Airtightness - precast floor and stairs

just do it · 13-09-2014 04:11AM #1

Both the precast floor and stairs are being prepared at the minute and we're looking at the airtightness detail for them.This is a new detail for my architect and arch technican so we're on a learning curve. We've settled on using Ampatex Solero as the membrane which I'm happy with as it is supposed to be tougher and more tear resistant than ordinary membrane.

I was talking to the architect yesterday and I was surprised to hear no mortar will be used between the membrane and precast. DPC will be laid upon it to protect it. Also where there are abutments with the external wall the membrane will be draped down during precast slab and stairs placement and not taped in place.

I'm a bit uncomfortable with this detail for 2 reasons:
1) the mortar would act to both protect the membrane and act as a bed for the slabs making up for unevenness along the top of the wall.
2) the detail for abutments seems very loose and also wasteful particularly for the stairs as he's talking of full lengths draping down the full height of the wall and then being cut back after placement. Surely taping it to the wall along where the stairs will abut would be more secure and less wasteful? How will we protect it during placement?

The debate on this detail is still open so any suggestions/ experiences welcome.

just do it · 13-09-2014 04:16AM

This is what I had in mind for the precast floor

just do it · 13-09-2014 04:18AM

Looking at this picture again it looks like dpc on it rather than mortar. I thought it was mortar!

just do it · 13-09-2014 04:50AM

For areas of abutment what about applying a scratch coat to the external wall before floor and stairs placement?

hexosan · 13-09-2014 07:13AM

I used solitex on mine. It's 1.5m in width so I cut it in half to 750mm and rolled it out on the wall. I used 4" expanded mesh to fix it to the bottom of the wall. All the corners were taped, the wrap was folded back into the cavity. Then the slabs were laid on top. Wrap was then folded back over the slabs. Block layer returned and laid blocks on top. I then went around and used the expanded mesh to fix it back to the wall.

MicktheMan · 13-09-2014 08:20PM

just do it wrote: »

For areas of abutment what about applying a scratch coat to the external wall before floor and stairs placement?

If the scratch coat is your air tight barrier on the wall then yes, scratch coat the wall before the stairs is installed. In fact, a scratch coat should be applied before any other work is done which may prevent the wall from being scratch coated later.

just do it · 14-09-2014 09:24AM

MicktheMan wrote: »

If the scratch coat is your air tight barrier on the wall then yes, scratch coat the wall before the stairs is installed. In fact, a scratch coat should be applied before any other work is done which may prevent the wall from being scratch coated later.

Thanks Mick
I've been coming to that conclusion over the weekend. You're right that the scratch coat will be my airtightness layer as it is a 250mm cavity. It is also the cheapest option due to saving on airtightness membrane.

Airtightness - precast floor and stairs

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