Wiki

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.

Please note: Any mention of specific commercial products in this page does not imply that they are in any way endorsed or recommended by The Restart Project. Such mentions are given simply as examples for illustrative purposes.

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 of glue may be highly flammable, or 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, one of resin and the other of hardener. 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 with care to fill gaps, but since it's quite runny it may not stay where you want it. There are several types of epoxy putty you can use instead. These tend to come as a stick containing both parts. You cut off as much as you need then nead it with your fingers to mix.

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. It's used in handicrafts, bookbinding, woodworking and as wallpaper adhesive. A screwed and glued joint in woodworking is very strong. You may have first met it at a tender age as school glue, which is a non-waterproof PVA glue.

Polyurethane Glue

You can use this for many of the same applications as PVA but it has the advantage of setting in only 5 - 20 minutes. Also, you can use it to stick a wide range of materials. It comes in an aerosol can, and as it sets, it foams up. Beware: if it gets on any surface which is shouldn't (including your fingers) it's very hard if not impossible to get it off!

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, forming a weld as it sets.

Latex Glue

Latex glue is basically just rubber solution, commonly sold under the name Copydex. Excellent for gluing fabric.

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, described later.

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. If you have nothing else to hand, this makes a surprisingly good glue for paper, card and fabric 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.

Kapton Tape

A characteristic transparent orange or brown, you may have seen this without realising what it is. Being able to withstand a very wide range of temperatures from −269 to +400°C it's useful for insulation where high temperatures may be encountered, as well as for protecting sensitive parts when using a heat gun for soldering or desoldering. Its weakness is that in the longer term it can be degraded by moisture or by mechanical chaffing.

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.

Heat-shrink Sleeving

A little different though useful in some of the same situations is heat-shrink sleeving. This comes in various diameters and shrinks to half the diameter when heated. Slipping a piece over a wire join is much better than using PVC tape. You can shrink it (ideally) with a hot air gun, or if you don't have one to hand, holding it very close over the barrel of a soldering iron will do it, but you need to be careful not to let it touch.

Stretch-release adhesive

If you've ever changed a smartphone battery or simply glanced at a repair guide for doing so, you will have come across the stretch-release strips that the batteries generally attached to the device shell with. These grip very strongly yet simply by pulling a tab on the end they stretch to many times their original length, releasing their grip in the process.

Similar products are available for general use, such as Tesa Powerstrips, which might be useful now and then in repair. Make sure the two items to be attached are accurately positioned before pressing them together as there will be little or no chance of adjusting them, short of removing the strip and using a new one.

Sellotape and Scotch Tape

These should normally only be used for paper and parcels. In an emergency you can use double-sided sticky tape to secure a smartphone battery within the smartphone shell but if it fails the battery might move and strain its connection to the main board.

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.

PCB pads

PCB Pads are not glue but flux coated copper strips meant for repairing a PCB with broken copper connectors. They are soldered onto the remaining copper that needs reconnecting.

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.

You can make your own Sugru-like substance, Oogoo with silicone paste, corn starch and food colour.

Shoe Goo

Recommended by iFixit and others for sealing and patching holes in rubber shoe soles etc, this comes in a tube and cures to solid rubber. Waterproof, with good adhesion to flexible surfaces.

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.

Fixits are very similar but come in the form of a stick. They appear to soften at a slightly lower temerature.

Epoxy putties

2-part epoxy adhesives are available mixed with a filler to make a putty-like product. The parts may come separately or as a stick with the hardener as a coating along its length. Cut off the required amount (equal amounts of the two parts if separate) and knead them together in your hands until they are thoroughly mixed.

Various different fillers are available, including steel powder, making a product which is extremely tough when fully set. Milliput is a more general purpose product which comes in several grades intended for different mending and model-making applications.

Epoxy putties may not all bond as strongly to whatever you're mending as strainght epoxy adhesive, so are best for filling gaps.

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.

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) such as Z-7 Debonder (acetone-based), especially any advertised for removing super glue.

The most effective glue removers contain heterocyclic ketone, which is a powerful glue remover. (Acetone is a ketone, but not a heterocyclic one. But if you want to know what heterocyclic means, don't ask us. Sign up for a course in advanced organic chemistry.)

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

External links

• If you're still not sure how to stick X to Y, then take a look at the website This to That.
• Tim Hunkin's video on different types of glue from his series "The Secret Life of Components" is well worth watching.
• Our Restart Radio show "Materials we use to hack and fix"