Top of Foundation Concrete Rough for DPM

[Mrs Ten Names]

I set the top of my foundation concrete to be level with the sand blinding when I got to that point
There's nothing wrong with the levels, they're spot on.
But the top of the foundation concrete is too rough to lay the DPM straight on, without worrying about punctures.
A lesson learned for the future!

What would anyone advise? A thin coat of mortar to smooth it out? A thin layer of insulation to go under the DPM? That'll give two "folds" of the DPM, from the sand blinding to the insulation, then the turn up the wall. I can 'notch' the floor insulation to accommodate the thin layer of insulation under the DPM.
I could use a layer of DPC, assuming that is tough enough to withstand any sharp bit of concrete.

 

[Deluks]

Confusing post.

Your dpm 'should' be at the finished floor level, lapped up onto the bricks with the dpc.
What's going on with your construction? it doesn't sound normal.

 

[noseall]

I set the top of my foundation concrete to be level with the sand blinding when I got to that point
There's nothing wrong with the levels, they're spot on.
But the top of the foundation concrete is too rough to lay the DPM straight on, without worrying about punctures.
A lesson learned for the future!

What would anyone advise? A thin coat of mortar to smooth it out? A thin layer of insulation to go under the DPM? That'll give two "folds" of the DPM, from the sand blinding to the insulation, then the turn up the wall. I can 'notch' the floor insulation to accommodate the thin layer of insulation under the DPM.
I could use a layer of DPC, assuming that is tough enough to withstand any sharp bit of concrete.

Foundation concrete and DPM rarely clash.
I think folk are baffled by your set up.

 

[Mrs Ten Names]

Confusing post.

Your dpm 'should' be at the finished floor level, lapped up onto the bricks with the dpc.
What's going on with your construction? it doesn't sound normal.

OK, in that case my levels are a bit adrift.
The top of my concrete floor will be level with the DPC in the walls..
So currently the top of the wall foundation concrete is level (or will be) with the sand blinding, which is 200mm below the DPC in the walls.
So there will be 100mm insulation, then 100 mm concrete which will bring it level with the wall DPC. Obviously the DPM will be lapped up the wall past the DPC in the wall.
This isn't a new build, it's a new insulated concrete floor going in to an existing building. And floor levels are predetermined.
The DPC is in newly constructed partition walls. The original walls have no DPC.

 

[Deluks]

So you need to get a couple of courses down onto the concrete, and bring your membrane up to that.

Why is your concrete so high, where will the outside ground level be in relation to your finished floor?

 

[noseall]

OK, in that case my levels are a bit adrift.
The top of my concrete floor will be level with the DPC in the walls..
So currently the top of the wall foundation concrete is level (or will be) with the sand blinding, which is 200mm below the DPC in the walls.
So there will be 100mm insulation, then 100 mm concrete which will bring it level with the wall DPC. Obviously the DPM will be lapped up the wall past the DPC in the wall.
This isn't a new build, it's a new insulated concrete floor going in to an existing building. And floor levels are predetermined.
The DPC is in newly constructed partition walls. The original walls have no DPC.

Where is the hard core layer, sand blinding, screed...?
We generally dig off 400mm of oversite material below DPC.
We generally set the foundation concrete 525mm below DPC where applicable.

 

[Mrs Ten Names]

So you need to get a couple of courses down onto the concrete, and bring your membrane up to that.

Why is your concrete so high, where will the outside ground level be in relation to your finished floor?

The walls, new partition walls, are already built.

The foundation concrete was trench fill for 100mm block partition walls which have no real structural value.
The outside ground level will be about level with the ffl. The outside walls are about 700mm thick stone walls.

 

[Mrs Ten Names]

Where is the hard core layer, sand blinding, screed...?
We generally dig off 400mm of oversite material below DPC.
We generally set the foundation concrete 525mm below DPC where applicable.

Top of hard core layer is about 250mm below DPC in the walls.
Then there'll be 50mm sand blinding, 100mm insulation, 100mm concrete to bring it up to DPC level.

The bottom of the foundation is 500 mm below DPC, and the foundation 300 mm thick concrete . There was no need to go further down for the foundation, it was already down to stone and rock.
The ffl will be about level with the outside ground,

 

[Mrs Ten Names]

This a diagrammatic view of the situation.

 

[martygturner]

You just blind off the fill with sand then dpm or shove insulation in and put the dpm over that ( note not all insulation are moisture resistance but most are.

 

[Mrs Ten Names]

You just blind off the fill with sand then dpm or shove insulation in and put the dpm over that ( note not all insulation are moisture resistance but most are.

Yes, but as in the OP, I'm concerned that the top of the foundation concrete is too rough for the DPM without some cushioning or smoothing.
I specifically want the DPM under the insulation because I'm fitting the pipes for WUFH. I will connect them up to a manifold, and pressurise them, but they won't be in use until I replace the floor in the adjacent room with a similar arrangement. Nor will there be an ASHP until the adjacent room is finished. There is plenty of room for a GSHP in the future.
I was intending on using self-levelling concrete.
I've found it gives a good level and smooth surface so there's no need for a screed, and it's so easy.
It's more expensive, but it saves the cost and time of a screed.

I'll probably put a thin layer of mortar on the foundation concrete to make it smooth.

 

[^woody^]

I suspect the whole concept of sand blinding comes into play here.

 

[noseall]

This a diagrammatic view of the situation.
View attachment 355017

You may struggle to fit standard bottle gullies without having to 'dish' the foundation concrete to suit.

 

[noseall]

Yes, but as in the OP, I'm concerned that the top of the foundation concrete is too rough for the DPM without some cushioning or smoothing.
I specifically want the DPM under the insulation because I'm fitting the pipes for WUFH. I will connect them up to a manifold, and pressurise them, but they won't be in use until I replace the floor in the adjacent room with a similar arrangement. Nor will there be an ASHP until the adjacent room is finished. There is plenty of room for a GSHP in the future.
I was intending on using self-levelling concrete.
I've found it gives a good level and smooth surface so there's no need for a screed, and it's so easy.
It's more expensive, but it saves the cost and time of a screed.

I'll probably put a thin layer of mortar on the foundation concrete to make it smooth.

As per Woody - it's what sand blinding was invented for.

 

[Mrs Ten Names]

You may struggle to fit standard bottle gullies without having to 'dish' the foundation concrete to suit.

No drainage required.