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Standing seam and R-panel metal roofs

Restore a metal roof from the fasteners up

On a metal roof the state of the metal decides the primer and the drainage decides the finish. Fasteners are tightened or replaced, laps, fastener rows and penetrations are closed, then an acrylic base and finish coat, or Silicone44 on its own, go over the whole field, with no tear-off. Genuine Sherwin-Williams Uniflex by part number, in stock and shipped in 1–3 business days.

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A low-slope standing-seam metal roof split along one seam, the left half coated white and the right half still weathered and rust-stained

Candidate or not

Surface rust is a primer job; rust-through is not

Low-slope metal roofs wear in the same few places: rust at the laps and panel ends, fasteners backing out or no longer biting, seams opening, and sealant cracking at curbs and pipes. None of that rules a roof out by itself. What decides it is the metal: panels still fastened to sound framing, with rust on the surface rather than through it. Applied over a sound, dry roof, a restoration system adds 10 to 15 years of service life. A thermal scan is the wrong tool on metal, where reflections spoil the reading, so the survey is a walk of every seam, lap, fastener row, curb and penetration.

  • Panels fastened to sound framing; whether the structure carries the work is the building's engineer's call
  • Rust that cleans back to sound metal; a panel rusted through is replaced before anything is coated
  • Fasteners that can be tightened, or replaced where they no longer bite
  • Laps, seams and small holes that seam tape and patching cement can close
  • Curbs, pipes and flashings that can be resealed and reinforced
  • Any insulation under the panels is dry; wet insulation is cut out and replaced before coating

Is this roof a candidate?

The build-up

What goes on a metal roof, from the panel up

Read it from the bottom. This is the acrylic system. The primer follows the metal: the red rust-inhibitive where steel has corroded, the acrylic white on pre-finished panels. Laps, fastener rows and penetrations are closed next, so the base coat runs over the details and the field alike. The finish coat is the surface the weather sees. Where water stands, Silicone44 takes the place of both coats, and the table further down sets out its build-up.

Metal roof, acrylic system

Section

  • Finish coat KST041300 White acrylic elastomeric, the surface the weather sees
  • Base coat KST041320 Gray acrylic elastomeric across the whole field
  • Details Seam tape KST020804, cement KST041220, sealant KST058300
  • Primer KST034520 or KST036520 Red on corroded steel, white on pre-finished panels
  • Existing metal panels Fasteners tight, loose rust off, clean and dry
Order of application, read from the panel up. Illustrative diagram — proportions are not to scale.

Order of work

Fasteners first, finish coat last

Part numbers are Sherwin-Williams Uniflex. Each product's data sheet names the preparation, the rate and the cure; a written specification wins over this list.

  1. Fasten, clean and take off loose rust

    Tighten fasteners that have backed out and replace any that no longer bite. Take loose rust and scale back to sound metal, replace any panel rusted through, then pressure-wash the roof and let it dry as the data sheet requires.

  2. Prime by the condition of the metal

    Rust-inhibitive metal primer KST034520, red, on iron and steel where corrosion is the problem. Acrylic rust-inhibitive primer KST036520, white, on pre-finished fluorocarbon panels: it is the primer listed for them.

  3. Tape, patch and seal every detail

    Butyl seam tape KST020804, 4 in, over end laps, side seams and fastener rows; 2, 6 and 8 in widths are in the line too. Patching cement KST041220 at open seams, small holes and splits, reinforced with tape or fabric. MS hybrid sealant KST058300 around pipes, curbs and brackets.

  4. Base coat over the whole field

    Premium acrylic elastomeric base coat KST041320, gray, across the field and over the taped details; KST041520 is the commercial grade. A gray base under a white finish lets the crew see coverage.

  5. Finish coat where the roof drains

    Premium acrylic elastomeric finish coat KST041300, white; KST041500 is the commercial grade. White finish coats reflect sunlight and keep the roof surface cooler. Where water stands after rain, the finish changes, as set out below.

Seams, fasteners and flashings

Materials

The metal roof system, in stock

Genuine Sherwin-Williams Uniflex by part number, in the maker's sealed packaging, shipped in 1–3 business days. The acrylic coats come by the pail, the 55-gallon drum and the 275-gallon tote; Silicone44 KST044300 (white), for where water stands, by the pail and the drum. Priced per project.

Finish coat and specification

Pick the finish, then test it on the roof

Acrylic is the finish for a metal roof that drains; under prolonged ponding it can lose adhesion and peel. Silicone44 is made for standing water but does not fix drainage. Whether the roof should be carrying standing water at all is a structural question for the building's engineer.

Where the roof drains Acrylic finish coat KST041300 over base coat KST041320; the commercial grades are KST041500 and KST041520
Where water stands: silicone Laps open more than 1/8 in fastened, KST034520 on every rusted area, laps striped with Silicone44, then Silicone44 KST044300 (white) or KST044320 (gray). No base coat
Silicone on pre-finished (Kynar) panels An adhesion test decides whether any primer is needed: send us the roof. KST036520 is the pre-finished panel primer for the acrylic system only
Silicone at curbs and penetrations Uniflex's silicone specifications use its OneFlash sealant there, which we do not stock: ask us on the quote form
Where water stands: solvent-based pair Solvent-based base coat KST042200 under finish coat KST042100, both listed for metal. Ships as regulated freight
Light rust: aluminum, the economical route Fibered aluminum KST020475, or the commercial KST020480, directly over lightly rusted metal once the details are closed: no primer, no base coat, a silver finish. Ships as regulated freight
Heavier corrosion Not aluminum: rust-inhibitive primer KST034520 under an elastomeric base coat and finish coat

The adhesion test patch

Questions

Before you coat a metal roof

How is a metal roof surveyed before it is priced?
On foot, with the roof plan. Measure the field, then walk every seam, lap, fastener row, curb and penetration, photographing what needs repair and noting the panel type and where the rust is. Laps and seams are counted in linear feet; fastener rows, curbs and penetrations by number. That becomes the material list. A thermal scan does not suit metal panels, but our drone moisture scan does suit membrane roofs over insulation, so a single-ply, modified bitumen or smooth built-up section on the same building can still be scanned.
Do I need a primer on a metal roof?
It depends on the metal and the finish. Corroded iron and steel take the rust-inhibitive primer KST034520 once the loose rust and scale are off, under acrylic or Silicone44. Under the acrylic system, pre-finished fluorocarbon panels take the acrylic rust-inhibitive primer KST036520, the primer listed for them. Under Silicone44 on pre-finished (Kynar) panels, an adhesion test decides whether any primer is needed, so send us the roof. The 500 and 300 fibered aluminum coatings go directly over lightly rusted metal without a primer.
What do I do about the fasteners?
Tighten every fastener that has backed out and replace any that no longer bite, before anything is primed. Then the heads are covered like any other detail. Under the acrylic system, along a straight screw line, contractors commonly run one strip of butyl seam tape, KST020802 at 2 in or KST020804 at 4 in, rather than working head by head; the tape goes down dry and is coated over. Under Silicone44, any lap open more than 1/8 in is fastened, and end laps, fastened seams and ridge-cap laps are striped with the silicone itself. The specification says what each head needs.
Can silicone go on a metal roof?
Yes, with no base coat. Wash the roof, tighten or replace fasteners, fasten any lap open more than 1/8 in, prime every rusted area with KST034520 and let it cure, stripe the laps with Silicone44, then coat the field with Silicone44 KST044300 (white) or KST044320 (gray). An adhesion test comes first. Uniflex's silicone specifications use its OneFlash sealant at curbs and penetrations, which we do not stock. Contractors commonly work to the rule that little adheres to cured silicone except more silicone, so choosing it also decides the next recoat.
How long does a restored metal roof last, and is there a warranty?
Applied over a sound, dry roof, a restoration system adds 10 to 15 years of service life. On metal, sound means panels fastened to sound framing, the rust treated, and every lap and fastener row closed before the field is coated. 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.
Who applies the system?
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. Roofing and coating contractors who apply these systems can ask to join the network through the quote form; a person answers.

Moisture survey methods compared

Get the metal roof counted and priced

Send the roof area, the panel type and where the rust is, the linear feet of laps and seams, a count of fastener rows and penetrations, and whether water stands. We reply with the price, the freight and a ship date. No contractor yet? Say so, and we can introduce one anywhere in the US.

We reply within one business day.

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