What is Selleys Flexiseal Multipurpose Sealant, and where should you use it?
Flexiseal Multipurpose Sealant (also branded ProSeries Flexiseal) is a non-slumping polyurethane construction sealant with high movement capability, low modulus and excellent adhesive properties. It is weatherproof, suitable for indoor and outdoor applications, and paintable after it has cured.
The two characteristics that decide whether it suits your joint are ±25% joint movement capability and low modulus. Low modulus means the cured bead is soft enough to stretch under load rather than pulling at the substrate — which is what you want on a construction joint between building materials that expand and contract at different rates. Non-slumping means the bead holds its shape in a vertical or overhead joint instead of sagging out of it before it cures.
What the key characteristics mean in practice
±25% movement capability means the cured sealant tolerates the joint widening or narrowing by a quarter of its width without failing. For that to hold, the bead has to have real depth in the joint and be free to stretch — which is why a backing rod is recommended for deeper joints. A backing rod sets the depth and stops the sealant bonding to the back of the joint, leaving it free to move between the two faces that actually shift.
Adhesion without priming is stated, with a condition. The manufacturer says it has good adhesion properties to the building materials indicated without priming — and then says to pre-test to ensure adhesion is suitable. Take that at face value: run a short test bead on an offcut of the actual substrate and let it cure before committing to a long joint.
Temperature affects both storage and application. The product stores and applies better at moderate temperatures, around 20°C, especially in cold weather. A cold cartridge is harder to extrude evenly, which shows up as an uneven bead and trapped air.
VOC content and green building compliance
Flexiseal has a published VOC Content Test Certificate. Tested in November 2022 by FORAY Laboratories (NATA Accreditation 1231) using ASTM D3960 and ASTM D2369, the sealant returned 93 grams per litre VOC content per material, against a Green Building Council of Australia limit of 250 grams per litre for acoustic and architectural sealants.
It meets the GBCA VOC content requirement for Green Star Design & As Built V1.3-13.1.1B and Green Star Interiors V1.3-12.1.1B. The certificate was issued 23 November 2022 with an expiry date of 23 November 2027 — worth checking if you are assembling documentation for a Green Star submission.
Where to use it
- Construction and movement joints between common building materials
- Indoor and outdoor applications — it is weatherproof
- Vertical and overhead joints, where its non-slumping character matters
- Joints that will be painted after the sealant has cured
It is described as having excellent adhesion to common building materials. For a related product with high bond strength, see Selleys Flexiseal FC Multi Purpose Sealant and Adhesive, and the wider construction sealant range.
How to apply it
- Prepare the joints. Surfaces must be clean, dry and sound, and free from oil, dust and curing agents. Curing agents on new concrete are a common cause of adhesion failure and are not always visible.
- Use a backing rod if needed, particularly on deeper joints, to set the joint depth and prevent the sealant bonding to the back of the joint.
- Cut the nozzle and load the cartridge or sausage into the gun.
- Extrude the sealant ensuring full contact with the joint sides, avoiding air entrapment. Trapped air is a weak point in the bead and shows as a void when the joint later moves — work the gun ahead of the nozzle so the sealant is pushed in rather than laid over.
- Smooth off with a spatula.
- After curing, paint if needed using water-based paints. If using a solvent-based paint, prime first.
Limitations — where it should NOT be used
- Not recommended for continuous submersion or below water line use.
- Not ideal over old or incompatible sealants. Previously applied polyurethane in particular may affect the cure.
- Colour, especially white, may yellow slightly with prolonged UV exposure.
The second point is the one that catches people re-sealing an existing joint. Cutting the old sealant out fully is more work than running a new bead over it, but a polyurethane laid over incompatible residue may not cure properly — and a bead that has not cured properly is not a seal at all.
The yellowing note is cosmetic rather than structural, but it is worth knowing before you specify white for a highly exposed external joint.
Packaging
Flexiseal is supplied in a 600mL sausage. Other sizes vary by colour and format.
Hazard classification
Selleys Flexiseal Sealant is not classified as hazardous under the criteria of Safe Work Australia GHS 7. No signal word is assigned, no hazard classification categories apply, and no hazard statements apply.
It is also not classified as Dangerous Goods under any transport mode — not by the Australian Code for the Transport of Dangerous Goods by Road & Rail or New Zealand NZS5433 on land, not under the IMDG Code by sea, and not under the IATA Dangerous Goods Regulations by air.
That is a worthwhile result for a polyurethane construction sealant, because polyurethanes are the family where you would most expect a classification to appear. Free isocyanate monomer is the usual reason a one-part polyurethane sealant carries respiratory-sensitisation or skin-sensitisation statements, and this one carries neither. Read that as what the classification shows rather than as a claim about the formulation, which the safety data sheet does not detail here.
The safety data sheet still asks for two things that are worth doing. Ventilate: the exposure-controls section calls for adequate ventilation during handling and use, and says that where an inhalation risk exists an organic vapour and particulate respirator meeting AS/NZS 1715 and AS/NZS 1716 should be worn. On an open site that is nothing; inside a plant room, a lift shaft or a sealed-up apartment it is a real instruction. And keep it out of your eyes — not classified as an eye irritant is not the same as harmless in an eye. If it gets in, wash out immediately with water and seek medical advice as a precaution. Store it in a cool, dry, well-ventilated place away from direct sunlight, heat and ignition sources, and wash your hands before eating, drinking or smoking.
Common questions about Selleys Flexiseal Multipurpose Sealant
What type of sealant is it?
A non-slumping polyurethane construction sealant with high movement capability and low modulus.
How much joint movement will it take?
±25% joint movement.
Can I paint over it?
Yes, after it has cured. Use water-based paints; if you are using a solvent-based paint, prime first.
Do I need a primer for adhesion?
It has good adhesion to the building materials indicated without priming, but the manufacturer asks you to pre-test to confirm adhesion is suitable for your substrate.
Can I use it outdoors?
Yes. It is weatherproof and suitable for indoor and outdoor applications.
Can it be submerged?
No. It is not recommended for continuous submersion or below water line use.
Will white stay white?
Colour, especially white, may yellow slightly with prolonged UV exposure.
Can I apply it over an existing sealant?
It is not ideal over old or incompatible sealants — previously applied polyurethane may affect the cure. Remove the old material.
Do I need a backing rod?
A backing rod is recommended for deeper joints.
Will it sag in a vertical joint?
No — it is non-slumping.
Does it meet green building requirements?
Its tested VOC content is 93 g/L against a GBCA limit of 250 g/L, and it meets the GBCA VOC content requirement for Green Star Design & As Built V1.3-13.1.1B and Green Star Interiors V1.3-12.1.1B.
What size does it come in?
A 600mL sausage; other sizes vary by colour and format.
Does cold weather affect it?
It stores and applies better at moderate temperatures, around 20°C, especially in cold weather.
What is Flexiseal Multipurpose Sealant made from?
Flexiseal Multipurpose Sealant is made using polyurethane joint sealant technology, which provides flexible sealing properties that accommodate movement and environmental changes.
What sizes and colours does Flexiseal Multipurpose Sealant come in?
Flexiseal Multipurpose Sealant is available in a 600 mL sausage format, with other sizes varying by colour and format. It comes in Grey, Black, and White colours.
What joint movement can Flexiseal Multipurpose Sealant handle?
Flexiseal Multipurpose Sealant has a joint movement capability of ±25%.
How should Flexiseal Multipurpose Sealant be stored and applied for best results?
The sealant stores and applies better at moderate temperatures, especially around 20°C, particularly in cold weather conditions.
Is Flexiseal Multipurpose Sealant suitable for underwater or submerged applications?
No, Flexiseal Multipurpose Sealant is not recommended for continuous submersion or below water line use.
Can Flexiseal Multipurpose Sealant be applied over old sealants?
It is not ideal to apply Flexiseal Multipurpose Sealant over old or incompatible sealants, as a previously applied polyurethane sealant may affect the cure of the new application.
Does Flexiseal Multipurpose Sealant change colour over time?
Yes, the colour, especially white, may yellow slightly with prolonged UV exposure.
How do you prepare a joint before applying Flexiseal Multipurpose Sealant?
Joints should be cleaned, dried, and made free from oil, dust, and curing agents before application; a backing rod should be used if needed.
What are the application steps for Flexiseal Multipurpose Sealant?
First, prepare the joint by cleaning, drying, and removing oil, dust, or curing agents, using a backing rod if needed. Next, cut the nozzle, load the sealant into a gun, and extrude it ensuring full contact with the joint sides while avoiding air entrapment. Then smooth off the sealant with a spatula. After curing, the sealant can be painted using water-based paints, or if using solvent-based paints, it should be primed first.
Can Flexiseal Multipurpose Sealant be painted after curing?
Yes, after curing, Flexiseal Multipurpose Sealant can be painted using water-based paints. If solvent-based paints are used instead, the sealant should be primed first.