Airtightness/Hollowcore

caddy16

As an alternative to wrapping the hollowcore I have been advised to:
- seal the ends of hollowcore
- mortar the joints
- apply airtight paint to the joint where it meets the external wall above & below.

Has anyone else gone this route or been advised the same?

Calahonda52

What is the plan for the rest of the A/T layer.
paint is a poor option in my opinion, no allowance for shrinkage/thermal movement

caddy16

Calahonda52 wrote: »

What is the plan for the rest of the A/T layer.
paint is a poor option in my opinion, no allowance for shrinkage/thermal movement

Every thing else proposed seems standard - membranes, openings taped etc.
The view was that what is being used to wrap in most builds is not fit for purpose and specialised airtight pant is more suitable.

Calahonda52

caddy16 wrote: »

Every thing else proposed seems standard - membranes, openings taped etc.
The view was that what is being used to wrap in most builds is not fit for purpose and specialised airtight pant is more suitable.

That is a big view.

Take a cross section drawing of your house and without lifting the pencil, trace the line of the A/T layer.

caddy16

Calahonda52 wrote: »

That is a big view.

Take a cross section drawing of your house and without lifting the pencil, trace the line of the A/T layer.

Sorry not sure what point your trying to make?

Calahonda52

caddy16 wrote: »

Sorry not sure what point your trying to make?

Using the paint as you describe, I want you to be able to visualise where the A/T is going to be all the way around: in other words what will you do with underside of the HC slab.

The wrap approach means that all of the HC is inside the A/T layer.

with the paint approach, it is less obvious.

My issue with products such as paints and spray on foams is:

How do you know the right, CE/BBA/NSAI/?? approved stuff is being actually used?

What thickness will be applied?

What thickness is required?

will the substrate be prepped properly?

caddy16

Calahonda52 wrote: »

Using the paint as you describe, I want you to be able to visualise where the A/T is going to be all the way around: in other words what will you do with underside of the HC slab.

The wrap approach means that all of the HC is inside the A/T layer.

with the paint approach, it is less obvious.

My issue with products such as paints and spray on foams is:

How do you know the right, CE/BBA/NSAI/?? approved stuff is being actually used?

What thickness will be applied?

What thickness is required?

will the substrate be prepped properly?

Ok with you now.
I don't know what thickness but this company specialises in this area so I am relying on their expertise. I'm just trying to gauge if anyone has gone down a similar route.

The concerns you mention are valid and I will discuss with them, thanks for your input.

BryanF

caddy16 wrote: »

As an alternative to wrapping the hollowcore I have been advised to:
- seal the ends of hollowcore
- mortar the joints
- apply airtight paint to the joint where it meets the external wall above & below.

Has anyone else gone this route or been advised the same?

You’ll struggle achieve continuity

Easier to wrap the perimeter of the sabs

caddy16

BryanF wrote: »

You’ll struggle achieve continuity

Easier to wrap the perimeter of the sabs

Thanks BryanF.

Is there a particular membrane you would recommend?

Calahonda52

caddy16 wrote: »

Thanks BryanF.

Is there a particular membrane you would recommend?

Well,based on this by you:
The view was that what is being used to wrap in most builds is not fit for purpose and specialised airtight pant is more suitable.

there may not be much point in you being told what we think in this area :cool:

mfceiling

Search the history on here for a poster called SAS. He built to almost passive standards and did a fantastic job wrapping his hollowcore. Posted pictures of his work as well.

caddy16

mfceiling wrote: »

Search the history on here for a poster called SAS. He built to almost passive standards and did a fantastic job wrapping his hollowcore. Posted pictures of his work as well.

Will do appreciate the response.

BryanF

caddy16 wrote: »

Thanks BryanF.

Is there a particular membrane you would recommend?

radon membrane

Have a talk with builder/ installers and explain they need to be careful.