Gotta be honest, marking a slate roof—even with chalk—makes me pretty nervous. Slate's expensive and delicate, and I'd worry about staining or scratching it. Photos are probably the safest bet here. I just snap a bunch from different angles before and after rains, then compare closely on my laptop. Seems like colors could get confusing anyway if you're tracking multiple leaks over time...
I've been there with the photo method, and honestly, it drove me a bit nuts too. After a while, all those pics started blending together, and I couldn't tell if I was looking at last week's leak or last month's. I get your hesitation about marking slate—it's pricey stuff—but I've used chalk a few times without any real issues. Just gotta be gentle and use a soft chalk stick, not the gritty sidewalk stuff my kids leave lying around. Rain washes it off pretty quick anyway, so staining hasn't been a problem for me.
Another trick I've tried is using painter's tape near the leak spots. It sticks well enough to slate without leaving residue, and you can jot down dates or notes right on it. Saved me from squinting at blurry laptop photos more than once...
I feel your pain on the photo method—been down that road myself and ended up with a phone full of nearly identical pics that told me absolutely nothing useful. I swear, at one point I was zooming in on water stains like some kind of amateur detective, trying to figure out if that shadow was new or just a trick of the light. Not exactly my proudest moment, haha.
Painter's tape is actually a pretty clever idea, though. Never thought about using it on slate, but I've used it on drywall and wood floors before without any issues. Slate can be tricky, though—have you noticed any trouble with it peeling off bits of the surface if it stays on too long? I guess it depends on the finish, but still, I'd be a little nervous leaving tape on expensive slate for more than a day or two.
The chalk thing sounds pretty safe, honestly. I've used chalk markers (the kind restaurants use on menu boards) on tile before, and they come off super easy with just water. Slate is porous, though, so maybe regular soft chalk sticks are safer. Have you ever tried those washable crayons they make for kids' bathtubs? I know it sounds weird, but they're designed to come off easily, even from porous surfaces. My niece scribbled all over my sister's bathroom tiles once, and it wiped right off. Might be worth a shot if you're feeling adventurous...
Anyway, hang in there. Tracking leaks is one of those tasks that always seems simple until you're knee-deep in blurry photos and mystery stains. You're definitely not alone in this struggle.
Painter's tape has been pretty safe on my slate tiles, but I never leave it more than a day or two—learned that lesson the hard way on some painted drywall. Those washable crayons sound intriguing, though I'm a bit skeptical they'd come off porous slate as easily as tile. Has anyone tried UV flashlights to spot fresh leaks? Heard plumbers use them sometimes, but not sure how practical they are for home use...
"Has anyone tried UV flashlights to spot fresh leaks? Heard plumbers use them sometimes, but not sure how practical they are for home use..."
I've seen UV lights used effectively to track down leaks in HVAC systems, but haven't personally tried them for water leaks around tiles or drywall. My concern would be whether you'd need to add some kind of dye to the water first—otherwise, would plain water even show up clearly under UV? Curious if anyone's had luck with this method without additives...
