> I'm looking for a way to cover plastic tables with an anti-static 
> surface. I
> need a solution that that is cheap, and if it is cheap enough I 
> don't mind
> if it only stands up to one year of high school student abuse. :)
...
> I have priced commercial anti-static mats and to buy the number that 
> I need
> would blow my budget... Does anyone have ideas or suggestions?


Butyl rubber sheet, used for industrial pond liners and roof 
waterproofing amongst other things, can be your friend. Conductivity 
is imparted (AFAIK) by the amount of carbon that is included to 
control colouring and hence is variable between brands and types. In 
almost all cases conductivity seems to be good enough to be entirely 
adequate for anti-static mat use. Worst problem is that many version 
have very low conductivity to the extent that the surface is usefully 
conductive when eg a circuit board is placed on it - you need to place 
an insulator under PCBs and anything else that doesn't appreciate 
being placed on a conductor. For personnel safety purposes such 
sheeting probably constitutes a conductive surface and may be a safety 
hazard in some cases.

I have used Butyl rubber sheet for this purpose for many years and 
apart from the occasional "conductive incident" have found it 
extremely useful. As a bonus it is used here as cover sheets for other 
material from the same bulk supplier and the cover sheets are sold at 
a very substantial discount from their normal price. As well as making 
anti static mats this sheet works well as playhouse roofing ;-).

Even at roofing material prices the cost is well below that of 
'proper" as mats, and when sold as used packing sheets it is vastly 
cheaper.

The material is robust enough to last indefinitely when subject to 
high school student abuse. The greatest disadvantage is that some 
versions smell extremely rubbery for a considerable period.

Conductivity "per square" can be assessed by sticking two multimeter 
probes into the rubber and measuring resistance. This is typically 
hundreds to thousands of ohms per square. Note that even when 
resistance is so high that it is essentially unmeasusrable the sheet 
may still be adequately effective for ESD protection purposes.

Totally different solution - spray or paint surfaces with conductive 
metal spray. Nickel works well but tends to be expensive. "Cold zinc" 
galvanising spray or paint may be cheaper. May not be appropriate for 
your purposes. I use nickel spray to adapt plastic boxes/trays for 
component storage.



        Russell McMahon 

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