Making sure the deck’s ready for underlayment - what’s your process?

I’m with you on the leaf blower - just ends up swirling stuff around, especially if it’s a bit windy. I’ve found that the push broom and shop vac combo gets things cleaner, but I always wonder about moisture. Even after a good sweep and vacuum, sometimes the boards still feel a bit damp, especially in the shaded spots.

Do you guys wait for a certain number of dry days before laying underlayment, or is there a trick to making sure everything’s actually dry enough? I’m worried about trapping moisture under there and ending up with mold or warped boards down the line. Maybe I’m overthinking it, but I’d rather be safe than sorry... Anyone else run into this?

I totally get the worry about moisture - trapping it under an underlayment is asking for trouble down the road. I usually go by touch and sight, but if I’m unsure, I’ll tape a piece of plastic down overnight and check for condensation in the morning. If there’s any, I wait another day or two. Shaded spots can be stubborn, especially after rain. Sometimes I’ll use a fan to speed things up, but honestly, patience is key. Better to wait than deal with warped boards or mold later.

I like your plastic test - simple but effective. I’ve run into issues where the deck *felt* dry but still had hidden dampness, especially in older homes with thicker boards. Ever try using a moisture meter? I find it helps catch those sneaky spots that look fine but aren’t quite ready. Curious if you’ve noticed any difference between plywood and OSB in terms of drying times or how they hold moisture? Sometimes OSB seems to hang onto it longer, at least in my experience.

I’ve used a moisture meter a couple times, but honestly I still rely on the “feel” test more than I probably should. OSB definitely seems to hold onto moisture longer, especially around the edges. Ever had issues with swelling or soft spots after drying? That’s tripped me up before, especially in humid weather.

Swelling’s been a headache for me, especially after a rainy spell. I’ve had spots that felt dry but turned mushy once I started laying underlayment. Now I always check the edges with a screwdriver - if it sinks in, I replace that section. OSB’s just tricky in damp weather, no way around it.

That screwdriver trick’s a classic - nothing like poking around and suddenly realizing you’re about to step through the deck. I’ve had my fair share of “looks fine, feels fine, oops, nope” moments, especially with OSB after a wet week. Sometimes I swear OSB just waits for you to turn your back before it starts swelling up.

I’ve started using a moisture meter on questionable spots, but honestly, it’s not foolproof. Some days I think it’s just a fancy way to confirm what my boots already told me. Curious if anyone’s tried sealing the cut edges of OSB before install? I’ve heard mixed things - some say it helps, others say it’s a waste of time and money.

Also, how do you all handle borderline cases? If it’s just a little soft at the edge, do you patch, or is it straight to full replacement? I always debate it, especially when the budget’s tight and the weather’s not cooperating.

Sealing OSB edges before install is one of those things that sounds great in theory, but in practice, I’ve only seen minor improvement - especially if the sheets are exposed for more than a day or two. I’ve used the green end-seal products and even just exterior paint in a pinch. It slows down water intrusion a bit, but if the deck gets hit with real rain before you’re dried in, the edges still puff up. Maybe it buys you a little time, but I wouldn’t count on it as a fix.

For borderline soft spots, I’m usually in the “replace” camp, but I get the budget struggle. If it’s just a small area and not in a high-stress spot, I’ve scarfed in patches with construction adhesive and ring-shank nails. Still, I always worry about long-term movement or delamination under shingles. Curious - has anyone tried using Advantech or a similar premium panel for repairs, or is that overkill for patch jobs?

Maybe it buys you a little time, but I wouldn’t count on it as a fix.

Couldn’t agree more. I’ve had crews try every “miracle” sealer out there for OSB edges, but if the weather turns before we’re dried in, it’s still a gamble. At best, I might get an extra day, but I’ve seen those edges swell up even with the green stuff. One time we got hit with an unexpected downpour and half the deck looked like it had been left in a puddle - sealer or no sealer.

When it comes to repairs, I’m usually pretty practical. If the spot is tiny and not in a high-traffic area, I’ll patch it and move on, but if there’s any doubt, I’d rather bite the bullet and swap the sheet. I’ve used Advantech for patching once when it was all I had on hand - honestly, it felt like overkill for just a patch, but that spot never gave me trouble again. That said, for most jobs, standard OSB does the trick if you can keep it dry long enough.

Budget always wins out in the end, but cutting corners on sheathing can come back to bite you... learned that one the hard way.

- Totally get what you mean about the “miracle” sealers.

“At best, I might get an extra day, but I’ve seen those edges swell up even with the green stuff.”

That “miracle” sealer stuff cracks me up - my builder swore by it, but after one surprise thunderstorm, I had edges curling like potato chips. I’ve started doing the flashlight walk too, though I admit my version is more “poke and hope.” Swapping a whole sheet feels dramatic in the moment, but I’d rather deal with that than listen to creaks every time someone walks by. The Advantech patch story hits home - I once used a leftover piece for a doghouse roof and now it’s basically bombproof. You’re not alone crossing your fingers for dry weather... sometimes it feels like half of building is just hoping the forecast is wrong.

I’ve started doing the flashlight walk too, though I admit my version is more “poke and hope.” Swapping a whole sheet feels dramatic in the moment, but I’d rather deal with that than listen...

- That “miracle” sealer is more hype than help, in my experience.
- I do the flashlight walk too, but I’m more of a “tap and listen” type - soft spots get flagged right away.
- Swapping a whole sheet feels like overkill, but I’ve regretted not doing it later when the floor squeaks.
- Advantech’s tough, but even that stuff needs a dry spell to set right.
- My process: sweep clean, check for bounce, screw down anything loose, and pray for no rain.
- Half the battle really is just timing the weather...

Swapping a whole sheet feels like overkill, but I’ve regretted not doing it later when the floor squeaks.

That’s the part that always gets me. I used to try patching just the bad spots, thinking I was saving time and money, but then you get that one spot that starts squeaking six months later and it drives you nuts. Now I’m in the “just do it right the first time” camp, even if it feels dramatic. And yeah, Advantech is solid, but if it gets soaked before you cover it up, you’re asking for trouble. Timing the weather is half science, half luck...

I get why folks want to rip out the whole sheet, but honestly, I think it’s a bit much unless the damage is really widespread. I’ve seen plenty of jobs where a solid patch, glued and screwed, holds up just fine for years - no squeaks, no bounce. The trick is making sure you’re not just slapping a patch on top of rot or delamination. If the rest of the sheet is sound, you’re not gaining much by tossing it all. Plus, you start pulling whole sheets and you risk messing with the joists or creating more seams than you need.

That said, I’ve walked enough houses where someone tried to save a buck and left soft spots, so I get the “do it right” mentality. But sometimes “right” just means being thorough with your inspection and not overreacting. I always check underneath if I can - crawlspace or basement access makes a big difference. If there’s any sign of water damage or mold underneath, then yeah, out it comes.

Advantech’s great, but I’ve seen it swell up like a sponge if it sits in standing water for even a couple days. Weather’s a gamble, but if you’re working in the rainy season, I’d rather patch and wait than expose a big open deck to the elements. Tarping only does so much.

End of the day, I’d say don’t default to full replacement unless you really need to. A careful patch job can be just as solid if you take your time and don’t cut corners. Squeaks usually come from movement or missed fasteners, not from the patch itself. Just my two cents after crawling around too many old houses...

I’m with you - no sense in tossing out good wood just to feel like you did something. My wallet definitely appreciates a solid patch job, especially when the rest of the sheet is fine. I do get nervous about missing hidden rot, though. Ever had one of those spots where it looks okay from above but turns out the ants have been throwing a party underneath? I’ve started poking around with a screwdriver just to be sure. Curious if anyone’s tried those moisture meters before cutting - are they worth it, or just another gadget collecting dust?

I totally get the worry about hidden rot - seen way too many “looks fine from up top” situations where the subfloor was basically mulch underneath. That screwdriver trick is classic, but I’ve actually started using a moisture meter more often. Honestly, it’s not perfect, but it’s saved me from missing a couple sketchy spots that felt solid but were wet inside. Not a must-have for everyone, but if you’re dealing with older wood or suspect leaks, it’s probably worth pulling out of the toolbox now and then.

I’ve run into a few cases where the deck looked solid, but once I started probing with a meter, the readings were off the charts - especially near old plumbing penetrations. I still use the screwdriver for quick checks, but honestly, the meter’s caught stuff I’d have missed otherwise. One thing I’ve noticed, though, is that high readings can sometimes just be surface moisture from condensation, not rot. It’s worth double-checking before tearing into things.

Had a similar thing happen last fall after a nasty hailstorm - deck looked fine at first glance, but the meter was lighting up like a Christmas tree around an old vent stack. I almost started pulling up boards, but after letting things dry out for a day, the readings dropped way down. Turned out it was just condensation from a cold snap the night before. That’s when I started carrying a cheap infrared thermometer too, just to see if there’s a temp difference that might point to trapped moisture versus surface stuff.

I still trust the old screwdriver for soft spots, but I’ve learned not to panic over every high reading. Curious if you’ve ever run into hidden damage that didn’t show up on the meter at all? Sometimes I feel like there’s always one spot that surprises me once the underlayment comes off...

Funny you mention that - last spring I had a spot right by the chimney that looked and felt solid, meter barely moved, but once we pulled the old felt off there was a patch of rot about the size of my hand. Must’ve been leaking for ages and just dried out on the surface. Now I always check seams and around any old flashing, even if the tools say it’s fine. Sometimes you just gotta trust your gut (and maybe your nose - wet wood has a smell).

- Gut feeling and sniff test are good, but I wouldn’t rely on them alone, especially after a big storm or if you’re dealing with older decks.
- Moisture meters can miss stuff, sure, but I’ve seen just as many folks tear up “suspicious” spots that turned out fine. Sometimes you end up chasing ghosts and wasting time (and money) on solid wood.
- Around chimneys and valleys, I always probe with an awl or screwdriver - if it sinks in, you’ve got rot. If not, move on. No need to rip up everything just because it looks a little off.
- Flashing is tricky. Even if it looks tight, water can sneak under. I usually pull up the first row of shingles around any suspect flashing and check the deck underneath. That’s caught more hidden rot for me than just sniffing around.
- One thing I’d add: check from the attic side too if you can. Stains or mold on the underside of the deck are dead giveaways, even if the top looks okay.
- End of the day, trust your tools, but don’t ignore what you see and feel. Just don’t go overboard tearing up good wood unless you’re sure.

I’ve definitely learned the hard way that looks can be deceiving, especially on older roofs. I always check from the attic when possible - caught a nasty patch of rot once that was totally hidden from above. Probing around chimneys has saved me a ton of headaches too. I still use a moisture meter, but yeah, it’s not gospel. Sometimes you just gotta trust your gut, but I agree, no sense in ripping up everything unless you’re sure there’s a problem.