Have you noticed your roof starting to look worse for wear? Maybe there are water stains creeping across the ceiling or rust beginning to show up on your metal roof fasteners or seams. If it’s a flat roof, pooling water might be sitting there for days after heavy rain. On pitched roofs, worn shingles, sagging sections, or granules collecting in gutters might catch your eye. UV rays, harsh weather, and time all have a way of taking their toll.
At this point, you might be bracing yourself for the cost of a complete tear-off and roof replacement. It’s an expensive, labor-intensive process that feels inevitable once the damage sets in. But is it really the only option available?
What are Roof Coatings?
Liquid-applied membranes or coating systems are the go-to way to reinforce existing roofs without demolishing them. They are waterproof, liquid-applied materials engineered to protect, seal, and extend the life of your roof.
Made from silicone, acrylic, polyurethane, or other elastomeric compound, a coating is quite similar to paint; it adheres directly to the roof’s surface via spraying, rolling, or brushing the liquid evenly over the roof. The number of coats you need depends on the product itself and the condition of the roof. Once the membrane is cured, it forms a uniform surface, often with a reflective white or light-colored finish. It is recommended to choose a coating that has a highly reflective finish to direct most of the sun’s harmful rays away and reduce the energy load on air conditioning systems.
The thicker the coating, the better it protects the roof. A thicker layer endures more wear and tear, so it lasts longer. That’s why manufacturers link the thickness of the coating to the length of the warranty they offer. For instance, a 10-year warranty generally requires 20 mils of coating (1 mil = 1/1000 of an inch), while a 20-year warranty might call for 30 mils.
But as incredible as modern liquid-applied membranes are, they work best on roofs that are still structurally sound. If the aging roof – be it a steep-slope or low-slope system – is nearing the end of its lifespan, the roof deck is rotting, the asphalt/concrete/other material has deteriorated too much, or there is extensive water damage, coating it won’t do much. Coatings only protect what is still functional; they can’t revive a roof that’s already beyond saving. You either need to take care of all the major repairs first or replace the roof altogether.
How Roof Coating Systems are Applied?
The roof must be prepped to make sure the sealing will perform long-term. Cutting corners here will have you coming back for repairs in no time.
Get rid of any wet insulation
If there is any part of insulated materials in the roofing that are moldy or soggy, they must come out right away or you risk bubbling, blistering, or coating failure down the line. Use infrared cameras or moisture meters to pinpoint wet areas, and replace them with compatible materials that match the rest of the roofing system.
Take out the old, damaged membrane
If the roof currently has an existing waterproofing layer, and it has developed cracks, punctures, or areas with delamination, you can’t just add a new coating on top. Patching the damaged membrane is not a good idea because that addresses only surface-level damage. If moisture is present underneath, not only will it spread, but also prevent a solid base for the new membrane to bond effectively.
Perform an adhesion test
Not all coatings work well with every roof substrate. Apply a small patch of the coating in a test area, let it cure, and then conduct a pull test to see if it sticks. This tells you if the coating is compatible or if the surface needs additional priming. Regardless of what the product claims to do, don’t skip this step or you could end up with peeling after the first weather event.
Note: For detailed adhesion test procedures, refer to our instruction brochure or watch our adhesion test video for step-by-step guidance. Ensuring proper adhesion is key to the long-term performance of your roof coating system.
Clean and prime the roof
A dirty roof won’t hold a coating. Remove all the dirt, grease, oil, debris, and any previous coatings that are flaking off. Depending on the situation, you may need to use power washing and a roof cleaner like PolyClean™ to do this the right way. When cleaning with PolyClean™, you don’t have to worry about soap residue interfering with adhesion.
The appropriate primer will depend on the specific roofing substrate. Some general guidelines include:
- Metal roofs – Typically require a rust-inhibiting primer.
- TPO roofs – Often require a solvent-based primer for acrylic or silicone coatings.
- Concrete roofs – May require a penetrating primer to seal porous surfaces and prevent excessive absorption of the coating.
- Wood roofs – Usually need a high-bond primer to prevent moisture penetration and improve adhesion.
- Asphalt roofs – Often require an asphalt-compatible primer to enhance coating performance and prevent solvent bleed-through.
Seal the seams
The space at the edges where roofing materials meet/overlap are inherently more vulnerable than the rest of the roof as the joints are prone to separation, water infiltration, and thermal expansion. Coatings alone are not enough to protect them; you will want to reinforce fasteners and seams with a sealant or a fabric-reinforced liquid membrane before applying the topcoat.
If you have a sprayed polyurethane foam, single-ply membrane (TPO, PVC), modified bitumen, or built-up roofing system, using a PolyBrite® single-component coating like PolyBrite® 75 along with PolyBrite® Reinforcing Polyester fabric on seams and transitions is a smart idea. It’s embedded in the base layer (mastic or elastomeric roof coatings) to fortify weak points and prevent any splitting.
Can All Existing Roofs Be Coated?
Assuming the roof isn’t heavily damaged, as we discussed earlier, you should have no problem coating it with a protective layer. Built-up, single-ply, modified bitumen, and metal all can be coated easily. The only types of substrates where a standard coating might not work is gravel BUR and asphalt shingles.
Gravel built-up roofing is not suitable for coating since the gravel requires a lot of material to penetrate all the nooks and crannies, which is rarely practical. As for shingled roofs, most coatings tend to stiffen the shingles up, thus reducing their ability to withstand impacts from, say, hail. It also compromises the shingles’ natural ability to breathe and resist algae growth. A coating should not affect any roof’s ability to fight against fire damage.
Other eligibility criteria to keep in mind are:
- At least 75%-85% of the roof’s insulation should be dry, and damaged seams/surfaces must be repaired beforehand.
- Yearly or half-yearly roof inspections (and necessary maintenance) must be done; most manufacturers require this as evidence for warranty compliance.
- Proper drainage is also necessary as ponding water for extended periods may destroy the cool roof coating.
If any of these is an issue, you’d be better off completely tearing off the old roof.
15 Signs You Need a Brand-New Roof (And Not a Roof Coating)
- Large, persistent water stains in the attic or on ceilings.
- Multiple, recurring leaks, even after repairs.
- Soft or spongy areas on the roof deck when walking.
- The underlayment (felt or synthetic) is falling apart.
- Insulation that is consistently wet, moldy, or compressed to the point its R-value has dropped too low.
- Roof joists or trusses are warped, buckled, or showing signs of long-term moisture exposure
- A thick layer of granules in gutters or downspouts (happens when shingles have lost their protective layer).
- A large percentage of shingles are cracked, curled, or missing (asphalt roofs).
- Consistent ponding or pooling of water that doesn’t drain.
- Never-ending moss or algae growth beneath roofing materials.
- Visible sagging/drooping along roof ridges or eaves.
- The roofing material has become extremely brittle or chalked.
- Broken or severely deteriorated flashing around chimneys, vents, or skylights.
- Extensive punctures or tears in the roofing membrane that cannot be patched adequately.
- Roof is unable to support the weight it was originally designed for due to extreme wear.
Why Building Owners Prefer Coating Systems Over a Complete Roof Replacement?
It goes without saying that a liquid-applied membrane is much cheaper, at about half the cost of a full replacement, if not even less. On top of that, the majority of roof coating manufacturers – including Polyglass® – offer warranties ranging from 5 to 25 years that cover both the materials and labor costs.
Think about it: you get a coating system installed today with a 20-year warranty; you most likely need the coating to be 30-mils thick for this. Twenty years down the road, when that thickness goes down, you can simply clean the roof and reapply the coating, bringing it back to 30 mils. Then, a fresh 20-year warranty can be given. You can save a lot of money and stress by repeating this process.
There is also a certain degree of DIY appeal to roof coatings. They are liquid-applied, which means they can be installed quickly, even around tricky areas like drains, vents, pipes, HVAC units, and other features on the roof. You don’t need to hire the same size of crew needed for a full replacement. Because coatings require minimal tear-off (only the damaged areas are removed) and equipment, they cause little to no disruption to building owners.
Request a Quote
Before you decide between a roof coating and replacement, you should get the roof inspected by professional roofers to learn the best course of action moving forward. They can help you decide by factoring in your budget, the current roof state, desired energy efficiency, and more.
If you want to go ahead with a roofing membrane, check out Polyglass® wide range of acrylic and silicone roof coatings, and asphalt roof coating products to accommodate direct-bond applications over flat or low-sloped roofing systems, spray polyurethane foam (SPF) systems, single-ply membranes, metal, concrete, granulated APP, and granulated Mod-Bit/BUR roofs. Contact our team to help you choose the right coating or to get a data sheet.