How To Glue Polystyrene
What is the best glue for sticking polystyrene together?
It depends on one thing: whether the finished item will get wet.
Indoors and dry: Selleys Liquid Nails Fast Grab. Polystyrene foam is named directly on its technical data sheet as a suitable material, and its water-based, low-odour formulation makes it comfortable to use indoors.
Outdoors or anywhere it will get wet: a neutral cure silicone such as Selleys Roof & Gutter Silicone.
That split is not arbitrary. Liquid Nails Fast Grab's technical data sheet states plainly that it is suitable for interior and sheltered exterior applications protected from moisture only. It is an excellent polystyrene adhesive right up until water reaches it.
Liquid Nails Fast Grab — what the numbers mean
| Property | Typical result |
|---|---|
| Technology | Water-based |
| Colour | Beige |
| Cure time | 72 hours |
| Grab strength | Up to 100 kg/m² instant grab (measured on timber to timber) |
| Bond strength in tensile shear | >1.5 MPa (AS 2329-1999E) |
| Long-term strength | Holds up to 500 tonnes/m² after 7 days |
| Gap bridging | Up to 9 mm |
| Paintable | After 12 hours |
| Pack sizes | 420 g cartridge; 130 g tube |
Indicative data only, not intended for the preparation of specifications.
Two things here are genuinely useful on a foam job. The instant grab of up to 100 kg/m² is what lets you stick a polystyrene piece to a vertical surface and have it stay there while it cures — no clamping, which is just as well, because clamping foam crushes it. And gap bridging up to 9 mm covers the fact that cut polystyrene is rarely flat or square; the adhesive can fill the hollows instead of relying on perfect contact.
The 72-hour cure is the number people ignore. It is not 72 hours before it holds — the grab is immediate — but it is 72 hours before the bond is at full strength. Expect longer in cold or humid weather, and longer again where neither surface is porous. Polystyrene is closed-cell foam, so if you are bonding foam to foam, both surfaces are non-porous and the cure will be at the slow end. Best results are obtained where at least one surface is porous.
How to glue polystyrene indoors
- Make sure both surfaces are dry and free from oil, grease and dust.
- Cut the cartridge tip, fit the nozzle and cut it to a roughly 5 mm opening — or cut the tube nozzle to size. If you have not used a caulking gun cartridge before, see how to open a cartridge.
- Apply a bead along the length of the joint. On broad flat surfaces, apply beads every 40 cm.
- Bring the surfaces together within the first 5 minutes.
- For heavy pieces or overhead work, support the job with temporary fixings — the TDS recommends supports for heavy items and overhead applications, because grab is affected by substrate porosity and weather.
- Allow the adhesive to set for a minimum of 24 hours before removing any temporary supports, and allow 72 hours for full cure.
- Clean up uncured product with water. Cured product has to be scraped or sanded off.
Where Fast Grab should not be used
- Anywhere it will get wet. Interior and sheltered exterior applications protected from moisture only.
- Not for polyethylene, polypropylene or PTFE. Pre-test other plastics and rubbers for compatibility.
- Avoid tightly clamped joints — cabinet making or joinery, for example. A water-based adhesive needs somewhere for the water to go.
- Not for mirrors, and not for metals heated by direct sunlight — bonds weaken at higher temperatures. Use Liquid Nails Mirror & Metal for both.
- Not as the sole bonding agent for structural bonding.
The outdoor answer: neutral cure silicone
Where the item will be outdoors or will get wet, Selleys recommends a neutral cure silicone such as Roof & Gutter Silicone. Its published figures: skin time 5–10 minutes, tooling time 5 minutes, cure rate 2 mm per 24 hours, joint movement ±25%, elongation at break 330% (ASTM D412), service temperature −60 °C to +150 °C, application temperature +5 °C to +30 °C.
Practical consequences for a foam job: you have about five minutes to position and tool the piece, and the bead cures at only 2 mm a day, so a thick bed under a foam block takes several days to cure through. Silicone also needs atmospheric moisture to cure, and both foam surfaces are non-porous, so allow more time than the headline rate suggests. Note too that it is not paintable, and is not for continuous submersion or below-waterline use — weather-resistant is not the same as waterproof.
Safety: what these products need
The two products recommended above have mild classifications. The two the page mentions in passing do not.
| Product | Classification |
|---|---|
| Liquid Nails Fast Grab | Warning — H317 may cause an allergic skin reaction. That is the whole classification; no flammability, no eye class |
| Roof & Gutter Silicone | Warning — H319 serious eye irritation, H317 allergic skin reaction |
| Kwik Grip High Temp Spray | H222 extremely flammable aerosol, H229 pressurised container, skin and eye irritation, Category 3 narcotic effects |
| Selleys Sealant Remover | Danger, Schedule S5 — H304 may be fatal if swallowed and enters airways, H226 flammable, H336 drowsiness, H315 skin irritation |
What follows for a foam job
H317 is the hazard that low odour does not warn you about. Fast Grab is chosen for indoor foam work precisely because it is water-based and comfortable to use in a room — which is exactly why people use it bare-handed, wipe excess with a finger and clean up with water. Skin sensitisation is not irritation; it is the immune system learning to react, generally permanent once acquired, and thereafter triggered by far smaller exposures. It is built from repeated casual contact over many jobs. Nothing about the smell tells you it is happening. Wear nitrile gloves.
The page already rules the aerosol out for polystyrene — the hazard profile is the second reason. Kwik Grip High Temp Spray is an extremely flammable aerosol carrying Category 3 narcotic effects. Spraying a solvent aerosol into an enclosed room while cutting foam is the exposure pattern that produces the drowsiness and dizziness in that classification, and the pressurised can adds an ignition risk that a squeezed cartridge does not. If you feel light-headed while spraying, that is the exposure standard being exceeded, not a cue to push on with the window ajar.
H304 is why the remover does not belong in a craft space. Aspiration hazard Category 1 means that if it is swallowed and any reaches the airways it can cause a potentially fatal chemical pneumonitis. The first aid is to never induce vomiting. It is a beige paste in a screw-top tub that looks like modelling filler, and foam projects are often done with children around. Lid on, stored high.
The lower-hazard choice is the one the page already makes. Fast Grab avoids flammability, narcotic effects and eye classification entirely, and it is water-based, so the clean-up is water rather than a solvent. Poisons Information Centre — 131 126 in Australia, 0800 764 766 in New Zealand.
Common questions about gluing polystyrene
Why not use a solvent-based contact adhesive?
Check the product before you reach for one. Kwik Grip High Temp Spray, for example, carries an explicit limitation: not suitable for use on polystyrene foam.
How long before I can move the piece?
Fast Grab holds immediately — up to 100 kg/m² instant grab. Leave temporary supports in place for a minimum of 24 hours, and allow 72 hours for full cure.
Can I paint over the glue line?
Liquid Nails Fast Grab is paintable after 12 hours. Roof & Gutter Silicone is not paintable at all — if you need to paint, paint first and allow at least 7 days before sealing.
Will the gaps in my cut foam matter?
Fast Grab bridges gaps up to 9 mm, so moderate irregularity is fine. Beyond that, cut the pieces to fit rather than filling with adhesive.
How much does it hold?
Tensile shear bond strength is greater than 1.5 MPa to AS 2329-1999E, and the TDS quotes up to 500 tonnes/m² after 7 days. Bear in mind the weak link on a foam job is usually the foam itself, not the glue line.
How do I clean up?
Fast Grab is water-based, so uncured product wipes off with water; cured product must be scraped or sanded. Silicone needs turps while wet, and mechanical removal or Selleys Sealant Remover once cured.
What about sticking polystyrene to timber indoors?
That is the same product — Fast Grab covers timber, MDF, particleboard, plasterboard, masonry, concrete, metals and polystyrene foam, and having one porous surface actually improves the cure. See also gluing polystyrene pieces to wood indoors.
What is the best glue to stick polystyrene together?
Selleys All Plastics is the recommended adhesive for bonding polystyrene. It is a specialist plastic adhesive specifically formulated to achieve excellent results on polystyrene without requiring priming.
What type of adhesive is Selleys All Plastics?
Selleys All Plastics is a cyanoacrylate-based adhesive, supplied as a 3g tube plus a primer pen.
Do I need to prime polystyrene before gluing it with Selleys All Plastics?
No. For nylon items, PVC, and polystyrene specifically, best results are achieved without priming, according to the product guidelines.
How should I prepare polystyrene surfaces before gluing?
Surfaces to be bonded should be clean, dry, free of dust, and close fitting. Use a clean, dry cloth to remove any debris or contaminants before applying the adhesive.
What are the steps for applying Selleys All Plastics to polystyrene?
First apply primer to each polystyrene surface using the primer pen (one coat only), then pierce the adhesive tube by attaching the nozzle and cap and turning clockwise. Apply a small amount of glue to one surface only, press the surfaces together, and apply slight pressure until the adhesive grabs, which takes approximately 30 seconds.
How long does Selleys All Plastics take to cure on polystyrene?
A minimum of 30 minutes curing time is needed for practical use, with maximum bond strength achieved within 24 hours.
How do I clean up Selleys All Plastics adhesive?
Uncured product may be removed with acetone, while cured product can be sanded and scraped away.
Can Selleys All Plastics bond polystyrene to other materials?
Yes, the adhesive will also bond polystyrene to non-plastic surfaces such as metal, timber, rubber, and leather.
Is Selleys All Plastics suitable for use on foam?
No, this product is not suitable for use on foam substrates.
Who publishes this glue-polystyrene guidance and what is Selleys?
This guidance is published by Selleys, an Australian adhesives, sealants and fillers brand founded in 1939 in Sydney, Australia, and a division of DuluxGroup (Australia) Pty Ltd.