Airtightness - Parge Coat vs Airtight Paint

[Johnny Jekyll]

Didn't know which thread to post this in. Hope this is ok.

For our new build, the walls are up and the roof is on, and my attention is turning to airtightness.

We haven't installed the midfloor yet, so have nice full medium dense blockwork walls to work with. We will be installing a posi-joist midfloor and MVHR, and we will batten the walls (not dot n dab).

My question is parge coat or airtight paint the walls?

If airtight paint, will be brush applying it myself.

If parge coat, how best to apply it myself? Declan52 said in another post to use a large bucket with water, bag of cement, sand, medusa, put it on with a roller? Is it that easy? If so what would the mix be?

Thanks very much.

[nod]

Neither

You need to make sure the air isn’t getting through the plaster 

Parge is a waste of money A fad 

[JohnMo]

3 minutes ago, nod said:

Neither

You need to make sure the air isn’t getting through the plaster 

Parge is a waste of money A fad 

Depends where you are in the country, in NE Scotland you can't easily get plasterers.  So a parge coat makes sene.

 

For a parge coat, I mixed 1 cement, 3 sand and about 1/5 lime, mix to a double cream thickness.  Get a few natural bristle brooms and apply with them.  Rub into surface so all pin holes are filled.  Plan on a couple of days for two people, depending on house size.

 

When attaching battens I used hybrid sealant in the holes.

[nod]

11 minutes ago, JohnMo said:

Depends where you are in the country, in NE Scotland you can't easily get plasterers.  So a parge coat makes sene.

 

For a parge coat, I mixed 1 cement, 3 sand and about 1/5 lime, mix to a double cream thickness.  Get a few natural bristle brooms and apply with them.  Rub into surface so all pin holes are filled.  Plan on a couple of days for two people, depending on house size.

 

When attaching battens I used hybrid sealant in the holes.

I presume you would plaster at some stage ?

[JohnMo]

No dry lined and taped - that's the Scottish way.

[nod]

6 minutes ago, JohnMo said:

No dry lined and taped - that's the Scottish way.

As a plastering contractor I use a lot of bagged Parge coat For soundproofing 

The problem I have is as soon as anyone mentions airtightness The plasterers don’t seal the dabbing properly If the D&D is sealed properly There should be no air getting through 

Using bagged sound coat A gang of two will do three to four houses in a day 

[Dudda]

Presuming you do both yourself Airtight paint will work out very expensive I'd have thought compared to a parge coat. I did a parge coat and found it fairly easy. It's messy but easy. We then had battens with a quick squirt of airtight sealant in the holes before screwing the battens to the wall. Worked well.

 

I think whichever method you go with (airtight paint, parge coat, AT membrane or plaster) it will depend on the quality of workmanship and attention to detail. 

[JohnMo]

We did parge, but at the DPC we did a coat of airtight paint, as the diagnostic air test showed a leak there.

[Johnny Jekyll]

Thanks very much everyone, very helpful.

 

The plan is to do the following myself - Parge coat, battens, plasterboard.

Then bring in the plasterer to 3mm skim finish.

 

May I ask regarding the parge coat for airtightness:

JohnMo info is very helpful and so is nod for the bagged Parge coat comment.

Rather than mixing everything from scratch, would Gyproc Soundcoat Plus do the job (or another brand)?

And is it as simple as spreading it across the wall using a roller or broom? Achieving a generally even spread on the surface?

Basically how would you best apply it? Trying to find a You Tube video to see the type of finish to look for.

 

[JohnMo]

I mixed mine to a double cream thickness, then got a few cheap natural bristle brooms, rubbed it well into surface, so it had no pin holes.  Once dried, had a look over and where pin holes had occurred during drying gave a second coat.

 

When attaching battons I used a hybrid seal in the holes for the batten screws.

 

We used tapered edge plasterboard and taped the joints. (Dry lined).

[Russell griffiths]

If your parge coat is a bit slap dash, then surely it’s going to make fitting battens a pain as you will need to add packers to get the battens straight. 

[JohnMo]

Hence put it on thin to fill gaps and pin holes only.  Broom in photo is the size I used for applying hithe parge coat.

 

Mine is on Durisol blocks and you can see the blocks clearly.

[Johnny Jekyll]

Great info and photo thanks JohnMo.

 

 

 

[ruggers]

On 18/01/2022 at 12:54, nod said:

Using bagged sound coat A gang of two will do three to four houses in a day 

 

Does this apply easier or require much less work than the likes of bonding and multi finish?

I can't even image one house being completed in 2 days with a float. Very hard to get plasterers where we are. 

[nod]

The Parge is just a 5 mil thick coat and then has dot and dab over it 

Normall two men will Parge a 4 bed house in a couple of hours 

If your bonding and skimming No need for parge 

[ruggers]

Nod that sounds really fast for what I'd expect. I understand you don't have to polish it up or get it tidy but it just seems a lot of area to cover in a few hours floating on. Do you prefer sand and cement or the sound coat or other? I imagine it plastered on being a better job than brushing it on thinner it's just getting the labour in Cumbria.

[TonyT]

Just like how they put artex on back in the day.

 

large round rubbish bin and a sweeping brush

 

[Johnny Jekyll]

I have researched this quite a bit and finally settled on @JohnMo method. I mix approx one cement (mastercrete), three sand (building sand) and a bit of hydrated lime (hydralime), mix to a slurry / double cream thickness. I apply it by hand one block at a time with a block brush, rubbing into the surface so all holes are filled, then after 3/4 metres go back and brush the excess off with a softish brush. It's taking ages but doing a good job of it, and saving a huge amount of money compared to airtight paint / membranes etc. I'll be using the paint and tapes at junctions and windows but for the large wall sections this is going well. As they say, want a good job doing, do it yourself. Here's a photo of the mid floor area done, before fitting the wall plate for hanging the posi joists with joist hangers.

[JohnMo]

Is that a photo after or before applying?  Looks like before.

 

I would apply it with a soft natural bristle brush, (12 to 14 inch) with the right mix there should be nothing to brush off.

[Chanmenie]

On 24/02/2022 at 15:57, nod said:

The Parge is just a 5 mil thick coat and then has dot and dab over it 

Normall two men will Parge a 4 bed house in a couple of hours 

If your bonding and skimming No need for parge 

@nod if applying the bagged soundcoat plus, do you trowel it on just like a plaster skim ? 

[nod]

2 minutes ago, Chanmenie said:

@nod if applying the bagged soundcoat plus, do you trowel it on just like a plaster skim ? 

Just trowel it on

about three times the thickness of finish 

We normally mix three bags at a time in a tub and use it within ten minutes Keep

It goes on really quick 

[bassanclan]

Parge coat mix it like double cream and put it on with a broom, no trowelling involved

[nod]

11 minutes ago, bassanclan said:

Parge coat mix it like double cream and put it on with a broom, no trowelling involved

Things have moved on since the 70s

Gypsum make it ready bagged 

Mix and trowel on

Soundblock coat 

[Chanmenie]

18 minutes ago, nod said:

We normally mix three bags at a time in a tub and use it within ten minutes Keep

It goes on really quick 

 

Thanks @nod
Not so easy if doing it on your own 

think I’ll try one bag at a time ?

[nod]

1 minute ago, Chanmenie said:

 

Thanks @nod
Not so easy if doing it on your own 

think I’ll try one bag at a time ?

You will be fine 

The lads that work for me Will often mix 20 bags without washing out If you wash the tub after each mix it will give you plenty of time Add a T spoon of Cream of Tata which will give you double the time to use it (30 mins )