance with the required overlap, then the edge is glued and rolled back. During the rolling process, the burner nozzle moves along the roll, while the flame is directed to the corner in order to simultaneously heat the surface and the side of the roll adjacent to it. In this case, rolling is carried out using a long hook, which can be used to adjust the position of the roll during the welding process.
Applying a protective layer
Unlike intermediate layers, the soft roof topcoat is rolled in the direction of the slope. Here, both cold and hot gluing methods are also permissible, however, the choice is determined not by the type of mastic used, but by the characteristics of the roofing material. So, the manufacturer can provide for the application on the back surface of an increased layer of bitumen, which melts, it is also possible to have an adhesive edge under the film.
During hot melting, it is necessary to ensure that the substrate warms up under the rolled material until a glossy shine appears, it is desirable that the surface even slightly boils and bubbles. In parallel, deep heating of the back side of the applied material should be ensured, especially for the edge, where the bitumen layer is slightly thicker for better sintering of the overlap. At the same time, there is no need to exert additional pressure on the roll, gluing occurs under the material’s own weight, although it will not be superfluous to roll the joints with a roller. A clear sign of correct laying is a flagellum of molten bitumen protruding from under the edge of the material.
With cold gluing, the material is pre-rolled and positioned, then the protective films are removed from the adjacent parts of the joint. After aligning the joint, it is rolled with a metal roller. On roofs with a slope above 5–7 °, the “cold” coating needs anchoring, which is done with nails for waterproofing. After that, a strip-strip is nailed along the attachment line or adhesive tape is glued. This not only provides additional resistance to leaks and protection of fasteners, the presence of stripes along the slope of the slope helps roofs with a steep slope to acquire a consolidated look.