Concrete slab above dpc

[deadfire19]

Hey!

I'm pouring a new concrete screed in my garage and discovered the old slate DPC level is below the garage floor.

I'm guessing this would cause moisture bridging in the future. I was planning to chip away a bit at the concrete slab around the edges, put down a liquid DPM and prevent the bridging.

The concrete slab has no DPM.

Is it worth the extra work or should I leave it as it is.

Many Thanks!

 

[jeds]

Chip away but don't fill with anything, leave a capillary gap of some description. A slip of PIR insulation with a groove cut in it (the groove bridging the dpc) would be perfect.

 

[deadfire19]

Chip away but don't fill with anything, leave a capillary gap of some description. A slip of PIR insulation with a groove cut in it (the groove bridging the dpc) would be perfect.

I was planning to use Ardex Liquid DPM 1C above the self-leveling compound.

Given that I already already own the liquid dpm do you think I just just apply it to the chipped away floor, then add the PIR Bridge (I have some 25mm)?

 

[jeds]

Just to check we're talking about the same thing; You don't want to be sealing the gap between the floor and the wall. It's far better off being left as a void, which is where the PIR comes in - it will create a capillary break to prevent moisture being able to bypass the dpc.

Moisture might get into the floor from below that level but there's not much you can do about that. What you don't want is moisture going from below dpc - into the floor - and then back into the wall above dpc.

If you are talking about adding Ardex to the floor surface, that's fine if the floor shows dampness and needs it. If not and there is nothing moisture sensitive involved, then it's down to whether you feel like doing the extra work.

Hope that makes more sense.

 

[deadfire19]

Just to check we're talking about the same thing; You don't want to be sealing the gap between the floor and the wall. It's far better off being left as a void, which is where the PIR comes in - it will create a capillary break to prevent moisture being able to bypass the dpc.

Moisture might get into the floor from below that level but there's not much you can do about that. What you don't want is moisture going from below dpc - into the floor - and then back into the wall above dpc.

If you are talking about adding Ardex to the floor surface, that's fine if the floor shows dampness and needs it. If not and there is nothing moisture sensitive involved, then it's down to whether you feel like doing the extra work.

Hope that makes more sense.

This was my plan given your comments. Undercut the concrete a little bit and then join it the same way you would if the DPC was above the concrete, The DPM going over the DPC level.

Do you think this is likely to cause any bridging?

 

[jeds]

The vertical liquid dpm (up the wall) isn't necessary and opens up the possibility of moisture bypassing the slate dpc. Add the PIR as shown but cut a groove where the slate is to form a break and just run the liquid dpm up to the PIR. The PIR itself acts as a barrier to moisture - you don't need the vertical Liquid dpm as well.