Smithtown Concrete by the Numbers: Climate, Moisture and Cure Windows

Last reviewed 2026-07-25. Journalists, researchers, and community groups are welcome to cite any figure on this page with attribution and a link.

Nearly every claim a floor coating contractor makes on Long Island rests on things that are published and checkable: how the weather behaves at the nearest long-record station, what the ground under these houses is made of, and what the ASTM test methods do and do not say. This page collects those figures with a source for each one. Nothing here is estimated, interpolated or recalled from memory, and where a figure comes from a different place or a different period than a reader might assume, the text says so rather than smoothing it over.

One geography note first, because it changes how you should read the temperature tables. The nearest long-record weather station to Smithtown is listed as ISLIP, NY in the National Centers for Environmental Information tables, station number 04781, or USW00004781 in the normals files. That is Long Island MacArthur Airport, roughly ten miles south of Smithtown on the outwash plain rather than up on the moraine. Searching those tables for Smithtown returns nothing. Two different periods appear below: the daily maximum and minimum normals cover 1991 through 2020, the day-count and snowfall tables cover 1963 through 2023, and the relative humidity table covers 1974 through 2018.

How cold does it get, and when can a coating actually cure?

The number that matters for a floor coating is not the average temperature, it is how often the slab crosses freezing and how long it stays below cure temperature. At Islip the count is 101 days a year with a minimum at or below 32 degrees, over a period of record running October 1963 through December 2023. What makes those days awkward for coating work is visible in the two normals columns beside them. In December, January and February the normal daily maximum sits above freezing while the normal daily minimum sits below it, and March sits exactly on the line with a 32.0 degree normal minimum against a 47.7 degree normal maximum.

Standard epoxy formulations want the substrate at roughly 55 degrees and rising. Read down the normal daily maximum column and only May through October clear that comfortably on the air temperature alone, and a concrete slab in an unheated garage lags the air by days because of its thermal mass. That is the practical reason polyurea and polyaspartic chemistry dominates winter installs on Long Island: it cures well into freezing conditions where epoxy stalls. It is also why a November or February epoxy job in an unheated Smithtown garage should come with a plan for heating the space, and why any quote that ignores the question is quoting a schedule it cannot hold.

Normals are 1991-2020. Freezing-day counts cover October 1963 through December 2023. Station ISLIP, NY (04781 / USW00004781), Long Island MacArthur Airport.

How humid is the air a coating has to cure in?

Relative humidity gets ignored in most floor coating conversations and it should not be. Two things depend on it. First, dew point: if the slab surface temperature falls within a few degrees of the dew point, moisture condenses on the concrete, and a primer applied onto that film is bonding to water rather than to the floor. Second, cure chemistry itself - amine-cured epoxies can react with atmospheric moisture and carbon dioxide at the surface during cure, producing the greasy, hazy film installers call amine blush, and high humidity makes it more likely.

At Islip, average morning relative humidity runs 76 percent annually and afternoon runs 58 percent, over a record covering 1974 through 2018. The morning figure never drops below 70 percent in any month and peaks at 82 percent in September and 81 percent in October. That is the practical case for coating in the afternoon rather than at first light on a Long Island job, and for measuring slab temperature and dew point on site rather than assuming. April and March are the driest mornings on the table, which is part of why spring is a good coating window here even though the temperature numbers alone would point at summer.

Station ISLIP, NY (04781), period of record 1974-2018.

How much water is moving through the ground here?

Snowfall at Islip averages 28.8 inches a year, with January and February carrying 9.3 inches each and March 5.0. That is well under what upstate New York sees and it is not the interesting number. The interesting number is frequency: 116 days a year with at least a hundredth of an inch of precipitation, spread remarkably evenly, with no month below 8 days and none above 11. A slab that gets wet roughly every third day, year round, never gets a long enough dry stretch to shed internal moisture the way a slab in a dry climate does.

Underneath, USGS mapping of the Huntington-Smithtown area describes deposits that are largely crudely stratified sand and gravel with kames and interspersed kettles, more than 300 feet thick beneath the terminal moraines and buried valleys, with a south-sloping outwash plain of stratified sand and gravel. The dominant mapped soils, the Haven and Riverhead series, are both classified well drained by USDA, with saturated hydraulic conductivity described as very high in the substratum. Well drained is not the same as dry - it means water arrives quickly and keeps moving, which is exactly the condition that keeps a supply of moisture available at the underside of a slab.

Station ISLIP, NY (04781), period of record September 1963 through December 2023.

What the Town of Smithtown code says about garages and paving

Two provisions in the Smithtown code come up often enough on garage jobs to be worth quoting. Chapter 322 Section 12F states that private garage floor area within principal buildings shall not exceed 750 square feet. That is a ceiling on the attached garage itself, and it is the number that ends a fair share of conversations about enlarging a bay before a coating goes in. Section 322-12I(8) then limits paving: for residential uses, other than garden apartments and townhouse dwellings, not more than 25 percent of the required front, side or rear yards shall be paved surfaces, with the front-yard maximum increased as necessary to accommodate a twelve-foot swath for a circular driveway, one side yard increased as necessary for a driveway not exceeding 10 feet in width serving a detached garage or increased to 50 percent for a side-entry garage, and paved surfaces set back at least one foot from side and rear lot lines.

On the building side, Chapter 112 Section 10A states that no person, firm or corporation shall commence the erection, construction, enlargement, alteration, removal, improvement, demolition, conversion or change in the nature of the occupancy or use of any building, structure or site without first obtaining a separate building permit, and Section 112-17A provides that no building or structure shall be maintained, used or occupied in whole or in part until a certificate of occupancy has been issued by the Chief Building Inspector. Applying a coating over an existing slab is maintenance rather than construction, but the Building Department is the only office that can answer for a specific property, and any project that adds slab or changes the use of the space needs that call made first.

• 322-12F: private garage floor area within principal buildings capped at 750 square feet.
• 322-12I(8): residential paved surfaces limited to 25 percent of required yards, with stated driveway and side-entry garage exceptions.
• 112-10A: separate building permit required before erection, construction, enlargement or alteration.
• 112-17A: no building or structure occupied until a certificate of occupancy is issued.
• Commack and Hauppauge straddle town lines - the Huntington and Islip codes govern their respective portions.

What these numbers do not tell you

Four limits worth stating plainly. First, the Islip station sits on the south shore outwash plain, roughly ten miles from Smithtown and considerably further from the north shore villages. Kings Park records an elevation around 174 feet while the airport sits near sea level, and the moraine ground under St. James and Head of the Harbor is a different substrate from the outwash under the station. The record describes the regional pattern reliably and any individual property poorly. Second, these are air temperatures at standard instrument height. A concrete slab is a thermal mass that lags air temperature by days, runs warmer than air in direct sun and colder on a clear night, and it is the slab temperature that governs cure.

Third, the 101-day figure counts days with a minimum at or below 32 degrees. It is not a count of freeze-thaw cycles, and the comparative climatic data tables do not publish a cycle count for any station. Fourth, and most important for anyone comparing quotes: ASTM F1869 and ASTM F2170 are test methods, not acceptance criteria. F1869 tells you how to run a calcium chloride test and report pounds of moisture per 1,000 square feet in 24 hours. F2170 tells you how to place in-situ probes and report relative humidity inside the slab. Neither publishes a pass limit. The threshold your slab has to meet is set by the manufacturer of the specific primer or coating going onto it, and anyone citing an ASTM limit without naming a product is citing something that does not exist.

Sources & Methodology

Every figure above was taken from the primary sources below (accessed 2026-07-25). Where a number is derived (arithmetic on published figures) or covers a broader period or area, the text says so.

1. NOAA NCEI Comparative Climatic Data - Days With Minimum Temperature 32F or Below — Monthly and annual counts of days with a minimum temperature of 32 degrees or below for ISLIP, NY, station 04781, period of record October 1963 through December 2023. Source of the 101-day annual figure and the freezing-days column.
2. NOAA NCEI Comparative Climatic Data - Normal Daily Maximum Temperature — Normal daily maximum temperature by month, 1991 to 2020, for ISLIP under station USW00004781. Source of the 47.7 degree March maximum and the maximum column in the temperature table.
3. NOAA NCEI Comparative Climatic Data - Normal Daily Minimum Temperature — Normal daily minimum temperature by month, 1991 to 2020, for ISLIP under station USW00004781. Source of the 24.6 degree January minimum and the 32.0 degree March minimum.
4. NOAA NCEI Comparative Climatic Data - Average Relative Humidity — Average morning and afternoon relative humidity by month for ISLIP, NY, period of record 1974 to 2018. Source of the 76 percent annual morning figure, the 58 percent afternoon figure and every value in the humidity table.
5. NOAA NCEI Comparative Climatic Data - Mean Snowfall — Mean monthly and annual snowfall in inches for ISLIP, NY, September 1963 through December 2023. Source of the 28.8-inch annual average and every monthly snowfall value shown.
6. NOAA NCEI Comparative Climatic Data - Days With Precipitation 0.01 Inch or More — Monthly and annual counts of days with at least 0.01 inch of precipitation for ISLIP, NY. Source of the 116-day annual figure and the precipitation column.
7. US Census Bureau QuickFacts - Smithtown town, Suffolk County, New York — Population 116,847 as of the July 1 2025 estimate and 116,296 at the April 1 2020 census, 88.7 percent owner-occupied housing units and a $669,900 median owner-occupied home value for 2020-2024, and 53.75 square miles of land area.
8. Town of Smithtown Code - 322-12 Placement of accessory buildings, structures and uses — Source of the 750 square foot private garage floor area cap in subsection F and the 25 percent paved yard limit and its driveway exceptions in subsection I(8).
9. Town of Smithtown Code - Chapter 112, Building Construction — Source of 112-10A requiring a separate building permit before erection, construction, enlargement or alteration, and 112-17A prohibiting occupancy before a certificate of occupancy is issued.
10. USGS Water-Supply Paper 1669-D - Hydrogeology of the Huntington-Smithtown Area, Suffolk County, New York — E. R. Lubke, 1964. Source of the description of the Ronkonkoma terminal moraine, the Harbor Hill end moraine, the intermorainal belt, the south-sloping outwash plain of stratified sand and gravel, and deposits more than 300 feet thick beneath the moraines and buried valleys.
11. USDA Official Series Description - HAVEN series — Well drained classification, loamy material over sandy and gravelly outwash, and saturated hydraulic conductivity described as moderately high or high in the solum and very high in the substratum. Type location Suffolk County, New York.
12. ASTM F1869 - Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride — Test method reporting pounds of moisture per 1,000 square feet over 24 hours on bare concrete. Confirms the standard defines a method and applies only to uncoated slabs.
13. ASTM F2170 - Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes — Test method for quantitative determination of percent relative humidity inside a concrete slab. Confirms the standard covers the determination itself and does not publish an acceptance threshold.