Adhering Materials
Techniques and advice for making things stick to other things.
Terms
Substrate
The surface to which an adhesive is to be applied for bonding.
We'll never use this term because it is very extra, but hey, now you know.
Wetting
The ability of an adhesive to stick to a surface immediately upon contact.
A more viscous adhesive will have better wetting and will spread more easily, but can also be runny and make more of a mess if used without care.
Tack
The stickiness or ability of an adhesive to affix to an object.
Adhesive generally has a period where it has very low tack immediately after applying, during which time it is best to leave it exposed to the air.
This is usually referred to as waiting for the adhesive "to tack".
It is best to connect surfaces once their adhesive coatings have achieved enough of a tack that they won't immediately come apart.
Set, Setting
The process of solid adhesion taking place after the application of the adhesive and the two surfaces coming together to form a bond. Once the adhesive sets, it should resist having the bonded surfaces manipulated.
Manipulating the surfaces after the adhesive has set and before curing has finished can cause weakness in the bond.
Open Time
The time you have once you apply the glue before it sets.
It is critical to get surfaces bonded before this time has passed.
Cure, Curing, Cured
The chemical process in which a material hardens. It can occur because of cross links forming between polymer chains. Other possible ways a material can harden include exposure to heat or UV light, and with the addition of special chemicals.
Offgass, Offgassing
the process by which an adhesive releases a gas or vapor. This can happen during the curing process or when the adhesive is exposed to high temperatures.
Contact Cement
An adhesive which, when coated on two mating surfaces and allowed to dry, provides a permanent bond when brought into firm contact and allowed to set/cure.
Epoxy
Epoxies are created by polymerizing a mixture of two starting compounds, the resin and the hardener (a catalyst paired with the given resin).
When resin is mixed with the hardener, curing is initiated.
Thermoplastic Adhesives
Also known as hot-melt adhesives (HMA), most commonly found as "hot glue" sticks for use with hot glue guns.
Thermoplastic adhesives are solid at room temperature but melt when heated.
A hot glue gun melts the glue with a heating element.
The user squeezes the hot glue out of the gun with a trigger or finger pressure.
The glue is sticky when hot and solidifies in seconds to a minute.
Synthetic Rubber Adhesives
The type of adhesive found on Carpet Tape.
Requires no set or cure times, can be trusted to instantly provide a strong, shear-resistant, bond between two surfaces.
Will generally be able to be removed from a surface and leave very little residue.
Comes in a variety of forms other than what is on Carpet Tape, many of which act and are used very differently.
Using Adhesives
Make sure surfaces are clean, dry, and free of foreign material. Remove any previous finishes and roughen painted or non-porous surfaces prior to applying the adhesive. A medium grit (150 or so) sandpaper or a rasp can be used to great effect.
Most adhesives will have issues with curing in cold environments. It is recommended to keep adhesives above 60 F during the 24 hours prior to use, to have the materials being bonded also be above 60 F when the adhesive is applied, and to store the bonded materials at above 60 F while the adhesive cures.
It is a good idea to cover your work surface with something that can protect it from the adhesives. Beyond protecting your work surface, this also makes cleanup much easier. Instead of laying out/taping down paper, it is actually best to use something stiffer, like sheets of cardboard; this is because the stiffness will make it easier to lift away foam that may be slightly stuck to it, as paper would often try to "come with" and often tear, undoing the protection it was providing and making more mess.
With any adhesive, you will want to be working in a well ventilated area. If you are working indoors, a table next to an open window, with a box fan blowing outside set in the window, is ideal. If you are working in a garage with an open door, it is still a good idea to have some sort of fan pulling the fumes away from you as you work. Adhesive will also offgas while curing, so storing them somewhere these fumes will not cause harm is also important; leaving things to cure next to your home's HVAC, a relatively sealed room, near your sleeping area, or in your car is not a good idea and should be avoided.
Contact Cement (from a can)
Contact adhesives generally have a longer "open time" than the other adhesives we use, meaning that they take longer to tack and set, allowing ample time to reposition the surfaces being bonded, but also creating a larger window where you can mess up any alignment. As such, these are the most time consuming adhesive to use for layered construction.
The materials to be bonded should ideally be above 60°F/15°C, and the adhesive should be stored at above that tempurature for at least 24 hours before using. The assembly should also be kept above this tempurature for the quickest and most effective cure.
Usage:
Where reasonable, roughen the surfaces to be bonded with a medium grit sandpaper.
Stir and apply adhesive
Stir the cement with a paint paddle or stirring stick. Apply an even coat to both surfaces with a paint brush, roller, or trowel.
You are trying to get even coverage, rather than saturating the material/surface with adhesive. Try to avoid putting so much on that there would be a large amount of "squeeze out" when you push surfaces together.
Let surfaces dry
Allow the surfaces to dry for 15–20* minutes, or until they feel tacky and look glossy.
Depending on how much you apply, this may take longer.
Align and press surfaces together
Align the surfaces and press them together firmly. Apply pressure across the entire surface.
Clean up any excess
Let the adhesive cure
Allow the adhesive to fully cure for at least 72* hours.
Contact cements can also be put in carpenter's syringes and injected into voids through gaps/holes in foam, which can be a great way to resolve lamination that has broken down in discrete locations without disassembling or cutting foam, saving work and materials during repairs.
Spray Adhesive
Spray adhesives generally have a relatively short "open time", and will tack more readily than contact cement that needs brushed onto a surface. Other than being sprayed onto a surface rather than being spread onto it with a sponge, brush, or roller, these work very similarly to contact cement (some of them are contact cement, just in a spray form). They generally have a shorter tack, set, and cure time, which is has both advantages and disadvantages, but leans much more heavily into the former for our purposes.
The materials to be bonded should ideally be above 60°F/15°C, and the adhesive should be stored at above that tempurature for at least 24 hours before using. The assembly should also be kept above this tempurature for the quickest and most effective cure.
The distance you hold the can from the surface can be used to control both the width of the spray when it contacts the material, which in turn controls how concentrated the adhesive is after a single pass.
Sometimes, to avoid using too much adhesive, it can be helpful to allow some of the spray to miss the surface.
Depending on what you are doing, it may instead be better to use a different angle of approach.
Generally, it is best to be 6-9 inches from the surface being sprayed, but as close as 3" is sometimes reasonable.
For the purposes of this document, consider a spray across a surface at 6" distance as a single "pass"
Usage:
Where reasonable, roughen the surfaces to be bonded with a medium grit sandpaper.
Apply adhesive
Hold the can as perpendicular to the surface being sprayed as is reasonable, preferably spraying horizontally or at a downward angle.
Press the spray cap down and move in a straight line from one edge of the material to the other.
Apply as many passes as is needed for the application, making sure to spray both of the surfaces to be bonded.
Let surfaces dry
Allow the surfaces to dry for 15–30* seconds, or until they feel tacky and look glossy.
Depending on how much you apply, this may take longer.
Align and press surfaces together
Align the surfaces and press them together firmly. Apply pressure across the entire surface.
Clean up any excess
Let the adhesive cure
Allow the adhesive to fully cure for at least 24* hours.
Hot Glue
Hot glue is a thermoplastic adhesive that must be heated to a liquid state in a glue gun in order to be used. Once it cools, the glue is set. It sets in a rigid state, can be used to fill voids due to the injection-action of the glue gun, and creates an excellent bond with rouged resin surfaces and foam, due to the effect of the heat on both when applied. Because hot glue requires heat to become malleable and cures simply by cooling, it is crucial that you work quickly when using it.
Because of the thermal action of the adhesive it doesn't care what ambient or surface temps are, other than the fact that it will get cold, and thus cure, faster in the cold.
Hot glue is prone to squeeze out, so making sure to not use more than is needed, and to plan for it to spread out between compressed surfaces is key to using it successfully.
Usage:
Let the glue gun heat up, put a glue stick in it, and make sure glue comes out easily when the trigger is pulled.
Where reasonable, roughen the surfaces to be bonded with a medium grit sandpaper. This is less necessary for surfaces the heat will partially melt the glue into, like foam.
Void-filling/Injection application
Place the nozzle of the glue gun between two surfaces until it is mostly buried.
Pull the trigger slowly, stopping if you notice that the void has been filled.
Slowly remove the nozzle from between the surfaces while still pulling the trigger, to apply glue to where the nozzle was when you started.
You may need more than a single trigger pull.
Open-Face application
On one of the surfaces, trace the outline of the face you are applying adhesive to, pulling the trigger slowly to lay down a bead of hot glue, inset about 1/2" from the outside edge.
Draw stripes to fill in the shape drawn by the bead of glue, each spaced 1/2" to 1" apart
Align and press surfaces together
Align the surfaces and press them together firmly. Apply pressure across the entire surface, avoiding creating squeeze out.
Epoxy
Epoxy is a two-part adhesive that forms when you mix epoxy resin and hardener. The two substances are stored in different containers and are only mixed together when you’re ready for gluing – which you can do using a double syringe, for example. You should keep the mixing ratio 1:1, otherwise the resin will not cross link. After you mix both components, the glue begins to set and cure. The open time can range from a few minutes to a couple of hours depending on the glue you use.
Prepare a tray to mix the epoxy on and something to mix/apply it with.
Where reasonable, roughen the surfaces to be bonded with a medium grit sandpaper.
Mix the resin and the hardener on the tray.
Apply the resin to the surfaces that are to be bonded, making sure to fill any spaces that would become voids when they are pressed together.
Align and press surfaces together
Align the surfaces and press them together firmly. Apply pressure across the entire surface, avoiding creating squeeze out.
Allow the resin to cure for the time specified by the product label, as this can vary between brands and strengths.
Carpet Tape
Carpet Tape comes in various forms, depending on the brand. Some have a plastic backing that is between layers of adhesive, some are adhesive on either side of a fiber mesh, and others are just bands of adhesive. Each kind is a double-sided tape, kept from sticking to itself with a non-stick backing that is removed during use. For ease of use and overall quality of adhesion the options that are geared towards outdoor use and have a fiber mesh are often the best bets, as they cut easily with the non-stick backing still in place and are still easy to manipulate as intended once it's removed.
Because the adhesive doesn't really cure in the same sense as the others do, tempuratures don't matter much during application.
Usage
Cut the tape to the desired length/shape.
To avoid using the entire width when not needed, the tape can easily be cut into thinner strips using a sharp knife.
Take the cut-to-length strip of tape and attach it to the edge of a table, or similar (can be good to have a bit of extra length incase the touching bit loses tack)
Near where the tape and table meet, insert the knife through the backing of the tape, with the blade edge pointed away from the table.
Pull the knife the length of the tape, taking care to travel in a straight line.
Either cut the tape horizontally to free the thinner strips from each other or place the knife back in the same slit, in reverse, and pull it through to the other end of the tape strip.
Apply the tape to one of the surfaces to be bonded.
Remove the non-stick backing.
Manipulate the tape as needed, folding down any that is sticking out over edges.
The tape can be folded back on itself without creating issues.
Align and press surfaces together
Align the surfaces and press them together firmly. Apply pressure across the entire surface.
Commonly Bonded Surface Pairings
Foam to Core
The foundation of nearly everything we do will rely on the connection between foam and core. If delamination occurs at this point it can allow the foam to twist around the core, introducing new stresses into the assembly, or cascading to further delamination of seams that are exposed to the core. As such, it is important to have good coverage on both the core and the foam, regardless of what adhesive you are using, and to not accidentally undo this coverage during application and assembly. Other than Carpet Tape, every adhesive in this list is capable of creating a bond that will be stronger than the foam it is attached to; in an ideal world, any delamination would occur because the foam tore, rather than the adhesive failing.
Ideal Adhesives
Striking Regions
3M Super 77
2 passes for each surface, apply 2nd pass after allowing first to tack, let tack, join surfaces.
DAP
Apply to core, let tack, apply to both surfaces, let tack, join surfaces.
Carpet Tape
Wrap around the core, allowing it to wrinkle if you aren't using a fry with a routed channel, press foam to wrapped core to bond.
Crossguards and Pommels
Hot Glue
Inject between foam and core, apply to open faces of foam before layering.
Epoxy
Apply to whichever surface is easiest, then align and compress surfaces.
3M Super 77
2 passes for each surface, apply 2nd pass after allowing first to tack, let tack, join surfaces.
DAP
Apply to core, let tack, apply to both surfaces, let tack, join surfaces.
Carpet Tape
Wrap around the core, allowing it to wrinkle if you aren't using a fry with a routed channel, press foam to wrapped core to bond.
Will require extra reinforcement from strapping tape around the pommel to not twist.
Foam to Foam
The next most important surface pairing is also the most common. Delaminated foam to foam connections can lead to catastrophic compression on impact, with the layup not holding its shape and reducing the effective padding provided by the foam. Other than Carpet Tape, every adhesive in this list is capable of creating a bond that will be stronger than the foam it is attached to; in an ideal world, any delamination would occur because the foam tore, rather than the adhesive failing. Adhesive seams can also be stiff and cause the surface to not be as forgiving, so avoiding over-application and squeeze-out is key. The best option for foam to foam connections is heat-welding the foam surfaces together, as this adds no additional weight and generally induces less stiffness, but this is only reasonable for certain applications.
Ideal Adhesives
Striking Regions
3M Super 77
Apply 1 pass for each surface, let tack, join surfaces.
DAP
Apply to both surfaces, let tack, join surfaces.
Carpet Tape
Apply with full surface coverage between each surface.
Stab Tips
Carpet Tape
Apply with full surface coverage between each stacked layer of the stab tip.
Makes for a much easier replacement job when the time comes.
Sticks very well to the strapping tape that will be over the biscuit if other recommendations are followed.
3M Super 77
Apply 1 pass for each surface, let tack, join surfaces.
Cover the biscuit in a fabric tape before using Super 77 to adhere a stab tip to it.
DAP
Apply to both surfaces, let tack, join surfaces.
Cover the biscuit in a fabric tape before using DAP to adhere a stab tip to it.
Crossguards and Pommels
Hot Glue
Inject between foam layers, apply to open faces of foam before layering.
Epoxy
Apply to whichever surface is easiest, then align and compress surfaces.
3M Super 77
Apply 1 pass for each surface, let tack, join surfaces.
DAP
Apply to both surfaces, let tack, join surfaces.
Carpet Tape
Wrap around the core, allowing it to wrinkle if you aren't using a fry with a routed channel, press foam to wrapped core to bond.
Will require extra reinforcement from strapping tape around the pommel to not twist.
Tape to Foam
Sometimes, tape doesn't stick good. In these instances, where you want the properties of the tape but the adhesive on it isn't up to snuff, you can sometimes help it along with other adhesives.
Duct/Gorilla tapes can be encouraged to not pull up by being put over a light application of Super 77 or DAP that has been allowed to tack to a relatively dry state, or over Carpet Tape.
The solvents in Super 77 and DAP will generally cause issues for strapping tapes, packaging tape, and tyvec tape, unless they are already quite dry, but Carpet Tape can be used as an intermediary without having to judge when it will be ready.
In both of these isntances, this adds extra weight, with the option of using Carpet Tape adding the most.
Foam to Tape
Sometimes, you will need to put foam over tape (and it won't always be over Carpet Tape). This is most significant around the Biscuit at the tip of the core, where you will generally see strapping tape or some other smooth-backed tape holding it in place. Using adhesives like Super 77 and DAP over smooth-backed tape is not recommended, as it will not adhere well to the tape backing, and because the solvents could interfere with the adhesive on the tape itself.
The best way to combat this is to wrap the smooth-backed tape in a layer of fabric tape, which will adhere well to the smooth backed tape and itself, while also creating a porous surface for the liquid adhesives to soak into and create a solid bond against, or to wrap Carpet Tape around the smooth-backed tape, and use that to adhere the foam. The former, of course, provides a much stronger bond.
Quartered PVC to Core
Just use thin strips of Carpet Tape, especially in the handle. If extending this up the core to reduce flex and increase durability, don't adhere the core to the last few inches of the PVC, and make sure to wrap the laminated core in Carpet Tape, stopping where you stopped the adhesion, which will hold the laminated layers together and provide a good surface for bonding foam to the composite core.
Handle Wrap to Handle/Core
Put a strip of Carpet Tape on each side of the handle, or a wrap of Carpet Tape around the handle.
Cover to Foam
Small strips of Carpet Tape can be used to great effect to tack down covers to the sides of arrow/dagger/spear/javelin cans before applying a fabric tape wrap to lock them in place. This can also be used for shield covers, to tack them in place for applying a duct/Gorllia tape seal, and help hold them down long term.
Weapon covers for swung weapons can also be taped on instead of having drawstrings or ties. Either have the cover extend past the end of the striking surfaces and do a tight tape wrap to secure it in place, or have it stop 2" shy of the end of what would ostensibly be the striking surface, tack it down with a vertical strip on opposite faces of the weapon, and then do a wrap, starting on the cover, that covers the last 2" of the cover and the 2" below it. The latter turns that tape-covered section into incidental padding, but this is a non-issue if you planned for it ahead of time, and the people you accidentally hit with that bit will happier it's softer than it could have been, and it can look really nice when done well.
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