2001-08-21 – Modular housing and the recycling effort

Eric H., from the LUF list, recently outlined a clever scheme for allowing members to send donations of materials, rather than money. This stems from a personnel project idea he has had, regarding construction. He mentioned, at one point, the use of recycled plastic decking boards, and it is this which I am going to address here.

We could use the recycled plastic planking idea quite easily, as polypropylene bottles are easy to melt down. The planks could be cast quite simply, rather than extruded, as the viscosity of the melted plastic mix isn’t all that high, and a mint surface finish isn’t going to be needed on all four sides, so the rough side could face downwards. Alternatively, you could make a proper mould, and end fill. The beauty of this is we could put bolts and the like through the mould, and then simply unscrew them when set, letting us bolt straight into the thread that was formed, saving even more money. Or leave them set in place, with captive heads, and a metal thread showing. Assuming we made them in standard sizes, or to order, it would be rather a cool way to recycle pop bottles and refuse sacks/bin bags.

One point I have noted, when using plastics, is that the co-effiecent of expansion is very high for most plastics. Typical values are shown below:


Material in/in/°F x 10-5 cm/cm/°C x 10-5
ABS (glass reinforced) 1.7 3.1
Polypropylene (glass reinforced) 1.8 3.2
Epoxy 3.0 5.4
Polycarbonate 3.6 6.5
Acrylic 3.8 6.8
ABS 4.0 7.2
Nylon 4.5 8.1
Acetal 4.8 8.5
Polypropylene 4.8 8.6
TP Polyester 6.9 12.4
Polyethylene 7.2 13.0


As can be seen, GRP’s have a lower expansion co-efficient than non-GRP’s, but these are still higher than, for example, Aluminium, and copper, (~3 and ~2×10-5 respectively).

This will undoubtly cause problems in the use of plastics for structural parts, if not rule them out all together. I often lie awake at night, listening to the sounds of the double glazing \”tink-ing\” as it cools after the day. However, most plastics will survive the highest summer temperatures without too much trouble, they are strong for their weight, and, importantly, we can get materials for very low cost.

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