Using Selleys All Clear on the Outside of a Wood Heater Flue
Can Selleys All Clear be used on the outside of a wood heater flue to seal old drill holes?
No — it is the wrong product for a flue, and the answer to the strong chemical smell is not to wait it out.
Selleys All Clear is a solvent-based product. Depending on the thickness of the application, it can take several weeks for all of the solvent to evaporate. Its final heat resistance is also limited to around 70–80°C. For sealing drill holes in an exposed flue, Selleys Roof & Gutter Silicone would have been the more suitable choice.
Given the nature of the job, it is best to remove the All Clear and replace it with the silicone. The silicone should then be allowed to cure fully before the heater is used.
Why the heat is the core problem
The two products sit at opposite ends of the temperature range, and a flue is the one application where that difference is decisive.
| Property | All Clear | Roof & Gutter Silicone |
|---|---|---|
| Technology | Co-polymer sealant, solvent based | Neutral cure, 100% silicone |
| Service temperature | −10°C to +80°C | −60°C to +150°C |
| Skin time | 15 minutes (weather dependent) | 5–10 minutes |
| Full development | Skins immediately; maximum toughness over several days | Cures at 2mm / 24 hours; tack-free in 30 minutes |
| Elongation at break | 500% (ASTM D412) | 330% (ASTM D412) |
| Shore A hardness | 35 | 32 |
| Colour | Clear | Translucent, white and a range of Colorbond-matched colours |
| Packaging | 80g tube; 250g cartridge | 300g / 310g cartridges; 90mL |
| UV and weather resistance | Water resistant | UV and weather resistant; 25-year guarantee |
| Paintable | Yes | No |
Indicative data only, not intended for the preparation of specifications.
Even on the outer skin of a triple flue, the metal around old fixing points gets hot when the heater is running. All Clear's stated ceiling is 80°C. Roof & Gutter Silicone's is 150°C, and it is formulated for exactly this kind of exposure — roofs, flashings, skylights and coated metal panels, with UV and weather resistance built in.
Why the smell was so strong, and whether it will stop
All Clear is solvent based, and the solvent has to evaporate for the product to reach its final state. The technical data sheet notes that it skins immediately and reaches maximum toughness over several days; Selleys' answer for this situation adds that, depending on the thickness of the application, it can take several weeks for all of the solvent to leave.
Heating the sealant accelerates that evaporation dramatically. Lighting the fire the same night the holes were filled drove the solvent out all at once, which is why the smell was extreme rather than mild. So the suggestion that it would "settle down" is not entirely wrong about the direction — but it misses the point that the product will still be sitting on a surface that exceeds its 80°C service limit every time the heater is used.
That is the reason the advice is to remove it rather than wait. Not because the smell will never fade, but because the product is outside its rated service temperature in that position, and it will keep degrading there.
Doing it properly
- Do not use the heater until the sealant has been replaced and the new product has fully cured.
- Wait for the flue to be completely cold before working on it, and take normal precautions for working at roof height.
- Remove the All Clear. Cured All Clear is removed by cutting and scraping — its data sheet gives no chemical remover, so this is mechanical work. Holes of 0.4mm diameter will have taken very little product, so there should not be much to take off.
- Clean the surface. Ensure it is clean, dry, sound and free of dust, oil, rust and other contaminants. For non-porous metal, wipe with a clean cloth dampened with IPA or white spirit, in one direction only, then immediately with a clean dry cloth.
- Apply Roof & Gutter Silicone, pushing it into each hole rather than smearing it across the surface, and tool it with a clean spatula dipped in soapy water within about 5 minutes.
- Let it cure fully before lighting the heater. The cure rate is 2mm per 24 hours, and tack-free time is 30 minutes. A small plug in a 0.4mm hole cures quickly, but give it a clear margin.
- Check the ambient temperature. Do not apply if the surface or air temperature is below +5°C or above +40°C.
Something worth checking separately
A wood heater that fills a room with fumes is worth having looked at on its own terms, independently of the sealant. Old drill holes around the perimeter of an outer flue casing are usually redundant fixing points from a previous roof line — but flue systems, their clearances and their fire-rated seals are the responsibility of a qualified installer, and an old free-standing heater that has just been reinstalled is exactly the case where that check is worth having.
For information on the chemicals in any Selleys product, the safety data sheet is available on the Selleys website, and Selleys can be reached on 1300 555 205.
All Clear's stated limitations
- Service temperature −10°C to +80°C.
- May damage some plastics, polystyrene and polycarbonate named specifically.
- Not for permanent water immersion, fish tanks given as the example.
- Not suitable for use over silicones.
- Not suitable for polystyrene foam.
- Use only in a well ventilated area; avoid contact with skin and eyes and avoid breathing vapours.
Where All Clear does suit a job — interior and exterior sealing on window frames and glazing, roofs and gutters at ordinary temperatures, stone, brick, cement, timber, shower screens, sinks and basins — it has genuine strengths: it works on wet, oily and dirty surfaces, it is crystal clear, and it is paintable immediately with water-based paints. None of that helps on a hot flue.
Common questions
Will the smell go away on its own?
The solvent does evaporate, and it can take several weeks depending on how thickly the product was applied. That does not fix the underlying issue, which is that the product's heat resistance is limited to around 70–80°C.
Can I just leave it if the holes are tiny?
Selleys' advice for this situation is to remove the All Clear and replace it with the silicone. Small holes mean less material to remove, which makes that easier rather than less necessary.
How do I get cured All Clear off?
By cutting and scraping. Uncured product comes off with mineral turpentine, but cured product has no chemical remover listed.
Which Roof & Gutter colour should I use?
The range includes translucent, white and a set of Colorbond-matched colours — pick whichever is least conspicuous on your flue casing.
How long before I can light the fire?
Let the silicone cure fully. Tack-free time is 30 minutes and the cure rate is 2mm per 24 hours; give a small plug a comfortable margin beyond that.
Is Roof & Gutter Silicone paintable?
No. If you want a painted finish, paint first and allow at least 7 days before sealing over it.
Would a high-temperature automotive sealant be better?
Products such as Auto Fix Instant Gasket (High Temp) have much higher ratings — −40°C to 260°C, intermittent to 343°C — but they are gasket sealants for flanged assemblies, not exterior weather seals, and they are not for use on painted surfaces. Selleys' recommendation for this job is the roofing silicone.
Where can I find the safety information?
On the product's safety data sheet, available through the Selleys website.
Can Selleys All Clear be used on the outside of a wood heater flue to seal old drill holes?
No. Selleys All Clear is not recommended for this application. It has a service temperature range of only -10°C to +80°C, which is far below the temperatures a wood heater flue reaches, so the sealant would likely fail, crack, or degrade when exposed to the heat.
What issue did the user experience after sealing drill holes on their wood heater flue with Selleys All Clear?
The user installed an old free-standing wood heater and used Selleys All Clear to fill old drill holes (no more than 0.4mm diameter) around the perimeter of the outer flue where the old roof line used to meet it. When they lit the fire that night, toxic, chemical-smelling fumes came from the fire that were unbearable.
Is Selleys All Clear designed for high-temperature applications like wood heater flues?
No. Selleys All Clear is formulated as a multipurpose co-polymer sealant for general building applications such as window frames, roofs, gutters, and shower screens, and is not engineered to withstand the thermal stress associated with heating appliances.
Will the smell from Selleys All Clear on a wood heater flue settle down over time as the builder suggested?
The page notes a builder told the user the smell would settle down after a while, but based on the product's temperature limitations, Selleys All Clear is not suited for this high-heat application, so continued curing under such conditions is not a recommended fix — the sealant should not be used here at all.
What should someone do instead of using Selleys All Clear to seal holes on a wood heater flue?
They should consult the flue or wood heater manufacturer for approved sealant recommendations, speak with a qualified heating technician, or use an alternative product specifically rated for high-temperature use (well above 80°C), since using an unsuitable sealant on heating appliances can pose safety risks and may void warranty coverage.
What is the maximum service temperature of Selleys All Clear?
Selleys All Clear has a service temperature range of -10°C to +80°C.