Bed adhesion: what actually works

A print that comes loose mid-job is the most common single failure in FDM printing, and the internet’s answer is usually to buy something. In most cases the actual cause is free to fix.

Start here: it is probably your first layer

Before buying adhesive of any kind, check that the nozzle is at the right height. The overwhelming majority of adhesion problems are a first layer printed slightly too high — the plastic is laid near the bed rather than pressed into it. A correct first layer looks like slightly squashed lines with no gaps between them, and it sticks without help.

The other free fix: clean the bed. Fingerprints are grease, and grease is the enemy. Warm water with a little washing-up liquid, then dry it. Isopropyl alcohol works on PEI but does not remove oils as well as detergent does.

Both of these are covered properly in first layer calibration. Do them before anything below.

Temperature, which is also free

A bed that is too cool will not hold PLA well; too hot and you get elephant’s foot. Rough starting points: PLA 55–60 °C, PETG 70–80 °C, ABS/ASA 90–110 °C with an enclosure. Raising the first-layer bed temperature by 5 °C fixes a surprising number of marginal cases.

Then: brims and rafts

A brim adds a skirt of material attached to the part’s first layer, vastly increasing contact area. It costs a little plastic and a trim afterwards, and it is the correct answer for tall thin objects and small footprints. Use it freely.

A raft prints the part on a disposable slab. It wastes more material and leaves a rougher bottom, and it is rarely needed on a modern machine with a decent surface. Reach for a brim first.

Only then: adhesives

• Glue stick (PVA). Cheap, works, and doubles as a release agent — on glass and on PEI printing PETG, a thin layer stops the part bonding too well and tearing the surface. Genuinely useful.
• Hairspray. Works on glass. Messy, and it coats everything nearby. Largely superseded.
• Purpose-made adhesives. Effective, and priced accordingly. Rarely necessary for PLA and PETG.
• Blue painter’s tape. The old standby for PLA on a cold bed. Still works; mostly obsolete now that heated beds and PEI are universal.

PETG needs the opposite advice

PETG sticks to smooth PEI too well and can pull chunks out of the sheet. Here a glue stick is a release layer, not an adhesive. Use one, or print PETG on a textured plate where the mechanical grip is easier to break.

When the surface really is the problem

Old PEI loses its grip and gouged plates never recover. If the bed is scarred, or a fresh sheet fixes it, that is the answer — see build surfaces compared. But replace the surface as a considered decision, not as the first thing you try.