Saltwater pools are gentler on skin, eyes and swimwear than traditional chlorine systems. They are harder on the concrete around them. That trade is real and most people are not told about it when the system goes in.
What a saltwater pool actually is
It is still a chlorine pool. A salt chlorine generator electrolyses dissolved salt to produce chlorine continuously, instead of you adding it. The water carries roughly 3,000 parts per million of salt, which is around a tenth of seawater and enough to taste faintly.
So the swimming experience is softer. The deck is now sitting beside a permanent reservoir of salt water that gets splashed onto it every time somebody gets out.
What salt does to concrete
Two mechanisms, and they compound in this climate.
Salt crystallisation. Salt water wicks into porous concrete. The water evaporates and the salt crystallises inside the pore structure. Crystals occupy more volume than the dissolved salt did, so they push outward against the concrete from inside. Repeated wetting and drying, which is exactly what a pool deck does all summer, drives this continuously.
Freeze thaw, made worse. Salt lowers the freezing point, so a salted slab crosses the freezing point more often across a New England winter rather than freezing once and staying frozen. Every crossing is a fresh expansion event. Salt also holds moisture in the concrete that would otherwise have evaporated.
Bare concrete beside a saltwater pool therefore deteriorates faster than the same slab beside a conventional one, and the damage shows up first exactly where you would expect: the two feet nearest the water, the steps, and under the ladder.
What it means for the coating
Sealing matters more, not less. The entire mechanism above requires salt water to get into the concrete. A non porous coated surface stops that at the first step.
Chemical resistance to salt and chlorine both. Polyaspartic handles both comfortably at the concentrations a residential pool produces.
The termination at the coping is the critical detail. That joint is where splash lands and sits. If the coating stops short of the coping, salt water gets under the edge and works from there. It has to terminate cleanly and tight against the coping.
Rinse the deck occasionally. Not because the coating is at risk, but because the salt crystals sitting on the surface are abrasive underfoot and around furniture feet.
Metal fixtures
Worth mentioning because it comes up. Salt is harder on metal than on concrete. Handrails, ladder anchors, furniture frames and any exposed fixings around a saltwater pool corrode faster.
Not our work, but if we are on your deck and a rail anchor is rusting into the concrete around it, we will point it out. Rust expanding inside a concrete anchor pocket cracks the concrete from inside, and that is a repair that gets worse quickly.
If you are converting to salt
If you already have a bare concrete deck and you are switching to a salt system, sealing the deck is worth doing before rather than after. You are about to increase the chemical load on that slab significantly, and protecting sound concrete is much cheaper than repairing scaled concrete.
Related
Reference
Salt driven deterioration and freeze thaw scaling in concrete are described by the Pennsylvania Aggregates and Concrete Association in its technical sheet on scaling.