hollowcore question?

LowOdour

is there anything that should be done to the hollow ends of the fitted hollowcore? could the be filled with concrete, covered with some kind of mesh/membrane? worried that any verman might get into them

RKQ

Airtightness, heat loss and vermin are serious considerations.
IMO install an airtight membrane to Manufacturers / Homebond / Dept of Enviro detail. There are a few threads here discussing same.:)

http://www.boards.ie/vbulletin/showthread.php?t=2055929405&page=2

sas

LowOdour wrote: »

is there anything that should be done to the hollow ends of the fitted hollowcore?

Are you saying the hollow core is already fitted because that greatly affects your options?

LowOdour

sas wrote: »

Are you saying the hollow core is already fitted because that greatly affects your options?

it is

LowOdour

im going to b & q today. is the membrane something i could pick up in there? the hollowcoew is 150mm deep

sas

LowOdour wrote: »

it is

In my opinion the membrane is of little use to you now because it needs to be fitted before the hollowcore.

You could try pouring concrete down to seal the end buts that depends on what your wall build up. If it's a standard cavity wall then I'll leave it to someone else to advise.

LowOdour

sas wrote: »

In my opinion the membrane is of little use to you now because it needs to be fitted before the hollowcore.

You could try pouring concrete down to seal the end buts that depends on what your wall build up. If it's a standard cavity wall then I'll leave it to someone else to advise.

crap, didnt know this had to go on. So is there anything else i can do with is as regards to air-tightness or heat loss at this stage?

RKQ

sas is right IMO membrane needs to be installed prior to slabs. (Nice photos sas)

Others might suggest ways of airtighting it now (good luck with that detail).
Anything that helps is worth trying but the membrane is the best solution.

Consider filling all holes in hollow slab with foam insulation - not vermin proof but it will help limit heat loss from slab into cavity. Limit wind / air flow.

You could try to fill end of holes with 50mm deep mortar / conc. to prevent vermin entering from cavity.

LowOdour

would it be possible to fill concrete deep in the holes, and put insulation foam in then! What type of foam could be used and where could i get it?

LowOdour

I dont want to be bumping this thread....i know its not the done thing.

But, if anyone could answer my question about the foam (see previous post) I would be most greatful.

RKQ

IMO any insulation is better than no insulation.

Wind / air movement in the cavity could blow through these holes. This cold air could cool your ceiling, increase draughts and increase heat loss from the rooms below. Vermin could travel along these holes.

Expanding Foam used around window frames etc should be fine. Google expanding foam as some manufacturers supply it in 5litre containers with hose and tap sprayer.

Some more expensive spray foams are airtight.

soldsold

Here is an idea:

You need to 1) stop air flow and 2) stop vermin

For 1) foam probably is the best. For 2) concrete is probably best but will be hard to fill the hollows full without the mortar collapsing and leaving a gap at the top of each hollowcore. So...

Stuff rolls of plastic/ paper/ used cement bags etc into the hollows well in so you have about 1 foot of space at the edges.

Fill a fairly dry mix of sand and cement mortar into this remaining space so that about 6 inches is left at the ends. Cram another roll of paper/ plastic/ anything available in to shove the mortar hard into the hole so the mortar fills the hollow between the paper rolls and leaves no gaps - use a round timber stake or something similar as a plunger to cram the rolls of paper in. Fill the final 3 inches or so with expanding foam

The mortar keeps vermin out, the foam helps stop airflow across the hollows.

Consider also foaming/ plastering the hollowcore above and below wherever you can to seal gaps between the hollowcore and the wall below it. You can tape the hollowcore to the wall above and below with for example contega pv tape later, or the equivalent Siga primur mastic or MOY equivalent, provided you get the gaps between each slab fairly well sealed. Wont be 100% but definitely better than nothing.

LowOdour

soldsold wrote: »

Here is an idea:

You need to 1) stop air flow and 2) stop vermin

For 1) foam probably is the best. For 2) concrete is probably best but will be hard to fill the hollows full without the mortar collapsing and leaving a gap at the top of each hollowcore. So...

Stuff rolls of plastic/ paper/ used cement bags etc into the hollows well in so you have about 1 foot of space at the edges.

Fill a fairly dry mix of sand and cement mortar into this remaining space so that about 6 inches is left at the ends. Cram another roll of paper/ plastic/ anything available in to shove the mortar hard into the hole so the mortar fills the hollow between the paper rolls and leaves no gaps - use a round timber stake or something similar as a plunger to cram the rolls of paper in. Fill the final 3 inches or so with expanding foam

The mortar keeps vermin out, the foam helps stop airflow across the hollows.

Consider also foaming/ plastering the hollowcore above and below wherever you can to seal gaps between the hollowcore and the wall below it. You can tape the hollowcore to the wall above and below with for example contega pv tape later, or the equivalent Siga primur mastic or MOY equivalent, provided you get the gaps between each slab fairly well sealed. Wont be 100% but definitely better than nothing.

Thanks soldsold,
i think im going to try this. Im not sure how it will work out, but as has been mentioned, its better than nothing. Cheers guys