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Sprayed polyurethane foam roofs

Recoating a spray foam roof starts with the foam

On a foam roof the coating takes the weather and the foam under it is the roof. The foam decides the recoat: sound, dry foam takes an acrylic base and finish coat, or Silicone44 on its own, with no primer; wet or damaged foam is cut out and replaced first. Here is the build-up in genuine Sherwin-Williams Uniflex, by part number, in stock and shipped in 1–3 business days.

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Candidate or not

The foam has to be sound and dry

Foam is protected by its coating. Once the coating wears thin or goes missing, the sun degrades the exposed foam, and every gouge from foot traffic or equipment and every hole pecked by a bird is a way in for water. So the first question on a foam roof is not which coating but what state the foam is in. Applied over a sound, dry roof, a restoration system adds 10 to 15 years of service life; on a foam roof, that means sound, dry foam.

  • Sound foam: it does not crumble under a screwdriver, and it is still bonded to what it was sprayed onto
  • Dry foam: where water got in, that foam is cut out and replaced before any coating goes on
  • Damage you can repair one place at a time: sun-worn foam, gouges, splits, pecked holes, blisters
  • Water that leaves at the drains and scuppers; where it stands, fix the low spot or change the finish
  • A deck that carries the roof, which is a question for the building engineer

Can this roof be restored?

The build-up

The recoat, from the foam up

Read it from the bottom. The foam stays: it is the insulation and the body of the roof, and the coating is the layer that takes the weather. Wet or damaged foam is cut out and replaced, and small holes, splits and blisters are patched. Then the base coat goes straight onto the clean foam with no primer, and the finish coat over it: a gray base under a white finish, so the crew can see coverage.

  • Finish coat KST041300 white, where the roof drains
  • Base coat KST041520 gray, straight onto the foam
  • Repairs KST041220 at holes, splits and blisters
  • Existing foam, cleaned Sound and dry; wet or damaged foam replaced
  • Roof deck Structurally sound: the engineer's call
Shown for a roof that drains; where water stands, Silicone44 goes straight onto the foam with no base coat, or the solvent-based pair goes on. Illustrative diagram — proportions are not to scale.

How the recoat goes

The order of work, by part number

Each step is finished before the next one starts. The data sheet names the preparation, the rate and the cure for every product here, and a written specification wins over this list.

  1. Survey the foam

    Our drone moisture scan is the wrong tool on foam: closed-cell foam does not hold water the way board insulation does. Walk the roof with a plan and take cores; mark worn coating, sun-damaged foam, gouges, pecked holes, blisters and every penetration. That survey becomes the material count.

  2. Clean the roof

    Wash the field, get dirt, ponded silt and anything loose off, and let the roof dry as the data sheet requires. What is left on the surface bears on whether the new coat holds.

  3. Cut out and repair

    Wet or damaged foam is cut back to sound foam and replaced; the foam itself is not in our catalogue. Small holes, splits, cracks and blisters, and the flashings at penetrations and walls, are closed with acrylic patching cement KST041220 under an acrylic finish; under Silicone44, ask us.

  4. Lay an adhesion test patch

    Put the system down on a small area, over the old coating where some remains, let it cure, then pull it. For Silicone44, Uniflex's test embeds a fabric strip, waits three days and looks for at least 2 lb per inch; a lower result goes to Uniflex. Nothing else settles whether it holds on this roof.

  5. Base coat, no primer

    Under an acrylic finish, gray acrylic elastomeric base coat KST041520, the commercial grade, goes straight onto sound, clean foam; the premium grade KST041320 lists polyurethane foam too. No primer in this build-up unless the data sheet or the test patch says otherwise.

  6. Finish coat

    White acrylic elastomeric KST041300 where the roof drains. Where water stands, Silicone44 KST044300 (white) or KST044320 (gray) goes straight onto the clean foam instead, with no primer and no base coat, or the solvent-based pair, base coat KST042200 under finish coat KST042100.

The adhesion test patch

Genuine Sherwin-Williams Uniflex

The materials for a foam roof

Genuine Sherwin-Williams Uniflex in the maker's sealed packaging, in stock and shipped in 1–3 business days; both acrylic base coats and the acrylic finish coat come by the pail, the 55-gallon drum and the 275-gallon tote. Priced per project; the solvent-based pair ships as regulated freight.

All finish coats

Questions

Before you recoat the foam

If a thermal scan is the wrong tool, how is a foam roof surveyed?
On foot and with cores. A walk-through with the roof plan finds the worn and missing coating, the gouges, the pecked holes and the blisters; cores show whether water has got into the foam. An impedance (capacitance) survey is another method: ASTM D7954, the standard practice for impedance moisture scanners, names sprayed polyurethane foam among the roofs it covers, and its readings are confirmed with cores too. A thermal scan is not used here because closed-cell foam does not hold water the way board insulation does.
What if water stands on the foam?
Then the finish changes. Acrylic is the finish for a roof that drains; under prolonged ponding it can lose adhesion and peel. Where water stands, Silicone44 KST044300 (white) or KST044320 (gray) goes straight onto sound, clean foam after an adhesion test, with no primer and no base coat; or the solvent-based pair, base coat KST042200 under finish coat KST042100. Silicone44 does not fix drainage: Uniflex's silicone specifications still expect at least 1/4 in per ft of slope and working drains, so fix the low spot first where it can be. Whether the deck carries the water is the engineer's call.
Does the old coating have to come off?
It depends on what the old coating is and how well it is holding. Clean it, lay the adhesion test patch over it, and pull the patch once it has cured: that settles whether the new system holds. Silicone44 goes directly over a sound, aged acrylic, silicone or urethane roof coating once it is washed, loose coating is scraped back and the adhesion tests pass. Going the other way is harder: contractors commonly work to the rule that little sticks to cured silicone except more silicone, so if nobody knows what the roof was last coated with, test before you order.
Can a foam roof be recoated without tearing it off?
The International Building Code, Section 1512, lists a spray polyurethane foam roof among the roofs a new protective coating may go over without tear-off. Florida's code is narrower on coatings than the model code, and it keeps that exception for foam. Whether it applies at your address, and what permit the work needs, is the building department's decision; nothing here is code advice.
What settles the specification, and can the recoat carry a warranty?
Three things, in order: the current data sheet, which names the preparation, the rate and the cure; the adhesion test patch on this roof; and, where a system warranty is wanted, the manufacturer's representative. Sherwin-Williams offers UNIGUARD system warranties of 10 or 15 years when one of its authorized contractors applies the system. The warranty is the manufacturer's, issued under its own terms; we supply the materials. Say at quote time if one is wanted, so the material list follows that specification.
I own a foam roof. Who does the work?
A roofing contractor; we never do the roofing work ourselves. If you already have one, we supply the materials to them. If you do not, we work with a network of installers, roofing contractors who apply these systems, and can introduce you to one anywhere in the US, who looks at the roof and says whether it is a good candidate for restoration. Ask through the quote form and say it is a foam roof. Roofing and coating contractors who apply these systems can ask to join the network the same way; a person answers.

Moisture survey methods compared

Price the recoat off the survey

Send the roof area, what the walk-through and the cores found, the penetrations to detail, whether water stands and whether a system warranty is wanted. Foam's orange-peel surface has real area in it; allow for it in the count. No contractor yet? We can introduce an installer anywhere in the US.

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