After the resurface: water balance keeps the finish
A new interior finish is the largest single bill most pool owners face, and the water you put back in can start dissolving it. This page explains why, using the National Plasterers Council's technical bulletins, and gives you a simple testing log.
What you just paid for
Pool Resurfacing Guide puts pool replastering cost at about $4,000 to $10,000 for white plaster, $6,000 to $12,000 for quartz aggregate and $8,000 to $15,000 for pebble. All three are cement-based. The National Plasterers Council (NPC) describes the same family: white cement, sands or other aggregates such as coloured quartz, pebble or glass bead, water and pigments.
Why unbalanced water eats cement finishes
When white cement hydrates it forms calcium hydroxide, which NPC says makes up roughly 24 to 27 percent of fully hydrated white cement and is the most soluble compound in it. Water with low calcium hardness, low pH or low carbonate alkalinity is what NPC calls "aggressive": it dissolves that compound first, leaving small etched spots around aggregate, tile and fittings.
| Water condition | What NPC says can happen |
|---|---|
| Low calcium hardness | Calcium compounds dissolve; discoloration |
| Low pH | General dissolving of materials |
| Low carbonate alkalinity | Slow dissolution |
| High cyanuric acid (stabilizer) | Dissolving and leaching; pigment fade |
| Direct contact with salt, granular chlorine, shock and similar products | Discoloration, pigment alteration |
Step 1: test the fill water before or as you refill
NPC Technical Bulletin 1 recommends testing tap or fill water before use, or immediately after the pool is full, with a kit that reads pH, total alkalinity and calcium hardness, plus a specialty kit for metals such as copper, iron and manganese. Low readings point to etching; high readings to scale; metals to staining.
Step 2: a testing rhythm
- One to two times a week
- pH, total alkalinity, free and total chlorine
- Once a month
- Calcium hardness, cyanuric acid (stabilizer), total dissolved solids
- Target
- A saturation index NPC puts at 0.0 to +0.3, narrower than the APSP ideal of 0.0 to +0.5
| Date | pH | Total alk. | Free Cl | Calcium (monthly) | CYA (monthly) | Action taken |
|---|---|---|---|---|---|---|
Does the finish choice change the routine?
Not the chemistry, which is the same family for all three. What changes is how visible mistakes are. NPC notes that smooth trowelled finishes show cosmetic irregularities more than exposed aggregate finishes. The site's plaster vs quartz comparison makes a related point: quartz needs less chemical balancing than plaster. If you are still choosing, pebble vs plaster works through the cost per year of service.
Sources used on this page
- National Plasterers Council: Technical Bulletin 3, Swimming Pool Interior Finishes & Chemical Etching Deterioration — calcium hydroxide, aggressive water, testing frequency, saturation index
- National Plasterers Council: Technical Bulletin 1, Testing Fill Water — fill water testing, metals