Standards
ASTM C309 Explained
ASTM C309 is the spec for liquid membrane-forming curing compounds. Type 1 is clear, Type 1-D is clear with a fugitive dye, and Type 2 is white. Class A puts no limit on the solids, Class B must be all resin. The film must hold water loss to 0.55 kg/m² in 72 hours. The current revision is C309-25.
ASTM C309 is a short performance spec. It tells you what a sprayed curing membrane has to do, not what it has to be made of. This page follows the C309-25 revision. Where the free ASTM abstract stops, the numbers come from manufacturer and DOT documents that restate the standard, and each is linked.
What does ASTM C309 cover?
C309 covers liquid compounds that form a membrane on fresh concrete and slow the loss of water while it hardens. The ASTM C309-25 abstract says white pigmented compounds also reduce the temperature rise in concrete exposed to the sun.
The same abstract says you can use these compounds right after finishing, after stripping forms, or after an initial period of moist curing. It is a performance spec: composition is left to the maker, within local, state and federal air rules. ASTM lists the current revision as C309-25, last updated November 13, 2025.
What are the ASTM C309 types and classes?
C309 sorts compounds two ways: by color (the type) and by what the solids are made of (the class). A product label such as “Type 1-D, Class B” tells you both. The Dayton Superior Guide to Curing gives the class definitions below.
| Designation | What it means | Typical use |
|---|---|---|
| Type 1 | Clear or translucent, no dye | Slabs where you do not want a visible tint |
| Type 1-D | Clear or translucent with a fugitive dye | Interior and exterior slabs where you need to see spray coverage |
| Type 2 | White pigmented | Paving, bridge decks and hot, sunny pours |
| Class A | No restriction on the vehicle solids; typically wax based | DOT paving and slabs that will stay bare |
| Class B | Vehicle solids must be all resin | Resin products, including dissipating cures and acrylics |
Color is covered in more detail in clear, dyed and white curing compound. For how wax, resin and acrylic products compare, see types of concrete curing compounds.
What test limits does a C309 compound have to meet?
A C309 compound has to pass four checks. The water loss limit is the one that matters most, and it is measured with ASTM C156 at a set application rate. A product that only passes at a heavier rate than your crew sprays will not cure your slab the same way.
| Requirement | Limit | Source |
|---|---|---|
| Water loss (ASTM C156) | Not more than 0.55 kg/m² in 72 hours | Dayton Superior summary |
| Test application rate | 200 ft²/gal (4.9 m²/L) | Dayton Superior summary |
| Daylight reflectance, Type 2 only | Not less than 60% (against a magnesium oxide reference) | ASTM abstract and Dayton |
| Drying time | Dry to touch in not more than 4 hours | ASTM abstract |
That 200 ft²/gal test rate is also the number many product data sheets give for field coverage. Plug your slab area into the curing compound coverage calculator at that rate before you order, and do not let the crew stretch it thinner.
What does ASTM C309 not cover?
C309 does not address every property a project might need. The standard’s own Note 1 says compounds with special properties are described in ASTM C1315, and Note 2 rules out silicate solutions. Things C309 does not require:
- Better water retention than 0.55 kg/m² at 72 hours
- A minimum solids content
- Resistance to UV light
- Acid and alkali resistance
- Non-interference with flooring adhesives
- Any set time for the film to break down or dissipate
- Chemically reactive silicate products, which the note says do not meet its intent
Dissipation is the gap that bites flooring jobs. Dayton’s guide states that wax curing membranes do not dissipate and stay until removed. If flooring goes on later, read about dissipating curing compound before you approve a Class A wax product.
How do DOTs tighten ASTM C309?
Many state DOTs start from C309 and add stricter numbers. Iowa DOT Section 4105 requires compliance with C309, then limits white compounds to 0.20 kg/m² in 24 hours or 0.40 kg/m² in 72 hours at 200 ft²/gal. That is tighter than the 0.55 kg/m² base limit.
The Iowa spec also requires no tracking after 12 hours, sets clear compounds as Type 1-D, Class A, and bars carryover lots that have frozen. If you bid DOT work, read the state section, because a product that meets C309 may still fail the state list.
What should a C309 spec line or submittal say?
A good spec line names the standard, the year, the type and the class. A good submittal shows the same four things on the product data sheet. The W.R. Meadows CC-309-1WS page is a typical example: it lists ASTM C309 Type 1, Classes A and B, with a 1-D version available.
Check each submittal for:
- The standard and year, for example C309-25 or the year your spec names
- The type (1, 1-D or 2) matching the spec
- The class (A or B) matching the spec, or both
- The application rate the product was tested at
- Any state DOT approval if the job needs it
- A note on whether the film dissipates, if flooring, coatings or sealers follow
If your C309 submittal was rejected
Many rejections come down to a mismatch between the data sheet and the spec line, not a bad product. Read the rejection against the four items above before you swap products.
- Wrong class. The spec asked for Class B and the product is Class A only, usually a wax. Swap to an all resin product.
- Wrong type. The spec asked for Type 2 white on paving and you sent a clear Type 1.
- Silicate substitute. A silicate densifier was offered as the cure. Note 2 of C309 says these do not meet its intent.
- No year or no test data. Ask the supplier for a data sheet that states the standard and year.
- DOT list. The product meets C309 but is not on the state’s approved list.
Frequently asked questions
What is the current revision of ASTM C309?
C309-25 is the active revision, last updated on November 13, 2025, according to the ASTM store. Earlier revisions include C309-19, C309-11 and C309-07. Specs that cite an older year still point to the same types and classes, but check the year your project spec names.
What is the difference between Type 1 and Type 1-D?
Both are clear or translucent. Type 1-D adds a fugitive dye so the crew can see where they have sprayed. The dye is meant to fade, so it does not leave the slab colored the way a Type 2 white compound does.
What does Class B mean in ASTM C309?
Class B means the solids in the vehicle must be all resin. Class A puts no restriction on the solids, and Class A products are typically wax based, according to Dayton Superior's curing guide. Many resin products are listed as meeting both Class A and Class B.
Does sodium silicate meet ASTM C309?
No. A note in the standard says silicate solutions react chemically with the concrete instead of forming a membrane, so they do not meet the intent of C309. Do not accept a silicate densifier as a substitute for a C309 cure.
Is ASTM C309 the same as ASTM C1315?
No. C309 covers basic water retention, color, reflectance and drying time. C1315 covers compounds with special properties such as better water retention, a minimum solids content, UV resistance and non-interference with adhesives.