Sticky Stuff

There are many different type of adhesives, glues and sticky tapes, each with its own strengths and weaknesses. Here you can learn which would be best for particular repair.

Summary

When things fall part there are various types of glue and sticky tape that you can use to stick them back together again, but different ones are good for different things. This page will help you choose the right one.

Safety

Broken mains electrical items repaired with adhesive and/or sticky tape will necessarily fail the visual inspection part of a PAT electrical safety test. If you decide on such a repair (at your own risk) you should at least ensure that any glue is supported by strong tape such as gaffer tape wrapped completely around the item, with a good overlap.

Some types may cause skin irritation or give off unhealthy fumes.

Types of Glue

There are lots of different types of glue. The first few below are the most useful in a Restart situation but others may come in handy for general repairs or for making stuff.

Always read the instructions or you may not get satisfactory results, and might be unaware of any potential hazards.

Superglue

Superglue will stick your fingers together instantly. You may find it rather embarrassing to have to go to A&E to get them unstuck.

Superglue will make a very strong join provided the surfaces to be mated fit together very closely, but it's not so good at filling gaps. Buy it in small tubes, try to clear the nozzle after use, and make sure you put the lid on tight as otherwise it will set solid.

If you do need to fill a gap then you can use the superglue and baking powder trick. Place a little baking powder in the gap - only as much as you can soak with one drop of superglue, then add the drop of superglue. You can repeat the process as often as needed to fill a larger gap. It will set in a very few minutes into a very hard and tough solid.

Epoxy

Epoxy glue comes in 2 separate tubes. Squeeze the same amount from each tube and mix well. Be sure to put the right lid back on the right tube, or you'll never get them off again!

Epoxy glue is very strong and sticks to most things. Although it's best if the mating surfaces fit well together, you can use it to fill gaps or you can build it up around a join to add strength.

Rapid epoxy sets in a few minutes and so is very useful, though it takes longer to achieve full strength.

Hot Melt

Hot melt glue comes in sticks which you have to feed into a glue gun. Cheap glue guns are available for just a few pounds. Apply the glue and join the parts together immediately. The glue will set in a few seconds as it cools but will take a little longer to gain full strength.

Hot melt glue remains flexible after it has set and so is good for repairing flexible things, like sticking the sole back on a shoe. Where a wire is soldered to a circuit board a blob of hot melt glue is very good for preventing the wire from flexing and breaking at the solder joint.

PVA Glue

This works well with porous materials such as paper, wood and cloth. You may have first met it at a tender age as school glue. It's used in handicrafts, bookbinding, woodworking and as wallpaper adhesive. A screwed and glued joint in woodworking is very strong.

Vinyl Adhesive

This is good for sticking PVC as it consists of PVC dissolved in a solvent. This partially dissolves the surfaces to be joined, formng a weld as it sets.

Glass Bond

This is a UV-cured adhesive which is good for sticking glass, transparent acrylic or metal to glass or acrylic. To cure it you can use a UV torch or bank note checker, available cheaply on eBay. Alternatively you can simply leave it in sunlight, though it will take considerably longer.

Polystyrene Glue

Mainly used for assembling "Airfix" and similar plastic models, but also for paper.

Silicone Glue

Silicone filler is most commonly used for sealing around bathroom and kitchen fittings, and around window frames, but can also be used as an adhesive. It remains flexible after it has set but is not especially strong, and surfaces need to be clean and dry. You may see its use in consumer electronics where a blob has been applied to retain a flying lead in position.

Sugru is a type of silicone, with hundreds of uses in fixing and crafts. It comes as a mouldable putty rather than a liquid and sets into silicone rubber. Perhaps the commonest use case in fixing is as strain relief on a headphone cable where the cable enters the jack plug - a point where the cable frequently frays and breaks.

A part used sachet of Sugru cannot be effectively resealed to keep it fresh, and once opened, a tube of silicone adhesive is difficult to effectively seal. After a few months you may find the nozzle if not the whole tube has set solid.

Flour and water paste

Mix a little flour with water to make a moist spreadable paste. This makes a surprisingly good glue for paper, card and fabric if you have nothing else to hand, and is child-safe.

Sticky Tapes

PVC Tape

PVC insulating tape is good for wrapping around exposed wires and electrical connections, however, it should never be use as the sole protection in the case of mains (or higher) voltages. If two wires are simply twisted together, heat may be generated when a current flows and this could melt the tape. (Use solder or a crimped or screw-secured connection - see Connecting and joining wires.)

PVC tape sticks reasonably well but it's stretchy and not especially strong, so shouldn't be used simply for fixing.

Gaffer Tape and Duct Tape

These are very strong tapes used for holding things together. Gaffer tape has a fabric backing and is designed to be removable; it is often used to tape cables down to avoid trip hazards or to conceal them on stage. Duct tape has a plastic-coated fabric back and is designed to stick permanently: it is used for all sorts of repairs and is waterproof and very durable. The two are similar, are often confused and are interchangeable for many uses.

These tapes are very versatile. It's said that Mission Control knew they had a chance of saving the Apollo 13 crew when they realised they had duct tape on board.

Self-amalgamating Tape

This isn't strictly adhesive, but when wrapped around an electrical junction or low pressure water pipe the layers fuse together seamlessly.

Sellotape and Scotch Tape

These should only be used for paper and parcels.

Conductive Sticky Stuff

Bare Conductive electric paint

Bare Conductive is an electrically conductive paint which you may be able to use to bridge a broken connection. It has a much higher resistance than copper or solder and so isn't suitable where a low resistance connection is required or where it must carry more than a few mA. It should be fine, however, for connections to an LCD, or to the momentary-contact push buttons on nearly all modern electronic equipment.

A slight problem with it is that once opened, the dispenser dries out over a period of months. You may be able to rejuvenate it if you can unblock the nozzle and introduce a little plain water, then shake vigorously. A hypodermic syringe would be ideal for this.

Conductive Silver Paint

If you need a low resistance join for example to mend a broken circuit board trace then conductive silver paint may well do the job, although it's expensive. Like bare Conductive, once opened it dries out quite quickly, and being solvent based can't so easily be restored.

Other Sticky Stuff

Sugru

Sugru comes in sachets and initially has a putty-like consistency but cures to a synthetic rubber. Excellent for adding protection and strain relief to a low voltage cable (such as a headphone lead) where the outer insulation is starting to crack on its entry to the plug. The website www.sugru.com gives hundreds of other examples of its use. It comes in black or white and several bright colours.

A drawback is that part used sachets can't be resealed and will very quickly go off, and unused sachets have a limited shelf life. This can be extended somewhat by keeping them in the fridge.

Thermoplastics

Polymorph consists of granules which turn soft when heated to 62 degrees centigrade, then harden again when they cool. The Register described it as 'the stuff of the gods, or would be if it had been around when the gods were choosing a construction material.'

Formcard is essentially the same except that it comes in convenient credit card sized pieces. The idea is that you can easily keep one with you for use whenever you might need it. It can be softened in hot water as required and then can be moulded for a variety of uses before it sets hard on cooling. It was launched in a Kickstarter campaign in late 2015 and is now available from the inventors website.

Modelling Clay

There are several types of modelling clay, mostly used for making rather than repairing. Polymer clay can be cured by heating to a modest temperature of 130⁰C for 15 minutes and doesn't shrink or change shape in the process. It can be obtained from hobby, craft and art stores.

Milliput

Milliput is a two-part, cold setting, non-shrinking epoxy putty which can be used for repairs on many types of materials including metals, plastics, masonry, wood, glass and ceramics.

How to remove glue

Sometimes your problem might actually be to unglue something, either because it wasn't glued properly or because you need to disassemble the item for repair. Different glues will respond to different solvents, but two of the best for difficult cases are:

• Acetone (or nail polish remover)
• Proprietary glue removers (search online) especially those advertised for removing super glue.

The latter often contain heterocyclic ketone, which is a powerful glue remover. (Acetone is a ketone, but not a heterocyclic one.)

Be aware that any solvents may irritate sensitive skin or discolour the glued item, especially fabrics.

External links

• Our Restart Radio show "Materials we use to hack and fix"