📌 Key Takeaway: Etching is a chemistry problem before it is a surface problem, and route techs who hold LSI between -0.3 and +0.3 on every plaster account will prevent the callbacks, warranty claims, and account losses that aggressive water silently creates.
Etching is one of the most expensive problems a service tech can cause, and most of the damage happens before the customer ever notices. By the time a homeowner spots a chalky white finish, rough spots on the steps, or a cloud of calcium dust at the main drain, your route has already been chewing through plaster for weeks. This post walks through what actually causes etching on a service route, how to dial in your chemistry to stop it, and how to protect your business from the warranty exposure that comes with new plaster accounts.
What Etching Actually Is on a Service Route
Etching is the dissolution of calcium carbonate out of the plaster matrix. When pool water is undersaturated with calcium, it pulls calcium out of the cement binder until it reaches equilibrium. The result is a roughened, porous surface that holds stains, grows algae faster, and ages a finish by years in a single season. On a route, you will see it first on sun-exposed shallow ends, around returns where fresh acidic water hits the wall, and on steps where bathers track in body oils that drop local pH.
The Langelier Saturation Index (LSI) is the single most useful number you can carry in your truck. Keep LSI between -0.3 and +0.3 and plaster stays stable. Drop below -0.3 and the water becomes aggressive. Most route techs never calculate LSI because they were trained to chase individual numbers, but a pool can have a "perfect" pH of 7.4 and still be etching hard if calcium hardness is 120 ppm and the water is 88 degrees.
The Chemistry Targets That Stop Etching
For plaster pools on a weekly service route, lock in these ranges and check them every stop:
- pH: 7.4 to 7.6. Below 7.2 is etching territory, especially after acid additions.
- Total alkalinity: 80 to 120 ppm. Lower for pools with high-pH fill water, higher for soft-water regions.
- Calcium hardness: 250 to 400 ppm. New plaster pools should run at the upper end for the first year.
- Cyanuric acid: 30 to 50 ppm. CYA artificially lowers carbonate alkalinity, so subtract one third of your CYA reading from total alkalinity when calculating LSI.
- Temperature: factored into LSI but not controlled. Warmer water is more aggressive at the same chemistry.
The most common etching trigger on a route is acid washing or acid slugging. When a tech pours muriatic acid directly into the shallow end to knock down pH, the localized pH at the floor can drop below 4 for several minutes. That single shortcut etches a permanent footprint into the plaster. Always pre-dilute acid in a bucket, walk it around the deep end with the pump running, and never add acid within 10 feet of a wall or step.
New Plaster: The 28-Day Window
Fresh plaster is the highest-risk surface you will ever service. For the first 28 days, the cement is still curing and calcium is leaching out of the surface naturally. If you start your normal route chemistry on day three, you can etch a brand-new finish badly enough that the plaster company will deny warranty and point the finger at you.
During startup, brush twice daily for the first week, hold pH at 7.2 to 7.4, keep alkalinity at 80 to 100 ppm, and do not add chlorine for the first 48 to 72 hours depending on the startup method. If you are taking over a route that includes recently replastered pools, get the startup log from the plaster contractor before your first service visit. Pool service business owners building their book should treat new-plaster accounts as a separate service tier with its own pricing, because the labor and liability are not the same as a mature pool. If you are evaluating pool routes for sale, ask the seller specifically how many accounts have plaster under two years old, because those carry inherited risk.
Soft-Fill-Water Markets Need a Different Playbook
If your route is in a region with soft municipal water, mountain runoff, or well water, you are fighting etching every week. Calcium hardness in the fill can be under 50 ppm, which means every backwash, splash-out, and rain event pulls the pool further out of balance. Route techs working these markets need to:
- Carry calcium chloride on the truck and add it preemptively, not reactively.
- Test fill water at every new account during the walkthrough.
- Bill calcium additions as a line item rather than absorbing the cost.
- Set customer expectations in writing that soft-water pools require higher chemical budgets.
This is also why route valuations vary so much by geography. Soft-water markets have higher chemical costs per stop but also higher barriers to entry, which protects margins for established operators. Reviewing pool routes for sale in different regions is a fast way to see how chemistry conditions shape route economics.
Brushing, Tools, and the Physical Side
Chemistry causes etching, but bad tools accelerate the damage. Use a nylon-bristle brush on plaster, never stainless steel. Steel brushes are for concrete and Gunite shells before plaster, period. Replace nylon brushes when bristles fan out past 45 degrees. A worn brush scrubs less surface area and tempts techs to press harder, which scratches the etched layer further.
Vacuum heads with stiff wheels or metal axles can leave tracks on softened plaster. Inspect vac heads monthly and retire anything with exposed metal. If you offer acid washes as an add-on service, train techs that acid washing is a finish-shortening procedure, not a routine cleaning. A pool plastered ten years ago typically has only one or two acid washes left in it before exposing aggregate.
Documenting Chemistry to Protect Your Business
The single best defense against an etching warranty claim is a chemistry log. Route software that records pH, alkalinity, calcium, CYA, and chlorine at every stop creates a defensible record. When a homeowner calls in March claiming your service ruined their plaster, a year of logs showing balanced LSI shifts the conversation from your liability to the plaster contractor's workmanship or the homeowner's between-service additions.
Train techs to photograph any pre-existing etching on the first visit to a new account. Time-stamped photos in the customer file have ended more disputes than any contract clause. If you are buying a route, walk every pool with the seller and document plaster condition before closing, because etched finishes you inherit on day one become your problem on day thirty.
The Bottom Line for Route Owners
Preventing etching is not about one chemical or one tool. It is about running LSI-balanced water on every plaster stop, treating new plaster as a specialty service, adjusting your playbook for local fill water, and documenting your chemistry so you can defend your work. Route owners who build these habits into their tech training keep finishes intact, keep customers off the phone, and keep accounts on the books for the full life of the plaster.