Javier and his crew have gotten really good at smoothing out the interior shotcrete finish on the domes we build! I call it a sponge finish because of the swirly, sandy finish we leave behind.
Years ago, we would add all kinds of additives to increase the time it took for the concrete to set — allowing us more time to work. And we needed it! However, as we improved our process and got a lot more practice, we were able to nix all the additives except one called Easy Spread. Easy Spread helps make the concrete more workable. We first trowel the final layer of shotcrete and then go over it again with a sponge.
Our smaller concrete pump and mixer system is also essential for achieving this finish since you can only spray and work one area at a time.
It’s interesting how our customers’ opinions about the best interior finish are so diverse. Some like the sprayed texture, and some can’t do without a smoother finish.
Back in the early 2000s, my dad wrote an article about different finishes for Monolithic Dome interiors. We haven’t used drywall mud or plaster much lately to smooth out the natural shotcrete finish on the houses we’ve built, but it’s still interesting information, especially for a DIYer who wants to do a little shotcrete smoothing in their current Monolithic Dome house.