Concrete shed floor

[muttley9050]

If you had a bobcat and big jcb running over a 6m x 6m pad what thickness would you use and would you reinforce it. I never thought about putting polythene down before I guess this would make it more workable for longer and give it more of a chance to self level.

 

I would go 6" reinforced with a124 mesh. Will be super strong. However Marcus may disagree.

[difflock]

Other than super specialized mixes with various additives, there is no such thing as "self levelling" concrete.

It should behave virtually like a sand castle on a beach, except it "slumps" a little.

For absolute max finished strength the optimium water/cement ratio is 0.4, i.e. for every 100kg of ordinary Portland cement (OPC) add 40kg=40litre of water only.

Assuming your sand and aggregate are perfectly dry.

Otherwise subtract the water already contained in the sand/agggregate. This is why the Premix truck's docket has a specific box with room for a signature for "added water" , because on professional jobs with test cubes taken, if the conc does not come up to strength, someone has to carry the can.

Gensetsteve.

No easy answer, depends what the substrate is.

I have seen 3" of good concrete, properly put down over an undistrubed farm "street" carry HGV's and premix trucks, without cracking.

The "rule of thumb for agricultural concrete laying is a 5" by 3" "stick" on its edge, which with the roughness of the stone below gives going on 6".

Said "sticks" being the standard purloins to span the 15' 9" agric shed bays to carry tin.

Unreinforced.

Mostly the reinforcing is added to cover for lazy/sloppy work practise.

cheers

marcus

[gensetsteve]

The substrate round here is chalk about 4 " under the dirt. If you disturb it 4 weeks later you cant touch it with a fork. I gave up trying to dig the veg beds by hand years ago. Now I just get the mini digger on it. I have always put 6" of premix without mesh but 4" it would go alot further.

[Goaty]

As a relief concrete mixer driver if you are going to get it delivered readymixed.

 

Don't skimp on the mix grade. A cheap mix is cheap because it has less quality ingredients in it. e.g power station "fly" ash is used to substitute portland cement!

 

Get the volume worked out right. You are better ordering a little too much than ordering an extra load for your mistake, as you will likely pay haulage for a full load, even if you order a barrow load.

 

Instead of rebar you can have fibres put in the mix at around £5 per cube. For reinforcement.

 

Concrete depending on mix and moisture weighs 2.4 ton per cubic metre.

 

The company I drive for allows 5 minutes per cube delivery time. Thats half an hour for a 6 cube load. This is average, not long to shift over 14.5 ton ish 1/2 a mile in your case.

After that time has elapsed. They charge £1 plus vat a minute. So please advise the company if you need the extra delivery time as its selfish not to, sometimes we have to just dump it and go as other customers are waiting and drivers have EU drivers tachograph rules to comply with. It sounds alot but due to delivery standing times we get around 9-10MPG with a 6 wheeler, plus a drivers wage at around £9 per hr.

 

Personally I would probably mix it myself due to logistics as Its going to need extra man power and probably 2or3 dumpers. Expense and stress.

 

Finally don't lay it when its frosty. If it rains after/during before it sets a plastic sheet on top can save it if its dry. Also pre wetting the subsurface can alleviate shrinkage problems.

[mad matty]

Loving the ford 4000 in the pics.....good old tractor!!

[pycoed]

Mix the stuff on site, it's only a day's work for two of you. In the summer I did our yard, mixing about 27 tons all in. Labour force was my wife & daughter. I am 63, my wife 61 my daughter is an arty farty type, not used to work at all! We easily did slabs of that size in one day.

 

Get the all-in delivered in bags ( 1 bag = 0.5 cu.m. approx 850Kg ). To get them to site, weld some rings onto your loader about half way back along the arms & use shackles to connect two bag loops to each, then your 4000 should be able to lift the bags fine. My loader wouldn't lift a bag at full length - I have an UTB445 which is about the same size, & modified with rings it handled them fine up a VERY steep slope. I used the loader & transit box to shift the bags of cement. Build a base of 2 or 3 pallets to lower the all-in bags onto, so you are always shovelling down into the mixer.

 

I had planned to use my old diesel site mixer but sods law prevailed: after being treated to new filters & an oil change, plus new nipples & a good greasing all round, the b*gger seized the engine on the second banker! Plan B was to use my cheapo Machine Mart "contractors" electric mixer, which will only just mix a single barrowful at a time if you are careful. Anyway we did the lot with that. Use a strong mix 1 cement to 4 all-in.

 

In hindsight, thank God for the girl-size 25Kg cement bags these days

Edited October 26, 2013 by pycoed

[difflock]

For smallish quantities, i.e. a couple of loads max.

I would always spec 20 or 25 newton, only fractionally more expensive per m3

Only downside is, if I recall, higher strength "cooks" off quicker, and is therefore less forgiving of delay.

On chalk (pure luxury lad) I would have thought 4" unreinforced should be fine.

If it cannot sink into the chalk, it cannot flex, therefore it will not crack.

Fibres are quite good to prevent cracking, but a bugger to get properly mixed in.

A good point about the wetting and covering and frost.

I take that so much as a "given" as not to be worth mentioning.

PS

Most of this is relying on 30 year old memories, with not a lot of experience since.

marcus

[Mull]

Can't think of any reason not to put mesh down, if cracks do appear then mesh will stop them opening up!

Someone once said " there are two types of concrete, that which is cracked and that which is about to crack!"

I'm told the wetter it is, the more likely it is to crack.

That's my tuppence worth!

[openspaceman]

Can't think of any reason not to put mesh down, if cracks do appear then mesh will stop them opening up!

Someone once said " there are two types of concrete, that which is cracked and that which is about to crack!"

I'm told the wetter it is, the more likely it is to crack.

That's my tuppence worth!

 

Marcus may well be right but we laid our workshop floor over an existing one so added mesh as we weren't sure of the base, that plus the trolley jacks have a high point loading.

 

4 quid/m2 extra cost didn't seem a lot to pay.

[ballibeg]

Cheers guys.

 

Will be weather proof as roof going on shed next week. Will look at mixing myself v bought in.

 

Really appreciate the advise. Why to do once and do well.

 

Dave