having stripped walls back to brick/block, when buying 13 amp metal back boxes, am i better getting the slim (25mm) boxes to screw onto the bricks then screed/plaster walls or should these be chased into the walls still with the larger depth 13 amp boxes?
back boxes
- Thread starter paulpa
- Start date
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It would depend on what size cable you are running to the back boxes.
Generally, 16mm back box for lighting switches, 25mm for 2.5mm T&E cable (Ring Final Circuits etc) and 35/40mm for 4/6mm T&E Cooker type circuits.
Depends on what type of socket face plates you are having and the method the walls are getting finished.
It's common now for brick and block walls to be dot'n'dabbed rather than basecoat and two coat finish.
If walls are d'n'd you will normally get away with the 25mm back boxes, but if walls are going to be base/finish coat the depth of the wall coatings is going to be about 13-15mm, so you need to make allowances for that.
Also if you are using flat plate faces on the boxes you will need 35mm back boxes as standard, so again some allowance for them need to be made.
It's common now for brick and block walls to be dot'n'dabbed rather than basecoat and two coat finish.
If walls are d'n'd you will normally get away with the 25mm back boxes, but if walls are going to be base/finish coat the depth of the wall coatings is going to be about 13-15mm, so you need to make allowances for that.
Also if you are using flat plate faces on the boxes you will need 35mm back boxes as standard, so again some allowance for them need to be made.
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I would not even consider using 16mm backboxes anymore with the modern requirements for dimmers, controls etc etc. 25mm minimum is the way to go (unless you think the wall might fall down 
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35mm is only needed for the flat plates, as these need a little more room for the plate to sit back in to the box.
if it's standard stepped face plate, you will be okay with the 25mm.
if it's standard stepped face plate, you will be okay with the 25mm.
Yes indeed, I hardly ever use 16mm switch boxes.I would not even consider using 16mm backboxes anymore with the modern requirements for dimmers, controls etc etc. 25mm minimum is the way to go (unless you think the wall might fall down
when you say stepped you mean like this?
http://www.toolstation.com/images/library/stock/webtables/58060.jpg
these
http://www.toolstation.com/shop/Electrical/Chrome+Wiring+Accessories/d190/sd2657
http://www.toolstation.com/images/library/stock/webtables/58060.jpg
these
http://www.toolstation.com/shop/Electrical/Chrome+Wiring+Accessories/d190/sd2657
If it's your place do 35mm and keep then options open, 25mm is okay for standard sockplates, but even they can be an issue should you extend the ring in back box or poorly route a 3rd spur cable.
Price wise it's pennies, and an extra 2 minutes at each box with an sds chisel is hardly too much extra time.
Future proof.
Price wise it's pennies, and an extra 2 minutes at each box with an sds chisel is hardly too much extra time.
Future proof.
Just make sure you calculate the depth in brick that the boxes will need to sit.
Top, bond, base coats = ??? back box depth = ??? Difference means the depth of the brick to be trimmed back.
If you do drill 1st, tape the tip at the depth you need to drill thus getting the holes all similar by keeping the drilling measurement to the tape marker.
Top, bond, base coats = ??? back box depth = ??? Difference means the depth of the brick to be trimmed back.
If you do drill 1st, tape the tip at the depth you need to drill thus getting the holes all similar by keeping the drilling measurement to the tape marker.
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