Workshop Floor

[Bongodrummer]

Hi Guys,

We are in the process of converting an old barn into a workshop and are about to put down the concrete floor. It will be going onto shale with hardcore on top, and be 150mm thick. The paln is that the workshop will have a number of reasonably big machines - some woodworking but also some metal working machines. Some of these will be quite heavy, at least 500kg, so the guys who we are looking at getting the concrete from suggested 'CP35 mix' which is supposed to be very strong, and adding polymers (that give a similar effect to adding lots of glass fibres in that they strengthen it further). The polymers were only £5 per cubic m extra, so we will probably go for that (anyone have any experience of these?).

Anyway, the question is, should we add regular farm pig netting to the concrete slab to try and strengthen it up? We have a mass of it just sitting about from some recent fencing jobs and could shove it in there as a sort of poor man's rebar. Some of the rolls are better than others - some have bits of rust - would including these be disastrous? Moreover, would the zinc coating on the rest of it react in any strange ways with the concrete? I have googled to try and find out if other people have done this, but not much luck, so I would be grateful for any input on this...

 

[miles_hot]

Don't know...I thought that rusting stuff was a good cause of cracking concrete but maybe that it only when the concrete has already started to leak and the rebar rusts as a result. After all rebar which goes in isn't exactly free of rust

 

[Bongodrummer]

Yeah, agreed, the stuff you see builders putting in is typically covered in surface rust :? The pig-netting we have is in comparably good nic I suppose. I wonder about the zinc/ galvanised coating and cement combo though.

 

[Dibs-h]

Hi Guys,

We are in the process of converting an old barn into a workshop and are about to put down the concrete floor. It will be going onto shale with hardcore on top, and be 150mm thick. The paln is that the workshop will have a number of reasonably big machines - some woodworking but also some metal working machines. Some of these will be quite heavy, at least 500kg, so the guys who we are looking at getting the concrete from suggested 'CP35 mix' which is supposed to be very strong, and adding polymers (that give a similar effect to adding lots of glass fibres in that they strengthen it further). The polymers were only £5 per cubic m extra, so we will probably go for that (anyone have any experience of these?).

Anyway, the question is, should we add regular farm pig netting to the concrete slab to try and strengthen it up? We have a mass of it just sitting about from some recent fencing jobs and could shove it in there as a sort of poor man's rebar. Some of the rolls are better than others - some have bits of rust - would including these be disastrous? Moreover, would the zinc coating on the rest of it react in any strange ways with the concrete? I have googled to try and find out if other people have done this, but not much luck, so I would be grateful for any input on this...

I get the impression that the folk supplying the concrete are a mobile batching wagon outfit. CP35 is their equivalent to C35 which is what's spec'd for commercial jobs (car parks, etc.)

For a concrete floor - it's way overkill. I'd reduce the spec to say something like C20 (or CP20 in their case) and add at least 1 layer of mesh 50mm up from the bottom - sat on proper spacers. If you are mega worried - you could always add another layer. Can't quite remember the spacing\spec of mesh - will ask my SE mate when I speak to him later this week.

Personally - I would use premix concrete (i.e. ReadyMix, Lafarge, etc.) and specify pump grade and get a pump firm in. I'm not referring to a Schwing type pump - there are others, where the pipes lay on the floor, etc. Going rate seems to be around £250-£300. Best money you'll spend and it'll be pumped in, in less than 30 mins, giving you plenty of time to tamp and float if you wish.

The batch-on-site ones - if it's a reasonably large area - probably start going off, before it's fully laid. Polymers, etc - sounds like marketing speak to me.

My 2c worth

Dibs

 

[Bongodrummer]

Hay Dibs, thanks for this. It was going to be ready mix style delivery...

For a concrete floor - it's way overkill. I'd reduce the spec to say something like C20 (or CP20 in their case) and add at least 1 layer of mesh 50mm up from the bottom - sat on proper spacers. If you are mega worried - you could always add another layer. Can't quite remember the spacing\spec of mesh - will ask my SE mate when I speak to him later this week.
Dibs

When you say mesh, do you mean proper rebar stuff, or the pig-netting I mentioned?

 

[Dibs-h]

Hay Dibs, thanks for this. It was going to be ready mix style delivery...

For a concrete floor - it's way overkill. I'd reduce the spec to say something like C20 (or CP20 in their case) and add at least 1 layer of mesh 50mm up from the bottom - sat on proper spacers. If you are mega worried - you could always add another layer. Can't quite remember the spacing\spec of mesh - will ask my SE mate when I speak to him later this week.
Dibs

When you say mesh, do you mean proper rebar stuff, or the pig-netting I mentioned?

Yes proper rebar sort of stuff, such as

Dibs

 

[Bongodrummer]

So you are basically saying rebar is more important than the mix strength, right? That is likely to up the price quite a bit though :?

 

[Dibs-h]

So you are basically saying rebar is more important than the mix strength, right? That is likely to up the price quite a bit though :?

The mix strength is important - but it isn't the end all and be all for a concrete structure.

For your application - I believe (and I believe the calcs would prove it) C35 is way overkill and without rebar - C35 or even C50 wouldn't stop localised cracking.

I'm building (shortly) a new garage with a basement. The garage floor\basement ceiling will be cast in situ. To hold a car on the deck, a 2 post lift weighing 1T (metric) and a 1 car in the air. That's spec'd at C35. Your loads are minor compared to that. So why would a none structural floor require C35? With or without Polymers.

HIH

Dibs

 

[bosshogg]

Hi Bogo,

Specs for concrete are wide and varied, But generally what your doing, converting a barn into a workshop, and your description of the floor build up (pre conc.) is OK, just one word though, is this inclusive of a dpc course?

General flooring for barns, sheds, garages and the like, look for C20 conc at say 150 _ 200mm, indeed you can come down to 100mm and still have a good floor,for floors where heavy weight bearing and appearance are to be considered C35 is better. as for the mesh it depends on the thickness of the steel rods making it up, sound though like you are using a interweave style of mesh, and for that reason I would recommend not using it at all. The idea of the welded mesh used in reinforced conc. is to provide a stiffener for the conc. that will also distribute the load, in your case as this is a roll the stiffness would be missing, what you could do though is get some 9 _ 12mm rebar and wire fix on your roll of galvanised mesh say every 200mm or so, the bars should be set @ 600mm approx. If all this sounds a bit to much work, go for the propriety steel mesh, overlap by 300mm at any joints (all directions) and basically the 50mm clearance from the ground advice given is correct, you get spacers for this.
Now where you are putting in heavy machines what you should be going for is mass, most often called footings, mass in the concrete will absorb vibration and provide a solid foundation for the machines, this applies both to woodworking and metal working machines but more so too the latter. there is no use installing say a metal turning lathe on a unsubstantial floor then wondering why it's inaccurate, that goes for all the other machines as well, dampening out vibration is one of the most essential factors for machines too work properly. How large are the machines intended to be installed? do they have feet where the bolts will be inserted through into the conc?? this could allow you to plan the floor space and put in machine footings say 600mm deep. Simply dig 450mm below the proposed floor excavation (assuming this is boulder clay, no shuttering required) infill as per your floor build up, make up some rudimentary reinforcement cages wire to your mesh reinforcement and pour.
Polymers are specified where there is a reason, as you don't appear to have a reason why add them, you might require a retarding agent though depends how quick you can get it down, normally retarding agents are inclusive in the costs...bosshogg

You can't solve a problem using the same thinking that created it...A.E.

 

[Bongodrummer]

Hay bosshogg.

Im going to go ahead and assume 'Bogo' was a typo :mrgreen: .

Thanks for the reply! Interesting stuff. Looks like there are lots of options here. Although what you say about adding mass to the spots where machines will be makes complete sense to me, it seems like a big step to 'solidify' the shop layout at this stage. I was imagining a bit more flexibility - sort of see how people, particularly me, use things and adjust positions as we go. Not that easy to move one of these big machines I know, but...

I suppose the two biggies will be the lathe (something like this: http://www.axminster.co.uk/axminster-sieg-cq6230b-910-metal-turning-lathe-prod570771/) and the milling machine (something like this http://www.axminster.co.uk/axminster-axminster-rf40-universal-mill-prod21300/).

I notice that both the stands are sheet metal anyway which will not help with vibrations , so maybe I would be better off retrofitting some concrete blocks inside the stand, than I would be making a deep pad, given I might want to move it at some point :?

Oh, one last thing - In terms of the polymer, the reason to specify was basically cost, we were advised that we might be able to do without the rebar if we had polymers added?

Looks like I will have to check out the prices of rebar...Thanks again for your thoughts on this - kinda important to get the floor right!

 

[bosshogg]

Bongo,

Iv'e been in the business for more years than I care and I aint never come across a polymer that replaces the steel mesh, I have seen polymers that have altered the slump, curing time, waterproofed the finish, allowed for the thinnest of screed out retarded the setting and curing times, but again not one that replaces the reinforcement steel. You are in the right location for an alternative to concrete... hempcrete which has some amazing properties worth checking out. Your contact there would be Tyˆ -Mawr Lime Tyˆ Mawr, Llangasty, Brecon, Powys LD3 7PJ Tel: 01874 658000 Fax: 01874 658502 a lady by the name of Helen was very informative to me last year...bosshogg

 

[chris_d]

I recently used C30 concrete incorporating 0.91kg/m-³ of Fibrin 23 polypropylene fibres over a suspended 'beam and polystyrene panel' flooring system. The fibres replaced A142 steel mesh, acting in a structural capacity (spread point load) and to prevent surface cracking whilst the concrete hardened.

However, that was for a domestic floor system with assumed light loading. Your structural engineer / competent person should be able to advise appropriately on the basis on your particular loading characteristics (current and future) and if really helpful, specify a number of options on the basis of cost.

HTH,
C

 

[Bongodrummer]

Ah - "polypropylene fibres", thanks Chris, that may have been what they were suggesting actually, oops

Hempcrete :shock: Now that's an idea worth looking into. I know very little about it, but isn't it usually a bit more lightweight? Maybe less appropriate for workshop application - as you said mass for damping is important ??
Will have to look into this - any quick heads-up on a cost comparison with regular concrete?

 

[chris_d]

For 3cu.m of C30 with fibres from Tarmac Ltd on 28-Aug-2010 = £293.62 + VAT.

For 6cu.m of GNE3 from Tarmac Ltd on 7-Aug-2010 = £400.00 + VAT

 

[Lons]

I find it difficult to accept that the polymers are an alternative to the welded mesh sheets which as already stated, spread the load of the concrete. I rarely lay a floor these days without mesh as the cost relative to the job is minimal. last price I paid for 3.6 x 2.0 x 9mm was around £15 +vat per sheet. As said, spaced 50mm off the bottom, overlap around 300mm and preferably tie overlaps with soft wire.

You should always put in a DPM and make shure the readymix supplier knows the concrete is to have reinforcement mesh.

You didn't say whether you will be putting floor insulation under the concrete but might be worth a thought if the rest of the barn is to be insulated as it would make a difference to comfort and heating costs.

Pig netting is too thin, too flexible to give any benefit IMO

Bob

 

[tomatwark]

You should always put in a DPM and make shure the readymix supplier knows the concrete is to have reinforcement mesh.

Bob

A DPM is a must I know a couple of people woh have built workshops and not bothered, thinking as it is a workshop it does not matter.

They have regreted it since as they have had probs with damp workshops, timber that does not stay stable and machinery that goes rusty.

Tom

 

[Dibs-h]

I find it difficult to accept that the polymers are an alternative to the welded mesh sheets which as already stated, spread the load of the concrete. I rarely lay a floor these days without mesh as the cost relative to the job is minimal. last price I paid for 3.6 x 2.0 x 9mm was around £15 +vat per sheet. As said, spaced 50mm off the bottom, overlap around 300mm and preferably tie overlaps with soft wire.

You should always put in a DPM and make shure the readymix supplier knows the concrete is to have reinforcement mesh.

You didn't say whether you will be putting floor insulation under the concrete but might be worth a thought if the rest of the barn is to be insulated as it would make a difference to comfort and heating costs.

Pig netting is too thin, too flexible to give any benefit IMO

Bob

When my foundations (shop) were designed - the recommendation by the SE was for the mesh to overlap by a min of 500mm, not 300mm. Admittedly I was using A252 mesh, and I suspect he wanted the mesh to overlap by 2 cells as opposed to one.

I'm seeing him later this week so will make a note to bring mesh overlap up in the conversation.

Dibs

 

[Bongodrummer]

Thanks for all the input guys. It looks like the ideal would be C35, overlapped rebar (maybe even 2 layers at different heights) with polypropylene fibers, a DPM and some insulation :shock:

We hadn't even started thinking about insulation, we were just sort of ignoring it in the floor thinking it would not be a cost effective place to focus on - anyone got any advice or experience on thicknesses/materials/cost/what to avoid etc. Most insulation is quite weak and as its a floor that's got to limit the choices quite a lot right?
Thanks again,

 

[Dibs-h]

Thanks for all the input guys. It looks like the ideal would be C35, overlapped rebar (maybe even 2 layers at different heights) with polypropylene fibers, a DPM and some insulation :shock:

We hadn't even started thinking about insulation, we were just sort of ignoring it in the floor thinking it would not be a cost effective place to focus on - anyone got any advice or experience on thicknesses/materials/cost/what to avoid etc. Most insulation is quite weak and as its a floor that's got to limit the choices quite a lot right?
Thanks again,

Sorry to be picky - but that's if money is no object, which I suspect it isn't.

I'd give the fibers a miss - can't see the need for them.

 

[Bongodrummer]

Dibs,
agreed about the cost issue :?

I cam across this article (http://www.ljmu.ac.uk/BLT/BUE_Docs/labib.pdf) yesterday, that was quite positive about the benefits of added polypropylene fibres. Although I can't find out where this was published (may have easily been 'commissioned' by fibre manufacturers for all I know), but it has an academic gloss

Either way, for just £5 per cubic metre extra (we are only talking 7), doesn't it seem worth it?