What is Selleys Auto Fix Auto Sealant, and where should you use it?

Selleys Auto Fix Auto Sealant is a versatile general purpose clear automotive sealant built on 100% neutral cure silicone. The high strength adhesive forms a waterproof seal unaffected by vibration and temperature extremes, it is salt spray and detergent resistant, and it adheres to most auto and caravan materials.

The thing worth knowing before you choose it is that it is neutral cure, not acetic cure. Neutral cure is why the manufacturer lists paint surfaces among the materials it is for — an acetic silicone releases acid as it cures, which is exactly what you do not want against automotive paintwork and fittings. That chemistry, plus the −40°C to 180°C service range, is what makes it a vehicle sealant rather than a general household one.

Technical specification

Property	Typical result
Technology	100% neutral cure silicone
Colour	Translucent
Density	1.02 g/ml
Application temperature	−20°C to 50°C
Skin time	5 minutes
Dry to touch / set time	30 minutes
Cure	24 hours
Shore A hardness (ASTM C661)	25
Elongation at break	370%
Movement capability (ASTM C719)	25%
Service temperature (ASTM C1246:2017)	−40°C to 180°C
VOC (USEPA Test Method 24)	26 g/L
Packaging	100ml tube, translucent

These are indicative data only, not intended for the preparation of specifications.

What the key numbers mean in practice

Skin time of 5 minutes is short, and it governs how you work. Everything you intend to do to the surface of the bead — smoothing with a gloved finger, pulling masking tape, tidying an edge — has to happen inside that window. Touch it afterwards and you tear the skin rather than smooth it. Plan the joint, have your glove and tape ready, then apply.

The three timing figures describe three different states and are easy to confuse. It skins in 5 minutes, dries to touch in 30 minutes, and cures in 24 hours. Dry to touch means you can handle the panel without marking the bead; it does not mean the seal has developed its full properties. Do not put a caravan back into wet weather or a component back into service on the strength of the 30-minute figure.

Elongation at break of 370% and movement capability of 25% are the numbers that matter for a vehicle. A body panel joint, a caravan seam or a trim line is subject to constant vibration and to thermal expansion between a cold night and a hot roof. A 25% movement capability means the cured bead tolerates the joint widening or narrowing by a quarter of its width without failing — provided the sealant has depth in the joint rather than being wiped across the surface.

Shore A hardness of 25 is soft, which is what you want in a sealant. It stays rubbery, so it absorbs movement instead of transmitting it, and it can be cut away cleanly when the joint is next serviced.

The −40°C to 180°C service temperature covers what a vehicle body sees in Australian conditions with wide margin. Note that this is the range the cured sealant tolerates in service, and it is different from the −20°C to 50°C application temperature — the narrower range within which you should be putting it on. A panel sitting in full summer sun can easily exceed 50°C, so move the job into shade or wait for the cooler part of the day.

Where to use it

The manufacturer lists it for use on materials such as:

• Glass
• Paint surfaces
• Fiberglass
• Most plastics
• Trim
• Most rubbers

It adheres to most auto and caravan materials, and its salt spray and detergent resistance suits it to surfaces that get washed regularly and to vehicles used near the coast. For a more targeted job, the auto sealant range also includes a windscreen sealant and a marine sealant.

How to apply it

Surface preparation first: clean the surface to leave no dirt and moisture. Silicone will not bond to a contaminated or damp surface, and no amount of pressure at application makes up for it.

1. Remove any dirt or moisture from the application area. Clean with mineral turpentine and dry.
2. Remove the cap, unscrew the nozzle and remove the seal. Replace the nozzle and cut it at a 45° angle. Cut to suit the joint — you can enlarge the opening later but you cannot make it smaller.
3. Squeeze the tube with steady pressure into the application area and smooth off with a gloved finger.
4. If further smoothing is required, smooth before the sealant skins — that is inside 5 minutes.
5. Clean up before the sealant cures, with mineral turpentine. Cured sealant can only be removed by scraping or cutting.
6. After use, replace the cap. Allow sealant to cure in the nozzle and remove it before next use.

For neater joints, mask both sides before applying the sealant and remove the tape before the sealant skins. Tape pulled after skinning drags the edge of the bead with it.

Limitations — where it should not be used

• This sealant did not adhere well to natural rubber, NBR and chloroprene/neoprene.

That single stated limitation is worth taking seriously, because those are common automotive rubbers. NBR (nitrile) and neoprene turn up in hoses, seals and gaskets, and natural rubber in older trim and mounts. The product is listed as suitable for "most rubbers" — these three are the named exceptions, and a bead applied to them may look fine and peel away later.

Note also that the application temperature range is −20°C to 50°C. Applying outside that range is working outside the manufacturer's stated conditions.

Clean up and storage

Clean up before the sealant cures, using mineral turpentine. Once cured, it can only be removed by scraping or cutting — there is no solvent step that will rescue a smeared panel a day later, so the minute spent wiping at the time is well spent.

Store in a dry and cool place at a temperature below 30°C, and use within 24 months from the date of production. Silicone in a part-used tube keeps best if you let it cure in the nozzle and pull that plug out before the next job, rather than trying to clear the nozzle immediately.

Hazard classification

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

• Eye damage/irritation — Category 2A. H319: causes serious eye irritation.
• Sensitisation — skin — Category 1. H317: may cause an allergic skin reaction.

It is not classified as Dangerous Goods for road or rail transport in Australia, or under New Zealand NZS5433, and no poison schedule applies.

What is in it

Chemical entity	CAS number	Proportion (w/w)
2-Butanone, O,O',O″-(methylsilylidyne)trioxime	22984-54-9	1–10%
2-Butanone, O,O',O″-(ethenylsilylidyne)trioxime	2224-33-1	1–10%
N-[3-(Trimethoxysilyl)propyl]ethylenediamine	1760-24-3	<1%
Cyclotetrasiloxane, octamethyl-	556-67-2	<1%
Ingredients determined to be non-hazardous or below reporting limits	—	Balance

That table is the neutral cure described at the top of this page, written out as chemistry. The two "trioxime" silanes are the crosslinkers: instead of releasing acetic acid as it cures, this sealant releases an oxime, which is why it can be put against automotive paintwork and trim where an acetoxy silicone cannot. The oxime crosslinkers are also the component class that carries skin-sensitisation classifications in neutral cure silicones generally, and that is the chemically obvious explanation for H317 here — though the safety data sheet does not attribute the classification to a named ingredient, so read it as inference rather than fact.

Sensitisation is not irritation. An irritant stings while it is on your skin and stops when you wash it off. A sensitiser can teach your immune system to react, which is generally permanent once it has happened and is afterwards triggered by far smaller exposures than the one that caused it. It builds up through repeated casual contact rather than one dramatic incident. The page already tells you to smooth the bead with a gloved finger, inside the five-minute skin window — that glove is doing more than keeping your hands clean, and it is worth wearing it on the small jobs too, not just the ones where mess is likely.

H319 is the one to plan the position of your head around. A 100mL squeeze tube worked into a caravan seam or an under-bonnet joint is often above you, and the safety data sheet's own eye first aid for this product is not a quick rinse — it is fifteen minutes of continuous flushing and a trip to a doctor. Safety glasses cost nothing by comparison.

Protection

• Eye protection — safety glasses. Essential for overhead or under-vehicle work.
• Gloves — nitrile rubber is suitable for intermittent contact.
• Ventilation — natural ventilation is adequate under normal use conditions. In a closed garage or a caravan interior, open it up.
• Overalls and safety shoes for workshop use; avoid contact with clothing.
• Keep away from food and drink, do not eat, drink or smoke while using it, and wash hands afterwards.

First aid

Exposure	What to do
Eyes	Hold the eyelids apart and flush the eyes continuously with running water. Continue until advised to stop by the Poisons Information Centre or a doctor, or for at least 15 minutes, and transport to a doctor or hospital.
Skin	Effects may be delayed. Remove contaminated clothing and flush skin and hair with running water. If swelling, redness, blistering or irritation occurs, seek medical assistance.
Inhalation	Remove the person from exposure without becoming a casualty yourself. Loosen tight clothing, keep them comfortable, warm and at rest until recovered. Seek medical advice if effects persist.
Swallowed	Rinse the mouth with water. Do NOT induce vomiting. Give a glass of water. Never give anything by mouth to an unconscious person. 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 Auto Fix Auto Sealant

How long before I can drive or use the vehicle?

It dries to touch in 30 minutes and cures in 24 hours. Handling the panel is reasonable after 30 minutes; the seal has its full properties after 24 hours.

How long do I have to smooth the bead?

Five minutes. That is the skin time, and all smoothing must be done before it skins.

Is it safe on painted panels?

Paint surfaces are listed among the materials it is for, and it is a 100% neutral cure silicone rather than an acetic one.

Will it stick to rubber?

It is listed for most rubbers, but the manufacturer states it did not adhere well to natural rubber, NBR or chloroprene/neoprene.

Can I use it on a caravan?

Yes. It adheres to most auto and caravan materials and is UV and weather resistant.

Will it survive engine bay temperatures?

Its service temperature is −40°C to 180°C. For higher intermittent temperatures, look instead at the Auto Fix Instant Gasket High Temperature Sealant.

Can I wash the car over it?

The cured sealant is salt spray and detergent resistant. Let it cure for 24 hours first.

What temperature can I apply it at?

Between −20°C and 50°C. A panel in direct summer sun can be hotter than that, so work in the shade.

What colour is it?

Translucent.

What size does it come in?

A 100ml tube.

How do I clean it off my hands and the panel?

Mineral turpentine, before it cures. Cured sealant can only be removed by scraping or cutting.

How do I store a part-used tube?

Replace the cap and store below 30°C in a dry, cool place. Let the sealant cure in the nozzle and remove that plug before the next use. Use within 24 months of production.