Liquid damp proof prior to self level compound on concrete?

[Mark Lewis]

My barn to gym conversion is coming along nicely and it is time to deal with the floor. Half of it is a concrete slab laid over earth and the other half is a newer concrete slab laid over a damp proof membrane. The entire surface is pretty dry and in good shape but I'm going to apply a self levelling compound anyway because I want it nice and neat and it looks good on YouTube )

Given that there is no DPC under half of the concrete (I know this because there are a couple of holes where 300 year-old beams used to go into the floor that show the Earth underneath!) should I pour down a liquid DPC before self levelling compound. I assume the self levelling compound won't like any damp coming up from below?

I know that there are issues with DPC pushing moisture horizontally into the walls, but the walls are 600mm stone and lime mortar and finished with a hot lime white wash internally so hopefully we'll be able to absorb any moisture and release it into the air-conditioned internal space without too much drama?

So - liquid damp proof course? Yes or no.

Oh, and the flooring that will go on top of it is simple 50 mm gym matting.

[PhilboSE]

Speak to the manufacturers of the SLC eg Mapei what they recommend for their product as it might not bond and then delaminate.

[DonkeyApple]

I believe you can do this and that it is a matter of choosing the correct materials that will. My guess is that it will be a particular self levelling compound that needs to be used.

[PhilboSE]

Yes, it can be done, but you can’t mix and match any old liquid DPM with any old SLC, and there will probably be a minimum thickness for the SLC. So the manufacturers of the SLC will be able to advise.

[wolfracesonic]

I’m sure I contacted some technical department about this, years ago, the advice was two coats of dpm, the second perpendicular to the first and to spread some sharp sand on the second coat before it dries to give a mechanical key for the slc, I think I used kiln dried sand for my job. Isn’t the theory of putting a dpm down and it forcing more water into the walls a myth, unless there is some hydrostatic pressure involved?

[Rob.]

If you do go down this route, check out Arditex NA.

[T1547]

Hi OP,
Something to keep in mind is that not all liquid DPM’s are suitable for application where there is no structural DPM present. Many liquid DPM’s are only suitable for the function of controlling residual construction moisture. Check on the manufacturer’s data sheet before purchasing, it should state suitability with/without structural DPM.

Here’s two examples of products that can be used for your required function, I.e where no structural DPM exists:

https://www.protilertools.co.uk/product/tilemaster...

https://ardex.co.uk/product/ardex-dpm-1-c/


With regards the SLC the common method of application for your scenario is to ‘sandwich’ the liquid DPM in between two layers of SLC. The first SLC layer is to smooth the existing concrete surface so that it is suitably flat to receive the liquid DPM (no point applying liquid DPM on an uneven surface that allows holes/gaps in the DPM).

For this first layer of SLC, it will need a product that is ‘moisture tolerant’ as it will be beneath the liquid DPM so could be damp. Not all SLC’s are moisture tolerant.

Here’s two that are moisture tolerant:

https://www.screedgiant.co.uk/product/kerakoll-pro...


https://www.mapei.com/gb/en/products-and-solutions...

Get this down (only needs to be thick enough to provide a flat surface). Allow to cure. Apply the liquid DPM. Prime if recommended by SLC data sheet. Apply the second layer of SLC over the top of the DPM @ 3-5mm thickness.

Job done

[T1547]

Rob. said:

If you do go down this route, check out Arditex NA.

Yep, Arditex NA will be moisture tolerant.

You could go

Arditex NA > ARDEX DPM 1 C > Arditex NA for a complete Ardex system which would do as I described above.

[Mark Lewis]

T1547 said:

Hi OP,
Something to keep in mind is that not all liquid DPM’s are suitable for application where there is no structural DPM present. Many liquid DPM’s are only suitable for the function of controlling residual construction moisture. Check on the manufacturer’s data sheet before purchasing, it should state suitability with/without structural DPM.

Here’s two examples of products that can be used for your required function, I.e where no structural DPM exists:

https://www.protilertools.co.uk/product/tilemaster...

https://ardex.co.uk/product/ardex-dpm-1-c/


With regards the SLC the common method of application for your scenario is to ‘sandwich’ the liquid DPM in between two layers of SLC. The first SLC layer is to smooth the existing concrete surface so that it is suitably flat to receive the liquid DPM (no point applying liquid DPM on an uneven surface that allows holes/gaps in the DPM).

For this first layer of SLC, it will need a product that is ‘moisture tolerant’ as it will be beneath the liquid DPM so could be damp. Not all SLC’s are moisture tolerant.

Here’s two that are moisture tolerant:

https://www.screedgiant.co.uk/product/kerakoll-pro...


https://www.mapei.com/gb/en/products-and-solutions...

Get this down (only needs to be thick enough to provide a flat surface). Allow to cure. Apply the liquid DPM. Prime if recommended by SLC data sheet. Apply the second layer of SLC over the top of the DPM @ 3-5mm thickness.

Job done

Perfect - will get those. If I need some extra thickness in the screed to counter a slight dip in the floor at one spot....do I put the thicker slice of screed sandwich down below or above the dpc?

And - what do I wear on my feet for the top screen apllication because I assume spiked shoes will pin hole the DPC???

[PhilboSE]

Bottom layer of the sandwich is just to level the floor so thicker layer on top.

Depends how big an area you have to do but you often don’t need to walk on the SLC if you apply it in a logical way. More important is to get some help with the mixing - it takes longer to mix up a bag than pour it, and the quicker it all goes down together, the better. Having 2 mixers to one pourer is ideal, but you can do it 1 and 1. Doing it all solo is only for smaller areas because you’ll be wanting to work it into corners and flatten it off a bit with a float as you go.

A spiked roller with a broom handle is a good idea as it helps to even up the edges between pours and reduces air bubbles.

[mart 63]

T1547 said:

Yep, Arditex NA will be moisture tolerant.

You could go

Arditex NA > ARDEX DPM 1 C > Arditex NA for a complete Ardex system which would do as I described above.

I've done quite a few council properties using this system, the properties had terracotta tiles down. The Ardex goes on easy over the first self leveling coat. It's expensive but very effective.

[Mark Lewis]

PhilboSE said:

Bottom layer of the sandwich is just to level the floor so thicker layer on top.

Depends how big an area you have to do but you often don’t need to walk on the SLC if you apply it in a logical way. More important is to get some help with the mixing - it takes longer to mix up a bag than pour it, and the quicker it all goes down together, the better. Having 2 mixers to one pourer is ideal, but you can do it 1 and 1. Doing it all solo is only for smaller areas because you’ll be wanting to work it into corners and flatten it off a bit with a float as you go.

A spiked roller with a broom handle is a good idea as it helps to even up the edges between pours and reduces air bubbles.

Just a thought - I'm not convinced we need a DPC as it is very dry in there despite the wet winter (I assumed it would be £50 tops to slap some down! )
Given it's expensive does this approach work.......JUST go with a SLC to get it flat and level. Use one that is damp tolerant.

If in the future damp some appear, whip off the gym floor tiles and put a liquid DPC down before returning the tiles. An afternoon work.