What is Selleys FlameFlex, and where should you use it?

Selleys FlameFlex is a fire and acoustic rated High Performance SMP sealant — a moisture curing silyl-modified polymer. It is fire rated up to 4 hours according to AS1530.4, complies with BCA acoustic requirements, requires no primer, and can be used indoors and outdoors on most surfaces.

Before anything else: prior to application of fire rated products, consult with the project fire certifier or engineer to ensure compliance with certification requirements. That instruction is the manufacturer's own, and it comes first in the data sheet for a reason. Fire rated levels depend on joint design, substrate and substrate configuration — a rating achieved in a test assembly is not a rating you inherit automatically by using the same tube of sealant.

Technical specification

Property	Typical result
Technology	Moisture curing silyl-modified polymer (SMP)
Colour	Grey
Density	1.45
Application temperature	5 to 45°C
Tooling time	Approx. 30 minutes
Skin time (23°C, 50% R.H.)	Approx. 50 minutes
Cure rate (23°C, 50% R.H.)	2–3mm per day
Tensile strength (DIN 53504)	1.1 MPa
Shore A hardness (DIN 53505)	31
Elongation at break (ASTM D412)	> 260%
Modulus at 100% elongation (ASTM D412)	0.67 MPa
Elastic modulus at 50% elongation (ASTM D412)	0.41 MPa
Movement capability (ISO 9047)	±20%
Service temperature	−40°C to 90°C
VOC content	15 g/L
Packaging	435g cartridge, grey

These are indicative data only, not intended for the preparation of specifications. FlameFlex is also halogen free and isocyanate free, and is stated to give no slump, better curing above 5°C without bubbling, and better extrudability above 5°C.

What the key numbers mean in practice

The cure rate of 2–3mm per day is what governs the schedule on a fire rated joint. The sealant cures by reaction with atmospheric moisture, so the rate depends on humidity, ambient temperature and joint size. Typically it forms a thick skin within 24 hours, and full cure can be expected after 7 days. In dry or cool conditions the cure will take longer. A 20mm-deep joint is not a 24-hour job, and it is not fully performing until it has cured through.

Being moisture-cured also gives you a lever. In dry conditions, surfaces can be misted with water to speed up the cure. That is a genuine acceleration, not a trick — the reaction needs water, and Australian inland air in summer often does not supply much.

Movement capability of ±20% is moderate, and it is deliberate. A fire rated joint has to hold its geometry under load, so this is a stiffer sealant than a general masonry silicone: Shore A hardness 31, tensile strength 1.1 MPa. It will absorb the normal thermal and structural movement of a control joint, but it is not the product for a joint that moves more than a fifth of its width.

Joint geometry is not optional for a fire rating. For fire rating, the joint width should be between 20mm and 40mm. The minimum joint depth should be 10mm, or half the width for joints wider than 20mm — for joints greater than 20mm the ratio of width to depth should be 2:1. Outside that geometry, the tested performance does not apply.

A tight fitting, non-absorbent, non-adhering backing material should be used to hold those dimensions and to prevent three-surface adhesion. Suitable materials include open cell foam backer rod or bond-breaking tape. Three-surface adhesion — where the sealant grips the back of the joint as well as both sides — is what tears a bead apart when the joint moves, because it has no free length to stretch.

Coverage

Joint size (mm)	Metres per cartridge
6 × 6	7.9
8 × 8	4.5
10 × 10	2.9
12 × 12	2.0
15 × 7.5	2.5
20 × 10	1.4
30 × 15	0.6
40 × 20	0.4

Note how sharply coverage falls once you are into fire-rated joint dimensions. A 40 × 20mm joint takes a full cartridge every 400mm, so estimate cartridge counts from this table before you start rather than from the length of the joint alone.

Fire performance

Testing was carried out to AS1530.4-2005, fire test in vertical concrete and AAC control joints. The results Selleys publishes are:

Substrate	Joint (W × D)	Sides exposed	Resistance to passage of flame	Insulation limit (181°C rise)	Rating
Concrete	40 × 20mm	1: fire side only	197 min	39 min	-/180/30
Concrete	40 × 20mm	2: fire and non-fire side	No failure at 241 min	145 min	-/240/120
Concrete/AAC interface	40 × 20mm	2: fire and non-fire side	178 min	117 min	-/120/60

Fire rated levels are dependent on joint design, substrate and substrate configuration. Further configurations may also be tested — contact Selleys Technical Service for details. The comparison worth drawing from the table is between the one-sided and two-sided applications on the same 40 × 20mm concrete joint: sealing both faces roughly quadruples the insulation performance. If your specification calls for an insulation rating, the sided-ness of the installation is not a detail.

Acoustic performance

Bead	Sealant depth	Area of gap (of wall)	Rw
Single	15mm	0.5	Up to 50
Single	15mm	1	Up to 47
Single	15mm	2	Up to 45
Double	15mm	0.5	Up to 60
Double	15mm	1	Up to 57
Double	15mm	2	Up to 55

A double bead consistently outperforms a single bead by around 10 Rw at the same gap area, and performance falls as the gap grows. Acoustic sealing is specified as part of a suitable design, not achieved by the sealant alone.

Where to use it

• External and internal, non-trafficable control joints in concrete, masonry, AAC and brick fire rated construction
• Acoustic sealing between most common building materials — concrete, masonry, aerated concrete, plasterboard, fibre cement, metals, timber and plastic — as part of a suitable design
• Construction joints and gaps where a fire rated seal is specified
• Installation over a wide temperature range

It has high UV resistance and adheres to wet surfaces, so it can be installed in conditions that would defeat many sealants. For dedicated fire rated products of other types, see the fire rated sealant range.

How to apply it

The directions below should only be used as a guide — the installer should apply all Australian Standards, BCA/NZBC requirements, and best practices when using FlameFlex.

1. Ensure surfaces are clean and free of oil, grease, release agents, dust or loose particles.
2. Prepare porous surfaces by grinding, brushing, wiping with cloths or blowing off with oil-free compressed air. Any laitance should be removed from concrete-based surfaces — laitance is a weak surface layer, and a sealant bonded to it is only as strong as that layer.
3. Prepare non-porous surfaces so they are free of scale, rust or oxides. They can be degreased with a solvent such as MEK, acetone or mineral turpentine. Note that some degreasing solvents leave a residue that should itself be removed.
4. Cut the tip off the cartridge and attach the nozzle. Insert into a caulking gun and cut the nozzle to the size required for the joint.
5. Fit a tight, non-absorbent, non-adhering backing material — open cell foam backer rod or bond-breaking tape — to set the correct dimensions and prevent three-surface adhesion.
6. Extrude the sealant smoothly into the joint, ensuring that all substrates are well wetted out with sealant.
7. Tool within the tooling time — approximately 30 minutes. For neat joints, use masking tape on both sides and remove it before skinning.

Painting

FlameFlex is paintable, with conditions. It is paintable with water-based paints after the product skins (60–90 minutes), and you should paint within 12 hours of application. Allow longer before painting in colder weather. Solvent-based paints may be used after first painting with a water-based paint — that is, the water-based coat acts as the tie layer.

Some paints may require the sealant to be sanded lightly before painting. Because of the number of paints and varnishes available, a preliminary test of compatibility is recommended.

Limitations — where it should NOT be used

• Not for permanent water immersion or below water-line use.
• Not suitable for use on polyethylene, polypropylene or Teflon.
• FlameFlex is not suitable for use in applications exposed to continuous temperatures greater than 80°C. DO NOT use to seal around stoves, ovens, chimney flues, pizza ovens etc.
• It is specified for non-trafficable control joints — not for joints that are walked or driven over.

That third point is the one most likely to be misread, because "fire rated" reads to many people as "heat resistant". It is not the same claim. A four-hour fire rating describes how the seal performs in a fire test; it says nothing about sitting next to a flue at 100°C every day. For continuous heat, this is the wrong product.

Clean up and storage

Uncured product can be removed with mineral turpentine. Cured product can be removed by mechanical action. Use Poly Cleaning Wipes to remove sealant from the skin.

Storage life is 12 months from date of manufacture if stored below 28°C. That is a shorter shelf life than many sealants, so check the date on cartridges that have been sitting in a site store.

Hazard classification

Classified as hazardous under Safe Work Australia GHS 7, with the signal word Danger.

• Reproductive toxicity — Category 1A. H360: may damage fertility or the unborn child.
• Eye damage/irritation — Category 2A. H319: causes serious eye irritation.

What is in it

Chemical entity	CAS number	Proportion (w/w)
Boron zinc hydroxide oxide	138265-88-0	<1%
Calcium oxide	1305-78-8	<1%
Bis(2,2,6,6-tetramethyl-4-piperidinyl) decanedioate	52829-07-9	<1%
Silicic acid tetraethyl ester, reaction products	93925-43-0	<1%
Bis(acetyloxy)dioctylstannane / N-[3-(trimethoxysilyl)propyl]ethylenediamine	1760-24-3	<1%
Non-hazardous or below reporting limits	—	Balance

H360 is the classification to take seriously, and Category 1A is the most severe level of it. It means the product is regarded as a known or presumed human reproductive toxicant — capable of damaging fertility or harming an unborn child. That is a stronger statement than the "suspected" Category 2 classification (H361) carried by, for example, Tradie's Bog.

The practical consequence is unambiguous: anyone who is pregnant, may become pregnant, or is trying to conceive should not handle this product. On a site where fire-rated sealant is being installed in volume, that belongs in the risk assessment rather than being left to the individual to discover from the pack.

Every declared hazardous ingredient is present at under 1% by weight. The organotin catalyst in that list — the dioctylstannane — is the component whose chemical class carries reproductive toxicity classifications; organotin compounds are used as cure catalysts in silicone and hybrid sealants precisely because they are effective at very low concentrations.

Wear gloves and eye protection, ventilate the working area, and do not eat, drink or smoke while handling it. Cured sealant in a finished joint is not the exposure route of concern; handling the uncured material is.

Protection

• Gloves — nitrile rubber; essential wherever a sensitisation classification applies.
• Eye protection — chemical goggles or safety glasses.
• Ventilation — work in a well-ventilated area; do not work in a confined space.
• Wash hands before eating, drinking or smoking, and wash contaminated clothing before reuse.

First aid

Exposure	What to do
Eyes	Rinse cautiously with water for several minutes, removing contact lenses if present and easy to do, then keep rinsing. If irritation persists, get medical advice.
Skin	Wash with soap and water. If a rash or itching develops, including hours later, get medical advice — this may indicate sensitisation rather than irritation.
Inhalation	Move to fresh air. If irritation persists, seek medical advice.
Swallowed	Do not induce vomiting. Rinse the mouth and seek medical advice.

If poisoning occurs, contact a doctor or the Poisons Information Centre — 131 126 in Australia, 0800 764 766 in New Zealand — with the container to hand. Selleys emergency line: 1800 220 770 in Australia, 0800 220 770 in New Zealand.

Common questions about Selleys FlameFlex

What fire rating does it achieve?

Fire rated up to 4 hours according to AS1530.4. The actual rating depends on joint design, substrate and configuration — the published test results are -/180/30, -/240/120 and -/120/60 for the three tested configurations above.

Do I need sign-off before using it?

Selleys states that prior to application of fire rated products you should consult the project fire certifier or engineer to ensure compliance with certification requirements.

What joint size does the fire rating require?

Joint width between 20mm and 40mm, with a minimum depth of 10mm or half the width for joints wider than 20mm. For joints greater than 20mm the width-to-depth ratio should be 2:1.

How long does it take to cure?

It typically forms a thick skin within 24 hours, with full cure expected after 7 days. The cure rate is 2–3mm per day at 23°C and 50% relative humidity, and it will be slower in dry or cool conditions.

Can I speed the cure up?

In dry conditions, surfaces can be misted with water to speed up the cure.

Can I paint over it?

Yes. Use a water-based paint after the product skins (60–90 minutes) and paint within 12 hours of application. Solvent-based paints may be used after first painting with a water-based paint. Test compatibility first.

Do I need a primer?

No primer is required.

Can I apply it to a damp surface?

Yes — adhesion to wet surfaces is one of its stated features.

Can I use it around a stove, oven or flue?

No. It is not suitable for applications exposed to continuous temperatures greater than 80°C, and the manufacturer explicitly says not to use it around stoves, ovens, chimney flues or pizza ovens.

Can it be used underwater?

No — not for permanent water immersion or below water-line use.

Will it bond to plastic?

Not to polyethylene, polypropylene or Teflon.

How much movement will it take?

±20% under ISO 9047.

How many cartridges do I need?

Use the coverage table above. A 40 × 20mm joint gives about 0.4 metres per 435g cartridge; a 10 × 10mm joint gives about 2.9 metres.

How long does it keep?

12 months from date of manufacture, stored below 28°C.

How do I clean up?

Mineral turpentine for uncured product; mechanical action once cured. Poly Cleaning Wipes remove it from skin.