Expanding foam 16 December 2022 at 5:59PM edited 16 December 2022 at 6:02PM in In my home (includes DIY) MoneySaving 7 replies 226 views

GDB2222

I wanted to fill a cavity in the wall in a bedroom where there's an air vent in the outside of the wall, and basically a big hole inside that. There was probably a coal fire in the room years ago, but we don't need the air vent any longer, as we have GCH. 

I squirted some expanding foam into the hole, and I now want to stick some Easyfill plaster on top, and redecorate. BUT, the foam isn't very rigid, so surely the plaster will crack? 

Is there a way of salvaging this, or should I just rake out the expanding foam , and start again?

diystarter7

Hi

How big is the aperture in the wall and what shape?

Thanks

Alter_ego

Sounds like a chimney vent, best not to block it.

silvercar

On another thread, about blocking a tumble dryer vent hole. the following was advised:

Mutton_Geoff said:

What's on the outside? A vent plate? Take that off, insert a square of plastic (couple of layers of a rubble bag or side cut out of large plastic laundry softener bottle will do). Replace plate. Get a good handful of loft insulation from a nearby skip. Push that into pipe from inside.

Alternatively once the outside is blocked, squirt some builders foam in and immediately tape/fix a piece of card larger than the hole on the wall to ensure end of foam squared off.

It doesn't matter that the pipe bridges the cavity. It won't be causing any issues/loss of heat etc.

Section62

GDB2222 said:

I squirted some expanding foam into the hole, and I now want to stick some Easyfill plaster on top, and redecorate. BUT, the foam isn't very rigid, so surely the plaster will crack? 

Is there a way of salvaging this, or should I just rake out the expanding foam , and start again?

Unless the wall is likely to be kicked or punched then the foam should give a reasonable foundation to the plaster once it has fully cured.  I'd be inclined to go with what you've got, but be prepared to do a repair in the future if it is a problem (i.e. keep enough spare paint/wallpaper to be able to make an invisible repair)

If you want an easy way to make the repair tougher now then I would trim the foam back sufficiently to be able to recess a piece of plasterboard in place, cut just smaller than the hole, and then 'glue' it onto the foam using whatever you've got to hand.  Then use the filler over the top of the plasterboard.  That will be more resistant to knocks and bangs.

GDB2222

Section62 said:

GDB2222 said:

I squirted some expanding foam into the hole, and I now want to stick some Easyfill plaster on top, and redecorate. BUT, the foam isn't very rigid, so surely the plaster will crack? 

Is there a way of salvaging this, or should I just rake out the expanding foam , and start again?

Unless the wall is likely to be kicked or punched then the foam should give a reasonable foundation to the plaster once it has fully cured.  I'd be inclined to go with what you've got, but be prepared to do a repair in the future if it is a problem (i.e. keep enough spare paint/wallpaper to be able to make an invisible repair)

If you want an easy way to make the repair tougher now then I would trim the foam back sufficiently to be able to recess a piece of plasterboard in place, cut just smaller than the hole, and then 'glue' it onto the foam using whatever you've got to hand.  Then use the filler over the top of the plasterboard.  That will be more resistant to knocks and bangs.

That's roughly what I had in mind. I bought some plasterboard the other day, to mend a large hole in the dining room ceiling. Stupidly, I threw the excess away. 

I do have some hardboard, and I hope that will do much the same? 

floppydisk1

hardboard will be good too, even big flat pebble stone will do, just something stronger than expanding foam to fill a little hole with and bit of easyfill to finish it off with....

Section62

GDB2222 said:

Section62 said:

GDB2222 said:

I squirted some expanding foam into the hole, and I now want to stick some Easyfill plaster on top, and redecorate. BUT, the foam isn't very rigid, so surely the plaster will crack? 

Is there a way of salvaging this, or should I just rake out the expanding foam , and start again?

Unless the wall is likely to be kicked or punched then the foam should give a reasonable foundation to the plaster once it has fully cured.  I'd be inclined to go with what you've got, but be prepared to do a repair in the future if it is a problem (i.e. keep enough spare paint/wallpaper to be able to make an invisible repair)

If you want an easy way to make the repair tougher now then I would trim the foam back sufficiently to be able to recess a piece of plasterboard in place, cut just smaller than the hole, and then 'glue' it onto the foam using whatever you've got to hand.  Then use the filler over the top of the plasterboard.  That will be more resistant to knocks and bangs.

That's roughly what I had in mind. I bought some plasterboard the other day, to mend a large hole in the dining room ceiling. Stupidly, I threw the excess away. 

I do have some hardboard, and I hope that will do much the same? 

That's why I never throw anything away ;-)

Hardboard should be Ok if you use it rough side out and scratch the smooth surface to improve the key.  If it is tempered though give it a miss as you may get leaching into the filler.

...unless you happen to be passing any skips in the next few days with offcuts of plasterboard asking to be taken.