fibre-reinforced cement - weight ?

Fibre reinforced cement / concrete (may have small aggregate in it) panel, size 2000 x 2500 x 30 mm, how much would I expect it to weigh (wet and then dry I guess) ? (This is the thing I am going to try and cast / render vertically for camden style sound insulation) I am really at the limit of my DIY on this one ! Cheers, Simon.

Reply to
sm_jamieson
Loading thread data ...

I dont know either, and couldnt work it out from known densities of the components, since packing of final product is denser than the components. But all you need is some lump of concrete to measure weight then volume.

NT

Reply to
meow2222

why not look up size & weight of a paving slab.

NT

Reply to
meow2222

I kind of thought of that. So, standard paving slab is 50x600x600 weights about 40kg. This covers 0.36m2. My wall is 5m2. So I would need 14 slabs. My wal weight 14 x 40 x 30 / 50 = 336 kg. So, my wall will weigh 3rd of a ton. Sounds heavy to me, to be supported by joist ends 16" centres near wall. But then again, I've removed a cast iron bath and a cinder block wall from the room, which must have added up to a fair bit. Cheers, Simon.

Reply to
sm_jamieson

Sorry, didn't read the beginning of this but the Knauff Aquapanel is 900 x 2400 x 12.5 and weighs 15kgs. That's resin bonded cement, which I'd guess is the only way to get any kind of stability at that thickness.

formatting link

Reply to
Stuart Noble

formatting link
An Aquapanel sandwich might save you a lot of work.

I'm sure the cast in situ solid fibre reinforced concrete would do the best job, and I'm sure that with the experience, doing this would be fairly straight-foreward, but its taking me a long time to figure all this out. I only have 50mm to play with including the air gap, and the aquapanel C studs are 50mm deep. Also, aquapanel seems very expensive for what it is. With no studs, does anyone think 2 sheets of aquapanel glued together would be stiff enough ? Simon.

Reply to
sm_jamieson

formatting link
An Aquapanel sandwich might save you a lot of work.

"Glass fiber cement about 3/4 inch thick weighs about 12 lbs a sq ft"

according to somebody in a sculpture group.

Not sure what exactly you're aiming for but Aquapanel can be bonded directly to brick, or fixed to any size batten.

I've no idea what camden style sound insulation is. Dave Plowman knows about all this I think. If he doesn't pick this up , try reposting with something about sound in the subject.

Reply to
Stuart Noble

formatting link
>

If you need to make it lighter you could always make a 1" thick mesh structure and render onto that from both sides. Corrugate some mesh to give the hollow core, add sheet poly each side to prevent saturation then tie on flat mesh each side, and render.

Is the 330kg going to be a problem? I've put those sort of weights onto wood floors on 6" joists with no problem.

NT

Reply to
meow2222

formatting link
> >

For the record, I've got a design that I can manage without possibility of it going horribly wrong ! From what I've read, the mix is very important to the strength of fibre-reinforced cement, so I will use a composite design that will be much safer. Its gonna be 25mm square hollow section steel "studs" with aquapanel (or cheaper equiv) on both sides, overall thickness 50mm. I'll fill between the studs with something like sand/cement (I dont think weight is a prob) and then fix aquapanel to form the front urface. Won't be that cheap, but never mind ! I could use ply on the inner skin. Or that thinner cement sheet they build garages out of. Thanks for the help folks, Simon.

Reply to
sm_jamieson

formatting link
> > >

If acoustic damping is your aim, you may be unpleasantly surprised with the result - all your materials sound very hard/dense (steel, cement)... woudl this really be any better than a couple of layers of plasterboard?

Reply to
Phil

formatting link
> > > >

The whole point is that I have an air gap loose-filled with mineral wool to do the damping, that may not have been reflected in this post. The wall in front of the gap is not linked to the main wall at all, and needs to be very dense and stiff so it does not resonate and can also be quite thin. If this structure was in contact with the wall, the requirements would be very different. Simon.

Reply to
sm_jamieson

Well, I'm sure you know what you're doing but, as a previous poster suggested, rendering on to a mesh of some kind would be miles cheaper. I can't see the advantage of steel tube over wood or, for that matter, aquapanel over 9mm plasterboard for the faces.

Reply to
Stuart Noble

I dont understand how that would be in any way or sense safer.

This is more hassle, more money and less result, I dont really know why youre considering it. Is it to avoid skimming the built wall? With just

2" to play with, for 2 skins plus airgap I dont think you can afford 3/4" for 2x 9mm smooth surfaced layers.

There are 2 things you need for a hollow wall:

  1. stiffness and mass - both obtained by making the 2 sides as thick heavy and rigid as possible
  2. an airgap - which in this case will be minimum size, eg half an inch.

The other option is of course a single 2" skin, no cavity, which I would seriously consider. 2" reinforced concrete is very very rigid stuff, and should do well at not transmitting sound.

Putting mineral wool in the cavity is a waste of time imho, this will have no serious effect on something as heavy and rigid as 3/4" fibre reinforced concrete. Its more suited to PB frame walls, where the PB is light and flimsy.

Adding steel uprights will add cost and reduce rigidity, counterproductive on both counts. Galv mesh should give effective reinfocement. The mesh puts half the concrete into compression, which is the very strong and tough mode for crete.

Making a half inch thick corrugated sandwich like I described earlier would give you a half inch cavity plus 2x 3/4" thick concrete sheets, with both sides reinforced and loosely flexibly coupled via the mesh. Almost perfect.

A wood mould could be used, progressively raised after each poured layer, for construction.

A 2" solid wall would be a good deal simpler, I think I'd go for that myself.

Well, I'm not convinced by some of those points. Good luck.

NT

Reply to
meow2222

The cement board was to give a smooth front and also a former for 1" ordinary (not fibre-reinforced) mortar for extra mass and rigidity between the 2 skins. The steel were to support the board. But I suppose all this fuss is to avoid relying just on a thin reinforced concrete wall that I don't have much confidence in making. I'm probably just chicken !

I think there is some confusion here. I am not building a hollow wall. I am building a solid wall in front of an existing brick wall, leaving an air gap to stop contact noise and other noise through the structure from next door. Putting mineral wool in this air gap stops resonance, which helps with sound insulation.

Yep, this is what I was originally going to do. By reinforced concrete, do you mean with glass fibre, or using mesh ? The glass fibre (alkali-resist) is actually quite expensive. I would actually want to make the solid wall about 30mm if possible and if still strong enough.

I believe this stops the sound from migrating across the air gap, which can only help, even if the solid concrete would stop most anyway.

If I can do galv mesh reinforment instead of glass fibre and it will be stiff and strong enough, this would be preferable. Where exactly wou

Surely even better if solid. I guess if you render it may end up almost solid anyway.

If poured in layers, I think you would lose lots of strength. How would you use this mould without getting something looking like a dripping ice-cream ? Also, would 30mm concrete be thick enough for the wall, or would you need 40mm etc. I orginally wanted 50mm including the air gap. Incorporating the air gap inside the new wall is an option, but does not isolate quite as well due to conduction through the mesh etc. I cannot risk pouring the concrete and finding it too brittle, but the corrugated reinforcement should sort that out, keeping one side in tension if you try to push it. I would also have to work out how to get the mould out at the top, and finish the wall off up by the ceiling. But this is closer to my original idea and would indeed be much cheaper. What mix would you use for this concrete, what aggregate size etc ? What mesh to use. I am a novice at this which is why I was trying to avoid it, but if I can get the necessary advice, it would be the best solution I agree.

Oh well, they were gleaned from reading uk.diy !

Thanks for your input, Simon.

Reply to
sm_jamieson

Simon Not wishing to put a damper on your plans but, if I were you, I'd post a new question stating the original problem rather than trying to find out how to implement your solution to it. I fear you might end up spending piles of money and getting in a mess (a situation I'm not entirely unfamiliar with). I don't know if you're trying to keep next door's sound out, or stop your own going next door. Maybe you're setting up a recording studio. Who knows? All I do know is you've probably deprived yourself of good advice by having the weight of cement as your subject. Not likely to catch the eye of the audio types on here :-)

Reply to
Stuart Noble

yep :) Its all quite doable once youre clear about it. Because this is a thin wall, its going to see tensile forces, so I would personally go for fibre reinforced throughout to maximise strength and much reduce the chance of cracking. It will also increase the life of the wall. Concrete is weak in tension.

I doubt it would make much difference to heavy stiff walls. It does of course with weak thin pb walls.

Mesh and fibres do 2 different jobs. Both increase strength, I'd go for both.

I'm not sure if it will have a big effect in this design. It will do in free air, but much less in a brick/concrete cavity where that air is driven by very a high impedance source, which the brickwork is.

maybe it will be, but I'd do both myself. If cost of glass is a problem, 1% polypropylene or nylon fibres are very cheap and much improve tensile strength and reduce cracking.

I agree, now that I'm clearer about what youre doing

why? Making sure the layers bond. This can be done by partial intermixing, by roughening the top of the layer below, or by sticking loops of galv wire or other attachments into the top of each layer to lock them together. The EML will help bond them too.

Im not understanding the issue there. A quick google for poured concrete walls shows poured walls are done.

I aint got a clue mate. The thicker the better soundwise. Unless someone knows more accurately I'd be inclined to go for 1cm & 4cm, but I cant offer any hard figures to back it up.

I guess you could pour as close to the ceiling as poss then finish the last bit either with no mould, just trowelling it in place, or with a short shallow section of mould that you trowel fill from its open end and move along the wall as you go.

Best use rustproofed screws at the top and sole, eg phosphated.

1:3:5 C15 is used for walls. cement:sand:stone by volume.

standard galvanised EML, as long as it will be dry. (expanded metal lath) If for some reaon the wall will be wet then you could use ss eml for long service life. SS generally has to be ordered in and costs several times the =A3. Galv will break the wall apart after 20 years if it gets wet often.

NT

Reply to
meow2222

Thanks for sticking with me on this. Polyprop fibres for tensile resistance and mesh for strength will do well. I'll look at the prices of SS mesh. All will be tanked to avoid continual soaking. Simon.

Reply to
sm_jamieson

Tanking isnt effective enough, if theres a likelihood of any water around I'd use ss mesh.

NT

Reply to
meow2222

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.