Production Of Lowdensity Strawboards

The manufacture of low-density strawboards follows a process developed in Sweden in 1935 and is suitable for local production in small industrial units (see Figure 15.32). The boards are usually produced in thicknesses of 50 to 100 mm. It does not matter what state the straw is in, as long as it is not beginning to rot.The moisture content before the process starts should be 6-10%.The procedure is as follows:

1. The straw is cleaned in a ventilation unit.

Paper drum

Paper drum

15.32

Production of strawboards. Source: Stramit.

2.The fibres are straightened and laid in the same direction. If extra adhesive is required, it is added at this stage, usually in the form of a polyurethane glue in a proportion of about 3-6 % by weight.

3.The boards are put under pressure in a closed chamber at a temperature of 200 °C.

4.The boards are cooled.

5.The boards are cut to size.

6.The boards are coated with an adhesive and covered with a stiff cellulose paper, preferably recycled, which gives them rigidity. The paper should also be treated with a water repellent, such as a latex solution.

Linoleum was first produced in England in 1864 and is made in thicknesses of 1.6-7 mm. A normal manufacturing procedure is to first boil linseed oil (23% by weight) with a drying agent, usually zinc (about 1%), and let it oxidize. This is mixed with 8% softwood resin and 5% cork flour, 30% wood flour, 18% limestone powder and 4% colour pigments, primarily titanium oxide. The mixture is granulated and rolled while heated on a jute cloth (11%) that is hung to oxidize at 50-80 °C.

Most manufacturers cover the linoleum with a layer of acrylate to make it easier to roll and stay clean. In certain cases polyvinyl chloride is used. Linoleum with no surface coating should be waxed before use. Several linoleum products are also provided with an elastic underlayer to make it soft enough to walk on and to reduce impact noise. This is usually based on foamed polyethylene or cork.

In smaller rooms, linoleum can be laid loose and held in position by the skirting. This will make it easier to renew worn out coverings. It is, however, normal to glue linoleum to the floor, but this should not be done before the base onto which it is glued is fully dry. Ideally, a concrete floor needs more than a year to dry out. If a floor finish is glued too early, fungus can form in the glue, spread to the floor construction and walls and even eat the linoleum. The adhesives usually used are acrylate glues, ethylene-vinyl-acetate (EVA) and polyvinyl-ac-etate (PVAC). Glue based on natural latex in a solution of alcohol can also be used.

Linoleum does not tolerate continuous heavy exposure to water and is therefore not suitable for bathrooms.

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