Sanding Fiberglass Discoloration

[Randy-Tracie W]

Moved from HERE.

Hey Texas Splash. I came across this post from 2018 and I’d like to ask you a question or three about your sanding experience-sorry for replying to such an old post. First, I’ll just say that I’m pretty dang sure that we have an identical situation in our two year old fiberglass pool. Our pool manufacturer suggested testing with 600 grit sandpaper as well-sanding is the only thing helping and I am getting ready to sand the entire pool. In your thread, you said that you used 120 grit sandpaper - did you have any issues with it’s that grit being too aggressive? Did you use other grits as well? I understand that the amount of pressure you apply has to be “enough, but not too much”. And, I’m not “new” to sandpaper....I just can’t see sanding the entire pool with 600 grit-that would take forever and be very labor intensive. Of course, I want to be as conservative as I can so I don’t cut into the gel coat. Have you needed to sand again/anymore...have you had any more of the same issue? Did you polish too or just sand? I think part of my issues came from a high pH and low CH over the first 12-15 months. I have since kept the CH over 200 and that is easy to maintain. But, I cannot keep the pH regulated. It goes up, seems like continuously. So In order to keep the pH around 7.4 and the TA around 90, I am playing the muriatic acid/baking soda hamster wheel game. I’m thinking about letting the TA go down to around 70 to see if the pH will then stabilize, at least some. But, you seemed pretty concerned with the TA - trying to keep it between 80-90. Do you have any continuously rising pH issues? Any ideas on that? Again, sorry for replying to an old post. Thanks in advance for any advice!!!!

 

[YippeeSkippy]

I'll bump this so @Texas Splash sees it.

 

[Texas Splash]

Randy, no issues that I was concerned with by using the 120 grit. If you get up close, you may seem some very fine, trace scratch marks, but only if you're looking for them. But it was the only way I could make reasonable progress. To me it was better than the faded stuff. Sometimes I would go over an area with 400 grit just in case, but those whole sanding thing was exhausting work. There really aren't a lot of tools designed for such underwater sanding either unless you pay big bucks, and I wasn't about to drain my entire pool. As for the longevity of my work, that's still being evaluated. When I stand back and look at the pool, I see the contrast between the old and the new (sanded). But it also seems like some of the sanded areas faded little again. Natural light influences those areas as well. I document my progress with photos. For the past couple years I've been trying to keep my CSI just slightly negative whereas before I may have been a little too aggressive with the CSI. Even though CSI isn't really supposed to apply to FG pools (no calcium/plaster), it's all I can imagine that could've effected my gelcoat because I've controlled my levels quite well - except when I "thought" I had a scale problem and it really wasn't (very low CSI). I never used a polish. In the end, all of this may just be a result of a poor gelcoat application. I realize that possibility, but I'm experimenting a bit with levels to see if my sanded areas remain dark or try to revert to the chalkiness look.

As for the pH, mine typically hovers around 7.8 with a TA of 70 or so. My CH is at 300. Over time (every 3-4 days or so), by controlling the pH, the TA may dip close to 50 and I'll bring it back up, but it's not a fast yo-yo game. I might have to raise the TA every 2-3 weeks or so. A lot depends on how much new water I add as well. I recently installed an SWG, so I'm more critical of my numbers for the longevity of my cell, but it works out for both too (CSI of about 0 to -0.2). But that's my latest. Hope it help, and good luck on your pool.

 

[Randy-Tracie W]

Thanks for the fast reply!! I had quotes from $3,000 to almost $10,000 to sand the pool...that is not feasible, so the only way this will get done is if I do it. Below is one pic of my “testing” area with 600 grit. Clearly, it made a huge difference. Our pool is 16x35 / 3-6 ft deep, so I’m trying to convince myself that it will kind of be like waxing 10 cars back to back. I was planning, and will, sand by hand. The thing is, by wet sanding, I can easily see where I have sanded...even though I am planning to drain as I sand and then completely refill with new water. Fortunately, our pool contractor did install a point pipe/sump pipe so I can drop my sump pump in that and not worry about the pool floating as I drain the water.

Sounds like I am good to go by trying the TA goal of 70 or so. If that would make my pH stabilize some, I’d be ecstatic. We do have a spill over spa-the water circulates thru that three times a day-I have wondered if the aeration from that causes our pH to continually rise?? Guess If the TA attempt works, I could rule out aeration.

I did start using The Magenta Stuff about two months ago and plan to continue using that even though I’m not certain it will help to prevent this same thing again...this “thing” that is truly a mystery. I will post some before and after pics when I am done....that will take a month or three....not quite warm enough in NC to get in the pool. Again, THANKS for your help!!

 

[Texas Splash]

did start using The Magenta Stuff about two months ago and plan to continue using that even though I’m not certain it will help

Yes, I experimented with several products like that as well, to include Scale-Tec and others. No effect. But yes, the spill-over will impact the pH, so try to keep it running as short as possible. I sanded a little each time I got in the pool. While the wife was swimming, I was sanding. I used a soft sanding block with the paper to help with the contours of the shell. Good luck!

 

[Randy-Tracie W]

Yeah, my spill over is only running for a total of 35 minutes per day(3 separate cycles)—just to get some chemicals in that water-you wouldn’t think that would make that much difference, you know.

You mean those sponge sanding blocks like you get at Lowe’s and then you wrapped your paper around that? I’m thinking I’ll swim and my wife can sand...think that will work? LOL. Thanks again