Interior work runs all twelve months here. Exterior does not, and the reason is not what most people assume.
It is not the air temperature. Polyaspartic cures down to about −10°F, which covers any day we would be working. The constraint is water: what the slab is holding, and what the sky is going to do for the next twenty four hours.
The three conditions
A dry slab. Concrete that has taken rain in the last day or two is still holding it, even when the surface looks and feels dry. Coating over that traps the moisture and you get blistering and poor adhesion. On a shaded north facing patio, drying takes longer than people expect.
A dry forecast. The topcoat needs to be past the point where rain will mark it. That is a matter of hours rather than days, but it means we are watching the radar, not just the morning.
A surface above the dew point. If the slab is colder than the dew point of the air, condensation forms on it faster than we can coat. This is what kills a lot of otherwise promising spring and autumn mornings.
The season, realistically
March to November is what we book, and the shoulders are weather dependent rather than guaranteed.
April and May are the busiest and the most likely to move, because spring here is wet.
June to September is the reliable window. If you want certainty, this is it.
October and early November are often excellent. Cool, dry, stable, and the schedule is opening up.
December to February we do not book exterior work. We will happily do your garage.
Why we move dates rather than push through
We would rather reschedule than coat a marginal slab, and it is worth explaining why that is not us being precious.
An exterior coating that was applied over damp concrete does not fail immediately. It looks correct for a season. Then blisters appear where the trapped moisture pushed up, usually in the second spring, and the repair is grinding the whole thing off.
So a date moved by four days costs you an inconvenience. A date pushed through costs the whole floor.
How to book so it actually happens
Book in late winter for a spring slot. By June everyone in the valley has remembered their patio in the same fortnight.
Be flexible by a few days. Exterior work benefits enormously from a two or three day window rather than a fixed date.
Clear it early. Furniture, planters and the grill off the slab a couple of days before, which also lets the concrete dry.
Tell us about shade and drainage. A patio under trees or at the bottom of a slope dries differently, and that changes which day we pick.
What we do if the weather turns mid job
Grinding can continue in most conditions. Once we are coating, we are committed to finishing that section, so we do not start a coat we cannot complete dry. If the forecast breaks between prep and coating, we prep and come back.
Related
- Patios and walkways
- Pool decks, which run on the same calendar
- Winter work indoors, which has no such constraint
Reference
Moisture in the substrate is an adhesion issue rather than a scheduling preference, and it is measured to the same standards used indoors, including ASTM F1869.