Ontario's Plain-English Guide to Custom Home Buildingπ 705-533-1633 | βοΈ 1-866-868-6606 | βοΈ info@icfhome.ca
Spray Foam Installation Problems: Shrinkage and Pulling Away, Off-Ratio Foam, Odour That Will Not Leave, Thickness Short of the Quote, No Thermal Barrier, and How Each One Is Checked and Fixed
Insulation & Air Sealing
Spray Foam Goes Wrong in Six Ways, Every One of Them Is Visible for About a Week, and After the Drywall It Is a Lawsuit
Spray foam is two liquids mixed at the gun that react into a solid in seconds, and everything about whether it works happens in those seconds: the drum temperatures, the ratio, the temperature of the wood or concrete it hits, the thickness of each pass and the time between passes. Done right it is the tightest insulation money buys. Done wrong it shrinks off the studs, stays spongy, smells like fish for a year, or is 2 in. thick where you paid for 3. All of that is checkable, with a flashlight, a stiff wire and the paperwork the installer is supposed to leave behind.
The six problems at a glance
| Problem | What you see | Usual cause | Check | Fix |
|---|---|---|---|---|
| Shrinkage, pulling away | A gap of 1/8 in. or more between the foam and the stud, sometimes a crack down the bay | Lifts too thick, cold substrate, bad batch | Flashlight along every stud edge | Cut back and re-spray the edge; a bad batch comes out |
| Off-ratio foam | Dark, brittle, crumbly; or soft, sticky, never hardens | One side of the rig starved | Press it, cut a plug, weigh it | Remove and redo |
| Odour | Fishy or sweet chemical smell still there after a week | Off-ratio, overheated lifts, no ventilation during cure | Smell it after 72 hours, windows shut | Ventilate; past a month, test and remove |
| Thickness short | Nothing, which is the problem | The quote said 3 in., the gun stopped at 2 | Wire probe, 10 points per 100 sq ft | Another lift, before drywall |
| No thermal barrier | Bare foam in a basement, garage or bonus room | Nobody priced it | Can you see foam from the room? | 1/2 in. drywall, or $1.25 to $2.00 per sq ft of coating |
| Wrong substrate | Foam over wet wood or knob-and-tube, open cell on concrete, foam at a chimney | Nobody looked first | Ask what was under it | Sometimes the foam comes off to fix what is under it |
Shrinkage: the gap along the stud
Closed cell foam goes on in lifts, and the installation standard holds each lift of 2 lb foam to about 2 in., with time between lifts for the heat to leave. The reaction is exothermic; a 4 in. pass gets hot in the middle, cures from the outside in, and when the core finally sets it pulls. The result is a bay of foam that looks perfect from across the room and has a 1/8 in. slot down both sides where it let go of the studs. Air goes through a slot, so the air barrier the foam was bought for is gone.
The check is a flashlight held flat against the stud, looking along the joint, every bay, both sides. A business card slid into the joint settles arguments. Cold substrate does the same thing: foam sprayed on a 2 C concrete wall in November bonds poorly and lets go in the spring. The installer should be checking the substrate temperature and should say so on the work sheet. The fix for an edge gap is to cut the foam back a half inch and re-spray the joint; the fix for a whole wall of it is a whole wall.
Off-ratio foam: the chemistry that did not happen
Side A and side B are meant to meet at the gun in equal volumes. A proportioner keeps them equal; a worn pump, a cold drum or a half-blocked line throws it off, and the gun does not stop. Too much A gives a dark, brittle foam that crumbles when pressed. Too much B gives a soft, sticky foam that never fully hardens and is the one behind most odour complaints. Neither has the R, the density or the air-sealing the data sheet claims, and neither can be fixed by spraying more over it.
Press it with a thumb. Good 2 lb closed cell is firm, like a dense cutting board; you cannot dent it. Cut a plug, 2 in. square, full depth, with a bread knife: the colour should be even through the thickness, no dark bands, no soft layers between lifts. Weigh it if you want to argue with numbers; 2 lb foam is 32 kg per cubic metre, and a kitchen scale and a ruler get you close enough. The daily work sheet is supposed to record the drum temperatures and the density at the start of the day. A contractor who cannot produce the sheet has told you something.
Odour: the one you cannot inspect with a flashlight
Fresh foam smells, and the house is supposed to be empty and ventilated for 24 hours at least, longer for some products. After that a properly cured foam has almost no smell at all. A fishy, sweet or cat-urine odour that is still noticeable with the windows shut after 72 hours is not normal. It is off-ratio foam, or foam that overheated in a thick lift, and it does not fade on a schedule you can plan around. I have heard of houses where it was still there a year on.
The honest sequence: ventilate hard for a week with the furnace fan running; if it is still there, call the contractor in writing; if it is still there at a month, have the foam tested and the worst areas removed. Removal is slow, by hand, and quoted after inspection, never by the square foot. The best defence is the one on the cost page under the quote: the CUFCA photo ID, the licensed contractor, and the daily work sheet with lift thickness and density. The men who carry the card and fill in the sheet are the ones who ran the rig right.
Thickness short of the quote
This is the common one and the cheap one to catch. The quote said 3 in. for R-18, or 3.5 in. for R-20, and the gun stopped at 2 in. across half the wall because 2 in. looks like a lot from the doorway. At $1.25 a board foot on 1,000 sq ft, an inch short is $1,250 of foam you paid for and did not get, and R-6 you did not get either. Open cell is worse, because the installer trims it flush with the studs, so the question becomes whether the bay is full behind the trim.
Push a stiff wire or a drywall screw through the foam to the sheathing at ten points per 100 sq ft, top, middle and bottom of bays, and write the readings down. The code and the heat-loss calculation both count the thinnest spot, not the average. Short in one or two spots is a touch-up; short across the wall is another lift, and it is the contractor’s lift, not yours. Do this before the drywall, because after it there is no cheap way to know.
No thermal barrier, and the wrong substrate
Spray foam burns, both kinds, fast and with black smoke. Anywhere it faces a living space the code wants 1/2 in. drywall or a tested intumescent coating over it, OBC 9.10.17, and that line is not on the foam company’s quote because it is not their trade. Bare foam on the walls of a finished rec room, on the ceiling of a garage under a bedroom, in a bonus room knee wall: each is a fire the code already named. Drywall at the drywall rate, or coating at $1.25 to $2.00 a square foot; in an attic or crawlspace entered only for service, an ignition barrier coat at $1.25. The whole rule is on the fire and thermal barriers page.
Then there is what was under the foam. Foam over wet or mouldy wood seals the moisture in and the mould keeps going; the wood has to be dry, under about 19% on a meter, before anyone sprays. No foam over or against knob-and-tube wiring; the Ontario Electrical Safety Code does not allow insulation in contact with it and the insurer will not carry the house. No foam within the 3 in. (75 mm) clearance of a chimney or against a non-IC pot light. Open cell is not for concrete or for roof sheathing in Ontario without a vapour retarder over it, which this page explains. The product itself, and what it is good at, is on the spray foam basics page; the contract lines and holdback are in the contractors section.
Questions people ask
Why is my spray foam pulling away from the studs?
Lifts sprayed too thick and curing from the outside in, foam applied to a cold or damp substrate, or an off-ratio batch. The foam shrinks as the core sets and lets go of the wood. Check every bay with a flashlight along the stud; the fix is to cut back and re-spray the edges, or replace a bad bay.
How long should spray foam smell?
The house should be vacated and ventilated for at least 24 hours, and a faint smell for a few days after is normal. A fishy or sweet odour still obvious after 72 hours with the windows closed points to off-ratio or overheated foam; report it to the contractor in writing.
How do I check spray foam thickness?
Push a stiff wire or a long drywall screw through to the sheathing at ten spots per 100 sq ft and write the readings down. Compare to the quoted thickness and the daily work sheet. The thinnest spot is the number that counts.
Does spray foam have to be covered with drywall?
In a living space, yes: 1/2 in. drywall or a tested intumescent coating under OBC 9.10.17. An attic or crawlspace entered only for service can use an ignition barrier coat at about $1.25 a square foot.
What paperwork should a spray foam contractor leave?
A daily work sheet with the product, lot numbers, drum and substrate temperatures, lift thickness and density, signed by a CUFCA-certified installer whose photo ID you have seen. Without it there is no record that the foam went in to CAN/ULC S705.2.
Know what the job should have cost
A foam job that is short an inch is also short the money for that inch. The spray foam cost calculator gives you the board feet and the price at the quoted thickness so you can see what a 2 in. wall should have cost against the 3 in. you were billed for. If the quote never said a thickness at all, the $99 review will find out what it meant.
Sources and further reading
- CUFCA Quality Assurance Program: Canadian Urethane Foam Contractors Association: certified installers with photo ID, licensed contractors, daily work sheets and the CAN/ULC S705 standards a spray foam job is held to.
- Canadian Construction Materials Centre: National Research Council: the product evaluations behind spray foam and other insulation products, and what an evaluation number means.
- Ontario’s Building Code: the official page with the current regulation; vapour barriers are 9.25, attic ventilation 9.19, thermal barriers over foam 9.10.17, radon 9.13.
