chasing into concrete screed floors - a risk to the neighbour's lights?

[laike]

Question guys: this is a maisonette with 2 floors undergoing a rewire. How to wire the lights on the lower floor? Options are 1) battening and 2) chase screed above and drop through floor. Everyone seems to prefer option 1 but me! Why is it so hard, especially as we'll be chasing the screed to lay pipework for central heating?
Are there any regulations against running lighting cables in the screed above?

 

[Engineer54]

Question guys: this is a maisonette with 2 floors undergoing a rewire. How to wire the lights on the lower floor? Options are 1) battening and 2) chase screed above and drop through floor. Everyone seems to prefer option 1 but me! Why is it so hard, especially as we'll be chasing the screed to lay pipework for central heating?
Are there any regulations against running lighting cables in the screed above?

Seeing as you'd be running a cable installation from one installations equipotential zone into another installations equipotential zone, what do you think??

 

[Deleted member 72666]

Hello Tony

yes, it should be "nowt", a slight erroneous transcription from brain to screen.

I may be slightly lysdexic

Me too! I have sex daily..... I mean dyslexia!

 

[KAS1]

If this is a maisonette with 2 floors and he's wiring the lower floor lights from the upper floor how would he be running a cable installation from one installations equipotential zone into another installations equipotential zone, or am I missing something?

Seeing as you'd be running a cable installation from one installations equipotential zone into another installations equipotential zone, what do you think??

 

[laike]

i'm not an electrician, what's an equipotential zone! :tounge_smile:

so the only option is battening the ceiling then? crap!!!

 

[KAS1]

Is it a flat or maisonette? there is a difference IMO "in my flat (i live in a 2-story maisonette)"

 

[laike]

it's a 2 story, ex council, 1960s built flat. with brick walls, concrete floors, and MICC cabling (to be ripped out for the rewire).

see pics.



structural report

Visual Observations

• At first floor level, adjacent to the stair well is a small airing cupboard with a water tank. The floor in this area was lifted to reveal a soft grey material, which on first impression was thought to be a floor screed.

• With the aid of a chisel, the soft grey material was easily broken away to reveal a water pipe buried within it.

• The depth to the bottom of the copper pipe was approximately 30mm.

• Below was a further pipe.

• It is believed that the two pipes are the flow and return to the water tank located within the airing cupboard.

• The depth of the screed is therefore most likely approximately 50mm in depth.

• The ceiling of the ground floor reception room was also exposed in one location to reveal a smooth concrete surface, of different colouration and texture to the soft grey material observed within the airing cupboard.

Figure 1 – Exposed Screeded Slab Surface – Airing Cupboard

Conclusions/Recommendations

Based on our visual observations, it appears that the floor structure is of reinforced concrete construction. It was not possible to conclusively determine if the floor slab was of precast or in-situ construction. Based on the surface finish to the soffit area exposed, it would suggest that the floor slab is most likely of pre-cast concrete construction.

To the top surface of the concrete floor slab is quite clearly a screed of approximately 50mm in depth, which has services within it as was seen in the airing cupboard.

We understand that you wish to run further new services within the screed layer. We can confirm that this will not affect the structural performance of the concrete floor slab. However, it should be ensured that the screed is broken out carefully (not with an angle girder or similar) to ensure that the concrete surface of the floor slab is not damaged or cut into.

 

[Engineer54]

If this is a maisonette with 2 floors and he's wiring the lower floor lights from the upper floor how would he be running a cable installation from one installations equipotential zone into another installations equipotential zone, or am I missing something?

Yep, your right, and that's fine if it's a two storey maisonette and he's using the screed on the upper floor to run his cables in, for the lower floor. Not too sure what he's going to do for the upper floor lighting though?? ..lol!!

My only worry would be, that the surveyor mentions that the floor slabs are of the precast type. Making penetrations in precast concrete slabs, need to be undertaken with caution, especially if they are of the pre tensioned variety!!

 

[laike]

Not too sure what he's going to do for the upper floor lighting though?? ..lol!!

it's the top floor maisonette, upper floor lighting run above plasterboard ceilings (no concrete)

My only worry would be, that the surveyor mentions that the floor slabs are of the precast type. Making penetrations in precast concrete slabs, need to be undertaken with caution, especially if they are of the pre tensioned variety!!

he said he was unable to determine, and IMO he was not the sharpest tool in the shed. are these photos any help in determining the construction?



those are the pipes that punch through the floor to go to the gravity water tank. notice there is a brick laid in the middle of the concrete! WTF?

that looks poured-in to me, not precast. any opinions?

 

[Engineer54]

From the photo's you posted, it certainly looks like an in-situ poured slab, rather than precast !!

 

[laike]

so what does that mean with respect to its structural integrity? am i ok to drill through it? what about chasing the underside of the slab, or is that a big no no?

 

[Engineer54]

You should be OK to drill through a poured reinforced slab. Rather you than me, if your thinking of chasing the underside of a concrete slab. Do you have strong arms?? lol!! Fine if your talking about the finish surface cover on the ceiling, but it's generally much thinner depth, than wall render/rough coat plastering...

 

[laike]

what do you recommend? to chase the underside plaster/slab to the depth of the cable, or drill through and chase the cable in plastic conduit into the screed?

and don't say drop a false ceiling!!!

 

[Engineer54]

what do you recommend? to chase the underside plaster/slab to the depth of the cable, or drill through and chase the cable in plastic conduit into the screed?

and don't say drop a false ceiling!!!

To be honest with you, that's the way i would go if it was my property!!

I'll leave your questions here to others, that have more experience of retro re-wiring domestic installations of this type. It might be an idea to check the depth of the ceiling plaster cover, you may well have enough depth to conceal intended wiring/cabling...

 

[somersetsparks]

To be honest with you, that's the way i would go if it was my property!!

I'll leave your questions here to others, that have more experience of retro re-wiring domestic installations of this type. It might be an idea to check the depth of the ceiling plaster cover, you may well have enough depth to conceal intended wiring/cabling...

Most flats that I have seen like this have no plaster at all, just artex onto concrete, I have seen one building which had the ceilings plastered and that was less then 1/8" depth. Why are you so adverse to having a battened ceiling? Could go with mt2 and coving trunking upstairs, looks just like real coving......

 

[Engineer54]

Most flats that I have seen like this have no plaster at all, just artex onto concrete, I have seen one building which had the ceilings plastered and that was less then 1/8" depth. Why are you so adverse to having a battened ceiling? Could go with mt2 and coving trunking upstairs, looks just like real coving......

Well, i'm only going by the fact he has MICC cable as his installation, and that was normally fixed to ceilings and plastered over, can't ever remember seeing that cable being embedded in the poured floor slabs, ...i may be wrong mind!! ...lol!!

 

[laike]

pulled off one of the ceiling mounted pull cords



there appears to be a layer of plaster (?), 10mm deep on the ceiling? i thought it was concrete as it is very hard.

 

[KAS1]

A nicely installed galv conduit or better still a copper conduit system may look very high class IMO if money tight some nice mini trunking lol

- - - Updated - - -

surface may I add

 

[laike]

omg are you trying to wind me up? it's working! :73:

 

[KAS1]

Just a bit of fun, chill out lol

 

[Guest55]

some nice mini trunking lol

lol
everyone loves the "poundstretcher" poverty look !

as to the OP , looking at those photos , you're in for a whole heap of aggro trying to chase the cement render off a concrete ceiling.
did anyone mention lowered ceiling ?
lol ;-)

 

[KAS1]

Festoon lighting always works you can string them where you what lol

 

[Guest55]

Festoon lighting always works you can string them where you what lol

dont take down those xmas fairy lights just yet........

were not helping are we ?
lol

 

[somersetsparks]

Well, i'm only going by the fact he has MICC cable as his installation, and that was normally fixed to ceilings and plastered over, can't ever remember seeing that cable being embedded in the poured floor slabs, ...i may be wrong mind!! ...lol!!

Your dead right, all the flats I have been in have had conduit systems, embedded in pre-cast concrete slabs, not MICC, completely forgot that the OP was even on about MICC lol

 

[laike]

:angry_smile:

 

[somersetsparks]

:angry_smile:

Sorry grumpy, it is a bank holiday Saturday and all! lol If you have got a 10mm skim of plaster, you could cut wide chases, borrow a nail gun and fix cables up in capping, even better metal capping, then get a friendly plaster (could also be a not so friendly plaster the choice is yours!) to patch the areas and then possibly re skim the whole ceiling for the modern clean look, or just get him to patch and artex it for the 'local authority' look. n

 

[Guest55]

:angry_smile:

what do you want us to say ?

you'll never get the chase depth needed for pvc conduit , the render / screed is only thick enough to cover the pyro & gland ( about 12mm )

and you'll make a complete mess of the structure in the attempt.

so unless youve got an incredibly compelling reason for not fitting a false ceiling then youre all out of luck.

 

[ipf]

Gonna be interesting when it comes round to installing the recessed light fittings :sweatdrop:

 

[KAS1]

I know the answer, cornice lol trunking around the bedroom walls with fittings installed like in HMP whitemoor and the like

 

[laike]

as to the OP , looking at those photos , you're in for a whole heap of aggro trying to chase the cement render off a concrete ceiling.

so i'm dealing with concrete slab ceiling, with MICC surface mounted and covered with a 10 mm layer of concrete 'render' (not a term i'm familiar with)? it appears to be much harder than plaster, stabbing it with a knife barely marks it.

ok, good to know your enemy... cheers

you'll never get the chase depth needed for pvc conduit , the render / screed is only thick enough to cover the pyro & gland ( about 12mm )

and you'll make a complete mess of the structure in the attempt.

forget the conduit, are you saying chasing the 10mm 'render' just to fit the cable, then plastering over is a no go? why not?

 

[Guest55]

i dont see why not , so long as those circuits will be rcd protected.

you could consider oval pvc conduit , it lays flat at around 10mm ish.
lay 2 lengths to each light point and skim over.
thats what i'd probably do.

 

[laike]

done. going to propose that solution. thanks a million. i don't want 30+ m2 of false ceiling!

btw, how the hell did they get the concrete render to stick to the poured in slab? it's so perfectly smooth as well.

so we're sure it's safe to chase that? i don't want the council bitching about structural compromisation.

 

[UNG]

it's a 2 story, ex council, 1960s built flat. with brick walls, concrete floors, and MICC cabling (to be ripped out for the rewire).

see pics.

View attachment 18865View attachment 18866View attachment 18867

structural report extract

We understand that you wish to run further new services within the screed layer. We can confirm that this will not affect the structural performance of the concrete floor slab. However, it should be ensured that the screed is broken out carefully (not with an angle girder or similar) to ensure that the concrete surface of the floor slab is not damaged or cut into.

I think that statement precludes drilling through the slab

pulled off one of the ceiling mounted pull cords

View attachment 18876View attachment 18877View attachment 18878View attachment 18879View attachment 18880

there appears to be a layer of plaster (?), 10mm deep on the ceiling? i thought it was concrete as it is very hard.

Looks like the old pyro octopus system has been used originally

what do you want us to say ?

you'll never get the chase depth needed for pvc conduit , the render / screed is only thick enough to cover the pyro & gland ( about 12mm )

and you'll make a complete mess of the structure in the attempt.

so unless youve got an incredibly compelling reason for not fitting a false ceiling then youre all out of luck.

Plaster depth pyro was never glanded it was terminated with a pot and the pot was clamped into an accessory box designed for pyro to maintain earth continuity

done. going to propose that solution. thanks a million. i don't want 30+ m2 of false ceiling!

btw, how the hell did they get the concrete render to stick to the poured in slab? it's so perfectly smooth as well.

so we're sure it's safe to chase that? i don't want the council bitching about structural compromisation.

If you mix a bit of PVA into the cement mix it will be nice and smooth when trowelled up, coating the chase with a 5:1 water / PVA mix before filling it in will help the adhesion as well works

 

[ayjay]

why do you need to rewire the flat?micc lasts forever

 

[ipf]

Sixties wiring, shortage maybe ? Sick to death of extension leads all over the place ?

 

[ayjay]

nothing wrong with 60s micc imo
doubht if theres any shorts
i,m only talking about the lighting so extension leads arn,t needed
cheers

 

[ipf]

nothing wrong with 60s micc imo
doubht if theres any shorts
i,m only talking about the lighting so extension leads arn,t needed
cheers

Say so then.
I'm not saying there's anything wrong with the wiring, just that in the sixties, nothing like as many appliances were readily available, hence, not as many sockets were required.

 

[laike]

why do you need to rewire the flat?micc lasts forever

fair question and sadly it doesn't *need* rewiring. but i'm moving a wall so 2 MICCs need moving. there's also (newer) surface trunking that looks crap and can't be chased due to the recessed MICC. and it would be nice to move a few switches and sockets. i'm doing the rest of the flat too so figure to do it all. feel conflicted about it though.

 

[ayjay]

personally jaike, and in my past experience(45 years) micc wired flats in the lighting is always fine although it will need testing-- if it works its good to go(imo)
socket-wize in old flats there wernt many!
one way is to run a new ringmain in plastic skirting trunking, also computer stuff ect
no need to mess about with the lighting

 

[laike]

question guys: can i chase the floor in front of the fuse box without fear of hitting the incoming mains? you can see 1 of those incoming mains looks to go into the floor in some direction (down?) where is the other incoming mains? or is there only 1 that splits between the 2 meters? FYI the council pay the bill for the lower meter as that's the UF heating included on the service charge.

 

[ipf]

Gawd.....someone made a mess of that. It's bloody hissing !!!

 

[laike]

looks a sight eh, wish i could gut the thing and bring it into this century.

so do i have to worry about hitting the incoming mains while chasing the floor or what?

took off the other panel, check this out:

 

[KAS1]

Get an experienced electrician to come to your address and assess the situation. How you can expect to get the "go ahead" on here, words fail me. Please be careful.

 

[laike]

i'm in discussions with 2 electricians atm and this mains issue is the latest concern - hence i'm asking you guys. isn't 100 heads better than 2? there's a lot of experienced people on this forum. what's wrong with using it? besides, what more can be seen in person than what's visible in the photo?

 

[Stroppy]

What a nightmare of a job! What on earth is that thing in the middle picture, on the right of the fuses?

 

[laike]

a mercury filled vial that detects when the UF heating is switched on.

 

[ayjay]

if the flat has u/f heating then any floor chasing is out of the question

 

[laike]

put in new UF matts. how am i going to get the new cables to the kitchen and lounge? the box is at the bottom of the stairs.

 

[Guest55]

this building owned by the local council ?
would just love to see the last inspection report...... ;-)