I can’t say for sure what’s going on without seeing it, but it sounds like your sister in law’s pool may have a low cement to sand ratio in the gunite. If the gunite crew fudged on the cement to save some money (not that uncommon), you’d notice more sand in the mix. That may be what’s causing the brown shade. Also can be that the gunite wasn’t mixed enough (i.e., more sand in some areas, more cement in others). Can be other causes, too, so I don’t want to jump the gun here.

Gunite should be batched at about 3.75 to 4 bags per ton of sand (or, if crew measures by yard, figure about 6.5 to 7 bags). You can check number of bags and tonnage of sand delivered to get a quick check to see if the gunite guys are staying honest. Lots of other little details, too.

The best way to test the gunite is to core drill it and take the sample in for a crush test. That tells you the pressure at which the gunite fails. Usually engineers specify about 2000 psi, sometimes more, but it should say on the engineering plan. If the core tests come up OK then it doesn’t matter what the color is. A simple test, though, is to just whack the gunite with the point of a pick. Hard. If if it bounces back and does nothing but make a pretty small divot and maybe hurt your hands, that’s a positive sign; if you take a hunk out of the gunite, well, it may be time to think about a core test.

And, about the weather: cold or heat don’t really affect the placement of gunite. I’ve gunited pools when it’s been over 110 degrees, and when it’s been in the mid-20’s.

If your sister in law is concerned about it, she should talk to her pool contractor. If that doesn’t satisfy her, she can go the core test route. If either of you want to email me with further question, please do so.

So what’s that mean? Due to weather when the gunite was done (ours in summer, theirs inwinter)? Is it bad to do gunite when it is cold?

By thw way, I like your blog and appreciate the time you’ve obviously put in it.