Plaster and chemistry

Wake9909

Silver Supporter
Mar 28, 2020
32
Broken Arrow, OK
Hi guys! Thank you for the wealth of information you provide on this website!!

My gunite/plaster pool is approximately 9 months old now. I’ve noticed these cracks in my plaster on the seat in the deep end (see pic attached). I don’t really notice this happening nearly as much anywhere else in my pool. Is this normal?

Also, is it more important to keep the CSI where it needs to be or keep the pH down? It seems like lately the higher pH yields a more balanced CSI, based on all my chemistry. Previously, I was told to not let my ph exceed 8.0. Now, with colder temps, a pH of 8.0-8.2(ish) yields a more balanced CSI. Thoughts?

Thanks in advance!!
 

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ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
21,902
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
Was your pool plastered on a hot day?

It looks to me like shrinkage cracks caused by the plaster drying out prematurely before the fill water got up to the level of the step.
 

onBalance

TFP Expert
LifeTime Supporter
In The Industry
Jul 25, 2011
1,081
Utah
Yes, this is severe plaster craze cracking. It can be caused by several different issues. Such as: plastering during a windy day, or a hot and dry day, or from adding too much water to the plaster mix (a high water/cement ratio), or by adding too much calcium chloride (hardening accelerator). It is unfortunate. The only possible remedy is by power sanding.
If the CSI is balanced at a high pH, a pH of 8.2 won't hurt anything.
 
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Wake9909

Silver Supporter
Mar 28, 2020
32
Broken Arrow, OK
Yes, this is severe plaster craze cracking. It can be caused by several different issues. Such as: plastering during a windy day, or a hot and dry day, or from adding too much water to the plaster mix (a high water/cement ratio), or by adding too much calcium chloride (hardening accelerator). It is unfortunate. The only possible remedy is by power sanding.
If the CSI is balanced at a high pH, a pH of 8.2 won't hurt anything.
Is it possible to be only in that one location and not throughout the entire pool?
 

duraleigh

Admin
Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
34,488
Sebring, Florida
I do not think a pH of 8.2 is good practice. Many phenol red tests only go up to pH 8.0 - 8.2 so it puts you at the upper limits of your testing capability and possibly not being able to tell when you exceed it.

Depending on the make up of your fill water, you may not need to be concerned about csi at all. Can you tell us the CH and TA of your fill water?

TFP does not suggest you maintain your pH above 7.8. Certainly, those with years and years of experience with pool water chemistry can push the "edges" of many things we teach......pH included. That does not say it is good practice for the majority of us.
 
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onBalance

TFP Expert
LifeTime Supporter
In The Industry
Jul 25, 2011
1,081
Utah
Wake9909, yes craze cracking (which are actually "shrinkage" cracks) can occur in just one area of the pool. One of the various batches of pool plaster can be mixed improperly, or that they over troweled and added water to only that area of the pool which then causes plaster shrinkage.
There are somewhat inexpensive pH meters that can accurately test various pH levels at any range so that you can accurately determine and keep your CSI in the proper balanced range for plaster-based pools.
 

Wake9909

Silver Supporter
Mar 28, 2020
32
Broken Arrow, OK
Wake9909, yes craze cracking (which are actually "shrinkage" cracks) can occur in just one area of the pool. One of the various batches of pool plaster can be mixed improperly, or that they over troweled and added water to only that area of the pool which then causes plaster shrinkage.
There are somewhat inexpensive pH meters that can accurately test various pH levels at any range so that you can accurately determine and keep your CSI in the proper balanced range for plaster-based pools.
Can craze cracking cause an actual pool leak, or is it primarily cosmetic?