A quality spray foam install is not a product you buy, it is a day of work you are trusting someone else to do correctly. The foam in your crawl space is only as good as the substrate temperature it was sprayed onto, the ratio it was mixed at, the thickness of each pass, and how it was cured. Get those four right and the material does everything it promises for the life of the house. Get one of them wrong and you own a problem that usually cannot be repaired, only removed.
So here is the whole thing, in public. What we do on a job, what you should ask before anyone quotes you, what to watch for on the day, what to check after the crew packs up, and the specific way homeowners get ripped off in this trade. Print it. Take it to whoever you hire, including us. A contractor who cannot answer these questions is telling you something useful.
The short version
Four variables decide the outcome: substrate temperature, mix ratio, pass thickness, and cure. Everything else is detail. The good news is that three of the four leave evidence you can actually inspect, and the fourth (ratio) shows up in the smell and the feel of the cured foam within a few weeks.
The four variables that decide whether your foam is any good
1. Substrate temperature
Every spray foam has a temperature window the surface has to be inside for the foam to bond and cure properly. In a Seattle February, a crawl space wall or the underside of a roof deck can sit well below that window even on a day that feels mild outside. Foam sprayed onto a cold substrate can fail to stick, fail to reach its rated R-value, and let go of the surface months later. That last one is the cruel version, because by then the drywall is back up.
What correct looks like: someone points an infrared thermometer at the actual surface, in several places, and compares it to the number on the product data sheet. If the substrate is too cold, the space gets heated first, or the job gets moved. It does not get sprayed anyway. We have rescheduled work over this, and we would rather have that conversation in advance than in a year.
2. Mix ratio
Spray foam arrives as two chemicals that only become foam when they meet in the right proportion, at the right temperature, at the right pressure. That is the whole job of the rig: keep both drums hot, keep the hose hot, keep the A and B side pressures balanced, and keep them there while someone is pulling the trigger for six hours.
Off-ratio foam is the source of almost every horror story you have read. It may never fully cure. It can keep off-gassing for months. It can be soft and greasy, or dark and crumbly, or smell like paint long after it should smell like nothing. And it cannot be fixed in place. There is no additive, no sealer, no amount of airing out. It comes out and you start again, which is why it is worth being fussy about the contractor rather than the product. If you are living with this now, read does spray foam insulation smell go away and can bad spray foam be removed.
What correct looks like: gauges get watched, not glanced at. A test pass gets sprayed and cut open before the crew commits to the whole cavity. Someone on site knows what the pressures are supposed to be and notices when they drift.
3. Pass thickness
Closed-cell in particular goes on in controlled lifts, commonly around an inch to two inches at a time depending on the product, with time between passes. It is not a single thick coat. The reaction that turns liquid into foam gives off real heat, and too much material in one pass traps that heat in the middle of the layer. A scorched core is weaker, bonds worse, and in the worst documented cases has caused fires.
Building four inches in three passes takes longer than building it in one. That extra time is most of what separates an honest bid from a cheap one, and it is exactly the corner a volume crew cuts when they have another house to get to.
4. Cure and re-entry
During the spray and for a period afterwards, the space needs mechanical ventilation and nobody who is not in proper protective equipment should be in the building. The re-entry time depends on the product, the amount sprayed, and the ventilation the crew can actually get into that space. Manufacturers publish a figure. A crew that knows what it is doing will give you that figure in advance, in writing, and will usually build in a margin.
What should worry you: anybody who tells you it is fine to sit in the next room, or who gives a re-entry time without knowing how much foam is going in or what the ventilation plan is. That is a guess, and it is your family in the house.
What to ask before anyone quotes you
These questions take five minutes on the phone and they sort the field faster than any review site. You are not being difficult. You are asking a specialist about their specialty.
- Which exact product, by manufacturer and name? Not “closed-cell.” The actual product, so you can look up the data sheet yourself.
- What installed depth, in each assembly? The rim joist, the crawl space wall, and the roof deck may all be different numbers. They should all be on the quote.
- What is the published R-value per inch, and the total R at that depth? Closed-cell generally lands around R-6 to R-7 per inch, open-cell around R-3.6 to R-4. If the answer is far outside that, ask why.
- What is the perm rating at that thickness? Only relevant if the foam is being sold to you as a vapor retarder, which in a crawl space it often is. One inch of closed-cell and the phrase “vapor barrier” in the same sentence deserves a follow-up question.
- What is the maximum lift thickness and how many passes will you use? A crew that has never thought about this will tell you on the spot.
- How will you check substrate temperature, and what is this product’s minimum?
- What is the re-entry time and the ventilation plan? Both, together. One without the other is not an answer.
- What happens if it fails? Who removes it, who pays for removal, and who pays for the replacement. Get the answer in writing before you sign, not after you smell something.
What to watch for on the day
You will not be in the house while the spraying happens, and you should not be. But you can look at the setup before you leave and you can look at the site when you come back.
| What you see | Good sign | Worth a question |
|---|---|---|
| Containment | Poly sheeting sealed at the openings, HVAC returns taped off, an exhaust fan moving air out of the space | Open doors, no plastic, the furnace still running |
| PPE | Full-face respirator or supplied air, hooded suit, gloves, on everyone in the space | A dust mask, a t-shirt, safety glasses |
| Surface temperature | Someone checking the substrate with an infrared thermometer before the trigger is pulled | Checking the weather app instead |
| The rig | Gauges watched through the day, hose and drum temperatures managed, a test pass cut open and inspected | Set it and forget it, nobody at the machine |
| Passes | Depth built in lifts with time between them | One thick coat, finished suspiciously fast |
What to check after the crew leaves
Give it a few days, then go look with a flashlight. None of this requires a tool you do not already own.
- Coverage. Look at the awkward places, not the easy wall. Corners, top plates, around pipes and wiring, behind ducts, the rim joist above the crawl space wall, the area right by the access hatch. Gaps hide where the work was uncomfortable.
- Depth consistency. Push a bamboo skewer or a thin probe straight in until it stops, mark it, and pull it out. Do it in a dozen spots. You paid for a number. You should get that number in the far corner too, not just at eye level.
- Adhesion. Press firmly along the edges and at a few random spots. Foam should feel locked to the wood. Foam that flexes, sounds hollow, or has visibly pulled back from a stud or a joist is not bonded.
- Texture. Cured closed-cell should look fairly even, a little like orange peel. Large voids, deep pinholing, shrinkage cracks, a crumbly surface, or anything still tacky or greasy to the touch is a reason to call the contractor back out.
- Trimming. Where foam was sprayed proud of studs or joists and drywall is going back on, it has to be shaved flush. Untrimmed foam means bowed drywall and a wall that never sits right.
- Smell. After the cure and a good airing out, properly mixed foam is essentially odourless. A faint new smell in the first days is normal. A paint or fishy smell that is still there at three or four weeks is not, and it is the single clearest sign of an off-ratio batch.
The rip-off to actually watch for: closed-cell on the invoice, open-cell in the wall
This is the one that has burned homeowners publicly, and it works because the two products look similar once they are in place. A crew fills the cavity with cheap open-cell, then lays a thin closed-cell skin coat over the face of it. You see rigid foam. You paid closed-cell prices. Most of what is in your wall is the cheaper material at roughly half the R-value per inch and none of the moisture resistance you were buying it for.
Here is how a homeowner can actually catch it, in an out-of-the-way spot where a small cut does not matter:
Press hard, in several places
Closed-cell stays rigid under a firm thumb. If a rigid shell gives way to something soft and spongy underneath, you have found the skin coat.
Cut a slice and look at the cross section
A serrated knife through the full depth in an inconspicuous corner tells you everything. Closed-cell is uniform, dense, and tight all the way through. Open-cell is soft, airy, and springs back when you squeeze it, a bit like a sponge or angel food cake. A thin hard layer over a thick soft layer is not one product.
Weigh it and wet it
Closed-cell is several times denser, so a palm-sized piece feels noticeably heavy. Drop that piece in a glass of water: open-cell soaks it up, closed-cell largely does not.
Then do the paperwork check. Ask for the product data sheets and the lot numbers, and ask how many sets of material went into the job. The manufacturer publishes a yield per set. Multiply your square footage by the depth you paid for and see whether the arithmetic lands anywhere near what was actually used. It is hard to argue with a material order. If you want the full comparison first, read open-cell vs closed-cell spray foam, and closed-cell spray foam insulation for what the premium product is supposed to deliver.
What you honestly cannot check yourself
We would rather be straight about the limits than pretend a flashlight and a skewer settle everything.
You cannot confirm the mix ratio by eye. Foam can be meaningfully off-ratio and still look acceptable, and the symptoms (odour, softness, poor adhesion) sometimes take weeks to declare themselves. You cannot verify aged R-value without lab testing. You cannot inspect anything once the drywall is up, which is why the check happens before the cover goes on, not after. And in a crawl space or a low attic, most people simply cannot get to the far corners where the problems tend to live.
When it is worth paying someone independent: if the smell has not gone away, if you suspect the product you received is not the product you bought, if the foam is soft or pulling away, or if a lot of money is involved and you want the work verified before it is covered. Look for a building performance contractor or energy auditor who is not connected to the installer. A lab can test a core sample for density and closed-cell content, which is the definitive answer on the skin-coat question. A blower door test measures whether the air sealing you paid for actually happened, and an infrared scan during heating season shows missed cavities through the finished surface. For the diagnostic walkthrough in more detail, see how to tell if spray foam was installed correctly.
Why we publish all of this
Because it is the argument we would rather not have. Every item on this page is a way for you to check our work, and putting it up in public is the only version of a promise that costs us anything. Paul has spent 15 years in Puget Sound crawl spaces and attics, a fair amount of it scraping out somebody else’s bad foam, and the pattern never changes: the job that went wrong was the job that was rushed. Cold substrate, one thick pass, a rig nobody was watching, a re-entry time somebody guessed at.
So we take the extra day. We heat the space if it needs heating, we build the depth in passes, we cut a test sample before we commit, and we walk the finished job with you and a flashlight before anything gets covered up. That is slower, and occasionally it means a date moves. We have made our peace with that, because the alternative is coming back in eighteen months to argue with someone about foam that has to come out. More about how we work.
Not sure what your house actually needs yet? We will come out, get into the crawl space or the attic, and tell you straight. Sometimes the honest answer is air sealing for a fraction of the price, and we will say so. Request a free estimate.
Common questions about install quality
How long should a spray foam install actually take?
It depends on square footage, depth, and access, but a typical residential crawl space or attic is usually a full day and sometimes two, including setup, containment, and cleanup. What matters more than the total is how the time is spent. Building depth in controlled passes, letting each lift cool, and stopping to check temperature and coverage all take time. If a crew is in and out of a whole crawl space in three hours, ask how many passes were used and how deep the foam actually is.
Can I inspect the foam myself before the drywall goes back on?
Yes, and you should. Ask for a walkthrough before anything is covered, with a flashlight. Check coverage in the corners and around penetrations, probe the depth in a dozen places with a thin skewer, and press along the edges for adhesion. Any contractor confident in the work will offer this without being asked. We do it as a matter of course, and we would rather find a thin spot together than have you find it in January.
What does off-ratio foam smell like, and how long is too long?
People usually describe it as paint, solvent, or a fishy odour. Some smell during the install and for the first day or two after is expected. A smell that is still noticeable after three or four weeks in a ventilated space is the classic sign of a bad batch, and the consistent experience in the industry is that it does not air out. That foam generally has to be removed. If this is happening in your house, do not let it go unaddressed for months hoping it fades.
Does a thicker pass mean better insulation?
No, and it is one of the more damaging misconceptions. Total installed depth is what determines R-value, and that depth is supposed to be built up in multiple controlled lifts. Putting it on in one thick coat traps the heat of the reaction inside the layer, which can scorch the core, weaken the bond to the substrate, and create a fire risk during curing. Thicker in a single pass is faster for the crew and worse for you.
Is a written warranty enough protection?
It helps, but read what it actually covers. The expensive part of a failed spray foam job is removal, not the foam itself, because getting cured foam off sheathing and joists is slow manual work in a confined space. A warranty that replaces material but leaves you paying to demolish and haul out the old install is not much comfort. Ask specifically who pays for removal, and get the answer in the contract.
What if my foam was installed years ago and I am only worried now?
Plenty of it is fine. Foam that is odourless, firm, well bonded, and not causing moisture problems is doing its job, and there is no reason to disturb it. The things worth investigating are a persistent smell, foam pulling away from the substrate, soft or crumbly material, or damp wood anywhere near it. Start with what you can see and smell, and bring in an independent inspection if anything looks off rather than assuming the worst.