The finish plaster is normally white all the way through. It sounds like you are dealing with a pool that has been replastered by the method of putting a "brown coat"/"scratch coat" (the gray plaster you noted) over the original finish plaster surface, and a new finish coat of white plaster on top of that. The scratch coat more like a thin concrete than plaster (doesn't have the white marble dust in it) and is used to get a better bond to the old surface.
A reputed recipe for pool plaster on a gunite pool is 1 part white cement to 2 parts white (preferably quartz or silica) sand. You should probably also add a bonding agent to the mix to make sure that your new plaster adheres to the old. All of these can be found at pretty much any home repair or hardware store. Mix the dry ingredients first and then make a shallow depression and gradually add water till you have the consistency similar to chunky peanut butter. Add the bonding agent per the instructions on the package and you are ready to go. Good luck!
The black (burn) marks show up on Gray plaster pools. White plaster pools will show up as a yellow or rust color. Remove the tabs and put them in a proper floating devise, the marks will go away in time. Try using wet and dry sand paper on the burn marks to reduce their visibility and roughened plaster.. additionally, tablets of any size should NEVER be placed or tossed into the pool or skimmer. K
Damage can occur within four hours on a hot sunny. That's only if your pool is plaster. The pool in question is gunite. A gunite pool can stay empty for as long as it takes to do the repairs, no long them a month. But you have to make sure, and this is very important, to open the plugs at the bottom of the pool to releave any water pressure that is under your pool, or your pool can lift out of the ground a couple inches. So remember to relieve the pressure relief valves at the bottome of your gunite pool as soon as possible. Our pool is 20 x 40, freeform, gunite inground pool. It's 3ft to 8 ft deep. As soon as the water is about knee high at the deep end, my husband walks in and removes the plugs at the bottom to release the water that is under the pool. It pours out for a few hours then slows to a trickle. The plugs stay open until we are ready to refill. Make sure, however, you put the plugs back in so they don't leak. He uses white plumbers tape around the threads of the plugs to secure a good tight fitting. Good luck, hope everything goes well.
Gray in white plaster is usually trapped moisture and will often go away as the plaster hydrates. If it does not then they can be removed by draining the pool, acid washing the area, heat it carefully with a torch to draw the water out and then polish the plaster smooth. This should absolutely be done by a professional experienced in this type of remedy. A ZERO alkalinity treatment may also work with the water still in the pool. Again, pros only. Trowel burns can also cause gray in pools but you need someone familiar with this to properly diagnose the cause. If the plasterer is an NPC (National Plaster Council) member a tech advisor may come to look at the pool and diagnose it properly.
Copyright © 2020 Multiply Media, LLC. All Rights Reserved. The material on this site can not be reproduced, distributed, transmitted, cached or otherwise used, except with prior written permission of Multiply.