Tutorial: How to use Dap contact cement

If you read any Dagorhir tutorial, it will tell you to use a kind of glue called Dap. If you’re new to foamsmithing and don’t have a background in construction, odds are you’ve never worked with this adhesive before. If you’re like me when I first started, you might not even know what it looks like! This tutorial will help you learn what Dap is, where to buy it, and how to get the best results when using it to assemble foam into Dagorhir weapons.

What is Dap?

Dap is a brand name, and there are dozens of their products on the shelves at the hardware store. Which one should you buy?

When Dagorhir people say Dap, they’re referring to Weldwood Contact Cement. It comes in a red can that looks like this:

HT-CC20

There are a few different varieties. You want the good old original kind. The ‘gel’ formula is ok, but many people report mixed results when using it. The non-flamable kind (green can) does not work well on foam and should be avoided.

dap compared

Where can I buy it?

You can buy Weldwood Contact Cement (hereafter, just ‘Dap’) at Walmart in 1 quart containers (next to the duct tape, near the paint) for $6-$7. Lowes and Home Depot carry it, but the price is usually a few dollars higher.

Hardware stores also sometimes carry 1 gallon jugs of Dap, which can sometimes be a better deal than the 1 quart containers (depending on the store’s prices), and depending on whether you plan to make swords for yourself or a whole unit.

I’d recommend buying the 1 quart can, as a gallon takes a long time to use and can start to dry out if you don’t use it quickly. A 1 quart can will be enough to make many swords.

00233Protip: If you happen to run across a 5 gallon tank of spray-grade Dap, and need to make a few dozen swords at a time, buy it. It has faster-drying solvents than ordinary red-can Dap, and it gives amazingly consistent results. Expect to pay $100, and to get about a hundred weapons out of the barrel. Some upholstery warehouses carry it.

How do I use it?

If you spent much time doing arts and crafts as a child, you know how to use Elmer’s school glue: squirt some onto thing #1 that you want to glue, then press it together with thing #2 and let them dry. Voila!

But if you do that with Dap, your weapon will fall apart. 🙁

Contact cements work differently from other glues. Dap is composed of an adhesive and a solvent. When you open the can, you’ll smell the solvent evaporating from the can (it smells awful, but you’ll grow to love the smell as it eats away enough of your brain cells!). Once most of the solvent has evaporated, the adhesive becomes sticky. Most importantly, it sticks best to itself. Remember this while you read the following steps.

Step 1:

First, find a well ventilated area to work. Those solvents will be evaporating, and if you open a can of Dap in your house or dorm room, anyone you live with will stop being your friend (and probably become ill). Working outdoors is best, but cracking a garage door open and setting up a fan works in a pinch. The fumes are flamable in high enough concentrations, so use common sense.

Step 2:

Using a cheap bristle paint brush, spread a thin coat of Dap onto both surfaces you want to glue together. This coat should cover the foam completely, but shouldn’t be so thick that the foam is drowning in liquid. It’s better to apply several thin layers on top of each other to get an even coat than to dump a thick lagoon of liquid onto the foam and try to get it to dry evenly.

Step 3:

Allow the solvents to evaporate out of the glue until it just begins to become dry to the touch If you are working somewhere warm, or somewhere with low humidity, this might take 5-10 minutes. If you are somewhere chilly, it will take longer. The instructions on the can say not to use Dap when it’s colder than 60°F, and that’s pretty good advice; you can use Dap in the cold, but as the temperature falls lower the solvents evaporate more and more slowly, the glue doesn’t become properly dry to the touch, and the adhesive doesn’t fully activate.

Step 4:

Once both surfaces are dry to the touch, stick them together. Be careful to line them up perfectly, because they’ll stick together firmly and be almost impossible to peel apart. If they slide apart easily, or peel away from each other (leaving little strings of sticky glue between them), you didn’t allow the glue to become dry enough before sticking them together. If the pieces come apart with a ‘SNAP!’ or ‘POP!’, you let the glue get too dry (no harm done: just add another coat and try again).

Step 5:

Press the seam together gently to be sure all the surfaces are in contact. Some people clamp the foam in a vice to dry, but this is not necessary if you followed all the steps above correctly. Just press it firmly to ensure everything is stuck securely.

After the foam is stuck together, you can proceed to the next step. Unlike other adhesives (like Elmer’s), you don’t need to let the glue dry after the pieces are stuck together, assuming you allowed the solvents to evaporate before sticking the two glued pieces together.

To recap, the steps are:
1) Well ventilated workspace
2) Glue BOTH surfaces
3) Dry to the touch
4) Stick them together!
5) Press once, firmly

After you’ve finished a weapon, there may still be traces of solvent left in the glue which prevent it from reaching 100% strength. If you leave the weapon sit for a few days, these will evaporate and the weapon will be ready to use. As a general rule, it’s good to leave a weapon sit for a week before you fight with it. But even 24 hours of curing time helps ensure the glue is fully dried. While it cures, the weapon will continue to smell like the offgassing solvents, so it’s best to let it cure outside of your living space.

Follow those steps, and the seams you Dap together will last longer than the foam itself. 🙂

A few other pointers for advanced foamsmithing

The advice above is perfect for using Dap on blue camp pads, ensolite / marine foam, and fiberglass / pvc. But there are some additional tricks for using Dap on other kinds of foam.

Dap on microcellular foams

If you use puzzle mat foam (4lb eva), Fun Foam sheets (4lb eva), or 4lb microcell / minicell, you need to use two coats of Dap. All these foams have a fine, smooth texture instead of the hard, plastic-like skin on blue foam. These surfaces are slightly porous, and absorb the first coat of Dap you apply. As a result, if you use only one coat, there won’t be enough adhesive left on the surfact to get a good bond by the time the glue is dry to the touch. The foam won’t stick properly. Applying a second coat, about 5-10 minutes after the first coat, solves this problem.

The second issue to be aware of is that the solvents from the first coat of Dap (which the foam soaked up) will slowly evaporate out of the foam for the next several hours. As they evaporate, they can sometimes loosen the bonds created by the second coat of Dap. This causes no problems for seams that are under no tension; but seams where the foam is folded (such as the tip of swords or routed 4lb fries) can pull themselves apart when the glue is weakened. As a result, when you use microcellular foams, it is often necessary to clamp tensioned seams (even if the initial adhesion seemed to be good) to prevent the evaporating solvents from loosening the seam and allowing the foam to pull itself apart while your back is turned.

Tl;dr for microcellular foams:
1) Two coats, not one
2) Clamp seams that are under tension

Open cell

Open cell is highly absorptive, but you can still use Dap on it. The key is to apply very small amounts of glue to the foam with each brush stroke; if you pour a lake of Dap onto the middle of the foam and try to spread it out, it’ll just soak into the place where you poured it (potentially ruining the open cell as it dries). Instead, put a little bit of glue onto the brush and spread it over an area of foam the size of a quarter or half dollar. The repeat until the open cell is completely covered in an appropriately thin coat of adhesive.

To sand, or not to sand?

Should you sand your foam and cores before using Dap?

Many people say that Dap sticks better to rough surfaces. This is sort of true: on a microscopic level, Dap does better when it has something for its adhesive to bond to. That’s why Dap doesn’t stick well to cellophane or oil. But you don’t have to roughen the surface of a fiberglass rod to get an indestructable bond with Dap: if you spread it on evenly and allow it to get properly tacky, Dap will stick to smooth fiberglass without difficulty.

The only things I would recommend sanding are:

  • Strapping tape. Its smooth plastic surface does have a difficult time bonding to Dap. Sanding it removes the outer layer of plastic, exposing the fibers beneath which stick to Dap just fine.

That’s it.

Sanding won’t hurt (but probably won’t help very much) the following:

  • Blue camp pad. Blue foam’s smooth outer skin can stick to Dap if you follow the directions correctly, but it will be more forgiving if you sand it off. This isn’t necessary, but won’t hurt anything and may help you get better results if your Dap technique isn’t yet at 100%.
  • Fiberglass. It’s not necessary to sand, but again – if your technique isn’t yet at 100%, sanding might help marginally (and it won’t hurt anything).
  • PVC. The same as fiberglass: sanding isn’t necessary, but it won’t hurt, and it may help you if you’re still getting the hang of letting the Dap get fully dry before sticking it together.

There is no reason to sand:

  • Microcellular foams (4lb, etc)
  • Marine foam / ensolite
  • etc.

How to clean up Dap spills

Did you spill Dap on your carpet? Your shirt? Your favorite pair of shoes?

They’re ruined beyond hope.

cute-cat-pet-looking-up-408x544
Here’s a picture of a cute kitten to make you feel a little better.

Dap does make a product that will help remove the glue (you can buy it anywhere that sells the industrial-sized 5 gallon barrels of Dap). But it won’t save your carpet if you spill a can of Dap on it.

If you want your security deposit back, use Dap outside your house, and wear your painting clothes.

If you get Dap on your skin, don’t panic. It’ll peel off just like old sunburn. You can use acetone (fingernail polish remover) to speed the process if you want, though I personally just peel it off with my fingers.

Is there anything I can’t use Dap on?

Dap’s solvents dissolve styrofoam. You probably won’t be using styrofoam to make a Dagorhir weapon (unless you’re trying to make one of those old styrofoam boogie boards into a shield); but if you try, you’ll see that it melts styrofoam almost instantly on contact. This is because one of Dap’s solvents is acetone, a product used to remove nail polish, which breaks down the chemical structure of certain plastics like styrofoam.

It should go without saying that pouring Dap into a styrofoam cup to share with your buddy will end badly.

Good luck!

Good luck, and have fun!

And if you ignore Step 1 and use Dap indoors with no ventilation, be prepared for the mother of all hangovers in the morning!

About the author: Alric