Roofing made of asbestos-cement sheets

Installation of asbestos-cement roofing. Asbestos-cement sheets are laid diagonally with an overlap, from bottom to top, in rows – from left to right or from right to left. Eaves and gutters are covered with pre-prepared strips of roofing steel. In the first row of the eaves, edge sheets are laid and fastened with two nails 2.5×35 mm. The second and the next four rows begin with laying the halves of the sheets, which are reinforced with staples and nails. All subsequent odd rows begin with the laying of whole sheets, reinforced with two nails (Fig. 1, 2, 3).

Fig. 1. Roofing made of corrugated asbestos-cement sheets:
a – general view; b – ridge knot; c – longitudinal overlap and fastening of sheets to the crate; 1 – lathing; 2 – a nail; 3 – steel washer; 4 – roofing felt gasket; 5 – roofing felt tape.

Fig. 2. Orderly laying of asbestos-cement sheets along the crate.

Fig. 3. Adjoining the slope to the wall in the longitudinal direction:
1 – lathing bar; 2 – VO sheet; 3 – a nail; 4 – angle 120; 5, 6 – ridge parts; 7 – solution; 8 – mastic.

Starting from the third row, the lower corners of each sheet are attached with anti-wind buttons. Before covering the ridge and ribs, the ridge bars and roofing felt tape are strengthened. The latter is laid to prevent snow from blowing into the attic (see Fig. 1). One of the main requirements when laying asbestos-cement sheets is to correctly break the mesh on the slopes with a step in the longitudinal direction – along the slope of the roof – 255 mm, and in the transverse direction – along the overhang – 235 mm. The sheets should not be nailed tightly. The heads of the nails should only be in contact with the planes of the sheets. Otherwise, the sheets will crack or vibrate in windy weather. A roof made of asbestos-cement sheets does not require special maintenance, its durability is 25 years or more. To increase the service life, it can be painted with light and weather resistant oil paints and colored enamels PF-115, PF-133. To obtain a silvery roof, add aluminum powder to the varnish XB-784 or GF-166 in an amount of 6 … 10% by weight of varnish. The sheets are fastened on the crate with nails, screws and partially with anti-wind brackets. The roof lathing is performed in such a way that it would be possible to lay a whole number of sheets on it both in the longitudinal and transverse directions (Fig. 2, 3).

Fig. 4. Laying and fixing VO sheets. Lengthwise cut.

Fig. 5. Adjoining the slope to the wall in the transverse direction:
1 – lathing bar; 2 – VO sheet; 3 – corner; 4 – a nail; 5 – mastic.

The sheets are laid in parallel rows in the direction from one pediment to another. Laying begins with a cornice row and ends with a ridge. Dormer and pipe finishes are shown in fig. 6, 7.

Fig. 6. Covering the ramp and assembling the dormer collar:
1, 2 – front and side corners 120; 3, 6 – screw; 4 – VO sheet; 5 – bracket; 7 – mastic; 8 – transition bar.

Fig. 7. Arrangement of a collar around the chimney head.

To eliminate cracks in the transverse and especially in the longitudinal overlaps of HC and VU sheets, sealing mastics are used, for example, thiokol sealants AM-0.5; sealing non-hardening construction; UT-31 sealant. The mastic is applied with wooden spatulas to the overlapping edges of the sheets with a strip 60 … 70 wide with a layer thickness of 6 … 7 mm, after which the overlapping sheet is lightly pressed.

Repair of asbestos-cement roofing. Asbestos-cement roofing sheets have insufficient frost resistance due to the high porosity of the asbestos-cement material during operation. When superficially wetted, the sheets warp, losing strength. The service life of such roofs is 10 … 15 years. The service life of roofs made of asbestos-cement sheets can be significantly increased if the sheets are subjected to hydrophobization before laying, which leads to the formation of a thin hydrophobic layer on the surface of the material, preventing the surface from wetting and water penetration into the pores. As a water repellent, an emulsion of liquid GKZH-94, as well as aqueous solutions of GKZh-10 and GKZh-11 are used.

To improve the quality of the protective water-repellent film, 1% of aluminum stearate is added to the composition of the water repellent. The application of a hydrophobizing solution to asbestos-cement sheets laid in the roof should be carried out in a dry warm season on a cleaned surface by spraying, brushes or compressed air. The hydrophobized surface does not require further special maintenance. The use of hydrophobization of asbestos-cement sheets allows them to reduce their water absorption by 3 … 5 times with a corresponding increase in their frost resistance. The service life of the hydrophobizing film is 5 … 7 years, after which re-hydrophobization is required. In the absence of mechanical damage on the roof, the asbestos-cement roof can be painted with liquid oil paint every 3 … 4 years. Sheets with cracks or chips are replaced with new ones. The damaged sheet is removed so that the adjacent one remains in place. The new sheet is laid by two roofers. One lifts the sheets weakened from the side and from above, and the other, placing a new sheet on the overlapping edge of the adjacent one, moves it towards the ridge. When the bottom edge of the new sheet coincides with the edge of this row, it is attached to the base. A broken or cracked tray is also replaced by two roofers.

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