I’ve definitely played the “how long can this last?” game with MDF and a tube of caulk. If you’re patching under a sink, I swear by slapping on some leftover vinyl flooring as a moisture barrier. Not pretty, but it keeps the science experiments at bay... for a while.
If you’re patching under a sink, I swear by slapping on some leftover vinyl flooring as a moisture barrier. Not pretty, but it keeps the science experiments at bay... for a while.
I get the appeal of quick fixes like that, but I’ve learned the hard way that moisture under the sink is just asking for trouble down the line. Mold creeps in before you know it. I’d rather spend a little extra time and actually replace any MDF with something water-resistant, even if it means cutting up some PVC board. Not glamorous, but at least I’m not worried about what’s growing back there.
Honestly, I’ve seen way too many “quick fixes” under sinks turn into full-blown headaches. If you’re dealing with a cracked sink or water damage, here’s what I’d do: First, pull out any damaged MDF or particle board—don’t bother patching if it’s already swollen or soft. Next, measure and cut a piece of PVC board or marine plywood to fit. It’s not fancy, but it won’t soak up water and rot. Seal the edges with silicone, especially around pipe cutouts. Takes a bit more effort up front, but you won’t be ripping it out again in six months. Trust me, mold is a pain you don’t want to mess with.
Honestly, I’d skip the DIY kits for a cracked sink unless it’s just a tiny hairline and you’re desperate for a stopgap. Here’s how I’d break it down:
- If the crack is through-and-through or leaking, those epoxy kits rarely hold up long-term. Water finds its way in, and you’re back to square one.
- For water-damaged cabinets underneath, totally agree—rip out anything soft or swollen. No point patching rotten wood.
- PVC board is solid advice. I’ve also used marine plywood, but only if I had some left over from another job. PVC’s easier to cut and doesn’t care about moisture.
- Silicone around the edges is key, especially where pipes come through. Miss that step and you’ll regret it next time there’s a drip.
I’ve seen folks try to “save” a cracked sink with caulk and paint... never lasts. If you want peace of mind, replace the sink or at least reinforce underneath with something waterproof. Mold under a sink is no joke—had to gut an entire vanity once because someone ignored a slow leak for too long. Not fun.
“If the crack is through-and-through or leaking, those epoxy kits rarely hold up long-term. Water finds its way in, and you’re back to square one.”
That’s been my worry with the DIY kits too. I tried one on a bathtub in my last place—looked fine for a month, then the crack reappeared and started leaking again. Agree that once water gets into the cabinet, it’s basically game over for particle board. I do think for a tiny hairline, a kit could buy you some time if you’re saving up for a replacement, but as a fix? Not really worth it. Mold is such a nightmare... I found a patch under our kitchen sink last year and ended up replacing half the floor. Wouldn’t risk it again.
