Why is my mortar skinning over so fast in this humidity?

Humidity actually messes with you beacuse it traps the heat in the substrate and prevents the moisture in the mortar from evaporating naturally, wich causes that flash-skinning you're seeing. The porcelain isn't helping either since it has zero absorption, so all that moisture is just sitting on the surface of the mud getting cooked. You need to switch to a **medium bed mortar** specifically rated for large format tile (LFT). Standard thin-set has too much water and not enough polymer to handle a 1/2 inch notch in those temperatures without sagging or skinning over instantly. Try back-buttering every single tile if you aren't allready. Even a thin scrape on the back of the porcelain will help create a bridge before the ridges on the floor can dry out. If you can, keep your bags of thin-set and your mixing water in the shade or even in an ice chest. Using cold water for the mix gives you an extra ten or fifteen minutes of bucket life and slows down the initial chemical reaction so it doesn't kick as soon as it hits the hot porch.

As for the misery of working in a sauna, the 'season of the chafe' is real once the humidity hits 80 percent. Most of us on the crew swear by **Gold Bond** or even some of those expensive quick-dry work pants to keep from getting thrashed by noon. Some guys go commando under those synthetic joggers just to stay breathable, but at the very least, keep a bottle of medicated powder in the truck.

If the skinning gets too bad, stop and wait for the evening. If you can't scrape a finger across the ridges without it sticking to your skin, the bond is already compromised and you're just begging for hollow spots. Sometimes the only way to beat the swamp is to start at 5:00 AM and pack it in by lunch when the air gets too thick to breathe.

I’ve fought that same battle more times than I care to count. One thing guys forget is that the slab is probly 110 degrees before you even start. Back when we did more thick mud beds, we’d always soak the substrate down first. These days, just take a damp sponge to the porch before you trowel. If the concrete is bone dry and hot, it’s acting like a sponge, pulling the moisture out of your mortar from the bottom while the sun skins the top. Also, if you’re not using a pop-up tent, start. Keeping the direct sun off the work area is the only way to save your sanity.

Oh man, I am so glad I found this thread! I'm just starting out and honestly, the heat is insane right now. I'm definatly going to try that ice water trick for my next mix becasue I was about to give up entirely. Speaking of working in a literal sauna though, do any of you guys use those neck fans or cooling vests while you're tiling? I saw an ad for one and I'm wondering if they acutally work or if they're just going to get covered in mortar dust and break immediatly.

You're spot on with the ice water and damping the slab, it's the only way to survive a porch job in this soup. One thing I'd add is to keep your mixing bucket out of the direct sun too. If that plastic bucket sits in the heat, it transfers that thermal energy right into the mix regardless of how cold your water was. I usally throw a piece of plywood or a scrap of Durock over the bucket between scoops to keep the ambient heat from cooking the batch from the top down.

Quick update — the damp sponge trick was a total lifesaver. Wiping down that hot slab made a massive difference in how the thin-set behaved. I also started using ice water for the mix like suggested, and it gave me way more open time. The tiles are set and the bond feels solid. Thanks for helping me survive this swamp!