How level does a sub-base need to be?

[aa44]

I am building a garage which will have a concrete floor in it. The concrete will be laid professionally so that I end up with a nice level, polished surface but I am doing nearly all the prep work. The floor will be:

natural rock
type 1 (250mm)
quarry dust (50mm)
DPM
insulation (75mm)
concrete (150mm with A193 mesh in it)

The type 1 and the quarry dust have been gone over again and again with the wacker in layers as it has gone in. My question is how level do I need to get the top of the quarry dust before I put the DPM on? I am using a laser level so I can get it to +/- 10mm without too much difficulty.

Is that flat enough?

Thanks
Andrew

 

[DAZB]

Yes it will be fine.

 

[Aqua]

As dazb says, that will be OK

 

[noseall]

Why are you putting insulation under a garage floor?

 

[RedHerring2]

Good point Noseall, but I did, in the workshop and garage, just future-poofing.

But, on another point, to the OP, I've used quarry dust as a blinding in France. I was concerned with the small sharp stoney bits cutting through the dpm, while walking on it. It was leaving a mark, but not quite cutting through it.
In hindsight ( and next time) I'll use
quarry dust:insulation:dpm:insulation:tape or other barrier:concrete.

In other words divide the insulation into two layers, one below the dpm and one above, in order to protect the dpm, but only when using quarry dust as a blinding.

e.g the OP could use 25mm below the dpm and 50mm above. Laid out in a bond type arrangement.

And having used tape in some instances and another (thinner) layer of dpm in others, I have to say the second layer (thinner/cheaper than proper layer)of dpm is far easier.

 

[tim00]

Why the quarry dust, 50mm of sand is a typical blinding - available and cheaper. Use boards above the DPM and or insulation to walk on and possibly barrow concrete.

 

[RedHerring2]

Why the quarry dust, 50mm of sand is a typical blinding - available and cheaper. Use boards above the DPM and or insulation to walk on and possibly barrow concrete.

Not always available and not always cheaper.

 

[aa44]

Why quarry dust? Two reasons:

1. I'm up in Shetland and quarry dust is available locally but I think that sand has to be shipped up from Orkney.

2. The guy who produced the spec for the building warrant said dust in the application.

Interesting point about putting the insulation above and below the DPM. I was anticipating having to use a mix of 25mm and 50mm boards anyway so I might stick the 25mm below and the 50mm above.

Thanks for all the replies.

 

[aa44]

Why put insulation under the garage?

We currently rent the house next door to the site which has an uninsulated concrete garage floor. Other than summertime the garage floor is so cold that you get condensation on the floor whenever you open the garage doors. I am trying to avoid that in the new house. The walls are ICF and the floor will be insulated so even though the garage won't be heated I expect it to be considerably warmer than the current garage.

 

[hotrod]

The walls are ICF and the floor will be insulated so even though the garage won't be heated I expect it to be considerably warmer than the current garage.

I think you need to have a rethink. Without a heat source the insulation is going to.............