Why some roof coatings actually make things worse

I get what you’re saying, but I’m not totally convinced every coating is a disaster waiting to happen. I used a silicone-based one on my old torch-down roof after patching a couple spots, and it actually held up fine for a few years. Maybe it depends on how dry you get it before coating? I do think if there’s already a leak, no coating’s gonna magically fix it long-term, though.

Silicone coatings can definitely buy you some time, especially if you catch the issues early and prep the surface right. I’ve seen them hold up surprisingly well after hail, but yeah - if there’s moisture trapped underneath or active leaks, it’s just a bandaid. Prep is everything, but even then, sometimes hidden rot or old seams come back to haunt you. The “magic fix” idea is what gets folks in trouble... coatings aren’t a cure-all, just a tool.

- Seen this a bunch - folks slap silicone on thinking it’ll fix everything, but if there’s already moisture in the deck or seams are failing underneath, you’re just sealing in the problem.
- Did a job last fall where the owner used coating right over wet plywood... six months later we had to tear up half the roof for rot repair. Not pretty.
- Surface prep is huge, but sometimes you can’t see what’s lurking under old layers - especially on older buildings.
- Coatings help, but if the bones are bad, it’s just delaying the inevitable. I’d rather fix leaks at the source than mask ‘em with a layer of silicone.

I’d rather fix leaks at the source than mask ‘em with a layer of silicone.

Yeah, that’s exactly the kind of thing I was worried about. My place is in a pretty humid area, and the roof’s got a couple decades on it - layers on layers, so who knows what’s trapped underneath. I’ve read that some coatings are “breathable,” but honestly, I’m skeptical. If there’s already moisture in there, seems like you’re just asking for trouble by locking it in.

I tried patching a leak with an acrylic coating a few years back (before I knew better), and it looked fine at first. But after one summer, I started noticing these weird soft spots and a musty smell. Ended up having to pull up part of the membrane and, sure enough, there was mold. Not fun.

I get the appeal of a quick fix, but now I’m leaning more toward actually addressing the leaks before even thinking about coatings. Wish there was a magic eco-friendly option that could handle minor leaks without making things worse, but I haven’t found one yet. Maybe some of those newer “liquid rubber” types are better? Still seems risky if you don’t know what’s going on underneath.

Been there with the “breathable” coatings - honestly, I’ve never seen one actually solve a moisture problem if there’s already water trapped. Had a client with a flat roof who tried liquid rubber over old leaks, and it just made the rot worse. If you can’t see what’s under those layers, you’re basically gambling. Sometimes ripping up a section is the only way to know for sure.

Had a similar mess with a “miracle” elastomeric coating on my old shed roof. Everyone swore it would seal things up, but all it did was trap the dampness from a hidden leak. By the time I noticed, the plywood underneath was basically mush. I get wanting a quick fix, but unless you know exactly what’s going on under there, it’s just covering up trouble. Sometimes you really do have to bite the bullet and peel things back, even if it’s a pain.

- 100% agree that coatings can backfire, especially on older roofs with hidden damage.
- Elastomeric products are often marketed as cure-alls, but if the substrate’s wet or compromised, you’re just sealing in a problem.
- I’ve seen this a lot on flat roofs - folks slap on white reflective coatings thinking it’ll solve leaks and help with heat, but trapped moisture just chews up the decking from below.
- Ventilation is huge. If the roof assembly can’t breathe, any moisture just festers. That goes double for green roofs (which I’m a fan of), where drainage and vapor control are even more critical.
- Quick fixes can be tempting - especially when budgets are tight - but they rarely last. Sometimes you have to do the messy demo to actually find what’s going on underneath.
- Minor disagreement: Certain coatings *can* work well as part of a system if you’re starting with a sound deck and you’re sure everything’s dry. But yeah, they’re not magic bullets for underlying rot or leaks.
- For anyone considering coatings, worth checking:
- Is your roof type compatible? (Metal vs. asphalt vs. TPO, etc.)
- What’s your climate like? Humid areas = more risk of trapped dampness.
- Have you checked for soft spots or signs of hidden leaks first?
- I did a torch-down patch job once on a low-slope section before applying any coating - took extra time but caught some nasty wet insulation that would’ve been sealed in otherwise.
- Bottom line: Prep is everything. If you don’t know what’s under there, you could be setting yourself up for bigger repairs down the road... Learned that lesson the hard way myself years back with an “easy” silver coat that turned into a full tear-off two seasons later.

Not saying never use coatings - they’ve got their place - but only after you’re sure the base is solid and dry. Otherwise, it’s like painting over rust... looks good for a bit, but the real trouble’s still brewing underneath.

Couldn’t agree more about the “painting over rust” analogy. I’ve seen a few folks get burned by skipping the prep - just slapping on a coating and hoping for the best. It’s tempting when you’re staring at a tight budget, but like you said, if there’s hidden rot or wet spots, you’re just making it worse. I learned that lesson patching an old mod bit roof - looked fine on top, but underneath was a mess. Coatings have their place, but only if you know what you’re working with. Good callout on ventilation too... that’s one thing people overlook all the time.

Seen this a lot after storms - folks rush to coat a roof thinking it'll buy them time, but if there’s moisture trapped underneath, you’re just sealing in the problem. Did a job last fall where the plywood looked okay from the attic, but when we pulled up the coating, half of it was mush. Prep takes time, but it’s always cheaper than ripping out rotten decking later. Ventilation’s huge too - especially with these humid summers.

Is there ever a time when a quick roof coating actually helps, or is it always just a band-aid? I get the urge to slap something on after a storm - especially when you’re juggling a bunch of units and tenants are calling nonstop. But I’ve wondered, is there a way to tell if you’re just trapping moisture without ripping everything up first? Maybe some kind of moisture meter? I’ve had a couple roofs where we coated and crossed our fingers, but now I’m second-guessing if we just set ourselves up for more headaches down the line...

I get the urge to slap something on after a storm - especially when you’re juggling a bunch of units and tenants are calling nonstop.

Honestly, I’ve been there - sometimes you just need to buy time. Quick coatings can help if it’s bone dry and you know you’ll do a proper fix soon. But yeah, if there’s even a hint of trapped moisture, you’re basically sealing in trouble. I’ve used a cheap pin-style moisture meter before, but it’s hit or miss through roofing layers. Usually, if the roof feels spongy or you see bubbling, it’s a hard pass for me... learned that the expensive way.

Yeah, I’ve tried to patch up after storms, too. It’s tempting when you’re stressed and don’t want leaks spreading. But if you trap any water, it just turns into a bigger headache later - mold, rot, you name it. Cheap fixes usually cost more in the end.

That’s what I’m worried about - quick fixes just hiding bigger problems. I patched a spot on my garage roof last fall with some cheap sealant, and now there’s a weird smell in there after it rains. Not sure if it’s mold or just damp wood, but I’m kicking myself for not checking underneath first. Has anyone had luck with those “liquid rubber” coatings, or do they just trap moisture too?

Not sure if it’s mold or just damp wood, but I’m kicking myself for not checking underneath first. Has anyone had luck with those “liquid rubber” coatings, or do they just trap moisture too?

I’ve been down that road - used a liquid rubber product on my shed roof a couple years back. It sealed up fine at first, but I didn’t realize there was already dampness in the plywood. Ended up with a musty smell and some black spots later on. Those coatings can definitely trap moisture if there’s any already in the wood. If you’re smelling something weird after rain, I’d check for soft spots or discoloration underneath. Sometimes it’s just damp wood, but mold can sneak up fast if things stay sealed up tight.

Those coatings can definitely trap moisture if there’s any already in the wood.

Had a similar thing happen with my porch roof. Thought I was being smart slapping on a rubberized sealant, but turns out the wood underneath was still a bit damp from a leak I hadn’t noticed. Couple months later, the boards felt spongy and smelled off. Lesson learned - if there’s any doubt about moisture, it’s better to wait or pull up a section and check. Those coatings are unforgiving if you seal in even a little dampness.

That’s a tough lesson, but honestly, it’s more common than people think. Those rubberized and elastomeric coatings are marketed like miracle fixes, but they’re basically a vapor barrier. If you’ve got even a little trapped moisture under there, it’s not going anywhere - just gets cooked in when the sun hits. I ran into something similar with a flat roof over my garage. Looked fine on the surface for about a year, then I started noticing a musty odor every time I walked in. Pulled up one of the boards and sure enough, black mold and soft spots.

A lot of folks don’t realize wood can hold onto moisture for quite a while, especially if it’s thick or the weather’s been humid. Even with a few dry days, you can still have dampness deep in the boards. I’ve started using a moisture meter before any sealing job now - one of those cheap pin-type ones from the hardware store. Not perfect, but gives you an idea.

Honestly, if there’s any doubt at all about whether something’s dry enough to seal, it’s worth waiting or even running a fan for a few days. In my area (southeast), humidity is brutal and things just don’t dry out as fast as you’d expect.

One thing I’ll add - if you’re dealing with older roofs or porches that have had leaks before, sometimes it pays to pull up a couple boards and check underneath before doing any new coating. It’s extra work up front but saves way more hassle down the line. Once rot sets in under a sealed layer, you’re looking at replacing whole sections instead of just resealing.

Not saying these coatings are bad across the board - they do have their place - but they’re definitely not “set it and forget it” solutions. The prep work makes all the difference... and unfortunately, skipping steps usually comes back to bite you later.

Had a similar mess with my back porch last year - thought I was being clever slapping on one of those “flexible” coatings. Fast forward to summer, and the boards underneath felt like wet bread. Is it just me or do those miracle products always leave out the fine print about moisture? Anyone else end up running fans for a week just to be safe, or am I just paranoid?

Is it just me or do those miracle products always leave out the fine print about moisture?

You’re not alone. I slapped one of those “waterproof” coatings on my deck, thinking I was a genius. Next rainstorm, the water just pooled up and sat there like it was waiting for an invitation inside. Ended up with soggy boards and a weird musty smell that wouldn’t quit. Ran two box fans for days - felt like I was trying to dry out a swamp. Lesson learned: those coatings are only as good as what’s underneath, and if there’s any moisture trapped, you’re basically sealing in the problem. Now I’m paranoid about every little creak underfoot...

That’s a tough one. I’ve seen similar issues on flat roofs - people slap on a coating thinking it’ll fix leaks, but if the substrate’s damp or there’s poor drainage, it just traps water underneath. Did you check for ventilation under your deck before sealing it? Sometimes airflow makes all the difference.