Minerjason,
Thanks for your thoughts, I hadn't replied for a bit because I was working things out and wasn't sure of a few things yet. I am still moving forward with this and actually am removing the old plaster myself. Believe it or not my Briggs and Straton 2000 psi electric power washer has helped me remove the clearly very old plaster. I have scraped out a lot with a wonderbar by hand as well (being wet helps for that I think). For the pressure washer I find a weak spot to start and then hit it from the side, if some doesnt come off I go back to it later, keeping it wet, and usually it'll go farther (I think being wet throughout helps the pressure exert more force through it). I have a larger rotary hammer with chisels I know will cut through plaster like nothing. It actually is quite thin most places, like a quarter inch and cleanup won't be the nightmare imagined. I have already removed abouy 1/8th of the pool surface just seeing what i could do.
Good deal. My plaster varied in thickness from ~1/4" to nearly 2", and some sections came right off, while others were a struggle even with a mid size demo hammer with a flat chisel attachment. Hopefully it will continue to go smoothly for you. The photos you posted seem to show the plaster being quite a bit thicker though. Are you removing all the way down to the gunite, or just the thin top layer that's shown flaking off in your photos?
I am going to treat the concrete with Xypex Concentrate and betweeb 12-24 hours later apply the HD Masonry Coating with an added pozzolan(s) and probably Xypex C-1000 NF admix. I have gotten mixed info on whether Xypex can be used with polymers but their own megamix calls for it's use and Quikrete only says to replace 1/3 of the water with acrylic fortifier. I think it will be fine. Talking to Xypex now, also wondering though if it will visibly show crystals on the outside.
Because of what you said about the cracking in sections of different thickness I will probably not do feathering or gradation, and just end a section abruptly, same thickness as the rest of it. I'm thinking there will probably be 3 trowel coats at least as the HD coating is normally applied in thin layers and it may not be formulated for preventing cracks in thicker coats. I could add anti-crak fibers to all but the last coating or two. The acrylic fortifier is said to help with cracks already though. Fritz-Pak makes an admix product called Plaster Supreme for pool plaster that also helps with that. I would think a layered approach with thin coatings would discourage cracking though.
Are you going to apply with a stiff brush prior to troweling as specified in the product instructions? That should be plenty water tight, but I still think you're going to see some cosmetic surface cracks/crazing at the cold joints. You may also have some additional cosmetic differences at the cold joints. I don't know much about the Xypex products, but from what I can tell the C-1000 NF is a powdered acrylic fortifier, and it's suggested to use no more than 1.5% by weight. The HD masonry coating already has some unknown amounts of unknown powdered acrylic fortifiers in it. I'm not sure I see the point of using two separate but unknown powdered acrylic fortifiers. In general, over use of fortifiers/admixtures results in low strength and other problems. If it were me, I'd be using high quality well washed masonry sand, portland cement, and known quantities of the desired admixtures. If you're going to use the Xypex admix, I'd suggest the "2000" product with the longer working time.
Have you gotten a quote for plaster? With you doing all the chip out and other work, it might not be that much. The pre-mixed masonry coating isn't cheap at all, nor are the admixes/fortifiers you're mentioning. Not sure what the going rates are in your area, but with me doing the chip out and prep work, I can get plain plaster done professionally for my mid-sized pool for just over $2k, which might be pretty close to the cost of the materials you're describing using.
I think that after applying the Xypex Concentrate, that leaking should not be a major concern, but the staggering of section seams should prevent cold joint leaks. Xypex heals cracks less than .4mm and the acrylic should also assist. The "old" cement from the previous section will still be chemically active too of course.
As mentioned above, I don't think leaks will be an issue, but you'll be hard pressed to eliminate cosmetic defects from the cold joints.
I will be waiting a full 28 days to fill the pool as Xypex needs at least 12 days for waterproofing before filling and I have not ran across a good reason why it must be filled right away yet.
It seems to me companies do it right away so that the pool's curing does not need to be babysitted (the acrylic fortifier says it takes care of the requirement to spray it down 3x a day in my case), the companies like to fill the pool and be done with the job. It also makes any imperfections less obvious.
The primary reasons it's filled right away are because the plaster cures stronger/harder and because it eliminates shrinkage cracking and other issues related to differential curing. For super high strength concrete pours, it's common practice to build a dam on the outside of the forms and flood the slab with water a few hours after the initial set, and keep it flooded/submerged for the first 28 days. This is the best way to ensure the highest strength and most even curing. Whatever you do, don't skip spraying it down, no matter what type of admixes you use. Yes, the acrylic fortifier helps minimize shrinkage cracking so that people can skip spraying down a slab, or spray it less, and still have a presentable product in the end without a bunch of shrinkage crazing. That does not mean that skipping spraying it is best practice, especially with thinner layers. Do whatever you can to keep it as moist as possible for the first 7 days at a minimum, and preferably for the first 28 days. This could include tenting, setting up misters, or simply spraying it down with a garden hose as many times a day as you possibly can. Also make sure the gunite is wet (but no standing water) before applying any bond coat or finish.
In order to adhere to ASTM concrete testing standards, we have to keep our concrete samples at room temperature and either submerged in a bath of water and lime, or in a chamber maintaining as close to 100% humidity as possible. The moist chambers are essentially walk in coolers with a whole bunch of misters running continuously. If the samples are not cured in this controlled nearly saturated environment, the resulting tested strengths will be significantly lower.
Doing it myself in sections with a trowel and not spraying it will mean it is more dense and less porous, and waiting to fill will mean it is more completely cured and less vulnerable to losing mass to the water.
If you or anyone else believes I have made an error please let me know.
Plaster isn't sprayed on like the gunite, it's pumped into the pool through a hose, and then troweled on. The process you describe won't result in a product that's any denser. In fact, there will likely be small air gaps near the base of every cold joint, which will technically make it slightly less dense.
Waiting to fill will definitely allow it to cure more completely and be way less vulnerable to losing mass to the water. With the flooding of slabs I mentioned above, the volume of water in comparison to the surface area of concrete is very small, so leaching calcium and other ions and loss of mass is really a non-issue. With a pool however, the massive volume of water can create some issues with losing mass to the water, particularly if the water is aggressive. That said, I think the slow and saturated curing of a filled pool eliminates a lot more risk than it presents, and the leaching of mass can be managed/minimized with proper water chemistry relatively easily.
Whatever you decide to do, make sure to keep us updated on the progress!
