Liquid DPM for airtightness

[R2021]

My ground floor is a partial basement formed of high density block work with the cavity filled with waterproof concrete to mid height and liquid DPM below ground level. The upper half is an empty cavity. Insulation with be internal PIR. Upper floors are airtight timeframe.

 

I want to ensure the upper half of the block work is as airtight as the rest of the build. Could this be achieved by painting the internal block work with liquid DPM or should I really be looking at a specialist product like BlowerProof, Soudatight LQ or Passive Purple?

[Iceverge]

A parge coat of sand and cement would be much cheaper.

 

Normal paint would not have the crack filling ability I would say. 

[R2021]

Thanks @Icevergethat's an alternative approach that I will consider. I will be doing this myself so a painted solution would be quicker (for me with my limited plastering skills).

The sales team at Soudal confirmed that Soudatight LQ will fill gaps up to 5mm, provide air tightness, and can be rollered. It's a 3rd of the price of the BlowerProof and Passive Purple so that's my contender for a specific air tight paint option. Liquid DPM would still be the cheapest and easiest for me though so keen to know if that is a viable option.

[Marv968]

Where are you going to buy the Soudatight LQ from? I asked my builders merchant for a price early last week, but they're yet to get back to me.

I've looked into Liquid DPM as an alternative, but I can't determine if it is suitable either.

[eandg]

36 minutes ago, Marv968 said:

Where are you going to buy the Soudatight LQ from? I asked my builders merchant for a price early last week, but they're yet to get back to me.

I've looked into Liquid DPM as an alternative, but I can't determine if it is suitable either.

I got some from Platinum Chemicals - was about the cheapest I could find and free delivery over £75. 

[Iceverge]

2 hours ago, R2021 said:

will be doing this myself so a painted solution would be quicker

 

You can paint on a parge coat, it's just a sloppy mix of sand and cement. Where I am €10 will buy you enough to make up at least 50l in sand and cement. 

 

We used Soudal I think for the junctions, wall to floor etc as parge coat/wet plaster wouldn't have the flexibility needed. Painting it on neat meant it used loads and loads of paint and tended to peal off if the substrate wasn't perfect. Putting down a dilute coat first maybe at 5:1 water/paint served as a primer, saving loads of paint and sticking much better too. 

[R2021]

On 31/01/2023 at 20:03, eandg said:

I got some from Platinum Chemicals - was about the cheapest I could find and free delivery over £75. 

@Marv968I found the same - my local builders merchant not only said they didn't sell the Soudal product but they didn't believe me that such things as airtight paints existed. Like @eandgsays, I found there to be a few places online selling it for around £35 inc. VAT.

[R2021]

On 31/01/2023 at 20:34, Iceverge said:

 

You can paint on a parge coat, it's just a sloppy mix of sand and cement. Where I am €10 will buy you enough to make up at least 50l in sand and cement. 

 

We used Soudal I think for the junctions, wall to floor etc as parge coat/wet plaster wouldn't have the flexibility needed. Painting it on neat meant it used loads and loads of paint and tended to peal off if the substrate wasn't perfect. Putting down a dilute coat first maybe at 5:1 water/paint served as a primer, saving loads of paint and sticking much better too. 

Thanks @Icevergethat sounds straight forward then and good value for money. Grateful if you could explain the principles though (my experience in these things is limited and I'm trying to learn). With a high density block, I assumed the weakness from an air tightness perspective was at the mortar joints. Those being sand and cement, how does a sand and cement parge coat over the top improve the air tightness?

[Iceverge]

Air will leak through the blocks themselves. 

 

If you're careful you can pour an entire bottle of water into a concrete block. They're far from 100% solid. The aggregate is large and leaves lots of voids. 

 

A parge coat will seal all the small holes with sand and cement as the particles are much smaller and the cement dries to fill all the gaps. 

 

 

[R2021]

20 hours ago, Iceverge said:

Air will leak through the blocks themselves. 

 

If you're careful you can pour an entire bottle of water into a concrete block. They're far from 100% solid. The aggregate is large and leaves lots of voids. 

 

A parge coat will seal all the small holes with sand and cement as the particles are much smaller and the cement dries to fill all the gaps. 

 

 

Thank you @Iceverge that makes a lot of sense.  From your comments I done a bit of Googling and found this video, which demonstrates exactly what your say. Interestingly after air testing the blocks, they apply a liquid membrane and test the improvement, but their final comment is that a render, as you suggested, is the best method.