Please can someone advise me: Does a ring main cable need to be derated if it is buried in 20mm of cement-based grout?
The problem: I have a problem with a floor that is floorboard on battens (w ith shims) on original concrete floor. Some battens are not properly resti ng on the concrete underneath and the floor moves (about 5mm) and squeaks w hen walked on. I really don't want to rip up all the floorboards (1000+ n ails, all hammered in by my wife) to redo the battening.
What I plan to do: As a simple fix I am thinking of pouring in about 20mm of cement-based grout which will flow under the supports of the battens and fill the little 5mm gaps. i calculate that it won't block the airflow too much but it will bury the existing ringmain cable which is simply lying on the concrete underneath.
Do I need to worry about derating. the cable will end up with concrete un der it and 20mm of cement grout above it, then a 50mm air circulation gap.
to answer my own question: mains cables are routinely chased into the wall and covered with a layer of plaster so I guess my situation is very similar and therefore within the design limits of the cable.
No. Buried in masonry counts the same as "clipped direct" to the surface.
See row C from this table:
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In fact you may actually improve the situation slightly. You could interpret the existing installation as using method 40 (cable in a building void - which you would treat as reference method B)
My thoughts too. If you are able to pour in screed, then, presumably, you have some of the boards up. Could you not take up a board here and there where the squeaking is bad and slide a plastic shim in the gap between the batten and the concrete?
Regardless of the electricity question, this plan has zero chance of working - you are going to be standing or kneeling on the timbers when you pour the screed (which won't run by the way, it needs to be worked under the joists), then when you step off the timbers, they will spring back up, away from the screed. I'd locate the joists that are springy and put plastic packers under them
Thanks for this comment, and for the others doubting that my scheme would w ork. I'll think about this some more. OF course I really should pull it u p and put shims under as people suggest. I have loads of shims. It's just a bit daunting having done all that squeezing and nailing.
In fact the set-up is less simple than I described. The boards are nailed to 60mm deep battens (joists almost) which stand on blocks of wood spaced roughly 400mm which in turn stand on the original flagstone floor (with som e shims).
Pulling up the boards would be a lot of work.
My proposed flood would use'Weber non-shrinking cementatious grout'. I've used this before and it is very liquid. it would reach the bottom of the b locks but not not reach the battens themselves. I have used this grout bef ore and it seemed to flow pretty freely, but maybe a 5mm gap would be too s mall.
Here's plan A: We stand on the floor (pressing it down), pour the grout th rough the few holes I do have. I let it run around the bottom of the suppor t blocks so they are all standing in a puddle of liquid grout. Then I walk away allowing the floor to spring up and draw the grout under the blocks. Then it sets.
Here's plan B: pack with plastic shims the blocks I can get at so the floo r is at the correct height but most of the blocks have a 5mm gap under them . This will probably not be enough to provide full support but will improv e things. Then pour the grout and hope it flows under enough of the other blocks to make everything OK.
If it fails to work then I have to pull the floor up but I am no worse off. So I might as well try it.
(with shims) on original concrete floor. Some battens are not properly res ting on the concrete underneath and the floor moves (about 5mm) and squeaks when walked on. I really don't want to rip up all the floorboards (1000+ nails, all hammered in by my wife) to redo the battening.
m of cement-based grout which will flow under the supports of the battens a nd fill the little 5mm gaps. i calculate that it won't block the airflow t oo much but it will bury the existing ringmain cable which is simply lying on the concrete underneath.
under it and 20mm of cement grout above it, then a 50mm air circulation gap .
It would be interesting to know the best way to do this job that would redu ce the change of the problem occurring in the first place. I might have to do this type of job some day ... Simon.
(with shims) on original concrete floor. Some battens are not properly resting on the concrete underneath and the floor moves (about 5mm) and squeaks when walked on. I really don't want to rip up all the floorboards (1000+ nails, all hammered in by my wife) to redo the battening.
cement-based grout which will flow under the supports of the battens and fill the little 5mm gaps. i calculate that it won't block the airflow too much but it will bury the existing ringmain cable which is simply lying on the concrete underneath.
under it and 20mm of cement grout above it, then a 50mm air circulation gap..
the change of the problem occurring in the first place.
At a guess, glue and screw battens to concrete before boarding?
Most likely, the glue would be sufficient on its own, but the screws would hold the battens down onto the glue while setting.
ns (with shims) on original concrete floor. Some battens are not properly resting on the concrete underneath and the floor moves (about 5mm) and sque aks when walked on. I really don't want to rip up all the floorboards (10
00+ nails, all hammered in by my wife) to redo the battening.
20mm of cement-based grout which will flow under the supports of the batten s and fill the little 5mm gaps. i calculate that it won't block the airflo w too much but it will bury the existing ringmain cable which is simply lyi ng on the concrete underneath.
te under it and 20mm of cement grout above it, then a 50mm air circulation gap..
reduce the change of the problem occurring in the first place.
I remember staying at a friends house whose bathroom was like this with the squeaks, I think to hide some plumbing under the floor (floors were solid concrete). It you went to the loo at night you'd be in fear of waking everyone up. I g uess they had got used to it. Simon.
s (with shims) on original concrete floor. Some battens are not properly r esting on the concrete underneath and the floor moves (about 5mm) and squea ks when walked on. I really don't want to rip up all the floorboards (100
0+ nails, all hammered in by my wife) to redo the battening.
0mm of cement-based grout which will flow under the supports of the battens and fill the little 5mm gaps. i calculate that it won't block the airflow too much but it will bury the existing ringmain cable which is simply lyin g on the concrete underneath.
e under it and 20mm of cement grout above it, then a 50mm air circulation g ap.
duce the change of the problem occurring in the first place.
It would have been fine if I had done it more carefully. the existing floor was very uneven. I used supporting blocks and plastic shims to get all t he battens level. I used a long spirit level both along the battens and ac ross them. This all went fine. What went wrong was that the floor continu ed through a doorway into a small utility room and I didn't get that floor properly 'coplanar' with the main floor. i.e. I didn't spend enough care making sure the two floors lined up properly.
As someone Rod says: screwing (or gluing) the battens to the floor would h ave helped and I have considered doing that retrospectively as a 'fix'. I could put a few resin anchors into the concrete to fix down the outermost ( worst) batten and that would 'bend' the floor a few mm and stop the moveme nt. The bend would not be noticeable. A few bolts in the outermost batte n would be enough to force down all the blocks&shims to sit where I origina lly intended. Whereas, to insert more shims under every block I would need to access every block which means taking up the floorboards completely.
I thought I'd round this off by letting you know what I eventually did. Aft er the discussion here I gave up my idea of the poured grout and decided to bite the bullet.
I pulled up a few floorboards (every 700mm roughly). This was not easy as they were squeezed together and nailed down. I broke most of them but I ha ve some spare. I then put proper supports under the battens. To do this I made many pairs of small carpenters wedges (15 degree) and tapped then in place. Once happy I took then out, one pair at a time, glued them and put back.
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