After grinding / polishing of Diamond Brite Surface on Sun Shelf we have white blots and stains

[mleibundgut]

Our pool has a sun shelf about 17" below the water surface. The pool contractor left about 4" of water on the sun shelf for the winter when winterizing, and we maintained it at that level. Nevertheless the freezing of this layer of water damaged the Diamond Brite surface to the point where it became very rough and showed dark spots. The Diamond Brite color is Onix (dark).
This summer our contractor came to grind and polish the surface and it indeed became smooth to the touch again. But the grinding created ugly light blots and stains that make things look worse than before, and nobody seems to know what to do. Would anybody on this forum know if and how this can be resolved?
- Markus

 

[sktn77a]

Partial acid wash (on the shelf)?

 

[ajw22]

@onBalance thoughts?

 

[onBalance]

Unfortunately, I think that it will require more sanding and polishing to remove the white spots.

 

[sktn77a]

^^^^^^^ I'd definitely go with what onBalance says..... He's "Mr Plaster"!

 

[mleibundgut]

Thank you all for your feedback - really appreciate it. We tried with some Ascorbic Acid. About one pound on a surface of about 2-3 sqft, letting the powder drop down as evenly as possible in non moving water and letting it sit there for about 30 minutes before brushing. This already improved things a lot. Currently the water is at about 14" above the shelf. We are thinking to drop the water level to maybe about 1" and try again so the Ascorbic Acid would be more concentrated and we might have to use less. Does anybody have any suggestions as to how to best apply Ascorbic Acid on a shelf like this?
Thanks again!!

 

[onBalance]

I assume you understand that allowing solid Ascorbic Acid to sit on the plaster surface may "etch" the plaster surface somewhat, which may then remove the discoloration. Hopefully, it doesn't make the plaster too rough and pitted. If it does, sanding and polishing can restore the smoothness.

 

[Rich D]

Hmmm... I have a on going similar issue with my pool company about how much water to leave on the ledge. The past 2 years they have drained below the ledge and covered it with a insulated blanket. I do not think this is a good approach. Where do you think you will leave the water this winter?


I am currently trying to choose between a diamondbrite finish or River Rok. Would you mind answering a few questions that might help my quandary..

How old is your finish?
What color is it?
Have you had any other discolorations?
Are you over all happy with it?

Thanks, Rich...

 

[mleibundgut]

In response to "onBalance", yes - I noticed that the Ascorbic Acid did etch the surface a bit, but I think that's related to make it look more crisp and true color. The original Diamond Brite surface is actually a bit "grainy" to the touch - not perfectly smooth. I think what happened with the grinding/ polishing was that some grinding dust got compacted into the grains of the surface which contributed to the white, blodgy look. Even after the first Ascorbic Acid application the surface still feels more smooth to the touch than the original Diamond Brite, so I think we will do some more Ascorbic Acid treatment to the point where the surface will feel about the same as the original.

 

[mleibundgut]

In response to Rich:
- Our finish was installed late 2016, so this is the 3rd season.
- The color we picked is Onyx, so it is almost black. Since we wanted more the appearance of a reflecting pool this worked well for us, but it does not give the typical blue Ocean look.
- After the Diamond Brite installation there was some white discoloration on the shelf for a while. But daily brushing in high acid pool water was able to get rid of that and everything looked nice and even.
- Overall we are happy with the Diamond Brite product. After the first problems with the winter damages we met with the Diamond Brite rep at our pool and he confirmed that this damage was related to winter freezing. He said he is seeing this now more with sun shelves in areas with winter freezing, but did not want to make a recommendation. The pool company then recommended to leave 3-4" of water on the shelf. This actually created the worst damage. I think the whole layer of water went through several full freeze and thaw cycles which did grind off a lot of material. There are two entry steps onto the shelf which were never covered by water in the winter. These actually have no damage at all and look like new. So I think for the next winter we will bring the water below the shelf and will keep it there. We are using a sump pump with a 1" plastic pipe, heated with heat tape, and controlled with an electronic switchable outlet to control the level. With that we can keep it pretty constant over the winter.

 

[Rich D]

Thanks for taking the time to reply..

. The pool company then recommended to leave 3-4" of water on the shelf. This actually created the worst damage.

So it sounds like you had some damage in the previous seasons as well but when they left 3-4" on the shelf you saw the worst damage. How much water was left on the shelf in the previous seasons? I find it odd the company rep did not have a suggestion on the best way to protect there product in the winter. What kind of winter cover do you use?

 

[onBalance]

In response to "onBalance", yes - I noticed that the Ascorbic Acid did etch the surface a bit, but I think that's related to make it look more crisp and true color. The original Diamond Brite surface is actually a bit "grainy" to the touch - not perfectly smooth. I think what happened with the grinding/ polishing was that some grinding dust got compacted into the grains of the surface which contributed to the white, blodgy look. Even after the first Ascorbic Acid application the surface still feels more smooth to the touch than the original Diamond Brite, so I think we will do some more Ascorbic Acid treatment to the point where the surface will feel about the same as the original.

Generally, I think most diamond brite quartz aggregate pool finishes are troweled to be smooth. I am not sure why the original finish wasn't smooth unless it was originally designed to be somewhat rough. It could be that a layer of calcium scale formed on the surface too, and the Ascorbic acid treatment (and/or polishing) may have removed it. But if you are satisfied with the result of your Ascorbic acid treatment on the top shelf, then that is great. Any kind of acid treatment is going to expose the color of the plaster and make it appear darker.

I have performed many sanding or polishing jobs on pools to expose the original color and make it darker, but never has the "grinding dust" been compacted into the plaster. It could be that the plaster finish was damaged and pitted somewhat at the start and the polishing didn't remove enough of the damaged plaster to completely restore the original color, but that the acid treatment did so. If it so happens that the acid treatment overly etches the surface, I believe you can always sand and polish it again to make it smoother. I hope it all works out to your satisfaction.

 

[mleibundgut]

Thanks for taking the time to reply..



So it sounds like you had some damage in the previous seasons as well but when they left 3-4" on the shelf you saw the worst damage. How much water was left on the shelf in the previous seasons? I find it odd the company rep did not have a suggestion on the best way to protect there product in the winter. What kind of winter cover do you use?

The first winter we left no water at all and had no damage. We did not even pay attention to this then. After that the second two winters there was water on the shelf an that did create damage, so hopefully our logic to not leave any water this winter will work out - we will know in spring! We do not use any cover - we are not here in winter and monitor the water level with cameras.

 

[Rich D]

The first winter we left no water at all and had no damage. We did not even pay attention to this then. After that the second two winters there was water on the shelf an that did create damage, so hopefully our logic to not leave any water this winter will work out - we will know in spring! We do not use any cover - we are not here in winter and monitor the water level with cameras.

We do not cover our pool in the winter either. We close as late as possible and open as early as possible.

Your shelf is a bit deeper then mine. I have about 12" of water on my shelf. So to safely put it 6" below tile it would only leave 3" on the shelf. This is the reason they drain below the shelf. However I had 9+ inches of ice this year so I really can not leave any water on the shelf and have it below the tile. I am starting to believe that it would be best to have tile installed sun selfs in a freezing climate.

I have started a thread to try and get some info on the best approach..

How much water do you leave on your sun shelf for the winter freeze ?

Trying to figure out the best practice for winterizing a gunite / shotcrete pool with a sun shelf. Please post --- - Depth of water you try to maintain over sun shelf. - how far down from bottom of tile that water level is. - how diligently you maintain that level - type and age of pool...

www.troublefreepool.com

 

[Rich D]

Curious on how your sun shelf held up this past winter?

Thanks, Rich..

 

[scormier]

Generally, I think most diamond brite quartz aggregate pool finishes are troweled to be smooth. I am not sure why the original finish wasn't smooth unless it was originally designed to be somewhat rough. It could be that a layer of calcium scale formed on the surface too, and the Ascorbic acid treatment (and/or polishing) may have removed it. But if you are satisfied with the result of your Ascorbic acid treatment on the top shelf, then that is great. Any kind of acid treatment is going to expose the color of the plaster and make it appear darker.

I have performed many sanding or polishing jobs on pools to expose the original color and make it darker, but never has the "grinding dust" been compacted into the plaster. It could be that the plaster finish was damaged and pitted somewhat at the start and the polishing didn't remove enough of the damaged plaster to completely restore the original color, but that the acid treatment did so. If it so happens that the acid treatment overly etches the surface, I believe you can always sand and polish it again to make it smoother. I hope it all works out to your satisfaction.

Could you recommend what to use to sand and polish the surface? What size sander works best and what grit is preferred?
Thanks!