site  contact  subhomenews

Planning simple basin still prototype 2

November 16, 2019 — BarryK

I posted a test of the simple basin prototype #1 yesterday:

The result was promising, so decided to go ahead and design prototype #2. A major requirement is that it be as flat as possible, so as to take up little space when slid into the back of a hatchback car or 4wd vehicle. In fact, that was one of the main reasons, that and promised improved efficiency, that I went for the tilted wicking-cloth type of still. However, I have now learnt that the glass can be very close to the water, water depth can be mere millimetres, and the glass angle can be as little a 5 degrees, maybe even lower.

It may be possible to design the still to be only about 100mm (4 inches) thick at the widest end, which would be great. However, might not quite get that thin. This reference recommends a minimum glass angle of 10 degrees (scroll to page 445): is unclear whether that 10 degrees figure is for plastic panes. Water droplets stick to glass better, and perhaps it would still work for angles less than 10 degrees.

The above reference also recommends water depth of 20-30mm and side and bottom insulation thickness of 20-30mm.

In all of my reading, I keep coming back to silicone as the superior product. Inert, extreme resistance to corrosion and UV light, and retaining its flexibility for 10-20 years.

Rather than build the still out of wood, as I have done so far, I am thinking of using aluminium insect screen mesh, coated with silicone sealant. This would give me a flat surface that I can bend into shape, to form the basin and support for the glass. There could be an outer frame, into which insulation is poured -- maybe polyurethane expanded foam -- or even silicone mixed with foam bubbles.

Thinking along these lines, I have started testing coating of insect screen mesh. I bought a roll of aluminium mesh, 1220x2050mm, AU$23:

Also some cheap Parfix brand acetic-cure white silicone sealant, AU$6.68:

I have a plastic spreader, that was used for the early wicking-cloth type prototypes:


I tested spreading on a mesh offcut, with newspaper backing, plastic backing, and hanging vertically in the air:


I then pulled the backings off and hung it up to set.

From this initial test, it looks like two or three coats will be required. For the final construction, I will probably do two coats of cheap white silicone, then one coat of black Silastic 732 silicone.  In earlier experiments I found that silicone-on-silicone adheres extremely well, so there will be no adverse issues with doing multiple coats. 

Tags: nomad