Flame-Retardant Treatment for Scenery and Fabric: What You Need to Know
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Flame-retardant treatment is easy to get wrong without noticing. There is nothing to see: treated material looks exactly like untreated material, and a treatment that has since washed out looks exactly like one that is still working. Here is how the treatment actually works, how to apply it properly, and how to check it took.
The three things that catch people out
1. Topical treatment is not permanent. Rosco's own words: Flamex products are “water soluble and are easily removed by laundering and exposure to water”.
2. The material has to absorb the treatment. Coverage per litre tells you how far a tin goes, not whether the treatment took.
3. Flamex PA treats the paint layer, not the material underneath it.
What flame retardant actually does
It does not make a material non-flammable. It changes how the material behaves when flame reaches it.
Rosco describes the mechanism as working two ways: lowering the ignition temperature at which the treated material starts producing inert gases, and retarding the production of flame. The treated material gives off gases that starve the fire of oxygen and forms a non-combustible char. In practice, a properly treated fabric may still ignite — but it should self-extinguish within about two seconds of the flame being withdrawn.
That is the standard you are aiming at, and it is worth being clear about it with a production team who may assume “flame-retarded” means “will not burn”.
Three products cover almost everything
Rosco has consolidated what used to be a longer list. The older single-purpose products — NF for natural fabric, SF for synthetics, PC for paper and card, WD for raw wood — are superseded by Flamex MC, which covers all of those materials and more.
| Product | For | How it goes on |
|---|---|---|
| Flamex MC | The all-rounder — timber, plywood, MDF, muslin, cotton, canvas, synthetic fabrics, paper, card, open-cell foam and most scenic and display materials | Dip, brush or spray. Premixed, no dilution needed |
| Flamex DF | Lightweight and delicate textiles — silk, chiffon, organza, taffeta — where drape and appearance have to survive the treatment | Spray |
| Flamex PA | A clear additive you mix into water-based paint, so the dried paint layer is flame retardant | Mixed into the paint, then applied normally |
Building in foam? Rigid and flexible foam props are generally handled by FoamCoat and FlexCoat rather than a spray-on Flamex — FoamCoat is described as inherently flame-retardant. Bear in mind that a coating protects the coated foam only, not the frame, fabric or dressing around it. Our coatings comparison covers the choice between them.
Absorption is the whole game
This is the part that separates a treatment that works from one that only looks like it did.
A topical flame retardant has to get into the fibres. It is not a surface film — it is an impregnation. Which means the material must be able to take liquid in. Anything sealed, painted, coated, laminated or inherently non-absorbent will shed the treatment rather than absorb it, and you will have spent the product without changing how the material burns.
Rosco's application guidance is built around absorption at every step: dipping is described as the most efficient method of impregnation; brushing is done in a crisscrossing pattern specifically to work the solution into the fibres; and with spraying, Rosco notes it is very important that an adequate amount is absorbed.
The test that actually tells you something
Coverage figures are a purchasing estimate. For Flamex MC, roughly 37 square metres per 3.79 L. That tells you how many bottles to order. It does not tell you whether the treatment took.
The check that does is weight gain: weigh a sample of the material dry, treat it, let it dry completely, and weigh it again. Properly treated material comes out measurably heavier, because the retardant is now in the fibres.
On the numbers: Rosco publishes weight-gain figures in different places that do not quite agree — the general guidance and the MC spec sheet give different ranges, broadly somewhere between 8% and 20%. Check the current technical data sheet for the product you actually hold, and if the job is being certified, confirm the governing figure with us or with Rosco rather than working from a blog.
Which application method, and why it matters
Dipping — best. Immerse the material completely for about ten minutes, then hang it to dry. Most reliable impregnation, and the easiest to get consistent across a whole drop.
Brushing — good, and practical on scenery. Use a wide lay-in brush and work in a crisscrossing pattern so the solution goes into the fibres rather than sitting on top. The obvious method for timber, flats and anything already built.
Spraying — workable, but the weakest. Use a garden-sprayer type unit with a medium nozzle, hang the material, and spray in a back-and-forth pattern. Rosco is candid that a substantial portion of the spray will not land on the fabric — so budget more product and check your weight gain rather than trusting the look of a wet surface.
One caution on delicates: over-saturating fine fabric can stiffen it. If drape matters, treat a sample and handle it before you commit the piece.
It is not permanent — and this is the big one
Roscoflamex treatments are water soluble. Rosco states plainly that they are easily removed by laundering and exposure to water. Wash a treated drape, get it rained on during a load-in, or steam it, and the treatment can be gone — while the fabric looks completely unchanged.
Dry cleaning is different: Rosco says treated materials will not be altered by dry cleaning, provided the solvent is free of moisture and detergents. Even then, their advice is to always retest after dry cleaning.
The practical consequences are worth spelling out for anyone maintaining stock soft goods:
- Anything laundered has to be re-treated afterwards, as a matter of course.
- Outdoor and touring soft goods are exposed to weather that the treatment is not designed to survive.
- Because there is no visible difference, you need a record of what was treated and when — the fabric will not tell you.
- Re-test rather than assume. A treatment applied two seasons and one wash ago is not evidence of anything.
Flamex PA: read this bit carefully
PA is genuinely useful and also the most misunderstood product in the range.
It mixes into water-based paint — latex and water-based paints, Rosco scenic paints, primers and acrylic glazes — at one full jar per 3.79 L of paint. It covers roughly 28 square metres per treated gallon, and the finished paint layer needs to be at least 4 mil thick for the treatment to work. So the result depends on the additive and on how heavily you lay the paint on.
PA treats the paint layer, not the material underneath. Flame-retardant paint on untreated timber gives you a flame-retardant paint film over combustible timber. If the substrate also needs treating, it needs its own treatment as well.
One useful compatibility note: PA cannot be used in metallic paints that contain metal flake, because it tarnishes the metal and curdles the paint. Rosco Metallix is the exception — it is formulated with mica rather than metal, so there is nothing to react, and it stays PA-compatible.
Treat first, or paint first?
This comes up on nearly every build, and we would rather tell you the honest position than a tidy one: Rosco does not publish guidance on whether material treated with MC can subsequently be painted, or on how a paint layer affects the treatment underneath.
What we can say is that the existence of PA suggests painting is treated as its own problem rather than as something you overcoat onto MC — the paint layer gets its own retardancy from the additive, and the substrate gets its own from a substrate treatment.
If your job depends on the sequence, ask us before you start and we will get a position from Rosco rather than guess. It is a quick question and a costly thing to get wrong after the scenery is built.
Australia and New Zealand: what actually governs this
In Australia, materials are often assessed to AS 1530
The AS 1530 family of fire tests is what Australian assessment generally runs on. Different parts of it do different jobs, and they produce different indices — which is why quoting “AS 1530” without knowing which part and which index a particular requirement calls for is not much use to anybody. If a specification names a part and an index, that is the thing to work to.
The building code governs the building, not your set
This is the structural point that saves the most confusion. The National Construction Code sets fire-hazard requirements for the materials that make up the building — its linings and surface finishes, fixed seating in an auditorium, and the proscenium safety curtain where one is required. Those are building elements, specified and certified as part of the building.
The set you build for a six-week season, or tour into four venues, is not a building element. The NCC does not set an index for it.
So the venue is the gatekeeper
In practice the requirement you have to satisfy is the one in your venue hire conditions or technical specification, and it is usually written broadly. Arts Centre Melbourne's Playhouse specification, for example, requires that all scenery, props and masking be rendered non-flammable to the satisfaction of the Victorian Arts Centre Trust — no nominated standard, no nominated certificate. The test is the venue's satisfaction.
Which means the only reliable process is to ask, early and in writing, what that particular venue wants to see. Requirements differ between venues, between states, and between a main-house season and a one-night hire.
New Zealand works differently. The New Zealand Building Code handles internal surface finishes through its own system, and it should not be assumed that an Australian venue's requirements or paperwork will satisfy a New Zealand one. Ask the venue.
A workable process
Before you treat anything
- Ask the venue, in writing, what evidence they require and when they want it. Do this at the start of the build, not the week of load-in.
- Confirm what your material actually is — fibre content and whether it has any existing coating, backing or finish.
- Check whether it is already inherently flame retardant or came pre-treated, and whether there is paperwork.
- Match the product to the material, and check compatibility on a sample before ordering in quantity.
When you treat
- Start with an offcut of the real material, not a substitute.
- Surface clean, dry, free of dust and grease. Treatment will not impregnate through grime.
- Prefer dipping, then brushing, then spraying.
- Check the weight gain on your sample, dry, before you treat the whole piece.
- Let it dry completely before it goes into service.
Document it
- What material, what product, what batch, what method, what date, who did it.
- Keep the treated sample. It is your reference if anyone asks later, and your comparison for a re-test.
- Label treated soft goods with what was applied and when.
- Re-treat and re-test after laundering, water exposure or long service.
This article is general information, not a compliance opinion. We are not a testing laboratory or a certifier, and nothing here establishes that any treatment will satisfy a particular venue, authority or standard. Where a job needs certification, that comes from testing the treated material and from the approver who has to accept it. Test first, ask the venue early, and get independent testing where the production requires it.
Tell us the material and the venue
We will help you match the right Flamex to what you are treating, work out quantities, and think through the sequence — and we would far rather have that conversation before the scenery is built than after.
Sources
Product information, application methods, coverage and the mechanism of action from Rosco's Roscoflamex MC, DF and PA pages, and Rosco's Understanding Fire Retardants article. Rosco's published weight-gain figures differ between documents; check the current technical data sheet for your product.
Australian and New Zealand context
Fire-hazard provisions for building materials from the National Construction Code, published by the Australian Building Codes Board. Australian Standards are published by Standards Australia. New Zealand Building Code guidance from MBIE Building Performance. The venue requirement quoted is from Arts Centre Melbourne's published Playhouse technical specification.
Creative Film & Theatre Solutions is the exclusive Rosco agent for Australia and New Zealand. This article is general guidance only and is not a substitute for the current technical data, the safety data sheet, your venue's requirements, or independent testing. Always test on a sample of your actual material first. Rosco, Roscoflamex, Flamex, Metallix, FoamCoat and FlexCoat are trademarks of Rosco Laboratories Inc.