Concrete Curing Compounds: Types, ASTM C309 and C1315 Classes and Application

Concrete curing compounds are liquids sprayed on fresh concrete that dry to a wax, resin or acrylic membrane and hold the mix water in the surface while the cement hydrates. Which type fits a pavement, a floor that gets tile, or a precast face, and what do ASTM C309 and C1315 require?

The same products are called curing agents, membrane curing compounds, liquid membrane-forming compounds or spray-on cures, and German specifications name them Nachbehandlungsmittel. Together with evaporation retarders and surface retarders they make up the curing family, one of the 15 families of construction chemicals.

ASTM C309-25 caps the water loss of a curing compound at 0.55 kg/m² (0.113 lb/ft²) in 72 h, and ASTM C1315-25 sets 0.40 kg/m² (0.082 lb/ft²) for cure-and-seal compounds. The common spread rate of 4.9 m²/L (200 ft²/gal) per coat lays down 0.20 mm (8.0 mil) of wet film. VOC limits run from 100 g/L (0.83 lb/gal) in the South Coast air district to 350 g/L (2.92 lb/gal) under the federal EPA rule, and Europe tests water retention by CEN/TS 14754-1:2007 without a harmonised product standard.

Standards, codes and regulations are checked against their issuing bodies, product values against the named data sheet and prices against the dated source named in the sentence; see our methodology and fact-checking.

What Is a Concrete Curing Compound?#

A concrete curing compound is a liquid membrane-forming product applied to fresh concrete that limits moisture loss during early hydration; ASTM C309-25 specifies it in the US. The curing family serves 3 functions: compounds retain mix water, evaporation retarders control evaporation from plastic concrete, and surface retarders delay the set of the surface paste for exposed aggregate.

Why does fresh concrete need curing?#

Curing keeps enough water in the outer concrete for the cement to keep hydrating, and in low w/cm mixes only the outer 4 to 8 mm (0.2 to 0.3 in) depends on it, according to FHWA-HIF-18-015. That outer zone carries the wear, the scaling resistance and the bond of every later coating, so a dry surface layer weakens the part of the slab that is loaded first.

Evaporation decides how fast the surface dries. The ACI nomograph (Menzel 1954, Lerch 1957, as reported in FHWA-HIF-18-015) sets the critical rate for plastic shrinkage cracking at 1.0 kg/m²/h (0.2 lb/ft²/h), and precautions are considered above 0.5 kg/m²/h (0.1 lb/ft²/h). Accelerating admixtures, internal curing and strength-gain schedules are covered on concreteadditives.net. Air temperature, humidity, wind and concrete temperature set the rate, and the rate for a pour is estimated with the concrete evaporation rate calculator.

How Do Curing Compounds Retain Water in Concrete?#

Curing compounds work by film formation: the water or solvent carrier evaporates and leaves a continuous wax, resin or polymer membrane whose low vapor permeability keeps mix water in the concrete. The membrane does not add water; it slows the loss of the water already in the mix during early hydration.

Wax, resin and acrylic membranes#

Three binder families form the membrane: paraffin wax emulsions, hydrocarbon resins and acrylic polymers, each carried in water or solvent. Wax films are dense and stay on the slab until they are removed, resin films break down over time, and acrylic films remain as a sealing layer.

How much binder does a compound need? Agency guidance in FHWA-RD-02-099 puts the total solids at about 12 to 15 % to meet ASTM C309 and about 25 % to meet ASTM C1315, which is why cure-and-seal products carry more solids than dissipating compounds. Water-based compounds use the same binders as emulsions or dispersions, so "water-based" names a carrier, not a class, and acrylic binder chemistry is covered under acrylic polymers.

PAMS resin in curing compounds#

Poly(alpha-methylstyrene), PAMS (CAS 25014-31-7, (C9H10)n), is a hydrocarbon resin binder used in Class B curing compounds. Wisconsin specifies a PAMS Type 2 Class B compound for its pavements, as summarized by Kevern (Iowa State University, 2023). In a 2016 study by Hajibabaee, Moradllo and Ley, reported by FHWA, solvent-borne PAMS retained water better than water-based wax and resin compounds.

White pigment and solar heat gain#

White (Type 2) compounds are pigmented with titanium dioxide to reflect sunlight; ASTM C309-25 requires a daylight reflectance of at least 60 %. The reflective film limits solar heat gain on pavements and decks in sun. Clear Type 1-D compounds instead carry a fugitive dye that shows where the compound has been applied and fades after the cure.

Curing and Finishing Products for Fresh Concrete in 3 Groups#

The curing family has 5 product pages in 3 groups: 2 membrane-forming curing compounds, 2 finishing and surface aids, and 1 page on curing without a compound. The table below compares the 3 groups by their pages, mechanism and the moment they are used.

1. Membrane-forming curing compounds (2)#

Membrane-forming curing compounds are sprayed liquids that leave a film on fresh concrete to retain mix water; this group has 2 pages: dissipating resin and wax compounds, and cure-and-seal compounds.

Dissipating resin and wax compounds#

Dissipating compounds are curing films that break down or come off after the cure. ASTM C309-25 Class B resin films break down under UV, weathering and traffic. Wax films do not dissipate and are removed before coatings, tile or striping.

Cure-and-seal compounds#

Cure-and-seal compounds are higher-solids acrylic copolymers that cure the slab and then stay as a sealing and dustproofing layer, specified by ASTM C1315-25. The federal 700 g/L (5.84 lb/gal) VOC category requires compliance with ASTM C1315-95.

2. Finishing and surface aids (2)#

Finishing and surface aids act on concrete while it is still plastic or before it sets; this group has 2 pages: evaporation retarders and finishing aids, and surface retarders for exposed aggregate.

Evaporation retarders and finishing aids#

Evaporation retarders are fatty-alcohol solutions or emulsions that form a monomolecular film on the bleed water of plastic concrete, commonly diluted 1:9 with water. They are not curing compounds, ACI PRC-305-20 names them as a hot-weather measure, and they never go on hardened concrete.

Surface retarders for exposed aggregate#

Surface retarders delay the set of the surface paste with lignosulfonates, hydroxycarboxylic acids or phosphates, so the paste is washed off to a graded depth. No ASTM product standard covers them; 40 CFR 59.401 defines their federal VOC category.

3. Curing without a compound (1)#

Curing without a compound keeps the surface wet or covered instead of sealing it with a film; this group has 1 page, which compares water, sheet and blanket curing with membranes.

Water, sheet and blanket curing#

Water curing covers ponding, sprinkling, fogging and wet burlap, while covers include plastic sheet to ASTM C171-20, insulated blankets and forms left in place. Precast plants add steam curing. Each method replaces a compound where the schedule and the next finish allow.

ASTM C309 and C1315 Classes: Types, Solids and Water-Loss Limits#

ASTM C309-25 classifies curing compounds by color (Type 1, 1-D, 2) and by vehicle solids (Class A, B) and caps water loss at 0.55 kg/m² (0.113 lb/ft²) in 72 h. ASTM C1315-25 sets a stricter 0.40 kg/m² (0.082 lb/ft²) for cure-and-seal compounds. The table below sets the US classes beside the European, UK and German documents.

ASTM C309 Types 1, 1-D and 2#

Type 1 is clear or translucent without dye, Type 1-D carries a fugitive dye, and Type 2 is white with at least 60 % daylight reflectance. Every type must be dry to touch within 4 h at 23 °C (73 °F) and 50 % relative humidity. ASTM C309-25 is the active edition (ASTM store, updated 2025-11-13), and C309-19 is historical. Note 1 of C309-25 sends products with special properties to ASTM C1315.

Class A and Class B vehicle solids#

Class A places no restriction on the vehicle solids, so wax-based compounds fall in it; Class B requires that all vehicle solids are resin. The class matters on highway work: Wisconsin calls for a PAMS Type 2 Class B compound, and the South Coast air district reserves its 350 g/L (2.92 lb/gal) roadway category for Class B compounds.

ASTM C1315 types and yellowing classes#

ASTM C1315-25 covers curing and sealing compounds with special properties, in Type I clear and Type II white, and in yellowing Classes A (non-yellowing), B (moderately yellowing) and C (unrestricted). The special properties include alkali and acid resistance, adhesion promotion and UV resistance. ASTM C1315-25 is active (2025-10-08). Yellowing classes belong to C1315 only; a C309 class says nothing about yellowing.

How water retention is tested#

ASTM C156-25 measures water lost through the membrane from mortar specimens held at 38 °C (100 °F) and 32 % RH for 72 h, coated at 4.9 m²/L (200 ft²/gal). The cabinet conditions correspond to an evaporation rate of 0.65 to 1.1 kg/m²/h, according to FHWA-RD-02-099, a range that spans the 1.0 kg/m²/h (0.2 lb/ft²/h) critical rate for plastic shrinkage.

State listings rely on the AASHTO Product Evaluation and Audit Solutions program (PEAS, the former NTPEP). PEAS tests water retention at 24 h and 72 h, dry time, reflectance, settling, solids and an FTIR fingerprint, and a listed product is resubmitted every 3 years.

Wax, Resin and Acrylic Curing Compounds Compared#

Wax, resin and acrylic curing compounds differ in what happens after the cure: wax films stay until removed, resin films break down under sunlight and traffic, and acrylic cure-and-seal films stay as a sealing layer. The table below compares the 3 binders with silicate solutions, which some suppliers market as cures.

Verdict: resin compounds suit slabs that get a later finish, acrylic cure-and-seal suits exposed slabs that stay bare, and wax suits work where the film can stay or be removed.

Dissipating or permanent film: what follows the cure#

The next layer decides the compound: a slab that gets a coating, tile or striping needs a film that dissipates or is removed, while an exposed slab can keep a cure-and-seal film.

Removal before a finish uses 13.8 MPa (2,000 psi) water blasting, scrubbing, chemical removal or light abrasion, and a water-drop test confirms that the surface absorbs water again. A penetrating sealer needs the same open surface, and penetrating and film-forming options are compared under concrete sealers.

Acrylic cure-and-seal compounds take a different federal VOC category from curing compounds. Under 40 CFR 59.401 a product must meet ASTM C1315-95 to use the 700 g/L (5.84 lb/gal) curing and sealing limit; otherwise the 350 g/L (2.92 lb/gal) curing compound limit applies.

Curing compound or silicate densifier?#

A silicate densifier is not a curing compound: ASTM C309-25 Note 2 excludes silicate salt solutions because they react chemically instead of forming a membrane. A "sodium silicate curing compound" therefore meets no C309 type or class, whatever its label says.

Densifiers belong after the cure, when the slab is hardened and a floor needs hardening or dustproofing. The curing film is dissipated or removed first so the silicate can enter the pores, and lithium, sodium and potassium types are compared under concrete densifiers.

Where Are Curing Compounds Used? Pavements, Decks, Floors and Precast#

Curing compounds are used wherever fresh concrete is exposed to drying: pavements and bridge decks, parking decks, floor slabs, and vertical or precast faces after the forms come off. What is applied next to the surface sets the type. The table below compares the 4 uses by drying risk, compound type and key rule.

Pavements and bridge decks#

Pavements and bridge decks take white Type 2 Class B compounds from a state DOT qualified products list (QPL), applied no later than 30 min after finishing in Iowa and Missouri practice. The white film limits solar heat gain over large exposed areas. FHWA-RD-02-099 gives 3.5 to 5 m²/L (143 to 204 ft²/gal) in two coats for pavements.

Parking decks#

Parking decks that later receive a traffic coating need a curing film that dissipates or is removed, because residue under a deck coating is a debonding risk. A water-drop test on the deck confirms the film is gone before the coating goes on.

Floor slabs that receive coatings or tile#

Floor slabs that will get resin coatings, tile or resilient flooring are cured with a removable or dissipating film, or with a product the flooring maker accepts. Debonding of coatings, tile or striping over residual compound, especially wax, is a listed failure mode, so the flooring system sets the cure.

Vertical faces, precast and tilt-up panels#

Vertical faces are sprayed right after stripping, and tilt-up casting slabs use bond breakers, a different category under the federal VOC rule. Clear Type 1 or 1-D compounds leave no white film on formed faces. EPA AIM sets 600 g/L (5.01 lb/gal) for bond breakers.

Which Standards and Rules Govern Curing Compounds in the US and Europe?#

Curing compounds are specified by ASTM C309-25 and C1315-25 in the US, with AASHTO M 148 and state DOT lists for highways. Europe has no harmonised product standard and tests water retention by CEN/TS 14754-1:2007 or BS 7542:1992.

US specifications: ASTM, AASHTO and state DOT lists#

AASHTO M 148 uses the same Type 1, 1D and 2 and Class A and B system as ASTM C309 and tests water retention by AASHTO T 155. FHWA-HRT-05-038 records M 148-97 as identical to C309-94 with SI units preferred, and clause-by-clause requirements are set out under ASTM C309 and C1315.

State specifications go further than C309. Wisconsin requires less than 0.15 kg/m² (0.031 lb/ft²) water loss in 24 h and 0.40 kg/m² (0.082 lb/ft²) in 72 h, reflectance above 65 % and solids above 42 %; Iowa accepts at most 0.20 kg/m² (0.041 lb/ft²) in 24 h or 0.40 kg/m² (0.082 lb/ft²) in 72 h (Kevern, ISU 2023).

Europe and Germany: test methods instead of a product standard#

No harmonised EN product standard exists for curing compounds, so European specifications cite a test method, CEN/TS 14754-1:2007 or BS 7542:1992, and the execution rules for curing. CEN/TS 14754-1:2007 measures water retention efficiency (published by BSI on 2007-08-31), and BS 7542:1992 was confirmed in 2012.

Execution rules set when and how long concrete is cured. EN 13670:2009 clause 8.5 (Curing and protection, CEN/TC 104, approved 2009-09-17) governs execution, and a revision, prEN 13670, was at enquiry in 2025-12. In Germany DIN 1045-3:2023-08 replaced DIN EN 13670 with DIN 1045-3 and sets curing classes (Nachbehandlungsklassen, NBKL); German road work names compound types VM and BM in TL NBM-StB 09 (FGSV). Spain's Código Estructural art. 52.5 accepts plastic coverings or filmogenous agents in place of moist curing where they are equally effective.

Curing guides from ACI#

ACI PRC-308-26, Curing of Concrete, Guide (2026, 44 pp.) is the current ACI curing guide; the 2016 guide (308R-16) is historical. It covers curing methods, materials and monitoring, with membrane-forming compounds among the methods. ACI PRC-305-20 adds hot-weather measures such as evaporation retarders, fog sprays and covers.

How Is a Curing Compound Applied? Timing, Spray and Coverage#

A curing compound is sprayed as soon as the surface water sheen disappears, in two passes at right angles, at the specified spread rate. The ASTM C309 test rate and common specified rate is 4.9 m²/L (200 ft²/gal) per coat.

When to apply: after the water sheen disappears#

Apply the compound once the bleed-water sheen has gone and the surface will not be marred, and on vertical faces right after the forms are stripped. Iowa and Missouri DOT practice (as summarized by Kevern, ISU 2023) requires application no later than 30 min after finishing. Late application is the cause of plastic shrinkage cracks in the failure list, because the surface dries before the film forms.

Spray pressure and passes#

Spray equipment works at 0.17 to 0.69 MPa (25 to 100 psi), in two passes at right angles, with pigmented products agitated before and during spraying (FHWA-HIF-18-015). Textured or tined surfaces need a heavier rate.

Coverage per coat and wet film thickness#

The common specified rate of 4.9 m²/L (200 ft²/gal) per coat lays down 0.20 mm (8.0 mil) of wet film, before the carrier evaporates. Every rate below is per coat on a wet film basis; the dry film is thinner by the share of carrier that evaporates. The table below compares the rates set by ASTM, FHWA and 2 state DOTs.

Under-application gives a dusting, weak surface, because a thinner film than the 0.20 mm (8.0 mil) assumed by the water-loss test lets more water escape.

Inspection and common failures#

Inspectors check the field rate by California Test 535, look for even color from the fugitive dye or white pigment, and can detect about 1 m²/L of rate variation with a portable reflectometer. A DOT job adds the QPL listing as proof of the lab results.

The 5 failure modes of curing compounds are listed below.

• Plastic shrinkage cracks from late application.
• Dusting and a weak surface from under-application.
• Mottling from uneven spray or dripping nozzles.
• Debonding of later coatings, tile or striping over residual compound, especially wax.
• Yellowing from over-application or oxidation.

Before a coating, the water-drop test shows whether residue still seals the surface, and preparation before a coating is graded under concrete surface profile.

VOC Limits and Safety for Curing Compounds#

VOC limits for curing compounds range from 100 g/L (0.83 lb/gal) in the South Coast air district to 350 g/L (2.92 lb/gal) under the federal EPA rule. Cure-and-seal compounds that meet ASTM C1315 may reach 700 g/L (5.84 lb/gal) federally.

VOC limits by jurisdiction#

The South Coast AQMD caps curing compounds at 100 g/L (0.83 lb/gal) under Rule 1113 (amended 2016-02-05) and allows 350 g/L (2.92 lb/gal) only for Class B roadway and bridge compounds that lose less than 0.15 kg/m² in 24 h. The roadway category excludes curbs, gutters, sidewalks, islands and driveways, and every category is listed under VOC limits for construction chemicals.

The table below compares the curing family's VOC limits in 4 jurisdictions, in g/L (lb/gal).

EU Directive 2004/42/EC names no curing-compound subcategory. Proposed Amended Rule 1113 was in working-group stage on 2026-10-22, with no adoption, so a South Coast specification is re-checked against the current rule text before bidding.

Solvent, pigment and residue safety#

Hazards are product-specific: solvent-borne compounds carry hydrocarbon-solvent flammability and aspiration hazards, and water-borne products carry their own classification on the product SDS. Curing compounds contain no isocyanates or epoxies, so the diisocyanate training duty of REACH Annex XVII entry 74 does not apply.

Titanium dioxide (CAS 13463-67-7), the white pigment of Type 2 compounds, has no harmonised CLP classification in force after the Court of Justice ruling of 2025-08-01; notified classifications vary, so see the product SDS. California's Proposition 65 lists "titanium dioxide (airborne, unbound particles of respirable size)" as a carcinogen since 2011-09-02.

Complete List of Curing and Finishing Products: All 5 Product Pages#

The complete list below gives all 5 curing and finishing product pages with their chemistry, US and European documents, typical use and federal VOC category. Each row links the page that owns the class.

No dated installed or material cost range for the curing class is published in the sources this page uses, because curing is a line item of concrete placement labor. A quote is therefore per pour, and its price basis is the area, the spread rate per coat, the number of coats, the VOC category of the region and any film removal before the next finish.

Which Curing Compound Is Best for a Project?#

No curing compound is best for every pour: the right one meets ASTM C309-25, C1315-25 or the DOT list for the job, fits the local VOC limit and suits the next layer. A brand question is answered by the data sheet: it should state the C309 Type and Class or the C1315 Type and Class, the VOC content in g/L and the category it claims.

The 3 checks for a data sheet are listed below.

• The standard and class, such as ASTM C309-25 Type 2 Class B or ASTM C1315-25 Type I Class A.
• The VOC content against the limit of the job's jurisdiction, such as 100 g/L (0.83 lb/gal) in the South Coast air district.
• The film after the cure, and whether the flooring or coating maker accepts it.

Is a curing compound necessary on every slab?#

No: a compound is one curing method; water curing, sheets or blankets do the same job where the schedule and the next finish allow. Ponding, fogging, wet burlap and plastic sheet to ASTM C171-20 leave no film, which suits slabs that get tile or coatings soon after the cure.

Can flooring or coatings go over a curing compound?#

Only after the film has dissipated or been removed, unless the flooring or coating maker accepts the compound. Wax films do not dissipate, and a water-drop test shows whether the surface is open again.

Does a curing compound replace water curing?#

It can, where the specification accepts membrane curing as equivalent. Spain's Código Estructural art. 52.5 allows filmogenous agents in place of moist curing if they are equally effective, and ACI PRC-308-26 treats membrane-forming compounds as one of its curing methods.