Why is my pool plaster rough or stained?
Most often the water, not the plaster, is the cause. Water that stays too basic leaves white calcium scale on the surface, and water that is too acidic eats into it. San Diego County's guide shows plaster damaged by unbalanced chemistry. Test pH, alkalinity and calcium hardness, correct them, and brush the shell before you decide it needs resurfacing.
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By Kasra Taheri, Founder, LoclisPublished
Researched and drafted with AI, then checked claim by claim against the sources listed below before it was published. Prices and rules change; the dates beside each source say when it was last checked.
Step by step
Read when to stop and call a pro, further down this page, before you start.
Step 1: Feel and photograph the problem
From the steps or edge, with the pool full and clear, note whether the roughness is gritty and white (likely scale) or smooth but worn, and photograph stains with the date. Do not go into an empty pool.
Step 2: Test the water
Test pH, total alkalinity and calcium hardness, and note the water temperature. A pH over 7.8 for a prolonged period leads to calcium build-up on plaster.[1]
Step 3: Work out the saturation index
Use the pool-industry saturation index: pH, temperature, calcium, alkalinity and total dissolved solids. Between -0.3 and +0.3 is balanced, below -0.3 is corrosive, above +0.3 is scaling.[1]
Step 4: Correct the water slowly
Adjust one measurement at a time following the chemical label, retest after the water has circulated, and aim for a pH of 7.4 to 7.6.[1]
Step 5: Brush the shell
Brush the floor, walls and steps routinely to remove algae and dirt build-up.[1] Use a brush made for plaster, not a steel one, which can scratch the surface.
Step 6: Recheck in a few weeks
Feel the surface again. Scale that has not hardened often brushes off; etched, pitted or flaking plaster does not.
Step 7: Get a written assessment if it stays rough
If the surface is still rough, flaking or stained after the water is balanced, ask a licensed pool contractor for a written assessment.
It is usually the water
When pool plaster feels rough or looks blotchy, the first suspect is water chemistry, not age. San Diego County's guide shows a photo of a plaster surface with damage caused by unbalanced water chemistry,[1] and the same guide explains the two ways it happens.
Water that stays too basic deposits scale. If the pH is over 7.8 for a prolonged period of time, it will lead to calcium build-up on pool plaster, recirculation pipes and equipment.[1] Calcium carbonate, also called scale, is a water-insoluble white solid that is the main component of scale.[1] That is the gritty, whitish coating you feel on steps and walls.
Water that is too acidic works the other way, dissolving and etching the surface, which leaves plaster pitted and rough in a different way. Hard water can cause cloudiness and scale buildup, and soft water can damage equipment and the pool shell.[1]
Why it matters
Roughness is not only cosmetic. Los Angeles County's public-pool inspection guide says plaster should be smooth and non-slip. Its inspectors mark the plaster OUT, a failed item, when it is not smooth or has extensive areas of etching or roughness enough to cause a hazard to pool users.[2] Rough plaster scrapes feet and knees, and it holds algae and dirt.
What to check
Start with a test kit or a pool shop's water test. You need pH, total alkalinity, calcium hardness and the water temperature.
The ideal range for pH is between 7.4 and 7.6, and keeping the pH there reduces corrosion of metal and calcium build-up on pool plaster.[1] Virginia's water quality rule for public pools requires a pH between 7.2 and 7.8,[3] which is a useful outer limit for a backyard pool too. San Diego County's table lists 80 to 120 ppm as the ideal total alkalinity and 180 ppm as the maximum.[1]
Pool professionals combine the readings into a saturation index. It looks at five factors: pH, water temperature, calcium, alkalinity and total dissolved solids.[1] A result between -0.3 and +0.3 is considered balanced, a result less than -0.3 is considered corrosive, and anything greater than +0.3 is considered scaling.[1] A pool shop can calculate it from your numbers.
Fixing the cause
Change one thing at a time, follow the chemical label, and retest after the water has circulated. Swinging pH and alkalinity back and forth is hard on a finish.
The pool shell must be routinely brushed to eliminate algae and dirt buildup.[1] A plaster brush with nylon bristles does this without gouging the surface. Light scale often loosens once the water is balanced and the surface is brushed regularly. Hard, thick scale and deep etching do not.
Stains
Stains are harder to read than roughness. Their colour and where they sit are clues, and a pattern that follows leaves, a rusty fitting or a recent chemical addition points to different causes. Photograph them with the date, note what changed in the pool around the time they appeared, and have a licensed pool contractor identify them before you treat them. A wrong treatment can leave the mark where it is or damage the plaster.
When resurfacing is the answer
If the water is balanced and the surface is still rough, flaking, cracked or etched, the plaster itself has worn out. How to know when your pool needs resurfacing covers the signs, how much pool resurfacing costs in Virginia covers the budget, and how to choose a pool resurfacing contractor covers the hire. Whoever resurfaces it, keep the water balanced afterwards or the new finish will fail the same way.
Stop and call a pro if
- The surface is flaking, peeling or hollow-sounding in patches, or cracks are widening. The finish may have lost its bond to the shell.
- The water level keeps dropping. That may be a leak, not a finish problem; see how to find a leak in a pool.
- The roughness cuts or scrapes swimmers, or sharp edges show on steps and walls. Stay out of the water until it is assessed.
- Stains stay after the water is balanced and you cannot say what caused them.
- You are thinking of draining the pool. Leave that to a pool contractor.
Getting help in Virginia
More pool guidance is in the pool and spa answers, and you can browse pool and spa services on Loclis.
When you are ready, describe the pool once and licensed local pool businesses quote it.
Common questions
- Is rough pool plaster always a sign I need resurfacing?
- No. Rough, gritty plaster is often scale from water that has been too basic, and scale can sometimes be brushed off once the water is balanced. Resurfacing is for plaster that is worn, etched, flaking or cracked. A licensed pool contractor can tell the difference in a written assessment.
- What pH should my pool be?
- San Diego County's guide gives 7.4 to 7.6 as the ideal range. Virginia's rule for public pools requires a pH between 7.2 and 7.8, and a home pool is easiest on its plaster at the middle of that band.
- Can unbalanced water damage plaster?
- Yes. San Diego County's guide shows a photo of plaster damaged by unbalanced water chemistry. Water that is too acidic corrodes, and water that is too basic builds scale. Tell any contractor how the water has been managed, because a new finish fails the same way in the same water.
- Should I drain the pool to look at the plaster?
- Not on your own. Draining a plaster pool can damage it, and an empty pool is a hazard to climb into. A pool contractor decides whether and how to drain it, as part of an assessment.
- What if the stains stay after the water is balanced?
- Photograph them, note when they started and what was added to the pool around then, and ask a licensed pool contractor to identify them. Treating a stain without knowing its cause can leave it in place or etch the plaster.
Sources
- [1] Swimming Pool Operator's Guide, 1st Edition, County of San Diego Department of Environmental Health, Food and Housing Division. Checked October 27, 2026.
- [2] Public Pool Inspection Guide, Los Angeles County Department of Public Health. Checked October 27, 2026.
- [3] 12VAC5-462-290. Water quality standards, Virginia Administrative Code, Virginia General Assembly. Checked October 27, 2026.
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