I have a balcony on my apartment with several cracks that are getting bigger because of the rain. I tried a generic sealant from Éxito but it peeled off after two months. Does anyone know which concrete sealant brand holds up well in humid weather without flaking?
The first thing is to clean those cracks really well with a wire brush and get all the dirt out, because if you apply sealant over dust or algae the product won't stick! For humid climates like yours, polyurethane sealers hold up way better than generic acrylics - they last for years without peeling if you apply them correctly in dry cracks.
Polyurethane sealers are the ones that hold up best outdoors with moisture, but there's a crucial detail a lot of people skip: the crack needs to be completely dry before you apply anything, and on a damp patio that's trickier than it sounds. If you put sealer on wet concrete or over condensation, no matter how expensive the brand, it'll fail just like what you already tried.
My recommendation is that you use a two-component polyurethane sealer, like the ones they sell for movement joints in construction. Yeah, they're pricier than the generic stuff, but they handle wet-dry cycles way better. Before you get started, keep the patio rain-free for at least two or three days if you can, or if that's not possible, dry the cracks thoroughly with towels and apply a primer for damp concrete if your product allows it. That really improves the adhesion.
One more thing: widen those cracks a bit before sealing if you can, even with a screwdriver or chisel. Sealers work better when they go into a V-shaped crack than when you're trying to fill something super tight. Let it cure for the full time the container says, because a lot of people mess it up by trying to use the patio too soon. With patience on the prep work and a good product, it should last way longer than two months.
I've had the same problem with my patio, and the issue isn't just the sealant - those generic ones shrink and expand with heat and humidity, which causes them to peel off. What worked for me was using polyurethane or silicone sealers from brands that specifically sell for outdoor use (the ones that say "UV resistant" and "flexible"), because they handle temperature swings way better. But before you apply anything, you have to let the crack completely dry - if it rains a lot where you are, wait a couple days without water or use an industrial dryer - because moisture is what kills any sealant. Also, put a backer rod in the crack (like a polystyrene cord) before the sealant, because if the crack is deep, sealant just on the surface is going to fail.
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