We’ve heard a lot about UV damage to polypropylene bags. I was interested in seeing for myself just exactly how badly they degrade so I set up a little experiment. I filled a bag with gravel and stuck it aside. Unfortunately I soon after forgot about it so I’m not sure exactly how long it takes to progress to this level of damage but one thing is for certain- this bag is toast.
I dragged a single finger through a patch in the bag that was splitting and you can see how badly it held up. So- protect your bags as you build. Anything from a light plaster to paint will work, just so long as the bag is protected from sunlight. And just a note- you do have to get on top of it pretty quickly. While not an experiment per se, I did think I had more time to get a light plaster up than I did. While the bags didn’t degrade like this one, they did loosen up slightly making plastering a bit more difficult. The smoother and tighter the bags, the easier the plaster goes up. Lesson learned.