Can you Parge onto wet blocks?

[GEO-PAR]

Sorry, another thread about parging (I've been reading through most of them and appreciate there's already a lot). 

 

I'm up to first floor level and intend to use posi joists hung off a timber ledger board bolted back to the concrete blockwork.  I'm just looking at options for how to achieve airtightness behind the ledger board.  Above and below will be wet plaster. 

 

The two options I understand I have: 

+ Airtightness paint.  Looks like Blowerproof is £50 a tub, and Soudal do a slightly cheaper version at £38 a tub. 

+ Parge Coat. Seems like people have suggested buying a big brush and brushing on a wet mix of sand and cement (anyone know the actual mix?).  Appears cheaper than airtight paint but possibility of cracking over time defeating the purpose? 

 

I'm trying to get my first floor in before the roof so my brickie can use it as a platform/deck to continue building the inner leaf (trying to minimise time I need scaffolding on site - had a quote an it's not cheap!).  The house is only 1.5 storey (rooms in the loft space like a chalet bungalow) so brickie only has a few courses plus the gables to do, which he can do from inside.  The issue I have is that after phoning blowerproof, I understand my blockwork has to be dry before painting it on.  Anyone know if this the same with applying a parge coat?  

 

Cheers! 

 

 

 

 

 

[Russell griffiths]

Parge coat onto wet blocks is not a problem, as you would want to wet the blocks down anyway

 

weak sand n cement mix with a shovel of lime. 
bucket and a soft broom head

or just a hawk n trowel. 
 

Edited Thursday at 13:15 by Russell griffiths

[Redbeard]

Trowel more reliable in terms of uniform (and 'useful' -from an air-tightness point of view) thickness, I feel. I have never done parge costs with a broom, though.

[GEO-PAR]

On 28/11/2024 at 13:06, Russell griffiths said:

Parge coat onto wet blocks is not a problem, as you would want to wet the blocks down anyway

 

weak sand n cement mix with a shovel of lime. 
bucket and a soft broom head

or just a hawk n trowel. 
 

 

On 28/11/2024 at 13:26, Redbeard said:

Trowel more reliable in terms of uniform (and 'useful' -from an air-tightness point of view) thickness, I feel. I have never done parge costs with a broom, though.

Cheers - Might give it a go with a trowel but have never plastered before so worry I'll make a right old mess of it and will be super uneven for when I put the joists against the wall?  I guess I can give this a go first and resort to a brush if all goes tits up 

[JohnMo]

10 minutes ago, GEO-PAR said:

guess I can give this a go first and resort to a brush if all goes tits up 

 

On 28/11/2024 at 13:06, Russell griffiths said:

weak sand n cement mix with a shovel of lime. 
bucket and a soft broom head

That is how I did mine, think I use 3 soft building sand, 1 cement and some lime. Mixed with water to double cream thickness. Then used a soft broom. Brushed in until I could see no more holes visible.

 

Mine was on wood Crete, so way more difficult than blocks.

 

I also used a hybrid sealant around the gaps between wall and wood as belts and braces.

[GEO-PAR]

22 minutes ago, JohnMo said:

 

That is how I did mine, think I use 3 soft building sand, 1 cement and some lime. Mixed with water to double cream thickness. Then used a soft broom. Brushed in until I could see no more holes visible.

 

Mine was on wood Crete, so way more difficult than blocks.

 

I also used a hybrid sealant around the gaps between wall and wood as belts and braces.

I've not come across Woodcrete before... I just gave it a google and came up with an ICF type system. Is this what you're referring to? 

 

Sounds like a good idea, cheers! 

 

 

[crispy_wafer]

I did try mortar in a bucket and a brush to start with, but found it ended up crumbly and didn't adhere too well to the blocks, just ended up grainy and on the floor so I went the expensive route and bought in soundcoat @ 10 per bag, never even attempted a plastering type motion before, 1st wall was a mess and more slopped on the floor than the wall, second wall better but still dropped loads. 

After that, spot on, got the hang of the hawk and trowel...  Although I could only manage 1/2 a bag at a time as my shoulders were crying. 

[JohnMo]

43 minutes ago, GEO-PAR said:

came up with an ICF type system. Is this what you're referring to? 

Yes.

 

This is it going on

 

You can see the brushes we used to apply in this photo 

 

[mjc55]

On 01/12/2024 at 21:26, GEO-PAR said:

I've not come across Woodcrete before... I just gave it a google and came up with an ICF type system. Is this what you're referring to? 

 

Sounds like a good idea, cheers! 

 

 

Have a look here - this is the ecobrick site.

 

I will be using them for our build, be careful however - this build method does raise some hackles on here! 🫣

[JohnMo]

16 minutes ago, mjc55 said:

Have a look here - this is the ecobrick site.

 

The wall can be built up to 2.5 metres (ten courses) in height before the first concrete pour.

 

This bit has changed since our build, it was 6 rows when we built.

 

I would ignore and do 6 rows at a time. It way more manageable and less likely to go wrong.

[mjc55]

Yes, we plan to do 6 rows for each pour on ours!