Expansion Joints in Concrete: Isolation, Control and Construction Joints, Fillers and Sealants

An expansion joint in concrete is a full-depth gap with a compressible preformed filler, sealed at the top where water or debris must stay out, that lets a slab move against walls, columns or another slab without cracking. In UK and international usage the same detail is called a movement joint, while ACI names it an isolation joint. The joint has two working parts: the filler board that holds the gap open over the full slab depth, and the elastomeric sealant that closes only its recessed top.

ACI PRC-302.1-15 sorts floor and slab joints into three types: isolation, contraction (control) and construction joints. Preformed fillers are bought to ASTM D1751-23 or D1752-18(2023), and the sealant on top is specified by its ASTM C920-18(2024) designation in the US and by EN 15651-4 in Europe. Expansion joint fillers and sealants are one product group in this reference of construction chemicals.

This page follows a joint from its definition and mechanism through uses, properties, standards, selection, layout and sealing, yield and cure by temperature, inspection, safety and VOC rules, dated costs, alternatives and sourcing.

The summary table below lists the attributes a specifier checks first on any expansion joint.

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 an Expansion Joint in Concrete?#

ACI calls the slab expansion joint an isolation joint: a full-depth separation from walls, columns and other fixed elements, closed by a compressible filler and, where water or debris must stay out, an elastomeric sealant over a backer rod. The separation lets the slab move freely without pulling on the element it meets.

Data sheets and specifications use several names for the same detail, such as concrete expansion joint, premolded joint filler, fiber expansion joint board, expansion joint seal and, in German, Dehnfuge or Bewegungsfuge. The sealant that closes the joint belongs to the wider family of elastomeric construction sealants.

Isolation, contraction and construction joints: the three ACI joint types#

ACI PRC-302.1-15 covers three joint types in floors and slabs: isolation joints, contraction joints and construction joints. Each type differs in depth, in its purpose and in what fills it, as the table below compares.

The isolation joint is the only one of the three that runs through the full slab and takes a compressible filler board. A construction joint is named here only as the joint where one placement meets the next; its detailing belongs to the slab design.

Control joint vs expansion joint: which one does what?#

A control (contraction) joint is a partial-depth saw cut, at least a quarter of the slab depth, that decides where shrinkage cracks form, while an expansion (isolation) joint runs the full depth and lets the slab move against fixed elements. The two are different joints with different jobs, even though trade usage mixes the names.

The fill differs too. A control joint is left open, sealed with an elastomeric sealant or, in industrial floors, filled with a semi-rigid resin. An expansion joint holds a compressible board over its full depth, and only the top centimeters above the board take a sealant.

Preformed fillers, sealants and preformed seals: what closes the joint#

Three product groups close an expansion joint: preformed fillers, poured or gunned sealants, and preformed seals. The three groups are listed below with their chemistries.

• Preformed fillers: bituminous fiber, bitumen, sponge rubber, cork, recycled PVC and closed-cell polyolefin foam boards, the bituminous grades built on bitumen and polymer-modified bitumen.
• Sealants: polyurethane, silicone and polysulfide elastomers, as one-part pourable Grade P or one- and two-part non-sag grades, the polyurethanes based on polyurethane resins and prepolymers.
• Preformed seals: precompressed impregnated foam seals on reels or sticks, and extruded polychloroprene compression seals for pavements.

How Does an Expansion Joint Filler and Sealant System Work?#

The filler carries the movement and the sealant keeps water out: the compressible board separates the concrete over its full depth, and an elastomeric sealant bonded to the two joint faces seals only the recessed top. The board compresses when the slab expands and recovers when it contracts, so the gap never closes on concrete.

The sealant must stretch and compress with the joint, which works only when it bonds to two faces. A backer rod or bond-breaker tape under the sealant prevents three-sided adhesion, because a sealant also bonded to the bottom of the recess cannot deform freely and tears. Manufacturer guidance seals every moving joint at the mid-range of its movement: a joint sealed at its coldest sees only compression, and one sealed at its hottest sees only extension.

Joint filler or joint sealer: what is the difference?#

A joint filler is a preformed, compressible board placed before or during the pour to keep the joint open; a joint sealer is a field-applied elastomer that closes the top of the joint against water and debris. The two follow separate standards. Fillers are bought to ASTM D1751-23, D1752-18(2023) or D994/D994M-11(2022), which test recovery, compression and extrusion of the board. Sealants are bought to ASTM C920-18(2024), which classes cured elastomers by type, grade, movement class and use. A data sheet that cites C920 describes the sealant, never the filler under it.

Where Are Concrete Expansion Joints Used?#

Expansion joints are used wherever a slab or deck meets something that does not move with it: slabs-on-ground against walls and columns, sidewalks and plazas, pool decks, parking decks, masonry and pavements. Residential flatwork contractors seal small jobs, while plazas and parking decks go to sealant and waterproofing contractors.

The six uses are listed below with the application that governs each.

• Slabs-on-ground: isolation joints around walls, columns, footings and equipment bases.
• Sidewalks and plazas: isolation joints at buildings and curbs, with contraction joints between panels.
• Pool decks: joints at the coping and between deck panels, part of swimming pool waterproofing.
• Parking decks: joints under traffic, set out in parking structure waterproofing and kept out of the traffic coatings for parking decks.
• Masonry: movement and control joints in walls, sealed as part of masonry waterproofing.
• Pavements and bridges: highway, airfield and bridge joints under pavement standards, covered in bridges, tunnels and marine structures.

Deck joints and the deck coating interact. Sika's vehicular traffic coating guidance for its Sikalastic systems does not coat over expansion joints wider than 25 mm (1 in), so those joints stay a separate sealed or preformed detail.

Which Properties Define Expansion Joint Fillers and Sealants?#

Eight properties set what an expansion joint material can do: movement class, hardness, recovery and extrusion of the filler, adhesion, elastic recovery, modulus, weight or volume loss, and fire behavior where the joint passes a rated floor or wall. Each property has its own test, listed in the table below with the reason it matters.

Standard requirement or product value: reading a joint sealant data sheet#

ASTM C920-18(2024) requires Shore A 25 to 50 for Use T traffic sealants, while a data-sheet hardness is what one product reached. The Tremco Vulkem 45SSL data sheet declares Shore A 40 ± 5 and the designation ASTM C920 Type S, Grade P, Class 35, Use T, M, A, O, I. That value sits inside the Use T range, but it describes one self-leveling polyurethane and not the class. A specification therefore names the requirement (Use T, Class 25 or higher) and checks each product value against it, never the reverse.

Which Standards Classify Expansion Joint Materials in the US and Europe?#

US expansion joint materials are specified by three ASTM filler standards and ASTM C920 for sealants, while Europe classifies joint sealants under EN 15651, and the US and EN sealant classes do not map one-to-one. The table below sets the documents side by side with their editions, classes and requirements. The full designation rules of the US sealant system are set out under ASTM C920 elastomeric joint sealants.

Preformed expansion joint filler standards: ASTM D1751, D1752 and D994#

Three ASTM standards cover preformed expansion joint fillers, each with an AASHTO twin. The three standards are listed below.

• ASTM D1751-23 (AASHTO M 213): bituminous fiber fillers that are nonextruding and resilient; D1751-18 is the historical edition.
• ASTM D1752-18(2023) (AASHTO M 153): sponge rubber (Type I), cork (Type II), self-expanding cork (Type III) and recycled PVC (Type IV), tested for recovery, compression, extrusion, expansion, boiling in hydrochloric acid and density.
• ASTM D994/D994M-11(2022) (AASHTO M 33): bituminous preformed fillers.

The filler choice decides the sealant detail. ACI 302.1R (section 9.10) states that asphalt-impregnated fillers are not used in isolation joints that will be sealed, so a sealed joint takes a non-bituminous D1752 board or a closed-cell foam filler.

Expansion joint sealant classes: ASTM C920 next to EN 15651-4#

ASTM C920-18(2024) designates an elastomeric sealant by Type (S or M), Grade (P or NS), Class (100/50, 50, 35, 25 or 12.5) and Use (T, NT, I, M, G, A, O); C920 does not cover highway, airfield or bridge joints. Class 100/50 means +100 % and -50 % movement, and the class is proven in the ASTM C719-22 cycle. ASTM C1193-25, the guide for cold liquid-applied sealants in buildings, plazas, decks and pavements other than highways, airfields and bridges, states that such sealants should meet C834, C920 or C1311.

EN 15651-4 covers sealants for pedestrian walkways (PW): the 2012 editions are cited in the Official Journal under CPR 305/2011, and CEN published the 2017 editions on 2017-02-14. A sealant counts as high modulus (HM) when its secant modulus exceeds 0.4 N/mm² (58 psi) at +23 °C (73 °F) or 0.6 N/mm² (87 psi) at -20 °C (-4 °F), and loss of volume stays at or below 10 % for the 25 and 20 classes and 15 % for 12.5E. Regulation (EU) 2024/3110 applies from 2026-01-08, while the 2012 citations stay valid until the family moves under a 2024/3110 implementing act, as set out in EN 15651 sealant classification.

Pavement and bridge joints: ASTM D5893 silicone and D2628 compression seals#

Highway, airfield and bridge joints use pavement standards instead: ASTM D5893/D5893M-16(2021) for cold-applied single-component silicone (Types NS and SL) and ASTM D2628-25 for preformed polychloroprene compression seals. D2628-25 is a purchasing specification and does not select the seal size or set out installation.

FHWA HIF-18-019 (2019) sets the sealant shape at a width-to-depth ratio of 1:1 for hot-pour sealants and 2:1 for silicone, over a closed-cell, non-absorptive backer rod. Pavement backer materials follow ASTM D5249-10(2021), Types I, II and III. Hot-applied asphaltic joint sealants (ASTM D6690-21) are asphalt products, not covered here.

Is ASTM C920 Class 35 the same as an ISO 11600 Class 25 sealant?#

No: ASTM C920 and ISO 11600:2002 + Amd 1:2011 classify movement on separate scales with no 1:1 mapping, and ISO and EN classes stop at 25. One sealant, Sikaflex-1A, carries C920 Class 35 and ISO 11600 25HM at once, so each label is read on its own terms.

How do you check an expansion joint sealant claim on a data sheet or DoP?#

Five checks confirm what an expansion joint sealant or filler claims. The checks are listed below in reading order.

1. Read the full C920 string: Type, Grade, Class and every Use, with Use T for any joint under foot or wheel traffic.
2. Read the filler standard and type: ASTM D1751-23, D1752-18(2023) Type I to IV or D994/D994M-11(2022).
3. Read the EU declaration of performance: it cites EN 15651-4:2012 with the class under AVCP system 3, as the EU Construction Products Regulation requires for CE marking.
4. Look for the ASTM C719-22 movement result, which SWR Institute validation certificates report.
5. Read the SDS for diisocyanate content: 0.1 % or more by weight triggers REACH Annex XVII entry 74.

How Do You Choose an Expansion Joint Material?#

Choose the joint type from what the slab meets, the filler by exposure and the sealant by movement, traffic and substrate, or a precompressed seal where the joint must close itself. An isolation joint that is sealed and driven on takes a non-bituminous filler and a C920 Use T sealant. The table below matches six situations with the joint, filler and sealant or seal to ask for.

The sealant chemistry follows the substrate. Sika's substrate guidance puts polyurethane on porous concrete and masonry, silicone on non-porous glass and metal, and silane-modified polymers on a wide range of both, so concrete joint faces point to polyurethane under that guidance. The two main chemistries are set against each other criterion by criterion in polyurethane vs silicone sealants.

When is a sealed expansion joint the wrong detail?#

Five situations call for another product class. The five are listed below with the class that fits.

• Interior joints under hard wheels: semi-rigid joint fillers of 100 % solids epoxy or polyurea, Shore A 80 minimum by ASTM D2240 as ACI PRC-302.1-15 recommends, full depth and without a compressible backer rod.
• Joints that must hold water under pressure: waterstops for concrete joints cast into the concrete of water-retaining structures.
• Joints through fire-rated floors and walls: a fire-resistive joint system tested to UL 2079 or ASTM E1966-24.
• Static cracks that do not move: concrete crack fillers instead of a movement joint sealant.
• Deck joints wider than 25 mm (1 in) under a traffic coating: a separate sealed or preformed joint detail, because the coating is not carried over them.

How Are Expansion Joints Laid Out, Prepared and Sealed?#

An expansion joint performs as well as its layout and faces, so the specification fixes four things: spacing and saw-cut timing, clean faces and the right filler, sealant size and yield, and temperature during sealing and cure. The sections below follow that order, from the slab plan to the cured sealant.

Joint spacing, panel shape and saw-cut timing for slabs#

ACI 302.1R-04 recommends contraction joints at 24 to 36 times the slab thickness in plain slabs, no more than 5.5 m (18 ft) apart, in panels no longer than 1.5 times their width. Square panels (1:1) are preferred.

The conventional saw cut reaches the greater of one quarter of the slab depth or 25 mm (1 in), and one third of the depth in steel-fiber slabs. ACI 302.1R-04 places conventional sawing 4 to 12 hours after finishing (4 hours in hot weather, 12 in cold) and early-entry sawing 1 to 4 hours after finishing, at 25 mm (1 in) depth for slabs up to 225 mm (9 in). Late sawing is a recorded cause of random cracking.

The table below applies the ACI 302.1R-04 rules to three slab thicknesses; the spacing and depth values are calculated.

Joint preparation, filler placement and sealant recess#

Joint faces are sound and clean before sealing: release agents, old waterproofing, dust, loose mortar and coatings come off by wire brushing, grinding or sandblasting (Tremco Vulkem 45SSL data sheet). Laitance and curing compound left on the faces cause adhesive failure, listed in the inspection table below.

The filler is set before or during the pour and stops below the surface, leaving a recess for a backer rod and the sealant; an asphalt-impregnated board stays out of any joint that will be sealed. Joint width is at least 4 times the anticipated movement and at least 6 mm (1/4 in) for a ±25 % sealant, a manufacturer rule. A manufacturer depth rule sets the depth equal to the width below 13 mm (1/2 in) and about half the width for 13 to 25 mm (1/2 to 1 in) joints, never deeper than 13 mm (1/2 in), with the full method set out under sealant joint design.

Expansion joint sealant yield per meter of joint#

Sealant yield follows from the joint section: 1 L fills 1,000 / (width x depth in mm) meters of joint, so a 10 x 10 mm joint takes 100 mL per meter, theoretical and without waste. In US units one US gallon holds 231 in³ (3.785 L), which fills 308 ft of a 1/4 x 1/4 in joint before waste.

Worked example, with every input labeled: a plaza with 120 m (393.7 ft) of joint, a joint section of 10 x 10 mm and a waste allowance of 25 % needs 120 x 100 = 12,000 mL in theory and 15,000 mL with waste, which is 50 cartridges of 300 mL. The table below lists calculated sections first and named product figures after them, each with its basis.

Sealing temperature and cure times#

Tremco Vulkem 45SSL, one self-leveling polyurethane, is applied to substrates at 5 °C (40 °F) or warmer and skins in 5 hours at 24 °C (75 °F) and 50 % RH. It then cures about 1.6 mm (1/16 in) per day, plus one day for each 5.6 °C (10 °F) drop. Every joint is sealed near the mid-range of its movement, and pourable grades stay off sloped joints. The table below lists the cure and window values with the product each comes from.

Preformed compression seals and precompressed foam seals#

Preformed seals close the joint by compression instead of adhesion: extruded polychloroprene compression seals to ASTM D2628-25 and precompressed impregnated foam seals on reels or sticks. A seal is sized for the maximum joint opening, since an undersized seal loses contact when the joint opens, and splices are a recorded failure point. For pavement compression seals, FHWA HIF-18-019 (2019) sets a minimum reservoir depth of 38 to 50 mm (1.5 to 2.0 in).

Fire-rated foam seals join the movement test to a fire test: UL 2079 and ASTM E1966-24 cycle the joint system before it is fire tested, and ASTM E2393-24 covers field inspection of installed systems. Rated penetration and joint products are compared under firestop sealants and penetration seals. The table below lists the published movement and cycling values of one maker's fire-rated foam seals.

How Are Expansion Joints Inspected, and Why Do They Fail?#

Expansion joints are accepted on adhesion, size and layout: a hand-pull test per ASTM C1193-25 Appendix X1 shows whether the sealant bonds, and depth, recess, joint spacing and saw-cut depth are measured against the drawings. ASTM C1521-19(2025) adds destructive and non-destructive field adhesion checks, and ASTM E2393-24 covers installed fire-resistive joint systems.

A failed sealant is classed in three ways: adhesive failure at the bond line, cohesive failure through the sealant body and substrate failure in the concrete edge. Adhesive failure points to the faces, cohesive failure to an undersized joint or excess movement, and substrate failure to the concrete edge itself. The table below lists eight failure modes with their cause and the check that finds them.

Resealing an existing expansion joint#

Replace polyurethane with polyurethane and silicone with silicone: Sika's joint sealing guide allows up to 0.5 mm (0.02 in) of sound old sealant to remain, and everything else is cut out before the faces are cleaned. The cleaned faces then follow the preparation rules above, a new backer rod goes in at the design depth, and the new sealant is tested with a hand pull before the run is accepted. Reseal prices per meter of joint are listed in the cost section below.

What Health, Safety and VOC Rules Apply to Joint Sealants and Fillers?#

Polyurethane joint sealants contain isocyanate prepolymers that can cause respiratory and skin sensitization, so EU training rules apply to them, and South Coast sealants meet SCAQMD Rule 1168 VOC limits by category. The table below lists the rules with their instrument and date.

Isocyanates in polyurethane joint sealants#

4,4'-MDI (CAS 101-68-8) carries a harmonised CLP Annex VI classification under index 615-005-00-9: H315, H317, H319, H332, H334, H335, H351 and H373; see the product SDS for each sealant. Polymeric MDI and HDI oligomers have no Annex VI entry, and polyurethane sealants as a class have none either, so the classification of a given cartridge comes from its SDS. REACH Annex XVII entry 74 (Regulation (EU) 2020/1149) covers products with 0.1 % or more diisocyanates by weight, individually and in combination: a pack statement since 2022-02-24 and documented training before industrial or professional use since 2023-08-24, renewed at least every five years.

Directive (EU) 2024/869 sets an EU limit of 6 µg NCO/m³ as an 8-hour TWA and 12 µg NCO/m³ short term, with transitional values of 10 and 20 µg NCO/m³ until 2028-12-31. In the US, OSHA sets a ceiling of 0.02 ppm (0.2 mg/m³) for MDI in 29 CFR 1910.1000 Table Z-1 and 1926.55, not an 8-hour TWA. Silane-terminated hybrid sealants are isocyanate-free by chemistry, which the SDS confirms for each product, and the training levels are set out under diisocyanates rules.

Bitumen-based expansion joint fillers#

Bitumen (CAS 8052-42-4) has no CLP Annex VI entry; ECHA C&L notified: not classified (97.8 %); see the product SDS for each bituminous fiber or bitumen filler. Asphalt (EC 232-490-9) is registered under REACH. The burn and fume hazards of bitumen belong to hot-applied products, while a preformed bituminous board is set in place cold, before the pour.

VOC limits for expansion joint sealants and primers#

SCAQMD Rule 1168 (amended 2022-11-04) limits All Other Architectural Sealants, the category of expansion joint sealants in buildings and plazas, to 50 g/L (0.42 lb/gal) less water and exempt compounds.

The same rule sets 250 g/L (2.09 lb/gal) for Roadway Sealant, and 250 g/L (2.09 lb/gal) for non-porous and 775 g/L (6.47 lb/gal) for porous architectural sealant primers. Product made before a limit takes effect may be sold for up to 3 years and used for up to 4 years under paragraph (d)(3). The federal EPA AIM rule (40 CFR 59 subpart D, Table 1) has no joint sealant category, and EU Directive 2004/42/EC lists none in Annex I, so the other categories are compared under VOC limits for construction chemicals.

How Much Does Expansion Joint Sealing Cost?#

Installed expansion joint resealing costs USD 45.93 to 59.06 per m (USD 14 to 18 per linear ft) on a British Columbia, Canada, contractor page dated 2025-07 (WCP Building Renewal), with prices in US$ as published. Joint sealant replacement in concrete, installed and without the sealant type stated, runs USD 26.25 to 65.62 per m (USD 8 to 20 per linear ft) on a Texas contractor page dated 2026-03 (Texas Structural Concrete). Joint work is priced per meter or linear foot of joint, never per square meter, and the quote depends on joint width, the removal of old sealant, access and traffic control. The table below lists four dated installed ranges.

Installed prices from contractor price pages, per meter of joint, each with its region and date.

What Are the Alternatives to a Filled and Sealed Expansion Joint?#

Six product classes compete with a filled and sealed expansion joint, and each wins where traffic, water pressure, fire rating or chemistry rules the joint. Semi-rigid fillers, waterstops, firestop systems, preformed seals and crack fillers replace the detail, and the chemistry comparison changes only the sealant. The table below compares the six.

Expansion Joint Fillers and Sealants: Grades, Packaging and Sourcing#

Expansion joint materials are sold in three forms: preformed boards and strips by thickness and depth, sealants in cartridges and pails, and preformed seals on reels or in sticks.

Buyers compare them on the standard and class printed on the data sheet, as the sourcing method under construction chemicals manufacturers and suppliers explains.

The five buyer checks are listed below.

1. Name the filler standard and type: ASTM D1751-23, D1752-18(2023) Type I to IV or D994/D994M-11(2022), with board thickness and depth.
2. Name the full C920-18(2024) designation, for example Type S, Grade P, Class 35, Use T, or the EN 15651-4 class for EU projects.
3. Name the pack: 300 mL (10.1 fl oz) or 29 fl oz cartridges, or pails for pourable grades.
4. Give the joint width range and maximum opening for preformed seals, and ASTM D2628-25 for pavement compression seals.
5. Ask for the data sheet, the SDS and, for EU supply, the declaration of performance.

Where Do Expansion Joints Fit in a Slab, Deck or Pavement Design?#

An expansion joint is one decision in a slab or deck design: ACI PRC-302.1-15 sets isolation and contraction joints for floors, and ACI PRC-224.3-95 (reapproved 2013) covers joints in concrete construction. The joint sealant, the deck coating and any waterstop or fire-rated seal in the same joint must agree on the same movement.

A deck joint wider than 25 mm (1 in) is detailed apart from the traffic coating, a water-retaining joint takes a waterstop, and a rated joint takes a system tested to UL 2079 or ASTM E1966-24. The sealant class, the filler and the seal are therefore chosen once the joint layout and its movement are fixed.

Concrete expansion joint FAQs#

Is a concrete sealer the same as an expansion joint sealant?#

No: a concrete sealer is a coating or penetrant for the slab surface, while an expansion joint sealant is an elastomer that closes a joint.

Penetrating, film-forming, densifier and hardener products are compared under concrete sealers.

Should concrete expansion joints be caulked?#

Yes where water, debris or traffic reach the joint: the filler stays below a recessed elastomeric sealant, and asphalt-impregnated filler is not sealed over. Joints under traffic take a C920 Use T sealant.

Is it too late to saw control joints after 24 hours?#

Yes for conventional sawing: ACI 302.1R-04 recommends cutting 4 to 12 hours after finishing (4 hours in hot weather, 12 in cold). Late sawing is a recorded cause of random cracking.

What is the difference between a joint sealant and caulk?#

Caulk is the US trade name for low-movement products, while joint sealants carry a movement class such as C920 Class 25 or higher.

The chemistries and classes are compared under construction sealants and caulk.

Does a 3 m (10 ft) square slab need control joints?#

It depends on thickness: at 100 mm (4 in), 24 to 36 times the thickness gives 2.4 to 3.6 m (7.9 to 11.8 ft), so a 3 m (10 ft) square panel sits inside the ACI 302.1R-04 range. A thicker slab allows a wider spacing.

Is self-leveling caulk an expansion joint sealant?#

Self-leveling (Grade P) polyurethane sealants are pourable expansion joint sealants for level joints, while self-leveling semi-rigid fillers for industrial floor joints are a separate class.