By Ted Paone
Austin Armor Builders Society
October 6, 2004 

Solvent based Cements - The Gooey Glue 

The first type of adhesive is the solvent.  These are usually used with polystyrene, the common plastic used in injected molded kits.  These work by dissolving some of the plastic on each piece and when the solvent evaporates, the parts are welded together.  This welding action forms very strong bonds.  The evaporating solvent fumes are strong and should only be used with adequate ventilation.  

The solvents vary in how “hot” they are, that is how quickly they react and evaporate.  There are several types of these solvents; the most common are liquid plastic cement and tube cement.  Liquid cement is the solvent alone while tube cement has plastic added to it to help form stronger bonds and increase its viscosity.  Liquid cements are more volatile than tube cement, most advanced modelers use liquid cements for most building.  We all started using tube glues, if applied too thick they tend to distort thin plastic and produce a weak bond.  

Tube cement is used for structural applications because it forms a stronger bond.  Testor manufactures cement, which is about half way between tube and liquid cement.  Solvents are usually specific to a type of plastic.  Modeling cement and Pro Weld can be used with multiple polystyrene.  Some solvents, such as ABS cement and Pro Weld can be used with multiple types of plastic so choose a cement with that in mind.  

Solvent based cements can be used for other things than just sticking models together.  It can be used to dissolve  plastic into a gooey paste to be used by figure modelers for adding hair and mustaches and beards or covering paper for clothing.  Liquid cement thins fillers such as Dr. Microtools for filling scratches or making mud or zimmerit.

Liquid glues can be applied using a wire applicator or an old small brush.  Most brushes supplied with the liquid glues are too big for use.  Tube glues should never be applied directly from the tube.  Squeeze out a small amount on a disposable palette and use a toothpick to apply it.

Types of Plastic Solvent Cements

Tenax 7R - Very hot liquid solvent.  This solvent provides a quick strong bond.  Works by capillary action so parts must be assembled before using this glue.  I don’t use this because it evaporates so fast and I work slow.

Tamiya Extra Thin Glue - Hot liquid solvent.  This solvent also provides a quick strong bond.  This is a new glue which is my favorite.  It comes in a square bottle, which makes it tip resistant.  It has the best applicator brush of any supplied with a glue.  Works quickly and flows well but allows parts to be assembled as they are glued.

Pro Weld #4 - Hot liquid solvent.  Inexpensive but has a strong odor.  This is used by professionals and is recommended by many modelers.  It can be purchased from a plastic supplier.  There are several varieties for the different types of plastic.

Testors Liquid Cement - This is the least hot solvent glue I have used.  It works with my building style and I use it as a solvent for thinning fillers.  I also use it for erasing small scratches on sanded plastic before painting.

Testors Model Master Liquid Cement - Semi liquid cement that is very strong but slow drying.  This comes in a neat applicator and replaces tube cement while retaining strength.

Plastruct Plastic-Weld - This is an ABS (Acrylobutyl Styrene) solvent, which can be used to bond Plastruct structural elements together.  It is also capable of bonding polystyrene and acrylics.  Use this to assemble anything using Plastruct elements.

TIPS:

1. Use an old paintbrush to apply liquid cement.
2. Apply a light coat to each side to start the solvent process, assemble the parts, and then touch the loaded brush to the joint to produce a strong weld.
3. Use a coffee can or yogurt plastic cover to hold a small quantity of tube or semi liquid cement and apply with a toothpick.
4. For bottles taller than they are wide, glue them to a larger base or push them into a clump of clay to keep them from tipping over.
5. If you spill the bottle or get too much on your model, DO NOT WIPE IT OFF.  Allow it to dry without disturbing it and you may be able to save your model.
6. Keep a bottle of Sprue solution, sprue dissolved in liquid cement (Testors is the best) for use with figures.

Epoxy Adhesive - Power to Stick

Epoxies glues are very strong two part glues, which can be used to glue together any two materials and should be a part of your glue kit.  The two parts are a resin and a hardener and are usually mixed in equal parts.  The mixing causes a chemical reaction, which hardens the glue and makes it adhere to the parts.  Epoxy dries very strong and hard with some flexibility so it can take some shocks and hold very heavy parts.  Epoxy comes in different minute designations, 5, 15, and 30 minutes, these are the working times after mixing.  Some like JB Weld, have metal mixed in to make it much harder for future machining.

Epoxies are very useful for parts, which need a strong bond.  They form the strongest types of bonds after solvents.  The longer the working time, the stronger the bond will be.  Epoxies can be used to join almost any two materials together as they bond strongly almost anything.  Epoxies clean up with acetone or Isopropyl alcohol.

Types of Epoxies

5 Minute Epoxy - 5 minutes working time, 15 minutes to setup before handling.  Full strength in 1 hour.  Flexible bonds, not waterproof.

15 Minute Epoxy - 15 minutes working time, 45 minutes to setup before handling.  Full strength in 2 hours.

30 Minute Epoxy - 30 minutes working time, 8 hours to setup before handling.  Full strength in 24 hours.  This epoxy provides the strongest bonds.

JB Weld - 30 minutes working time, 8 hours to setup before handling.  Reaches full strength in 24 hours.  Machinable, can be used for making new parts.

TIPS:

1. The epoxy bonds best to clean textured surfaces so you may want to scruff with sandpaper before gluing.
2. Place a series of small dots of each of the epoxy parts on your disposable pallet so you can mix a very small quantity at a time.
3. Tack large parts together with small amounts of CA in strategic locations to hold the parts in place while the epoxy dries.
4. The time designations are the working times so do not over mix a large quantity.
5. Heat can be used to speed the curing of the epoxies and makes the flow easier.  If they are too cold, they many never cure so do not store them in a refrigerator.
6. Use epoxy to assemble metal models as they can have heavy parts, which need the strength of the bonds.
7. Assemble resin-using epoxy for the joints, which need the strength.
8. Glue your gun barrels in with epoxy
9. Thin layers increase the working time.
10. High air temperatures decrease the working time, up to 25% at 90 degrees F.
11. Use a toothpick or wire to mix and apply epoxy.
12. Excess epoxy can be cleaned up with alcohol or baby wipes.
13. Slow setting epoxies can be mixed with micro balloons to make strong filler.
14. Slow setting epoxies can be used to represent puddles and water in dioramas but stir them carefully so you don’t mix in air bubbles.
15. Slow setting epoxies can be used as a substitute for resin when making parts in a RTV mold.

Cyanoacrylates - Like Krazy Glue, Man

Cyanoacrylates have become the adhesive of choice for many model builders.  It comes in various thicknesses, capabilities, and bonding times.  Its main advantage is the speed with which it bonds.  Its main disadvantages are its costs and its short shelf life once it is opened.

CA can bond most materials.  It has a good separation strength but does not have strong shear resistance (the reason many photo etch parts fly off your model when it is bumped).  The thicker ones can be used as gap filler and can be easily sanded in the first 24 hours.  The glues can be instantly set using an accelerator.

CA’s are reactive monomers that chemically link (polymerize) when pressed into a THIN film.  The very thin layer of moisture on most surfaces acts as an alkali or weak base, which is the catalyst that triggers the bonding.  However, detectable amounts of water usually degrade the bond.  CA’s give off an irritating vapor when curing so be sure to work in adequate ventilation.

Types of CA

Different manufactures make CA with slightly different formulas.  I usually purchase my CA from a knowledgeable hobby shop to make sure I am getting fresh CA.  I do not recommend buying tubes of Krazy Glue, I have thrown away more of this crap than can justify any saving over the bottles bought at hobby shops.

Thin - This water thin viscosity CA is the fastest cure, 1-5 seconds.  It wicks deeply into joints by capillary action.  Because it relies on a very thin film to trigger the bonding and does not fill gaps, the surfaces to be bonded must be tight fitting and held together while bonding.  There is NO adjustment time, your photo etch must be in the right place when glued.  They work well with wood as they penetrate the wood fibers.

Medium - I probably use this gap filling CA more than any other glue.  It is thicker than thin and takes 5-15 seconds to bond allowing alignment before it sets.  Use with accelerator to fill gaps or sink marks.

Thick - This CA takes 10-15 seconds to cure.  This is great for gap filling although I usually use medium thick.

Rubber or Flex CA - Addition of rubber and carbon make this ideal for many applications.  Flex CA does not turn brittle so the bonds will absorb some shock.  IT comes in thin and medium consistency.  Good for bonding moving parts or photo etch which may be subject to shock or bumps.  Find this CA where RC modelers shop.

Accelerator - This is a catalyst, which quickly cures CA in thick layers by enhancing the alkaline conditions during polymerization.  Freeze CA so it can be reused for filling gaps.  Accelerators cause a minor degradation on the bond strength.  Sometimes comes in a pump spray bottle, throw away the sprayer and use a micro-brush to apply.

Debonder - Softens cured CA.  Use it to remove bonded parts, clean up excess CA or unstuck your fingers.  May remove paints from some surfaces.  Before you use any CA, get yourself some debonder or you may be singing “Stuck on you”.

TIPS:

1. Never get CA in your eyes, if so go to the Emergency Room immediately.  If you do, it can make you blind, really.
2. CA can bond skin, which is what it was originally developed for, replacing stitches during emergency operations.
3. If you glue yourself to something, even yourself, use debonder as your skin will tear before the CA joint will.
4. If you cut yourself with a knife, chisel, or something, use CA to glue your skin together.
5. Do not use CA if you have a puncture wound or have a deep cut below your skin layer.
6. Keep CA refrigerated when not using them, they seem to last much longer before getting too thick to use.
7. Moisture is the enemy of CA in the bottle.  When finished smack the bottom of the bottle on your table to knock down any CA in the spout so it does not clog and then squeeze out any air in the bottle before closing with the cap.
8. More is NOT better.  CA works best when you use the least amount of glue necessary.
9. Do not use CA directly from the container.  Put a small amount on wax paper on a plastic yogurt or coffee can top and use a wire, toothpick, or micro brush to apply the right amount of glue.
10.  Make your surfaces are clean and grease free.  Use alcohol to clean them if necessary.
11. Thin Rubber CA works well for gluing photo etch parts on plastic as it will take some shocks.
12. Use CA to glue resin parts, especially the smaller parts.
13. Do not use CA on clear parts, as it will eventually fog them.
14. Apply accelerator with a micro brush, micro drop applicator or just hold the joint above the open bottle of the accelerator and let the fumes do the work (Thanks Russ).
15. Too much accelerator can weaken the joint.
16. Seal the accelerator bottle and do not store with your CA as the fumes will affect the bottled CA.
17. Tack the parts together with quick setting CA and then use the slower setting CA or epoxy to fill any gaps. 
18. If the joint does not stick, let it dry for about 10 minutes and then try again applying less adhesive.
19. Sand the CA area within 20 minutes if using as filler in plastic.  After 24 hours, it is harder than the surrounding plastic and may not san as easily leaving an obvious fill mark.
20. Mix talc or micro balloons with medium CA to make a fast setting, easily sanding filler.

PVA - White Glue

PVA or Polyvinyl Acetate is a great group of glues, which are very useful in the modeling community.  PVA’s are a class of adhesives, which has the most variance of bonding strength.  There are many different types, good old Elmer’s Glue All (weak), Microscale Liquid Tape (medium to weak), Weldbond (strong).  PVA dilutes and cleans up with water.  They dry quickly and get stronger over 24 hours.  They all dry clear gloss and can be easily covered with flat.  I keep several PVA’s in my toolkit.

  TIPS:

1. Use PVA to glue clear parts.
2. PVA bonds foam!
3. Mix PVA with Celluclay for groundwork, this will help prevent the Celluclay from curling at the edges or cracking.
4. Use dluted PVA to glue static grass.
5. Use PVA to gue your groundwork, rocks, twigs, degris, etd.
6. Use PVA glues on Plaster buildings.
7. Thick PVA can be used to simulate shallow puddles or water splashes.
8. Diluted PVA can be used to cover tissue paper to simulate canvas coverings or clothing.
9. Flags can easily be made out of PVA soaked tissue.
10. Use weak PVA to glue pieces together temporarily so the can be sanded or shaped as a group.
11. Use PVA on the backs of your decals if its glue has gone bad.
12. Use PVA to glue the packs and additional equipment to your armor models.  It can be used without removing the paint although this is a weak bond.
13. Use strong PVA to glue photo etch to plastic.
14. Glue paper templates to plastic for shaping or scribing.
15. Color the glue with acrylic paints.

Miscellaneous Adhesives 

Here is a short list of other adhesives, which are handy in model building.

Rubber Adhesives - So called Rubber Cement – Used as a temporary glue to join parts together for common shaping.  Temporarily glue parts in place to test fit.  Glue paper templates on plastic for cutting.  Use Rubber Adhesives for temporary mask, although a little hard to remove.  Also bonds paper and cardboard permanently if used as contact cement.

Dry Glue Sticks - Use on paper to create temporary paper masks.  Much like Post-It-Notes ^TM.

Hot Glue Gun - Used to affix groundwork to bases.  Be very careful as it remains hot after it is dispensed.

Silicon Based Adhesives - GOO - This group of adhesives is very good for gluing groundwork and affixing models to bases.  Takes shocks well so I use it to glue anything, which has much mass and must be transported.

Yellow Wood Glue - If you are gluing two peices of wood together, this is the best stuff to use.  It creates a bond stronger than the wood itself and cleans up with water.

Summary 

There are many different kinds of adhesives, which can be used in modeling.  Each adhesive has its own use as you mix the model media.  I hope this gives you a start in understanding the different types of adhesives and the materials with which they work best and by applying this knowledge, improver your skills.

Please excuse any bad puns that stick in your mind.

References 

Using Cyanoacrylate and Epoxy Adhesives - Bob Smith Industries - Product Brochure.

Glue Basics - Matthew Usher - Fine Scale Modeler Vol. 22 No. 7 - September 2004, Kalmbach Publishing Company, Waukesha WI .

The Modelmakers Handbook - Albert Jackson and David Day - 1981 - Alfred K. Knopf, Inc.  New York , NY .

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