Boulder advice? Any geologists?

NorCalX

Gold Supporter
Feb 3, 2011
97
Brentwood, CA
We are in the rock shopping phase and it is nuts here.

Since the rains ended in late March all the builders have been buying up and using all the local inventory.

The place we thought would be our vendor only has moss rock left and we are trying to avoid using moss rock for the grotto/weeping wall features

We wanted a little more durability and different coloration options

I have names of boulders staff told me during prior visits but I'm having a hard time tracking down more information on them and nobody has them in stock nearby
-gold country
-great falls
-waterwash
-siskiyou gold


Today we found a place with plenty of CALISTOGA boulders in stock.
*Our PB went with us to the last few rock suppliers that were out of supplies but he was not with us today b/c it just happened to be on the way an errand we were running

I put our tile and our coping sample near it and we think it might work.
I forgot the bottle of water and sponge to wet test it though

Calistoga comparison.jpg

I tried asking the nearest staff member for more detail about calistoga boulders but they had no clue.

Can anyone tell me what kind of rock that is (sedimentary family....granite etc.)?

Higher density and better durability than moss rock?

Good for water feature application in salt water pool like we need?

I know the warning is avoid rock that flakes etc.

Any advice is appreciated
 

Rich D

Bronze Supporter
Aug 3, 2018
204
MA
I am not a geologist so I can not speak to what type of rock that is. I used all site boulders for my waterfall and walls so I did not have a huge selection and the only advice I can give is to be sure to avoid the orange ones.. Here is my rookie mistake.. I am told it might stop bleeding in a few years and it does clean up nicely with acid but if I had known about the staining issue this one would have been in the reject pile.MVIMG_20190421_114128-3024x2268.jpgIMG_20190420_195702.jpgIMG_20190330_105303-3628x2721.jpg
 
  • Like
Reactions: NorCalX

MinerJason

Bronze Supporter
Jan 29, 2018
198
Tucson, AZ
Geological engineer here. Those look like granite at first glance, but it's really hard to tell without being able to really look at them up close. "Moss rock" can be any type of rock with moss growing on it, so I have no reference as to how a particular moss rock would compare to those boulders in any way. I can say that those boulders appear to have some oxide alteration on the joints, which can cause staining issues as already mentioned.

Unfortunately quarries and boulder resellers rarely indicate what type of rock they're selling, and name them based on color or origin location, which doesn't tell you much. I'm guessing that "Calistoga boulders" come from somewhere near Calistoga CA, which only narrows down the possible rock types slightly.
 

NorCalX

Gold Supporter
Feb 3, 2011
97
Brentwood, CA
@MinerJason

woo hoo an expert!

one of the things my wife is looking for is color.

brown...orange...gold are things catching her eye.

does "color" in general indicate potential staining or are there safe ones to focus on?
 

MinerJason

Bronze Supporter
Jan 29, 2018
198
Tucson, AZ
@MinerJason

woo hoo an expert!

one of the things my wife is looking for is color.

brown...orange...gold are things catching her eye.

does "color" in general indicate potential staining or are there safe ones to focus on?
An orange coating on rock joints is almost always iron oxide, basically rust, which has a tendency to stain. Gold sparkles are typically pyrite, and while that's often the source of iron for the rust stains on the joints, it usually takes very long periods of exposure for them to create any significant stains (unless they're exposed to an acidic environment).
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,052
Tucson, AZ
I was going to tag @MinerJason but he beat me to it! He’s an expert in cementitious materials and stone work.

I have boulders in my waterfall that we’re all locally procured from the Catalina range, mostly granite with a “red stone” or two but none of the reds are in the water path. However, when they did the exposure (acid wash) of my PebbleTec during install, they accidentally hit one of the rocks and it caused a stain on my wall. 6 years later and I can still faintly see it. So yeah, be very careful...
 
Last edited:
  • Like
Reactions: NorCalX

jtburf

Well-known member
Jun 8, 2015
319
Houston, TX
MinorJason,

Can he get a piece of the rock and drop it in a Muratic Acid bath to confirm it is not from the sedimentary family?

John
 

MinerJason

Bronze Supporter
Jan 29, 2018
198
Tucson, AZ
MinorJason,

Can he get a piece of the rock and drop it in a Muratic Acid bath to confirm it is not from the sedimentary family?

John
Only some sedimentary rocks dissolve in acid, but it's a worthwhile test. Typical test is just applying a few drops of 5-10% hydrochloric acid and seeing if it fizzes or bubbles. If it does, the rock has carbonates in it.
 

NorCalX

Gold Supporter
Feb 3, 2011
97
Brentwood, CA
So I got more info on the Calistoga boulder today.
Appears to be a common rock at the different places in the SF Bay Area and I was able to ask questions at a new rock place.

I viewed it dry and wet (they were awesome and drove a pallet to their hose and soaked it for me).

The employee at this location told me Calistoga is a SEDIMENTARY rock but he considers it much more durable than moss rock and says it should be perfectly fine in a salt water pool.

I don't think there is a blanket rule against sedimentary rock but have no idea how I can verify whether it is a good candidate for use in a pool (grotto and weeping wall application).

Anyways here are the images for those who are curious.

Any advice or opinions on use in a pool are greatly appreciated.

My wife likes this the best of everything we have viewed so far and the color when wet is exactly what she wants (nice warm tones)

Calistoga dry.jpgCalistoga wet.jpg
 

MinerJason

Bronze Supporter
Jan 29, 2018
198
Tucson, AZ
Looks like maybe sandstone. No, there's no rule against sedimentary rocks in pools. Some sedimentary rocks can be prone to flaking, some are very soft, and some will deteriorate in an acidic environment. Plenty of non-sedimentary rocks with similar issues too though. Those don't look like they'll have any of those issues. The surface coating does appear to be rust, so be careful about placement of the more rust colored ones with regards to potential staining. Shouldn't be a huge issue with a bit of care. You could also consider using a stone sealer of some kind on them to help prevent staining.
 
  • Like
Reactions: NorCalX

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,052
Tucson, AZ
I have some similar stones like that in my waterfall. They are not on the water flow path but they do get wet. My pool has no detectable iron.

The trick is when the plaster contractor does the final finish, many of them use an acid wash procedure. That is when staining will be most likely to occur (splash out hitting the rock and then runoff onto the plaster). You’ll have to work with your plaster applicator and ask them to either be really careful OR do extra prep work to cover the rock. Offering to pay a little extra cash for the additional prep work will likely get you the best possible outcome.
 
  • Like
Reactions: NorCalX

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,052
Tucson, AZ
I would reiterate @MinerJason ‘s point about sealing the stone. If the any stones are going to be submerged or have water flowing over them or if multiple stones are going to be mortared together to form a water-bearing surface, then sealing them may be very worthwhile, especially the mortar joints. I have mortar joints that have held up very well BUT they tend to develop a thick calcium deposit due to the fact that the mortar is an alkaline substance and the high CH water that runs over it is constant going through a wet/dry cycle and thus depositing a fresh layer of calcium scale. So there are some patches along the mortar joints that have very thick, smooth, off-white colored deposits that are basically calcium carbonate with some trapped dirts (hence the off-white color). As gross as it sounds, it looks like a giant wad of mucus (I know, gross, but that’s the coloration and smoothness of it). It can be easily chipped off but, I bet if the mortar were sealed there, it wouldn’t happen as easily.

So, long story short, try to think of what your rock design and layout will be and then try to decide what you can do to minimize the impact of flowing water. We had a separate contractor that did the waterfall and he was really smart and knew his stuff because his whole business was building backyard koi ponds and river/water features. So he was well aware of all the pitfalls and intricacies of stone work.
 
  • Like
Reactions: NorCalX

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,052
Tucson, AZ
  • Like
Reactions: NorCalX

NorCalX

Gold Supporter
Feb 3, 2011
97
Brentwood, CA
After more boulder browsing we keep coming back to the calistoga but only if we can maintain the wet look (the warm tones are exactly what my wife wants)

after some research i think i need to find a penetrator and enhancer to get that result. does that sound right to the experts?

these boulders will be above the waterline but still used in either the grotto or weeping wall so there will be SWG pool water flowing over some pieces

what are the long term concerns with that approach?
- $ for maintenance and resealing (see stuff that says annually...3 years...5 years and 10 years for external use)
- does the wet look fade over time until reapplication? best is day 1 and slowly gets worse from there?
- any other notes i should be aware of?

will reach out to my PB after gunite and let him know which direction we want to go
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
15,052
Tucson, AZ
Look up StoneTech or DryTreat 40sk. Those are the top of line but they get pretty pricey. You will need to reseal every 18-24 months to keep the “wet” look.
 
  • Like
Reactions: NorCalX

Other Threads of Interest