Do I need to use plastic back boxes for Lime plaster?

[HappyHippyDad]

The customer has specified plastic recessed back boxes and stainless steel screws for a rewire, as it will all be lime plaster. Is this absolutely necessary?

If so, I have found the marshall tufflex boxes, but finding the right screws seem harder. I can find 30mm stainless stell socket screws, but it would be great to have some 40mm and 50mm or longer (that I can chop). Does anyone know where to get these?

Also, any cheaper options than the expensive Marshall Tufflex recessed plastic boxes?

Thanks.

 

[westward10]

They seem to be very hard to find especially in raised countersunk which is what they should be.

M3.5 x 30mm Slotted Raised Countersunk Machine Screws - Stainless Steel A2 DIN 964 - Bolt World

Material: Stainless Steel Class / Grade: A2 (304) Thread Diameter: M3.5 Thread: Metric Thread Thread Direction: Right Pitch: 0.50 Head Shape: Slotted Raised CSK Thread Length: 30mm (Thread length includes screw head) Code: DIN 964

boltworld.co.uk

 

[R-fur]

Normal socket screws are chrome plated brass, is the customer aware of this? Is he specifying stainless because he thinks normal screws are mild steel.

 

[mainline]

Normal socket screws are chrome plated brass, is the customer aware of this? Is he specifying stainless because he thinks normal screws are mild steel.

I thought the standard ones that come with socket outlets etc were plated mild steel.

 

[westward10]

You can get brass and steel both generally nickel plated.

 

[Avo Mk8]

I thought the standard ones that come with socket outlets etc were plated mild steel.

A quick sample of my box of leftover socket/switch screws from recent accessories shows they're all magnetic .

 

[brianmoooore]

Crabtree 3.5mm screws were plated brass a few years back, but changed to plated steel at the same time as the 4000 range were completely redesigned internally. My stock of 3.5mm screws of various lengths, bought separately from fittings are all plated brass, but I haven't bought any for a year or two.
While it's true that lime plaster will attack the zinc on metal boxes until the plaster is dry, afterwards, when fittings with screws are fitted, there shouldn't be a problem with steel. If there is, then it will show in your IR readings, and you should be fitting surface boxes, not flush.