Air tightness membrane for hollow core ends

[cwr]

Hi folks

What is the recommended air tightness membrane for sealing the ends of hollow core slabs?

 

Does it need to be a specialist membrane or would a 1200 gauge PE sheet or wide dpc do?

[willbish]

Without knowing your airtightness strategy, I would think membrane and tape would be tricky to detail on hollowcore slabs.

 

Take a look at FM330 foam and blowerproof liquid.

[tonyshouse]

Tony tray, or fill ends with foam 

[cwr]

Thanks for the suggestions.

 

I have read a little about Tony Trays. I like the concept and it works with out air tightness plan of wet plastering the inner block skin. The hollow cores are for the first floor by the way, so wet plastering above and below.

 

Just wondering about exactly what to use for the membrane.

[tonyshouse]

I used an airtight breather membrane,  I see poly as too slippy, dpc as bit too stiff 

[Gus Potter]

12 hours ago, cwr said:

Hi folks

What is the recommended air tightness membrane for sealing the ends of hollow core slabs?

 

Does it need to be a specialist membrane or would a 1200 gauge PE sheet or wide dpc do?

 

43 minutes ago, tonyshouse said:

I used an airtight breather membrane,  I see poly as too slippy, dpc as bit too stiff 

Hi cwr.

 

Run this by your SE. The thing is that the SE may be relying on the frictional / bond resistance between the floor slab and the wall to provide lateral stability to the building. If you introduce a slippy bit of plastic between the slab and the wall as tonyshouse says you could be making a rod for your back.

 

Foaming up the ends of the slab looks a bit simpler as suggested.

[cwr]

Thanks for the advice. Good point re the structural concerns. 

Hollowcore slabs went in today, on top of walls that I parge coated over the weekend.

FM330 and blowerproof delivered and ready to be applied tomorrow eve.

 

[Johnny Jekyll]

On 24/05/2021 at 22:26, cwr said:

Thanks for the advice. Good point re the structural concerns. 

Hollowcore slabs went in today, on top of walls that I parge coated over the weekend.

FM330 and blowerproof delivered and ready to be applied tomorrow eve.

 

Would you be able to post photos after you've applied the FM330 and blowerproof? Would be interesting to see how you did it.

And out of interest how much did you use of each product?

I'm currently going for tony tray mid-floor but looking at the other two for windows and floor/wall junctions.

 

[cwr]

Yes of course. The placing of the slabs highlighted a bit of an issue elsewhere, so its going to be a few days before i seal it up as the slabs need a little more positioning...

[cwr]

And finally the slabs were lined up correctly (long story) and I was able to seal them up just this week.

 

I first applied the foam to the open ends. Maybe could have used a little less in places, though not much less as it tended to slump over if applied to thinly. Expanded out quite a bit and I found it necessary, or at least neater, to apply it at least 50mm into the hollows. 

 

Plan had been to use the blower proof paint to seal the parged walls to the slabs, but with some gaps I found it easier to just use the foam. Probably cheaper too. You can see in the photo a bit of the dark blue blowerproof.

 

In all I used 4 cans of FM330. There's 13m of slabs, so 26m of slab ends.

[Johnny Jekyll]

Good photo and info thanks cwr

[tonyshouse]

Is it blocks laid flat? 

[cwr]

The inner skin is 140mm thick, at the structural engineers request.  140 X 100mm blocks were used, laid flat.

[tonyshouse]

My engineer would never allow me (the builder or client) to use blocks laid flat in load beating situations.

 

I can’t see why if wall is 140mm thick they couldn’t have been laid in the normal fashion? 

[Thorfun]

8 hours ago, tonyshouse said:

My engineer would never allow me (the builder or client) to use blocks laid flat in load beating situations.

 

I can’t see why if wall is 140mm thick they couldn’t have been laid in the normal fashion? 

we've got a load bearing wall in our basement that runs through the spine of it to take the load of the block and beam ceiling. SE specified 215 x 100mm blocks laid flat to give enough room for both beams to rest. maybe it depends on the engineer?