Cavity liner finishing

[Paene Finitur]

Hi all. One of the cavity liner vents in our front room has not been finished properly and is in a bit of a sorry state. If the aperture were smaller I could simply put a decorative vent over it, but  I'm going to have to make good round the edge to bring it in a bit. It's a bit awkward since it's quite deep at the top, so I believe I'm going to have to use a combination of materials/techniques. Can anyone suggest something to bring it out with?

[Marvin]

HI @Paene Finitur

 

Make shuttering that fits inside the the box sticking out as much as the wall.  4 pieces of OSB or ply or whatever. fill the inside with wate ever to hold it tight - bricks, bits of wood - then plaster around the outside of the shuttering. I coat my shuttering with bits of plastic so it comes out easily. Y0u could pop each piece of wood in a plastic bag.  Don't leave to long before removing the shuttering in case you have to do a bit of adjustment..

Edited December 10, 2022 by Marvin
minor change.

[Marvin]

Looking at the picture again you my wish to add a bit more cavity insulation first in any holes to stop the plaster bridging the cavity.

 

If your really adept you could adjust the inside wall surface position of the opening to fit grill on to that wasn't lop sided...

 

 

Edited December 10, 2022 by Marvin
further thought

[Radian]

How about getting a length of 160mm or 110mm drainage pipe (depending on what would fit best in the liner) to come out flush with the finished wall. Then use illbruck fm330 to foam around it. I'd mask the wall first and cut it back when set and skim over. A round or square grille to finish.

[Paene Finitur]

Thanks for the great replies. This looks like a plan. I'd considered foaming it but I've not plastered onto foam before and was assuming that I might get movement and cracking. @Radian, have you had good results skimming illbruck? I've not used that before but can give it a try. 👍

[Radian]

1 hour ago, Paene Finitur said:

Thanks for the great replies. This looks like a plan. I'd considered foaming it but I've not plastered onto foam before and was assuming that I might get movement and cracking. @Radian, have you had good results skimming illbruck? I've not used that before but can give it a try. 👍

 

My experience is limited to using a one strike ready-mixed filler over the foam. The filler gives a little so is more resistant to cracking and adheres to foam very well. It's hard to tell how big an area you will be filling from your photo though.