Fosroc Thioflex 600
Two-part cold-applied polysulphide sealant for structural expansion and construction joints, engineered to move with the building for two decades or more.
What is it?
A two-component, cold-applied polysulphide joint sealant that cures to a tough, rubber-like elastomer for sealing moving joints in concrete and masonry structures.
Where is it used?
Structural expansion joints, construction and contraction joints in basements, subways, reservoirs, retaining walls, floors, brickwork and high-rise superstructures.
Why use it?
It accommodates continuous cyclic movement (25% MAF in butt joints), resists fuels, oils and weathering, and is specified to BS 4254, US Fed Spec TT-S-00227E, IS 12118 and ASTM C920.
How is it applied?
Prime porous or non-porous edges as required, fit a bond breaker or backing rod, mix base with curing agent for 5 minutes, gun or pour into the joint, then tool to a smooth concave finish.
About Fosroc Thioflex 600
Fosroc Thioflex 600 is one of the longest-serving polysulphide joint sealants on the Indian market, and for good reason. It is a two-part system: a base compound and a curing agent that, once mixed in the correct proportions, react chemically to form a tough, elastic, rubber-like seal. That cured elastomer bonds tenaciously to concrete, stone, masonry, aluminium and stainless steel, which is exactly what a movement joint needs when it has to flex thousands of times over its life without losing adhesion or splitting. Because it cures by chemical reaction rather than solvent loss, it develops full-depth properties even in deep sections, making it dependable for the wide, deep joints common in civil structures.
Space Arc supplies Thioflex 600 in both grades. The gun grade is the general-purpose version for vertical and overhead joints, supplied in a single tin with base and curing agent in the right ratio. The pouring grade is a self-levelling version for horizontal joints such as floors, decks and pavements, where it can be poured straight into the slot or gunned into narrow horizontal joints under 15 mm. It is the sealant engineers reach for on high-rise facades, subways, basements, reservoirs and retaining walls, particularly where later access for maintenance is difficult and the cost of an early joint failure is high.
The technical insight
The performance of Thioflex 600 comes from its liquid polysulphide polymer backbone. When the base is mixed with the heavy-metal-oxide curing agent, the polysulphide chains cross-link into a three-dimensional elastomeric network. The sulphur linkages give the cured rubber two properties that matter in a joint: high elastic recovery, so it returns to shape after the joint opens and closes, and genuine chemical resistance to fuels, oils, dilute acids and alkalis that would degrade many other sealants. This is why it carries a 25% movement accommodation factor (MAF) in butt joints and up to 50% in lap joints. The key design rule is the 2:1 width-to-depth ratio: keep the sealant roughly twice as wide as it is deep, over a bond breaker, so the material can stretch and compress freely across its two bonded faces rather than being over-restrained by a third face. Get that geometry right and the seal works with the structure; get it wrong and even the best polysulphide will tear.
Where it is used
- Structural expansion joints in building superstructures and high-rise facades
- Construction and contraction joints in basements, subways and retaining walls
- Horizontal floor and deck joints using the self-levelling pouring grade
- Water-retaining structures such as reservoirs and tanks after full cure
- Brickwork and masonry movement joints
- Joints exposed to occasional fuel, oil, petrol and diesel spillage
- Perimeter and abutment joints in civil engineering structures
- Joints in structures where future maintenance access is limited
Key advantages
- Cures to a tough, elastic rubber-like seal with high recovery from cyclic movement
- 25% movement accommodation factor in butt joints, up to 50% in lap joints
- Excellent adhesion to concrete, stone, aluminium and stainless steel
- Resistant to petrol, diesel, aviation fuel, kerosene, lubricating oils and dilute acids and alkalis
- Complies with BS 4254, US Fed Spec TT-S-00227E, IS 12118 and ASTM C920 Type M Class 25
- 100% solids, so it cures with negligible shrinkage even in deep joints
- Available in gun grade for vertical joints and pouring grade for horizontal joints
- Proven long service life of two to three decades in protected and partly exposed joints
Limitations & considerations
- The curing agent contains a heavy-metal oxide, so it is toxic; gloves and eye protection are mandatory and cured sealant must never be burnt off
- Requires accurate site mixing of two components for a full 5 minutes; poor mixing leads to incomplete or uneven cure
- Not resistant to chlorinated solvents, aromatic solvents or dilute oxidising acids
- Must be fully cured before permanent water immersion, and cure at low temperatures is slow (up to 4 weeks at 5 degrees C)
- Porous substrates always require priming, and re-priming is needed if the primed joint is left unsealed too long
- For potable water contact the exposed sealant surface area must be limited to stay within heavy-metal migration limits
Selection & best practice
Start with a dry, clean, frost-free joint. Remove dust and laitance by wire brushing, grinding or grit blasting, strip rust and lacquers from metal, and clean off oil or grease with Nitoflor Sol. Confirm any joint filler is tightly packed with no voids, then install a bond breaker tape or closed-cell backing rod so the sealant bonds on only two faces. Prime as required: Primer 4 on glass, ceramics and metals, Primer 7E on concrete, stone, brickwork, timber and unglazed tile edges, and apply the mixed sealant while the primer is tack-free but before it has fully reacted; re-prime if that window is missed. Mix the full curing agent into the base with a slow-speed drill and paddle for a complete 5 minutes until an even grey with no streaks. Load and gun the material, or pour the pouring grade into horizontal joints, then tool to a smooth concave profile using minimal dilute detergent or white spirit as a lubricant, and remove masking tape immediately. Respect the 2:1 width-to-depth ratio and the minimum depths: 5 mm for non-porous surfaces, 10 mm for porous, 20 mm for trafficked or hydrostatic joints. Work within the 5 to 50 degrees C application window and allow full cure before flooding or trafficking.
Specifications
| Product type | Two-part cold-applied polysulphide joint sealant |
| Grades | Gun grade (vertical) and Pouring grade (horizontal, self-levelling) |
| Movement accommodation (MAF) | 25% in butt joints, 50% in lap joints |
| Joint width range | 5 to 50 mm, designed at 2:1 width-to-depth ratio |
| Application temperature | 5 degrees C to 50 degrees C |
| Pot life | Minimum 2 hours at 25 degrees C |
| Setting / full cure | Sets in 18 hrs at 25 C; full cure 1 week at 25 C, 2 weeks at 15 C, 4 weeks at 5 C |
| Shore A hardness / density | 18 plus-minus 2 at 25 C; density 1.60 to 1.65 kg/litre; 100% solids |
| Standards | BS 4254:1983, US Fed Spec TT-S-00227E, IS 12118, ASTM C920 Type M Class 25 |
| Pack sizes | 2.5 litre (4 kg) and 6.25 litre (10 kg) packs |
Industry use cases
Metro & Infrastructure
Sealing expansion and construction joints in subways, underpasses and retaining walls where fuel and oil exposure and constant traffic-induced movement demand a durable, chemically resistant elastomer.
Water Retaining Structures
Reservoirs, tanks and treatment works rely on its watertight cured seal and long service life, with the pouring grade used for horizontal floor joints once fully cured before filling.
High-Rise & Commercial Buildings
Facade and structural expansion joints on tall superstructures where later maintenance access is difficult and a two-to-three-decade service life protects the building envelope.
Industrial Floors & Pavements
Self-levelling pouring grade fills horizontal floor, deck and pavement joints exposed to occasional petrol, diesel and lubricating oil spillage in plants and warehouses.
Basements & Below-Grade Works
Movement and contraction joints in basements and podiums, where bond-breaker detailing and correct joint geometry keep the seal watertight against hydrostatic pressure.
Frequently asked questions
What is the movement capacity of Thioflex 600?
What is the difference between the gun grade and the pouring grade?
Do I need a primer, and which one?
How long does Thioflex 600 take to cure?
Is it safe for potable water tanks?
What are the pack sizes and how much joint will a pack seal?
How we position Fosroc Thioflex 600
Thioflex 600 is the workhorse polysulphide sealant for civil and structural movement joints, chosen when chemical resistance, proven standards compliance and long service life matter more than one-part convenience. Within the Fosroc family, pair it with Fosroc Primer 7E for porous concrete edges and Primer 4 for glass and metal, and use Nitoflor Sol for cleaning substrates and equipment. Where a project prefers a faster, one-component, moisture-curing sealant for facades, windows and general building joints, Fosroc Nitoseal MS600 (an MS polymer) is the modern alternative from the same brand. Space Arc also stocks polyurethane and hybrid sealants across Sika, MC-Bauchemie and STP for teams standardising on other systems, so we can match the sealant to the specification rather than the other way round.
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