What Is the Best Way to Work With Self-Adhesive Magnets?
Clean the surface, peel the liner, press the magnet firmly into place and wait at least 24 hours before you load it. The 3M VHB 4920 adhesive on most of our magnets reaches about 90% of its strength in 24 hours and full strength in 72 hours. It bonds best to smooth metal, glass, hard plastics and painted surfaces, and poorly to polyethylene, polypropylene and other slick plastics. Most of our adhesive magnet packs come half with adhesive on the north face and half on the south face, so one of each makes a closure that attracts.
How to Apply Adhesive Magnets
- Clean the surface with a 70/30 mix of isopropyl alcohol and water (plain 70% rubbing alcohol works) and let it dry. The adhesive needs a smooth, dust-free, oil-free surface.
- Plan the pairs. If two magnets have to attract each other, test them before peeling the liners.
- Position it before you press. The adhesive grabs as soon as it’s pressed down and can’t be moved afterward, so line it up first.
- Press hard across the whole magnet. 3M calls for about 15 psi, which is about 3 lb of force on a 1/2 Inch disc and about 12 lb on a 1 Inch disc. Firm pressure is what makes the bond, so press with your thumb or a roller rather than just setting it in place.
- Wait 24 hours before putting stress on it, and 72 hours for full strength.
About Our Adhesive: 3M VHB 4920
Most of our adhesive magnets, and all of our 3M Adhesive Dots, use 3M VHB 4920: a thin, white acrylic foam tape with adhesive on both sides. VHB stands for “very high bond.” The foam core lets the adhesive conform to small surface irregularities, and the acrylic adhesive holds up well to heat, moisture and sunlight.
- Thickness
- 0.015 in (0.4 mm)
- Full strength
- 72 hours
- Apply at
- 70 to 100 °F (21 to 38 °C)
- Heat resistance
- 200 °F (93 °C)
The tape adds 0.015 in (0.4 mm) to the magnet’s height, so allow for it if the magnet sits in a recess that needs to end up flush.
How Long Does 3M VHB 4920 Take to Cure?
VHB tape doesn’t dry or harden like glue. It builds strength as the soft adhesive flows into the surface and makes closer contact over time. At room temperature, 3M rates it at:
- Light use after 24 hours. Leave it alone for the first day.
- Wait the full 72 hours before a closure gets opened and closed every day, or before the magnet holds anything heavy.
- Cold slows it down. Below about 60 °F (15 °C) the adhesive is too firm to flow well. Apply it at room temperature, and keep it there for the first day.
What Surfaces Does 3M VHB 4920 Stick To?
An adhesive only bonds well if it can spread across, or “wet out,” the surface. Metals, glass and most hard plastics have a high surface energy and let it spread and grip. Slick, waxy-feeling plastics such as polyethylene and polypropylene have a low surface energy, so the adhesive beads up on them the way water beads on a waxed car, and the bond stays weak no matter how hard you press.
| Surface | Bond | Notes |
|---|---|---|
| Steel, stainless steel, aluminum, zinc | Excellent | Wipe off oil first. Copper and brass may need extra prep |
| Glass, mirror, ceramic, porcelain | Excellent | Clean thoroughly. For glass outdoors or in damp areas, test first |
| ABS, acrylic, polycarbonate, rigid PVC, nylon, polyester | Good | Includes most electronics housings, signs and displays |
| 3D prints in PLA, PETG or ABS | Good | Bond to the smoothest face; layer lines reduce contact |
| Painted metal, enamel, epoxy and polyurethane finishes | Good | The bond is only as strong as the paint |
| Sealed or finished wood | Good | Raw wood must be sealed first |
| Painted drywall | Light Loads Only | The paint can peel off before the tape lets go. Give fresh paint at least a week |
| Paper, cardboard, chipboard | Light Loads Only | Fine for paper crafts; heavy loads tear the paper |
| Powder coat | Varies | Powder coatings range from easy to hard to bond. Test first |
| Raw wood, particleboard, concrete, fabric | Poor | Porous surfaces need sealing, or use glue or screws |
| Polyethylene, polypropylene, PTFE (Teflon), acetal, silicone | Poor | Low surface energy. Use a mechanical mount instead |
| Soft vinyl, plasticized rubber | Poor Over Time | Plasticizers migrate into the adhesive and soften it |
| Textured, dusty, oily, wet or cold surfaces | Poor | Too little contact for the adhesive to wet out |
How to Spot a Slick Plastic
Check the recycling number molded into the part. 2 (HDPE), 4 (LDPE) and 5 (PP) are low surface energy plastics, common in food containers, storage bins, cutting boards and outdoor furniture. For these, use Countersunk Magnets with screws, or a pocket that holds the magnet mechanically.
For tougher surfaces, 3M recommends a few extra steps. Clean heavy oil or grease with a degreaser before the alcohol wipe. Lightly sand dull or oxidized surfaces (about 180 grit), then clean again. Seal porous materials such as wood, particleboard and concrete so the adhesive has a continuous surface to bond to.
Temperature Limits
The tape handles more heat than the magnet does. 3M VHB 4920 holds up to 200 °F (93 °C) long term and 300 °F (149 °C) for minutes to hours, but our adhesive magnet listings are rated 149 °F to 176 °F, so the magnet’s maximum operating temperature on its listing is the limit to go by. See how heat affects neodymium magnets.
Add Adhesive to Any Magnet
Our 3M Adhesive Dots are the same 3M VHB 4920 adhesive, sold separately, so you can turn any magnet into a peel-and-stick magnet.