Waterproofing and Damp proofing treatment with glass tissue based felts

Most of the civil and industrial roofs are protected by a water proofing system which normally consists of two or more bituminous membranes of either modified (by thermoplastic polymers) or oxidized bitumen and reinforcement felt.

Twiga Glass Tissue can be used in two manners:

1. Conventional felt method ‘IN-SITU’ water-proofing method when the glass tissue is embedded into bitumen at the site.

2. The bituminous membranes are subjected to severe operative conditions therefore the reinforcement layer needs to conform to the following requirements:

  • It must be rot-proof.
  • It must offer optional dimensional stability.
  • It must be easily and uniformly impregnated by bitumen during the manufacturing process.
  • It must offer sufficient tension resistant to allow a correct manufacturing speed and grant the required mechanical resistance to the bituminous membranes, both for the application work and to withstand the most severe operative conditions.
  • The characteristics of Twiga Glass Tissue conform to the various requirements of the sector and the membranes manufactured with the reinforcement material are suitable for all types of waterproofing systems, Twiga Glass tissue conforms to the standards for reinforcement of felts and bituminous membranes for waterproofing systems.

    Glass fiber Base Coal Tar Pitch and Bitumen Felts (IS 7193-1994)

    As a base membrane in Coal Tar Pitch and Bitumen Felts, Twiga glass tissue used is flexible uniformly bonded, mat composed of chemically resistant borosilicate staple glass fibers, distributed in a random open porous structure, bonded together with a thermosetting resin with following physical properties:

    • Weight - the minimum weight of the tissue shall be 40g/m2.
    • Thickness - the nominal thickness of the tissue shall be 0.5 + 0.1 mm.
    • Tensile strength - the minimum tensile strength of the tissue shall be 45 kg/150 mm width in the longitudinal direction.
    • Porosity - the tissue shall have a porosity when related to pressure difference across the sample of not less than 06 mm and not more than 1.9 mm at an air velocity of 1m/s.

    Glass fiber base bitumen felts are suitable for waterproofing and damp-proofing in buildings and other situations where penetration of moisture to be stopped. Glass fiber base felt has the advantage that it does not rot by continued exposure to moisture conditions.

    Glass fiber felts used for water proofing and damp proofing are:

    a) Type 2, Grade I - talcum mica or sand surfaced glass fiber base bitumen felts for waterproofing.

    b) Type 2, Grade II - talcum or sand surfaced glass fiber base bitumen felts for damp proofing.

    Features & Benefits:

    • Does not absorb moisture and therefore prevents the ingress of moisture into the material. Thus incidence and fear of moisture pockets and blisters are greatly reduced to the minimum.
    • Non-wicking.
    • Strong and flexible and follows roof contours quite easily.
    • Non-inflammable, reducing the fire hazards due to flame spread.
    • Porous and hot bitumen impregnate it easily and strongly.
    • Non-rotting. When an organic based waterproofing is damaged as a spot, it wicks moisture and rots, both moisture and rots spread rapidly. Repair in this case involves removing a large area of the organic reinforcement. With glass tissue any external damages may be patched up quickly and with comparative ease.


    The bitumen glass fiber base felt consists of a continuous sheet of resin-bonded glass treated with bitumen. The coating shall be uniformly applied. The resultant coated felt shall be given a superficial application of mineral powder to prevent the layer of the coated felt sticking together in the roll. This also gives useful protection against effect of the sun and when laid on roofs, does not need further treatment unlike other types of self-finished felt.


    • Unless otherwise specified, glass fiber base bitumen felts shall be supplied in widths of one metre and generally in lengths of 1 metre, 10 metres and 20 metres. Coaltar treated glass fiber felts shall be supplied to the required widths generally in the length of 75mtr.
    • Weight - the weight of the ingredient used in the manufacture of glass fiber felts for 10 m2 shall be not less than those specified in Table 1.

Table minimum weight of bitumen glass fiber base felts for 10 m2

Sl. No Type of Felt Untreated Bas Constant Total Weight in Dry Condition Including Surfacing Material
(1) (2) (3) (4) (5)
(1) Kg Kg (4) (5)
i) Type 2 Gr. I 0.4 15.3 18.0
ii) Type 2 Gr. II 0.4 22.0 25.0

“In-Situ application of REINFORCED GLASS TISSUE and BITUMEN”

The system is comparatively easy to lay and is monolithic in its entirety from the surface it is laid upon to the finish. It acts like continuous reinforced matting over the substrate irrespective of the number of layers of bitumen/glass tissue, since the glass fiber has an open texture into which bitumen can permeate. The first bitumen/glass tissue layer bonds itself to the surface upon which it is laid and a very subsequent unit layer bonding to the layer below homogeneously because the hot bitumen poured over the previously set course dissolves a part of it and interdiffuses into it, resulting in perfect compatibility of the two.

The bond of the bitumen with the glass tissue, i.e. the internal bond of the system within itself and its bond with masonry is good since no failure of this type has been observed in the pull out test. The confirmations of the adhesive bond of the glass tissue with bitumen have been further borne out by the visual observation in the pull out tests, natural and accelerated weathering tests in which no separation of the reinforcement has been observed. This bond is an important factor which contributes to the ultimate strength and durability of the system. High heat resistance and durability of the glass reinforcement of the system due to its ceramic nature is another positive point in the longevity of its life.

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