What is Selleys Plasti-Bond Heavy Duty, and where should you use it?

Selleys Plasti-Bond Heavy Duty is a multi-purpose plastic putty for building and repair work where filling, bonding or moulding is needed. It is a two-part product: a base and a hardener that you mix together immediately before use. Once mixed it sets in 20 minutes without shrinkage, and the hardened putty can be sawn, drilled, sanded and painted.

The thing to plan around is the working time. The page gives approximately 5 minutes at 23°C from mixing before the putty starts to go off, and a set in about 20 minutes. Mix only as much as you can place and shape inside those five minutes, and have the surface prepared and your spatula in hand before you start mixing.

What the key numbers mean in practice

• Approximately 5 minutes at 23°C — your working window once the hardener is in. Small batches, applied straight away.
• Sets in about 20 minutes — after which it can be sanded, drilled, sawn or painted.
• No shrink or crack — the reason you do not need to overfill and come back for a second pass, and the reason it holds a moulded shape.

Twenty minutes from mixed putty to a surface you can machine is quick, and it changes how a repair job runs. On a filler that takes hours to dry you fill everything, then come back later to sand. With Plasti-Bond you can fill, set, shape and paint one area before moving to the next — but only if you mix in small batches, because five minutes is not long enough to spread one batch across a whole job.

The no-shrink behaviour is what makes it usable for moulding rather than only filling. A filler that shrinks as it dries loses the profile you shaped into it, so a cast or moulded feature comes out undersized. This one holds the shape you give it.

Where to use it

Plasti-Bond Heavy Duty is for building and repair work where filling, bonding or moulding is necessary, and it is rated for indoor and outdoor use. It is also colourable before use, so it can be tinted in the mix rather than only painted afterwards — useful where the repair will not be painted over, or where you want the base colour closer to the surrounding material before the top coat goes on. There is more on tinting this kind of filler in the Selleys rigid fillers advice, including a specific question on tinting Plasti-Bond or Tradie's Bog.

For casting work, Selleys gives one practical tip: use light oil or silicone car polish on the mould before casting. That is the release agent — without it, a non-shrinking putty that has set hard in a mould is difficult to get back out.

The rest of the specialist repair range, including the Knead It epoxy putties and Tradie's Bog, is on the specialist fillers and putty page.

How to apply it

1. Mix the base with the hardener thoroughly until the colour is uniform. Uniform colour is your indicator that the two parts are properly combined — streaks mean part of the batch has no hardener in it and will not set.
2. Apply with a spatula, pressing firmly into the surface. Pressing rather than laying it on is what gets the putty into contact with the substrate and removes voids behind the repair.
3. Allow it to cure — about 20 minutes.
4. Sand, drill, saw or paint once hardened.

If you are colouring it, do that at the mixing stage. Once it has gone off there is no working the colour through it.

Limitations — where Plasti-Bond Heavy Duty should not be used

These are the manufacturer's stated limits:

• Not suitable for continuous immersion. It handles indoor and outdoor exposure, but permanently submerged is a different condition.
• Not suitable for flexible joints. The cured putty is rigid. A joint that moves needs a product that moves with it.
• May not adhere to PE, PP or PTFE. These plastics have too low a surface energy to be relied on. Despite the product's name, "plastic putty" describes what the putty is, not a guarantee that it sticks to every plastic.
• Can discolour if left unpainted outdoors. Outdoor use is fine; outdoor use with the repair left bare is what causes the discolouration. Paint it.

Two separate safety data sheets apply, one for the bog and one for the resin, because this is a two-component product. Consult both.

Hazard classification — the hardener

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

A two-pack polyester filler. The hardener carries the classification worth knowing about.

• Organic peroxides — Type E. H242: heating may cause a fire.
• Skin sensitisation — Category 1. H317: may cause an allergic skin reaction.
• Eye irritation — Category 2A. H319: causes serious eye irritation.

What is in it

Chemical entity	CAS number	Proportion (w/w)
Dibenzoyl peroxide	94-36-0	30–60%
Dibutyl maleate	105-76-0	10–30%
Non-hazardous or below reporting limits	—	Balance

Dibenzoyl peroxide at 30 to 60% is the catalyst that sets the filler, and it is an organic peroxide — a class of compound that can decompose exothermically when heated, which is what H242 describes. In practice: keep the hardener away from heat, direct sunlight and any source of ignition, do not leave it in a hot vehicle or on a sunlit bench, and store it separately from the filler.

It is also a Category 1 skin sensitiser. Benzoyl peroxide is a well-recognised cause of allergic contact dermatitis, and sensitisation is generally permanent once acquired. Gloves for mixing, every time — and do not knead catalysed filler with bare hands.

Mix only what you need. A large catalysed mass generates its own heat as it cures, which accelerates the reaction further; this is why the pot life shortens dramatically with batch size and warmth.

Sanding the cured filler produces respirable dust — wear a dust mask and eye protection.

Protection

• Respiratory protection — an organic vapour respirator where the product is sprayed, dispensed or mixed in quantity; a dust mask for sanding cured material.
• Gloves — nitrile rubber; essential where a sensitisation classification applies.
• Eye protection — chemical goggles or safety glasses.
• Ventilation — active ventilation, not an open door. Do not work in a confined space.

First aid

Exposure	What to do
Inhalation	Move the person to fresh air at once and keep them at rest. If breathing difficulty, wheeze or tightness develops, seek medical attention immediately and say the product contains isocyanates or solvents as applicable — symptoms can be delayed by several hours.
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. Remove contaminated clothing and wash before reuse. If a rash or itching develops, including hours later, get medical advice — this may indicate sensitisation.
Swallowed	Do not induce vomiting. Rinse the mouth and seek medical advice immediately.

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 Plasti-Bond Heavy Duty

How long do I have to work with it after mixing?

Approximately 5 minutes at 23°C. Mix in small batches.

How long before it sets?

About 20 minutes, after which it can be sanded, drilled, sawn or painted.

Does it shrink?

No — it sets without shrinkage, and does not crack. There is no need to overfill to allow for shrinkage.

Can I use it outside?

Yes, it is suitable for indoor and outdoor use. Paint it, though: it can discolour if left unpainted outdoors.

Can I paint it?

Yes, once cured.

Can I colour it?

Yes. It is colourable before use, so the tint goes in at the mixing stage rather than being applied afterwards.

Will it stick to plastic?

Not reliably to PE, PP or PTFE. Selleys states it may not adhere to those three.

Can I use it underwater or in a permanently wet spot?

No. It is not suitable for continuous immersion.

Can I use it in a joint that moves?

No. It is not suitable for flexible joints.

Can I cast with it?

Yes — it can be moulded, and it does not shrink. Use light oil or silicone car polish on the mould first so the cast releases.

Why does my mix have streaks in it?

It is not mixed yet. Keep going until the colour is uniform, or the unmixed portion will not harden.

Can I drill and screw into it?

It can be sawn, drilled, sanded and painted once hardened.