Bituminous waterproofing

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Bituminous waterproofing systems are designed to protect residential and commercial buildings. Bitumen (asphalt) is a mixed substance made up of organic liquids that are highly sticky and viscous, and are waterproof.

Roofing felt components

Roofing felt is made with Bitumen which may be mixed with a filler component such as limestone or sand or polymers are added to the bitumen such as APP (atactic polypropylene) a plastic additive that gives rigidity and tear resistance, or SBS (styrene butadiene styrene) a rubber additive that gives more elastic benefits. The bitumen is applied to a base product such as polyester, fibre glass, rag fibre (hessian), or paper. These products are bought in roll format and are pulled through the bitumen mixes on huge rollers. The base product becomes saturated in huge tanks by the tar like bitumen substance, creating rolls of waterproof material.

Roll roofing components

Roll roofing is a bitumen product which is exposed to the weather. To protect the base from ultraviolet degradation mineral granules are added on top of the felt, also decreasing the products fire vulnerability. Thin, transparent film is added to the base of the felt during manufacturing on all torch-on products. This stops the felt from sticking to itself when rolled up during the packaging process.

  • A flat roof under construction. Note the opening left for the eventual connection of drainage piping.

Composition

The complex chemical composition of bitumen makes it difficult to identify the specific component(s) responsible for adverse health effects observed in exposed workers. Known carcinogens have been found in bitumen fumes generated at work sites. Observations of acute irritation in workers from airborne and dermal exposures to fumes and aerosols and the potential for chronic health effects, including cancer, warrant continued diligence in the control of exposures.

Reasons to use a roofing underlayment

  • It protects the roof deck from rain before the roofing is installed.
  • It provides an extra weather barrier in case of blowoffs or water penetration through the roofing or flashings.
  • It protects the roofing from any resins that bleed out of the sheathing.
  • It helps prevent unevenness in the roof sheathing from telegraphing through the shingles.
  • It is usually required for the UL fire rating to apply (since shingles are usually tested with underlayment)."[1]

Negative aspects

  • Bitumen is mostly produced from crude oil and is not regarded as a sustainable building product
  • Bitumen is combustible
  • Exposure to extreme heat and UV radiation decreases the lifespan drastically
  • The fumes that are produced during hot application of asphalt or tar can cause dermal and respiratory problems

Malthoid

From 1905 to 1988 The Paraffine Paint Co. of San Francisco had Malthoid as a trademark for waterproof and weatherproof building and roofing materials made of paper and felt in whole or in part.[2] However, it had become well known before that.[3] About 1913 Paraffine promoted its Malthoid roofing materials with a 16 page booklet.[4] In 1941 the Duroid Company began making Malthoid in Onehunga, New Zealand.[5]

Malthoid was once common enough to be used as a generic description of flat roofing material in New Zealand and South Africa (item 26). A description of a New Zealand house built about 1914 says it was, "built of timber framework. covered by sheets of asbestos. The roof was closely timbered, then covered by strips of Malthoid paper. This was then painted with tar and topped off with a sprinkling of sand."[6] Railway vehicles in Australia were roofed with Malthoid.[7] Malthoid is still available for flat roofs and damp courses.[8]

See also

References

  1. ↑ http://inspectapedia.com/roof/Roofing_Underlayment.htm
  2. ↑ LegalForce information on trademark
  3. ↑ Manawatu Times, Volume XXVII, Issue 7998, 21 June 1904
  4. ↑ Powerhouse Museum. "93/281/1 Brochure, 'Malthoid Bungalows', paper, The Paraffine Paint Company, USA, c. 1913". Powerhouse Museum, Australia. Retrieved 21 September 2013. 
  5. ↑ Scie Construction Ltd history of flat roofing materials.
  6. ↑ Off the Sheep's Back: Bill Richards Lindon Pub., 1986 ISBN 0864700148, 9780864700148
  7. ↑ photo and some history of Malthoid on Australian heritage railways.
  8. ↑ Tremco technical specs

External links

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