i am ready to pour a 12cm slab for my floating floor and i have this (silly?) question:
should i pour concrete (cement-stone) or cement/sand screed would work?
Both will be reinforced and i'm looking for a load between 240-280kg/m2.
I couldn't find a specific dencity table on the net for cement/sand screed but from what i found it should be above 2000kg/m3.
The advantages of the screed(for me) would be the ease of pouring using a pump (i am in a basement) and the top finish being ready for a laminated floor. On the other hand i assume that the concrete should be a better sollution regarding strenght etc. Keep in mind that the inner drywalls will be on the floating floor (more load on the edges)...so PLEASE I NEED HELP :)
Nikodemos
concrete vs cement/sand screed ????
Originally posted at johnlsayers.com, topic 9854.
it should be concrete - the aggregate is a part of the structural composition - a sand mix does not get the job done.
BUT - this shouldn't be a run away train here - you need to sit down with someone from your concrete supplier to come up with a mix that will work structurally - and you don't mention what you are installing for reinforcing throughout the slab - you are planning something for that aren't you?
Your best possible bet would be to pay a few bucks to a structural engineer who can dovetail everything for you - you really do not want to screw this up even a little bit.
Sincerely,
Rod
thanks for the reply mr.Gervais...you've been very helping all the way!!
I've disscused this matter with lots of endineers and i think i got more confused :cry:
Most, if not every, floating floors (in studios) around here is actually screed....and that's what all engineers who have done something simmilar told me...on the other hand a friend of mine (engineer) who's been helping me and he is building major constructions (industrial buildings etc) told me that concrete is the best way but cement/sand screed would probably work...... :?
Some more details:
I'm planning to use a steel reinforcment mesh or "web" (don't know if it's the right word) about 1-1,5cm thick. The slab would be poured on hardwood that is laid on the elastic pads...does this make any difference? I'll post a drawing later...
another question is:
does screed and concrete have (more or less) the same density?
I mean, in case i got the ok form a structure engineer, would the screed give me the same amount of load as the concrete?
I built the "spring" underlay based on a dead load of 240-280 kg/m2 to get a resonance frequency below 10HZ so this is an important factor too.
Nikodemos
Nikodemos, They are about the same density - shouldn't be enough difference at this thickness to amount to a hill of beans. Sincerely, RodMost, if not every, floating floors (in studios) around here is actually screed....and that's what all engineers who have done something simmilar told me...Nikodemos, That doesn't make sense to me - but then again I don't build in Greece. But - unless Greecian screed has some special properties I am not aware of- after pouring - it I were to take a cection of this deck - and make a score line the width of it (using a simple stone chisel) I could knock off a nice square edge piece of it without a problem. What that means (to me) is that if any sort of shrink crack were to develope in this slab over time - that vibration (under dead load) could be enough to complete the fracture without difficulty. On the other hand - with aggregate as a part of the mix - If I were to make a score line in a 5" slab a full 2" deep - and tried to clean that edge - it would break off very jagged due to the strength of the aggregate and it's inability to shear cleanly. In over 35 year experience in concrete - ranging from industrial to residential projects - I have never even specified screed for a slab on grade application - never mind an elevated slab. In fact - the only time I ever use screed in an application is if I first have a structural layer below it - and I am then (basicaly) using the screed as either a leveling operation to finished floor elevation - or as a base for an applied flooring finish (what we refer to in the States as a mud-job tile finish for example).Well it sounds to me as if he has more experience than the others - although I don't agree that non-structural cement is ever adequate. I would sugest that you spend some time and read through this: http://forum.studiotips.com/viewtopic.p ... &start=280 Some more details you should check out : http://www.earsc.com/HOME/engineering/T ... asp?SID=61on the other hand a friend of mine (engineer) who's been helping me and he is building major constructions (industrial buildings etc) told me that concrete is the best way but cement/sand screed would probably work...... :?I wouldn't _ I would use 10mm deformed rebar grade 60 (US grade - I don't know the EU equivilent - but it should be hardened steel) on 12" centers - placed at the center of the slab. The problem with the mesh is that if it is stepped on during the pour (almost impossible to not step on it) it get's pushed to the bottom of the pour and stays there - then your contractor has to try to pull it up wjhere it belongs as they work through the pour. With rebar =- should you step on it by mistake - it will spring back into place - you have no guarantee where the mat will wind up height wise in the pour. Ands the bar being in the center of the pour is really pretty critical seeing as you have forces working in both directions on these slabs -I'm planning to use a steel reinforcment mesh or "web" (don't know if it's the right word) about 1-1,5cm thick. The slab would be poured on hardwood that is laid on the elastic pads...does this make any difference? I'll post a drawing later...another question is: does screed and concrete have (more or less) the same density? I mean, in case i got the ok form a structure engineer, would the screed give me the same amount of load as the concrete? I built the "spring" underlay based on a dead load of 240-280 kg/m2 to get a resonance frequency below 10HZ so this is an important factor too.
Thanks so much mr.Gervais.....i had my doubts regarding this whole matter and that's exactly why i asked for help here, and i was really hoping that you would show up :)
I sometimes ask myself how some buildings are still one piece over here :shock:
I've read the whole(!!!!) Paul's diary a month or so ago and i remember seeing the pics on this very page and wondering how different things are in other countries. I actually asked an engineer the other day if we should use something to keep the mesh in the right place(in the middle) during the pour
and he told me that we just have to pull it up after we've poured 2-3cm of concrete...well that made some sense (some...) but i still wander why can't we just do things right in this country :oops:
Anyway i don't know if i can find this kind of reinforcment over here but i'll surely try...
a last question:
Do you think i could pour about 8-9cm of reinforced concrete and then 3-4cm of cement/sand screed in order to have an even and nice top finish?
I mean are 8-9cm of concrete enough for a safe construction?This way i could have the desirable load for the floating floor and an even finish without sacrifising any more height. If so how much time should i wait before pouring the screed for the concrete to gain its strength....or is it best to pour 12cm of concrete?
Well that was 5-6 questions and not just one... :D
thanks again
Nikodemos
Nikodemos, I would pour a 15cm slab (5.91") and would pour the entire slab with structural concrete - I don't understand the finish issue - you can finish concrete so it is as smooth as a piece of glass if that is the finish you want....... what makes you think differently? You can also install some beautiful finishes directly into the concrete if you choose to do that......... Look here: http://tinyurl.com/39sztu Sincerely, RodDo you think i could pour about 8-9cm of reinforced concrete and then 3-4cm of cement/sand screed in order to have an even and nice top finish? I mean are 8-9cm of concrete enough for a safe construction?This way i could have the desirable load for the floating floor and an even finish without sacrifising any more height. If so how much time should i wait before pouring the screed for the concrete to gain its strength....or is it best to pour 12cm of concrete?
thanx Mr.Desart
I am going to follow your advice on this one :D
one question:
Is it possible to put vertical steel bars on the perimeter of the floor for the wall studs to be bolted on after the concrete is poured like Paul did(http://forum.studiotips.com/viewtopic.p ... &start=120)? I mean i've allready layed the wood framework on the elastic pads...can i just bolt them on the wood or is this something it should be done before laying the wood framework?
it seems like a good idea and it would probably save a lot of time and effort in drilling holes in the concrete afterwards.
Niko, one of the great things about Paul's thread is how he shows you step by step what you can accomplish. The fact that he did it proves that it can be done - so if you want to do this (and you're right 0 it does save a lot of work - as well as the possibility of damaging the slab when adding inserts close to the edge after the fact) then by all means do it. Sincerely, Rodthanx Mr.Desart I am going to follow your advice on this one :D one question: Is it possible to put vertical steel bars on the perimeter of the floor for the wall studs to be bolted on after the concrete is poured like Paul did(http://forum.studiotips.com/viewtopic.p ... &start=120)? I mean i've allready layed the wood framework on the elastic pads...can i just bolt them on the wood or is this something it should be done before laying the wood framework? it seems like a good idea and it would probably save a lot of time and effort in drilling holes in the concrete afterwards.