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Thread: I am wondering if this is spot etching

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    I am wondering if this is spot etching

    I am wondering if this is the type of spot etching you guys are talking about. The pool is almost one year old and it has this white splotching around the steps and swim-outs. I have always tried to keep my csi on the lower side 0/-.35ish. I have never had the need to clean my SWG yet. The surface is smooth and it just seems to be discolored.

    Questions: Does this plaster surface look normal and is it expected to have this look or is this an example of what is being discussed

    Is there anything I can do to prevent this except try to run the csi on the positive side?

    Thank you for all your input,
    Paul
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    JasonLion's Avatar
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    Re: I am wondering if this is spot etching

    Etching would be rough. There is no way you could describe etching that visually obvious as smooth.

    That looks like mild metal staining to me. I suggest trying a vitamin C tablet held against a dark area for 30 seconds and see what happens.
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    Re: I am wondering if this is spot etching

    The discoloring is actually whiter than the surrounding areas. Would metal staining be whiter than the white plaster? The majority of the area in the pictures is normal white plaster that just looks dark on these pics. The small darker specks are debris from not being brushed. The DW just removed the cover in that area and did not brush the area.
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    Re: I am wondering if this is spot etching

    Calcium deposits are often white. Does the area feel rough and raised?

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    Re: I am wondering if this is spot etching

    Quote Originally Posted by 257WbyMag
    Calcium deposits are often white. Does the area feel rough and raised?
    No, running my fingers over the area I can not feel any difference in the surface texture.
    16k gal plaster with raised spa, Jandy DEV60 filter, 2 HP 2-speed SHPF Jandy Stealth pump
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    Re: I am wondering if this is spot etching

    It is easy enough to try the vitamin C on both dark and light areas. It is a very simple test and it will completely rule out iron stains if it has no effect.
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    Re: I am wondering if this is spot etching

    Quote Originally Posted by JasonLion
    It is easy enough to try the vitamin C on both dark and light areas. It is a very simple test and it will completely rule out iron stains if it has no effect.
    I will try it tonight and while I'm at it I will use it on two small rust spots from the girls hair bands.
    16k gal plaster with raised spa, Jandy DEV60 filter, 2 HP 2-speed SHPF Jandy Stealth pump
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    Re: I am wondering if this is spot etching

    I tried the vitamin c in several areas and it didn't do anything to the surface.

    I got in the pool yesterday and did a very close inspection of the entire pool surface. I was wrong to say that the spotting was limited to the steps and swim outs. The entire surface of the pool has this what I'm now calling discoloration throughout the surface. It looks like the surface has freckles with some of the areas having some streaks that are about a foot long or so, but in a line that almost looks like a trawl could have made it. The freckles are a brighter white than the surrounding plaster.

    I did notice a couple areas where the whiter spots had some roughness to them. I also had the vitamin c on those areas with no results. I then used 220 grit wet/dry sandpaper on the surface and it did smooth out the rough areas but the coloration and size did not change. When sanding the smooth surfaces the plaster just smoothened out some more but the pattern did not change at all.

    If this is scaling would sanding have removed the whiter spots?

    I also found 2 dime size darker spots in the surface that the vitamin c did nothing to nor did the sanding. Right now I'm not too concerned about those spots as I had to search the entire surface to find them. I will keep an eye on them to make sure they are not growing in size.

    So with this new info would you say this is just normal in a white plaster pool or do I need to investigate more as to what is happening?

    Thanks again.
    16k gal plaster with raised spa, Jandy DEV60 filter, 2 HP 2-speed SHPF Jandy Stealth pump
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    Re: I am wondering if this is spot etching

    Where have your FC and CYA levels been over the last year? What are they currently?
    Dave S.
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    Re: I am wondering if this is spot etching

    Quote Originally Posted by duraleigh
    Where have your FC and CYA levels been over the last year? What are they currently?
    Current levels:
    FC 5
    CC 0
    CYA 80
    TA 100
    PH 7.8
    CH 280
    SALT 3100
    BORATES 45ish

    The first month, November 2010, we tried to keep FC 1-2. We tried to keep this level during winter also. Now we know better.
    CYA rose to 50 with stabilized chlorine
    TA 100-120
    PH 8.0-7.4
    CH 220
    SALT none added

    We had a nascent algae problem at the start of spring and that's when I read as much as I could here at TFP. I shocked the pool using bleach only and I brought the FC levels high at that time. I thought we might of had mustard algae due to a few yellow stains starting to show up. Ended up being an old polo ball making the stains. So the FC did get too high for the algae we had. It still took 5 days of shocking before we passed the OCLT. CYA did drop down to 30 at this time. THE FC DID REACH 25 FOR 2 DAYS AT THIS TIME.

    Since spring we have maintained these levels:
    FC 5. At times we rose it to 10 after swim parties. I have always measured it between 4-7 otherwise.
    CYA 50-80 it has been at 80 for the last 5 months.
    TA 70-100 dropped to 70 when we added borates but it rose back to 90/100 range and stays there.
    PH 7.2/7.8 are the ranges I have measured.
    CH 280 it has risen slowly from 220.
    Borates started off at 50 and it has lowered a tad and I'm calling it 45.
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    Re: I am wondering if this is spot etching

    Certainly no iron stains then. Your description does fit calcium scaling, but your water test results don't fit with calcium scaling, unless your PH has been going up above 8.4. High FC levels wouldn't normally be enough to do it. Sanding can remove calcium scaling, especially when it is new/minor.
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    Re: I am wondering if this is spot etching

    It seems to sound and act like calcium scaling to me, too. Organic stains would not be lighter than the finish and you don't have iron stains.

    I would test an area with wet/dry sandpaper and observe the results. I wouldn't be surprised if it comes off rather easily.
    Dave S.
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    Re: I am wondering if this is spot etching

    Quote Originally Posted by JasonLion
    Certainly no iron stains then. Your description does fit calcium scaling, but your water test results don't fit with calcium scaling, unless your PH has been going up above 8.4. High FC levels wouldn't normally be enough to do it. Sanding can remove calcium scaling, especially when it is new/minor.
    I have never measured the PH above 8.0 and I measure a minimum twice a week. My SWG has never had scaling in it either and I look inside it every two months. If it is calcium scaling, would the sanding remove it completely? The few spots that I did sand the surface, it just smoothened out but did not change the coloration at all. Note that 99.9% of the pool surface is smooth and feeling the plaster along the color changes with my fingers and finger nails I couldn't tell you there was any change in the plaster surface. Tomorrow I will try to get some better pictures by putting a cheap camera in a ziplock bag if you would like to see some more of the surface.
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    Re: I am wondering if this is spot etching

    Yes, your pool plaster has what has been known as "spot etching" for years. The appropriate term is now known as "white soft spotting." The spots have turned white over time because some cement compounds in these plaster areas has leached (some call this "weeping") out and has resulted in a high degree of porosity. The surface of these spots is still smooth (just like the rest of the unaffected surface) because there has not been any etching or aggressive action caused by aggressive water. In other words, these white spotted areas are weak, soft, and deteriorating and losing plaster material, even in balanced or positive SI water. The porosity is what makes these spotted areas lighter or whiter in color. The white spots go somewhat deep into the cement matrix, about 4 mm. It is not a calcium scale issue either. You would have to remove about an eight of an inch by sanding with sandpaper to remove the white spots.

    You are right that the smooth non-whitened areas around the affected white areas is slightly gray in color. It is not a metal staining issue. It is not white like it should be and normally is. The overall grayness is due to the addition of calcium chloride by the plaster mixer into the cement mix. Therefore, the contrast between the two areas are significant enough to see. The grayness has increased since the beginning, and the white spots have becomes lighter in color over time as it loses material. This is an issue that sometimes develops within the first year of new plaster jobs. And the grayness of the plaster cannot be sanded off either.

    There are usually several factors that combine to cause this to happen. Mainly, adding too much calcium chloride to the plaster mix (to speed up the hardening process), performing hard troweling too late in the process, and adding too much water while troweling trying to get the plaster surface smooth. Spraying down the plaster before filling, or filling the pool too early, can also contribute to this issue.

    Finally, "white soft spotting" is not caused by aggressive water. Aggressive water early on would have sped up the white spots showing up, but isn't the cause to this plaster defect. Please don't do a "zero alkalinity" (very aggressive) treatment to try and remove the contrasting discoloration. It won't work and it will age (by etching) the plaster.

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    Re: I am wondering if this is spot etching

    OnBalance,
    I did an earlier search in this forum about this topic and that's why I thought it might be this problem but I wasn't too sure. It does fit exactly with what you are saying due to the fact that sanding didn't affect the color contrast what so ever and that I haven't seen any calcium scale that I know of. I guess that I'll have to live with a freckled pool. Thanks everyone for all your input.
    16k gal plaster with raised spa, Jandy DEV60 filter, 2 HP 2-speed SHPF Jandy Stealth pump
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    Re: I am wondering if this is spot etching

    The plastering of your pool was not done correctly. You should talk to your pool plasterer and insist that he redo your plaster job. Southern California is where this problem happens a lot. You can get help to pursue that.

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    Re: I am wondering if this is spot etching

    This looks exactly like the marks on my pool. See this thread: what-s-this-on-my-plaster-t33332.html

    I thought it was early stages of calcium scale caused by high CH and by pH going up to 7.8-8.0 for very short periods. After reading this thread and the other one on spot etching I'm convinced that that's what I have on my pool. So long as it's only an aesthetic issue, I'm not concerned--you can barely notice it in full sun or at night with the lights on. But if it indicates that my plaster will fail prematurely then I want to do something about it.

    My plaster subcontractor (I don't have a PB--he walked the job) looked at the pool a few months ago and blamed "aggressive" water and he suggested I do a no-drain acid wash.

    Based on my experience, and thinking my problem was calcium scale, I've been sceptical of the value of the CSI because my water has never approached +.6. It may have been in the +.45 range for very short periods (less than a day) in between MA additions, but for the vast majority of the time I've kept it slightly negative or slightly positive. Right now it's -.21. Sounds like CSI is more useful than I thought even in pools with high CH levels.
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    Re: I am wondering if this is spot etching

    Sorry I didn't see your previous post in June, but yes, it appears your quartz plaster has the same issue. What has happened to your plaster is not water chemistry related. Not scaling from high CSI, or etching from low or negative CSI. Unfortunately, it is not just a cosmetic issue, the spotting will probably become more apparent as time goes by, but possibly not. The plaster will still last a long time, but just with the spotting showing. It just depends on how affected or inferior the plaster spots are. The plasterer should explain why he recommends a No-drain acid wash, IF the spotting was caused by aggressive water to begin with. Again, the fact is that this spotting problem is not caused by aggressive water. Your pool plaster should be still under warranty, and you might want to push the plaster guy. There are ways of proving that the plaster has been compromised by poor plastering practices.
    I, for one, am tired of seeing pool owners and service techs get blamed for something they did not do.

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    Re: I am wondering if this is spot etching

    One more thing, the spot areas are very porous and will attract metal staining easier, a no-drain will only age the surface.

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    Re: I am wondering if this is spot etching

    Here is my plaster guy's email to me from early this summer after he inspected the pool:

    "I went by yesterday to check on the plaster. Here are the chemical readings that I came up with.

    FC 4.5-5.0
    P.h. 8.0
    TA 80-90
    CYA 60
    CA 570

    With these readings especially the CA at 570 is has your water at a very aggressive state and is etching your plaster. The only way to drop your CA is to drain the water and add fresh water. To repair the damage that has been done we will need to do a no drain acid wash 1st then drain the pool pressure wash and refill the pool. The cost for this work is $500.00. Let me know if you have any questions. Have a nice day."

    I suspect he will not easily accept the spot etching theory.

    I'm not sure about his pH result. if it was accurate it was at 8.0 for a very short time. This summer my pH was still going from 7.2 to 7.8, or slightly higher, over a 2-3 day period. He might have tested just before I added MA. Now I'm keeping my pH between say 7.3 and 7.8--the colors don't match 7.2 and 7.8 exactly so I assume the pH is in between those levels. My TA is 60 and CH is 600 (I lowered it to 450 but the drought and 150 CH refill water caused it to go back up to 650 in a couple of months--it's down to 600 after some recent rains). My other test results show that my CSI ranges from -.44 to -.21 over a 3 or 4 day period. Is that ok? I could easily allow the pH to rise or get my TA up. But the lower TA seems to be helping with my rising pH.

    As for my plaster job, I'm watching my water chemistry like a hawk. Assuming I keep my chemistry within the recommendations on this site, should I be concerned about my plaster job? It does not look bad at all--especially in full sun or at night under the lights. The only time you really notice the etching is before sunset in low light conditions.

    onBalance, thanks for your input on this.
    9,200 gal. Gunite Luna Quartz French Grey pool with spill over spa, two fountains on tanning ledge (rarely used)
    Pentair Whisperflo 2HP, Pentair CCP Cartridge 420 Sq. Ft., Polaris 280 with booster pump
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