How to fill these holes…And why are they there?!

KnownMaynard

Hi All,

I’d like to know what’s the best way to fill these holes in my spare room. They go all the way through an internal breeze block wall. I’m not bothered about how it looks on one side as this is just an airing cupboard but would like the bedroom side to be filled in. 

Out of curiosity why are they there? I suspect a previous occupant had something like a boiler or heater on there? Seems like an odd place for one though as it would have been in a bedroom, and no sign of ventilation to outside. The two pairs of holes are about copper pipe sized, around 2cm, the lower one about 5cm diameter. On the other side in the airing cupboard there used to be a complication of pipes and pumps and an immersion heater, mostly now gone. Just wondering, but more importantly I want to fix the wall and put something in front of it.

Thanks in advance!

Eldi_Dos

Could have been sink in room at one time?

NSG666

Expanding foam - use enough for it to expand and protrude from the holes but be careful not to get it on the floor covering. Once set, trim it back with a handsaw or bread knife if the other half isn't looking. Use your finger or an appropriate tool to press the foam back in to the hole to form a recess then fill with Polyfilla Easy Sand and sand back with something like 120 grit (fill and repeat if necessary) then paint it.

 It's so easy you might as well do both sides.

FreeBear

The bigger hole, squirt some expanding foam in there. If you don't have a can (it isn't worth buying one for just that hole), scrunch up some newspaper and push it in about 25mm. Mix up some bonding plaster and fill the holes. Once hardened, skim with finishing plaster or a fine filler.

Alternatively, you can use a ready-mix mortar to fill the holes and then finish off with a fine filler. Being internal, and breeze block (aerated cement block), you don't need anything technical or expensive.

Eldi_Dos

To cut expanding foam flush a piece of waxed string wrapped round two bookies pencils and used as a cheese cutter should work once foam is cured,

FreeBear

Eldi_Dos said: To cut expanding foam flush a piece of waxed string wrapped round two bookies pencils and used as a cheese cutter should work once foam is cured,

If you are plugging a hole with expanding foam, it needs to be recessed enough to put a layer of filler over the top. No point in having it flush in this instance.

A serrated kitchen knife is an ideal tool for cutting foam - I favour Kitchen Devil knifes as they give a clean cut without ripping and also a minimum of dust.

Eldi_Dos

FreeBear said:

Eldi_Dos said: To cut expanding foam flush a piece of waxed string wrapped round two bookies pencils and used as a cheese cutter should work once foam is cured,

If you are plugging a hole with expanding foam, it needs to be recessed enough to put a layer of filler over the top. No point in having it flush in this instance.

A serrated kitchen knife is an ideal tool for cutting foam - I favour Kitchen Devil knifes as they give a clean cut without ripping and also a minimum of dust.

Yes but my tip was for anyone who did want to cut expanded foam flush,especially in a confined space.

greyteam1959

I would get a piece of MDF or plywood & cover all the holes in one go.
A lot easier than faffing about with expanding foam or plaster filler.
 

KnownMaynard

Thanks everyone, I'll go with the expanding foam. There are other random holes in this house to fill, the rest being a lot less visible than this one.

stuart45

The only thing to bear in mind if you are doing the inner skin of a cavity wall that has a clear cavity, is not to put in so much foam so it expands through to touch the outer skin.
This would make a path for moisture to penetrate through to the inside.

Section62

KnownMaynard said:

Thanks everyone, I'll go with the expanding foam. There are other random holes in this house to fill, the rest being a lot less visible than this one.

Remember that unless you use a gun-type foam you will only have a limited time (<1 hour) to use the whole contents of the can before the foam will set in the valve mechanism and delivery tube.  After that anything left in the can will be wasted.

So make sure you have all the different jobs you want to do prepared and ready to go. And make sure furniture and carpets are covered as the foam is near impossible to remove if spilt (especially important if you are moving room to room).

For future repairs, if you don't have any already, it is worth skip diving for some offcuts of PIR (e.g. Celotex or Kingspan etc).  These can be cut to shape with a knife and wedged into holes or gaps.  Cheaper than expanding foam, less flammable and absorbent than newspaper, and much less flammable than polystyrene.  And if you drop any on the floor or furniture you can just hoover it up.