What Off-Ratio Foam Looks Like
The two components have to meet in the correct ratio, at the correct temperature, through equipment that is working properly. When any of that is wrong the result is off-ratio foam.
The signs: a chemical smell that is still there weeks or months after the job. Foam that is crumbly or brittle rather than firm and resilient. Discolouration. Foam that has pulled back from the framing, sometimes half an inch or more, reopening the exact gap it was installed to close. Cracking within days or weeks.
The most frequent cause is spraying onto a substrate that was too cold. Product minimums refer to the surface, not the room, and on a damp coastal winter day the surface is a long way below the air.
It cannot be sprayed over and it will not improve. It has to come off, back to clean framing, and that is the whole of the remedy.
Old Batt And Loose Fill
Decades-old material comes out for different reasons. It settles and loses depth. It gets contaminated. It has often been disturbed by rodents, and in an older building it frequently has been.
There is also no point spraying over it. Foam needs to bond to a solid substrate and material with air in it is not one.
Removal is contained, bagged and taken away, and the surface underneath gets inspected before anything new goes on. That inspection is worth having on its own. It is often the first look anybody has had at the sheathing or the framing in fifty years.
What The Inspection Turns Up
Damp staining on the underside of the roof deck, which points at an air leak from below rather than a roof leak.
Knob and tube wiring, which changes what can legally be buried and needs an electrician before we go any further.
Rot at the rim joist or at the wall plate.
Old chimney chases running open from the cellar to the roof, which in a balloon framed house is a straight vertical air path through the whole building.
We stop and tell you rather than covering it up. Foam over a problem makes the problem harder to reach later.
Then The Replacement
Once the surface is clean and sound, the new specification is written against the space as it actually is, not as it was assumed to be before anything came out.
Where the original problem was a bad foam job, we will tell you plainly what went wrong with it. You are entitled to know, particularly if there is a warranty conversation to be had with whoever did it.