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Fitting backbox to thermalite blocks, what screws & plugs?
- Thread starter veedee
- Start date
Red wall plugs, 1.5 inch pozi size 8 countersunk screws. Don't drill holes on rotary hammer action, drill on ordinary rotary action.
People may tell you the screws should be dome headed, personally I feel the countersunk ones are best.
People may tell you the screws should be dome headed, personally I feel the countersunk ones are best.
Thanks @sparkwright
I use 5.5mm drill and make the holes at horrible angles then gently hammer the plugs in.
This gives a better grip in the thermalite dust, countersunk definitely works better when the screws are crooked like these.
This gives a better grip in the thermalite dust, countersunk definitely works better when the screws are crooked like these.
thermalite is very prone to crack. I prefer to drill a roomy hole and put builders adhesive into it before pressing in the plugs. when set, it will hold the plugs firm and they will not spin.
my holes are often rather ragged so I like to pack the boxes in with S&C mortar after wetting the brickwork. Improves the hold and is much stronger than filler or plaster, prevents any wobble. It has a good working life.
my holes are often rather ragged so I like to pack the boxes in with S&C mortar after wetting the brickwork. Improves the hold and is much stronger than filler or plaster, prevents any wobble. It has a good working life.
Funnily enough, I was taught to drill such fixings at angles (dovetail was the term he used) to give a bit more strength to the fixing, so it couldn't be pulled straight out directly.
Red "Uno" plugs normally need a 1/4 (6mm) drill. I tend to drill 3/16 (5mm), and tap the plug home, securing with a No8 screw (think that's 3.5mm in euro-speak) and then use No More Nails or similar around the box to ensure that if the screw does move the box remains where I put it!
Plus one for No More Nails before the final filler/plaster.
I tend to use a 5.5 drill bit, red wall plug (not a fancy one, just bog standard), and a no 10 screw. I find a 10 screw in a red plug with thermalite holds far better. I'd not recommend that in anything other than thermalite. As above post, a slight angle also helps, it prevents the screws pulling forward.
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