# Forum Home Renovation Concreting  How thick should garage floor be?

## Wombat2

My daughter in Melbourne is getting quotes for a garage. Some have specified 25mm concrete slab and the one they like the most is specifying 32mm slab. 
Isn't that somewhat thin for a garage floor?

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## commodorenut

If a driveway needs to be 100mm, then so should a garage. 
Sure they're not specifying 25 MPa & 32 MPa concrete? 
(it's the cured concrete's compressive strength, not thickness).

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## autogenous

_Some have specified 25mm concrete slab and the one they like the most is specifying 32mm slab. _ I think there is some confusion hereIts sounds like MPa as above

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## Terrian

> My daughter in Melbourne is getting quotes for a garage. Some have specified 25mm concrete slab and the one they like the most is specifying 32mm slab. 
> Isn't that somewhat thin for a garage floor?

  as others have said, the 25 & 32 are the Mpa rating of the concrete (how strong it is) not the thickness. 
25mpa, 100mm thick, f72 reo

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## Bloss

:Wat they said:  but that's the minimum and depends on what the slab is going to have on it. If it is a slab inside an existing structure and will only ever hold a car then that's fine. If the slab is part of the garage structure then it should be to the specs of the garage maker and that might include reinforced edge beams and/or centre beams (or might not). These are simply thicker sections of the slab with some additional reo. I have always done standard slabs 125 mm and used stronger concrete as the additional cost is generally not much and for to 150mm and use additional mesh strips if there is likely to be a heavier load. But from you description Terrian's advice seems to be right.  :2thumbsup:

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## Terrian

> But from you description Terrian's advice seems to be right.

  at the garden supplies / mini mix yard I use to run we built 15 or so 'bins' 3.3m wide x 6m deep, f72, 25mpa, 100mm thick, good enough to support 22.5t of tandem tipper without any problems  :Smilie:

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## DvdHntr

> but that's the minimum and depends on what the slab is going to have on it. If it is a slab inside an existing structure and will only ever hold a car then that's fine. If the slab is part of the garage structure then it should be to the specs of the garage maker and that might include reinforced edge beams and/or centre beams (or might not). These are simply thicker sections of the slab with some additional reo. I have always done standard slabs 125 mm and used stronger concrete as the additional cost is generally not much and for to 150mm and use additional mesh strips if there is likely to be a heavier load. But from you description Terrian's advice seems to be right.

  The "strength" of the concrete is not a concern in garage slabs. The determination in using a certain MPa is the exposure to the elements. The compressive strength of 20MPa is sufficient for the compressive strength but the higher the MPa, the slower the rate of salt ingress into a slab. This is why cover of concrete is important also. 
The difference in strength between a 20MPa and a 32MPa is approximately 2%. 
It is more important in deflection of the slab but as this is slab on ground that is not a consideration. Increasing the mesh from SL72 to SL82 would be a significant increase in the strength. I think the disagreement is whether the exposure class is A2 or B1.

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## Bloss

"If the slab is part of the garage structure then it should be to the specs of the garage maker " regardless .  .  .   :2thumbsup:

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## intertd6

> The difference in strength between a 20MPa and a 32MPa is approximately 2%.

  Back to school for you, 32 mpa is 60% stronger in compression than 20 mpa 
regards inter

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## Bloss

This is useful for DIYers http://www.concrete.net.au/publicati...retebasics.pdf

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