A layer of glue stick or hairspray has gone onto the plate and the print still lifts — or, more confusingly, it sticks worse than it did on the bare sheet.
Work out which job you are asking it to do
This is the step that is almost always skipped, and it is why the same product gets opposite reviews.
Adding grip. On materials that key poorly into common build surfaces — polyamides, polypropylene, some polycarbonate blends — an adhesive provides a surface the plastic can hold onto that the plate itself does not offer.
Providing release. On PETG and PCTG over smooth polyetherimide, a glue film is there to keep the two apart, because the bond between them is strong enough to remove the plate's coating. Here the adhesive is protecting the sheet, not helping the print.
If you are applying glue for the first reason on a material that needed the second, you will conclude glue does nothing, because you were using it to solve a problem you did not have.
Why a thick coat is worse than none
A bed adhesive works as a film that is thin enough to be part of the surface. Applied thickly, it becomes a soft layer sandwiched between two harder ones, and the whole assembly fails by shearing inside the glue rather than by unsticking. The print then lifts with a coat of glue attached to its base — which looks exactly like an adhesion failure and is really a cohesion failure in the adhesive.
The other half of the same story is temperature. PVA glue stick spreads and levels into a film on a warm plate. Applied to a cold plate it goes on in ridges and lumps, and those ridges become texture in the first layer.
Applying it so it works
- Warm the bed first, to whatever the print will use. Do this before opening the glue.
- Apply a thin coat in one direction, then a second thin coat crossing it. Two thin passes level better than one heavy one.
- Do not build up layer on layer over weeks. Accumulated glue turns into a crust with its own uneven thickness, and that crust is now part of your bed mesh.
- Wash the plate with warm water every few prints. PVA is water-soluble by design — that is the whole point of using it — and the sheet comes back clean in a minute.
- For hairspray, spray off the machine. Overspray onto rails, belts and a leadscrew is a genuinely unpleasant thing to clean off, and the propellant is flammable near a hot end.
Matching product to material
| Situation | What to use |
|---|---|
| PLA on clean PEI | Nothing. Adhesive here is solving a problem the plate does not have |
| PETG on smooth PEI | A thin PVA film, as a release layer |
| ABS or ASA on a hot plate | Usually nothing; an ABS-in-acetone slurry if the plate is glass |
| Nylon | A dedicated polyamide adhesive, or a garolite sheet, which works without any adhesive at all |
| Polypropylene | Packing tape of the same polymer — like sticks to like, and nothing else does |
| Glass plates generally | PVA stick, always, because the alternative is a chipped plate |
Fix the free things first
Adhesive is a fourth-line measure, and reaching for it early hides the three cheaper causes. Wash the plate with hot water and washing-up liquid; skin oil defeats any adhesive laid over it. Check the first layer is genuinely squashed rather than sitting on the surface. Put the bed at the top of the material's range rather than a generic default.
If those three are right and the part still lifts, the problem is more likely to be contraction force than surface chemistry — in which case the answer is an enclosure and a brim, not a thicker coat. The warping page covers that side.
What to avoid
Sanding a textured plate to "give the glue something to hold". The texture is the adhesion mechanism and it does not come back.
Mixing products. Glue stick over dried hairspray over old glue is three interfaces to fail at instead of one.
Applying adhesive to a plate you have not cleaned. All you have done is glue the contamination down more securely.
The materials that genuinely need help
Polypropylene is the extreme case: almost nothing bonds to it except itself, which is why the tape trick is the standard answer rather than a workaround. Polyamides need either a dedicated adhesive or a surface chosen for them. Everything else in common use — PLA, PETG, ABS, ASA, TPU — sticks well to a clean, correctly heated plate, and adhesive on those materials is a symptom of something else being wrong.