Can someone please advise me of the best practice for chasing ( an
finishing) a slot in a plaster + brick/ breezblock wall to take powe and video cables from about 2ft off the floor to behind the screen
6ft high). I have purchased a wall mount for the screen, and som conduit to house the cables and a stone cutter attachement for drill.Thanks for any advic
-- JohnB
I'm not really sure about best practice but some observations...
1) Embedding a power cable in the wall will be covered by electrical regulations. Read up on what your'e doing in some IEEE literature, but as a starter the most relevant regulation is that you can hide a cable in a wall in a horizontal or vertical line from a visible electrical fitting (usually a socket or light switch) or within 15cm of the sides and top of the wall. Anywhere outside of this area must be covered by armoured or buried more than 50mm deep. Please note - I THINK this is corretc. I have no doubt someone will correct me if I've made a mistake. I have no idea whether a permanently fixed plasma screen counts as an electrical fixing? 2) Chasing into plaster makes an unholy god awful mess. The last time I did it I sealed the room with blankets and gaffa tape and it still got out. Just chasing out three columns from ceiling to light switch made me think I'd gone blind. I could not see a thing. Doing this work with furniture in the room is completely unfeasible in my opinion. I suppose you could manage it with a dedicated chasing tool and some SERIOUS extraction power vented outside. A dyson is not going to cut it. 3) Patch it up with plaster when you've finished. The appearance will be down to your plastering skills. You could make it look perfect or a complete dogs arse. When you cut into the wall cut at an angle so that that the hole is a wedge shape this will help the plaster stay in the hole.I'm afraid that's all the help I can be.
Don't even think about it on an occupied house - the dust will go everywhere and still be reappearing in a year.
What I've done to get neat chases is to drill two vertical rows of holes about 25mm deep either side of the chase which act like perforations: you can then knock out the chase very easily (by hand or SDS chisel) without shaking up the wall to much or loosening great areas of plaster.
Not sure what your stone cutter is, but it sounds like it has the potential to create dust in a big way. (anything angle grinder like - i.e. rotating abrasive or diamond disc, will certainly cut a chase - but will leave the room uninhabitable).
The neatest way I have found to chase walls without too much mess (using machine assisted means) is with a SDS drill and an ordinary chisel bit in it[1]. Cut a couple of parallel lines about an inch apart (or whatever size you need), then break out the middle. The special chasing chisels you can get for SDS drills can also work well, but I found them more likely to dislodge large areas of skim coat if your plaster is at all dodgy.
[1] You will still get as much mess as with a bolster and hammer obviously, and it pays to have a good SDS with a speed control so you can take it slowly and not spray fragments all over the place!
Just completed this exact task ... although I used the lot's of holes technique to sink the box ... (use the envelope masking-taped under intended position to catch the brick dust); I 'notched' the two edges of the vertical channel with an 88mm? (SDS) chisel from Screwfix it's the same width as a single bac-kbox. This seems to give a line of least resistance so that plaster doesn't flake at the edges. The bits between the lines was hacked away with a 20mm SDS chisel - again from Screwfix. I did cover the floor below the work with a bin-liner bag masking-taped to the floor - {did I mention removing the carpet?) and had an assistant holding a work-shop vac near the chisel. There wasn't too much migration of dust.
BTW; the vertical channel must; - #A;- go vertically iaw Regs ... #B;- line up with one of the knock outs on the box! It's unlikely that the box will have a knock-out centrally so; put the box where it'll line-up with the channel :)
HTH
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