Cavity walls

[JonnyRed]

I have always been suspicious of cavity wall insulating material inserted after construction. Particularly the plastic foam (?) injected material. It strikes me that after a period of time it will settle and compress under its own weight, dust will then settle on this in turn, and a bridge formed between the wet outer and the dry inner walls. This is important in the wet west of England.
I really don't see the point of it of it. After all air is a very good insulator - you rely on it for double glazing. After all its not the foam or glass wool that is the insulator but trapped air ( this is proved by the non-insulating properties of a soggy cotton padded jacket. )
As I see it what is required ( if at all ) are non-bridgeable baffle plates to stop the circulation of air in the cavity ( convection loses ) or alternately live with it by putting insulating material on the underside of the roof so that the loft becomes part of the insulated volume warmed by air coming up from the top of the cavity wall.
As a DIY project I would like to know how to remove existing 'insulating' material from a cavity wall?

 

[Grenage]

While air isn't a bad insulator, I've experienced the before and after of cavity wall insulation, and it is a massive difference.

Would it not make more sense to leave it be, and benefit from the savings? You could attempt such a hellish job if and when you started experiencing problems.

 

[theprinceofdarkness]

On what basis do you think the foam will settle and compress and turn to dust? The only problem with foam is that it contracts slightly after a few years leading to cracks in it of a millimeter every meter or so. But that depends on the grade of foam and its "fixings" (pierced by wall ties).
The size of the air voids are crucial in insulation, "baffles" will only direct water back to the outer skin, it will do nothing for thermal insulation.
I would not touch the cavities until you are sure there is something wrong.
Frank

 

[Flyboytim]

Air is a good insulator if trapped, but can circulate heat to the top of the cavity if free to convect and carry that heat away, if there are any gaps in the upper part of the cavity - which could include loosely trapped air in mineral wool or fibre fill insulation.

The only post-construction infill which is both waterproof, and permanently traps gas, without significant shrinkage or settlement is expanding polyurethane foam, which has other problems, like the long term release of chemicals, and the potential to prevent inner and outer skins of brick from adequate evaporation of water taken in from interstitial condensation on the interior or rainwater soaking on the exterior - leading to potential corrosion failure of some types of wall ties, and long term weakening of the mortar joints, and excessive brick spalling.

The foam is hellishly sticky, and adheres to brickwork and other surfaces well, but over time becomes more brittle and expansion/contraction cracking occurs, but with a very small ratio of cracking to total volume of foam.

 

[JonnyRed]

Your only confirming what I stated that cavity walls are best left alone.
This is all part of the air-head ( sic ) heat saving movement.
Cavity walls have been filled without thought of the consequences
.
In the long term plastic always decays and becomes brittle, if it's windows you can replace them but how do you get at the inside of cavity walls?
I repeat my point air is nearly a good insulator as foam or glass wool - all they are is trapped air.
Convection loses will depend on height and cavity thickness
My post was really about removing what I suspect is compacted foam causing dampness in walls adjoining what I suspect was the injection hole.