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Pouring a new garage floor


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Need some advice on sorting out our garage (finally) and couldn't think of a more helpful forum than this one!

Garage floor is currently concrete slabs laid straight onto soil, the damp is awful and the surface is far from flat! Floor is 4.5x3.8m.

The plan is to remove slabs, dig out the floor, then hardcore, sand, damp proof membrane, and concrete.

Will be doing all of the work ourselves, not adverse to DIY at all. But I'd like some help/advice with the concrete floor - the garage isn't tall enough for the 110 (or big enough), but I also work on a 1950s Singer and have an eye out for an MG B so I'd like it to be structurally sound enough for axle stands and jacking. I foresee a lathe in my future too...

I've seen that concrete can be purchased with reinforcing qualities (ST4/GEN3), but know that steel reinforcement could also be used.

Can anyone offer any pointers on which way to go with this? 

Thanks!

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Just on that re-inforcing topic, for a DIY install (and 90% of commercial come to that) I would always put decent weldmesh in,.... particularly if you are considering mixing yourself.

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If I did it again I would tie some underfloor heating pipes to the weld mesh.

Also, while I'm happy to DIY anything, breaking concrete and digging stuff out is back-breaking grunt work and it may very well be almost as cheap to hire a "man + mini-digger" outfit to just do it for you + get the rubble hauled away.

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Thanks for the comments so far.

59 minutes ago, Blanco said:

Just on that re-inforcing topic, for a DIY install (and 90% of commercial come to that) I would always put decent weldmesh in,.... particularly if you are considering mixing yourself.

I think weld mesh is probably the way to go too, I can use a lower grade of concrete then too. We'll not be mixing ourselves, can get a lorry nice and close so should just be a straight pour hopefully!

32 minutes ago, FridgeFreezer said:

If I did it again I would tie some underfloor heating pipes to the weld mesh.

Also, while I'm happy to DIY anything, breaking concrete and digging stuff out is back-breaking grunt work and it may very well be almost as cheap to hire a "man + mini-digger" outfit to just do it for you + get the rubble hauled away.

I keep wondering about heating the slab. Might run some pipes as you suggest, even if they just get tied into some sort of back boiler on a wood burner in the future. Cheap to run the pipes while we're in there!

Still considering a man&digger - you're probably right!

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Concrete wise, the mix-on-the-truck type ones are great as you haven't got to pay for a full load and have somewhere to dump any excess.

Grab hire for taking soil and concrete etc away is a lot cheaper than a skip, you've just got to have somewhere to pile it.

As for digging the concrete out, I'd see it as an excuse to hire a digger and breaker for the weekend :D 

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Don’t skimp on the concrete - a decent C30 mix won’t be expensive and combined with some reinforcement mesh will give you good strength. If you can get the truck right up to the building then it will be fairly easy to get it in there and smooth it off.

Doing it within the building will give you a challenge in terms of tamping/levelling as the walls will prevent you using the top of forms to do this. Perhaps you could set some angle iron a few inches in from each side which you could then run the tamping board along?

Underlying ground conditions will dictate the thickness of slab you’ll need. On decent ground I’d have thought that 100mm would do given that you’re not putting a building on it?

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47 minutes ago, Retroanaconda said:

Don’t skimp on the concrete - a decent C30 mix won’t be expensive and combined with some reinforcement mesh will give you good strength.

^ this, the price difference between "cheap" and the "overkill" grade is very little so you may as well have the good stuff.

ISTR when I extended the concrete pad at my last place I got the C30 or similar (reinforcing fibres mixed in) the chap asked why I'd need such a high grade for a shed when I could have the cheap stuff - but the cheap stuff was only about £20 cheaper for the load.

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8 hours ago, Hazza said:

even if they just get tied into some sort of back boiler on a wood burner in the future.

underfloor is low temp if its water, just be aware that you'll need some kind of heat soak and blender for a woodburner fired system.

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You can also specify self-levelling concrete which takes out a lot of the hassle of floating it. OK this was letting some pros do it but so worth it. For reference was 10.5 cube C40 with A252 mesh and DPM underneath, nominally 300mm thick. I think the price difference between C20 and C40 was £2/cube, at the time was £76+VAT/cube for C40, but it's going to have some pretty substantial machine tools on it so high point loads.

Drove in through the entrance at 2.30pm and were driving out at 3.45pm

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It was pumped but you could wheelbarrow / pour it out of the mixer but they had the pump so why not use it.

All they did was spread it out a bit - tamp it once and spray a hardener over it. 24h later it could be walked on (including dogs), 72h later cut an expansion joint down the middle (4.5" grinder with stone cutting disc) and it was ready to drive a 6.5t JCB on it.

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Close up of the floor - note absolutely no floating or polishing involved.

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NOTE - if you're going underfloor heating then ideally you'd want to insulate under the slab (don't have to but I think if you want it ever to be converted for "habitation" then it has to be insulated underneath).

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20 minutes ago, elbekko said:

Dog on the right: "damn it, I buried a bone there"

I'd believe you except for one thing - with Lyra (left / mother) and Tali (right / daughter) no bone would last long enough to be buried...

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On 3/29/2021 at 11:27 AM, Hazza said:

I've seen that concrete can be purchased with reinforcing qualities (ST4/GEN3), but know that steel reinforcement could also be used.

One thing that hasn't been mentioned - the "reinforcing" that most people refer to is the fibres being added into the mix. They are not there for reinforcement - they're primarily there to help reduce surface cracking in the slab.

I've just looked up and my workshop floor is roughly 11x5m so got 5 sheets of A252 mesh (4.8x2.4m) - at the time (summer of last year) they worked out at £30.24+VAT per sheet so not very dear at all. A393 mesh which is required for my garage floor / retaining walls (some serious arse covering going on by the structural engineers since it's might as well be sitting on bedrock) was £46.13 but that would be massive overkill.

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A1 concrete is right on your doorstep, they do everything you have mentioned, and can do as much or as little as you would like them to do. Im sue they can advise you.

 

Will.

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Thanks everyone for your comments and suggestions. I'll start pulling the pricing together and will get a mini-digger booked. 

 

As always - this forum is great!

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  • 1 month later...

Busy day today, but ready for the next stage.

Thanks for the suggestion of a mini-digger, having spent all day digging today I can't begin to imagine how hard it would have been doing it by hand!

Next is hardcore, Wacker plate, DPM, mesh, and concrete pour!

Just for interest, I've also re-roofed using insulated warehouse roof sheets. What a great and simple roofing solution!

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And done!

This is the first time I've worked with concrete at anywhere near this volume, but having get everything prepared and a few people to help wheelbarrow from the truck to the garage, we had it all level in 25mins. Couple of goes with the float and now waiting for it to cure. Very happy!

Thanks for the help and advice!

 

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