Hollowcore

[RossH]

Hi all,

 

Have found this forum helpful over the last year while completing my self build in Ireland.

 

I am wondering if anyone has advice on the best way to seal Hollowcore ends before pouring the next lift of ICF walls.

 

Currently weighing up a sand and cement mix vs a rockwool plug (both pushed 100mm inside the core). Curious whether there are other better suited options I haven't considered.
 

Thanks

Ross

[saveasteading]

I don't recall ever doing it. But your way seems sensible. Push a plug of rockwool to give a stop  then a sharp sand mix as facing.

[-rick-]

What is your air tightness strategy and target?

[RossH]

Thanks for the responses.

 

The external walls are being built up with ICF. The way the standard interface works, is that the hollower bears 80mm onto the concrete core of the ICF wall below. We then build up ICF walls from this level for the next wall pour.

 

The main objective is to stop the concrete from the ICF flowing freely and uncontrolled into the cores. If there is no 'stop' there, there is nothing to prevent it. 
 

Airtightness in my understanding shouldn't be effected in reality, as either way the cores will be sealed by the external wall pour. It's more to do with managing the flow of concrete into the core.

[Gus Potter]

22 hours ago, RossH said:

Have found this forum helpful over the last year while completing my self build in Ireland.

Hope you are enjoying BH, we have lots of fun here. Remember there is no such thing as a stupid question! 

 

16 minutes ago, RossH said:

The external walls are being built up with ICF. The way the standard interface works, is that the hollower bears 80mm onto the concrete core of the ICF wall below. We then build up ICF walls from this level for the next wall pour.

As an SE I often look at bearing lengths for say Hollo core slabs. Generally on masonry standard is 100mm, on concrete (ICF)  min 75mm, I then deduce your SE is taking into account construction tolerance, hence the 80mm. That's a good sign! The bearing length is vitally important as the floor slabs often act as diaphragms that tie the house together. 

 

But now we need to look at your pour sequence. Normally we would cast the first lift up to underside of Hollo slab, set the slabs, then carry on. 

 

A standard ICF domestic core is 150mm of concrete, sometimes a bit more.  Now if you have a 80mm rest on your Hollo core that technically leaves 150 - 80 = 70mm of concrete before the outside skin of insulation, and that bit is going to be very hard to compact properly as it's going to be at the bottom of the next shutter lift. 

 

Have you considered extending the Hollo core slab rest to the full thickness of the concrete core so it sits flush with the outside edge of the concrete core? Then you'll have much better tying and can foam up the Hollo cores to your hearts content as they will be easily accessible? If you really want air tightness you can seal off any gaps within the floor depth as the end of the Hollo slabs will be flush with the inside face of the outside insulating layer of ICF,, that's a tongue twister!

 

I may have missed something here. You SE may have introduced some extra floor to floor tying rebar, hence the reason for the 80mm bearing? Can you post the details you have? 

 

To finish, good question and hope you enjoy BH, folk chipping in, but also remember that folk that come after you will learn from your posts and experience. For me, it's also my day job, I also learn from your innovation, so thanks.