Finishing with CA Glue
Cyanoacrylate glue, or CA for short, is commonly known by trade names such as Super Glue and Krazy Glue. It is an extremely strong and fast-setting adhesive available in three viscosities: thin, medium, and thick. Thinner glues have faster set times, while thicker versions have better gap-filling abilities. Once cured, CA is hard, crystal clear and waterproof but can be reversed with a special solvent or acetone. Though the solvent specifically for CA is expensive, it has the advantages of being faster acting and safer.
CA polymerizes, or hardens, when it comes in contact with moisture in the air and on surfaces it is applied to. Surface area is key to how quickly polymerization takes place – the thinner the CA is spread, the greater the surface area and, thus, the faster it will cure. Thicker pools of glue take longer to cure, from 10–60 seconds, or even longer.
To instantly harden the glue you can use accelerator, which comes in a pump bottle. Hold the pump bottle vertically, with the spout about eight inches above the workpiece and about one foot from the workpiece and disperse the accelerator. It is important to apply accelerator sparingly or it will turn the surface white, an effect called blooming. Too much glue or high humidity can also cause blooming; regardless of the cause, it is only cosmetic.
piece of paper (right) will work well for simpler surfaces. A section of folded paper towel (left) will allow you to apply the CA glue to a more contoured surface.
Too Much of a Good Thing
To speed up the drying process, you can spray accelerator on the newly finished piece, but too much will cause blooming.
Not Just For Turnings
This type of application is possible on almost any project, but start with the smaller items first.
0000 Steel wool, mineral oil, an extra-fine sanding block and abrasive compounds will allow you to fine tune the amount of gloss the surface has.
Pens Are Perfect
A pen is a great place to try a finish (Photo by Mack Cameron)
Smooth and Even
To produce a glossy surface, the finished piece should have a smooth and even coat of CA finish on it.
Making it Last
To ensure CA glue in its liquid state lasts as long as possible, you need to protect it from moisture. The best way to do that is to keep it in its specially designed container with the cap on. Whenever glue comes in contact with dust or other material, it will harden and become a lump of hardened glue. In order to keep the tip free of blockages, it is important to keep the tip away from anything that would cause the glue to cure – never touch the tip to the workpiece!
The gradual introduction of contaminants and moisture in the air will also cause the CA to thicken over time. There is really only one additional thing you can do to prevent this; buy smaller bottles so they will be used up quicker, hopefully before it thickens too much. Thickened glue doesn’t need to be thrown out; instead, it simply acts like a thicker-viscosity CA glue.
CA Glue as a Finish
I first discovered the idea of using CA glue as a finish while searching for a more durable finish for turned items subject to high wear. I found that the finishes marketed towards woodturners work quickly to build a gloss finish but aren’t as durable as I’d like.
Hard, clear, waterproof … even reversible with the right solvent. Those are four of the most important properties of a finish. Like any finish, CA requires careful technique for it to be applied successfully. There are many different methods, each suited for specific situations. Regardless of which method you use, you will end up with a resilient finish. Once the finish is applied, rub it out to achieve either a wet look or a finish as matte as bare wood. I usually apply two or three coats for a gloss finish and four and five coats for a satin finish.
Like many finishes, CA glues give off strong fumes so good ventilation is a must. Low-odour CA glues are available but cost roughly twice as much as the regular version, so I would use them only if the fumes are an issue. Unlike other finishes, CA is a strong, fast-setting adhesive so you must be a little more careful when applying it. You can protect your hands by wearing polyethylene gloves, which CA glue won’t stick to. Although nitrile and latex gloves are more commonly available, they are poor substitutes.
On unadorned spindles like your average pen barrel, I use thin CA, one polyethylene glove, and a scrap of plain white note paper roughly 2″x 3″. After sanding, I remove any sanding dust with a cloth dampened with methyl hydrate. Then I put the glove on my right hand and hold the paper, folded in half, ready for application. With my left hand, I add two drops of CA to the paper and apply it to the workpiece, quickly sliding the paper along the axis of the lathe while rotating the lathe’s hand wheel with my left hand. I continue until I’ve made it all the way around or when I start to feel the paper dragging. When you feel the drag, it means the CA is starting to set and if you continue to spread it, you will end up with smears that will have to be sanded back later.
For more complicated turnings with beads, coves, or other details, a different technique is required. I use the medium-viscosity CA because of its slightly longer open time. It’s also thicker so it won’t splatter as much. Instead of notepaper, I use a folded paper towel, which will conform to the contours of the workpiece, ensuring more even distribution. Don your face shield, set your lathe to its lowest speed and turn it on. Drip CA onto the workpiece while using the paper towel to distribute it evenly, stopping before it gets tacky. You should have an even coat over the entire workpiece.
With the first coat applied, I tidy up around the shop while waiting for the finish to set on its own; if your shop is already clean, you can use a spritz of spray accelerant to instantly set the CA. Once the finish feels smooth and no longer tacky, I apply the next coat exactly the same way as the first coat. I don’t bother sanding between coats unless the surface feels really rough.
Not Just For Turnings
With a slightly different technique, you can apply the same tough finish to other woodworking projects. When finishing larger surfaces, knowing how much glue you need becomes more important. Satellite City did an experiment with their thin CA glue, Hot Stuff, and found that one ounce covered 55 square feet of cardboard.
To apply CA to a flat surface, I use two polyethylene gloves, thin CA, and a rigid spreader (polyethylene is best but an old credit card or business card would also work). Apply a couple of drops and spread it out. Continue until the surface is covered. The first coat will soak in a lot – one drop will cover about one square inch. The second coat will also soak in, though not as much.
Once the wood is sealed, expect one drop to cover more than 10 square inches. Don’t apply many more than half a dozen drops at a time or you may find it sets before you can spread it out. Be careful of runs, which require more work later. As with any brushed finish, you can avoid runs by applying the finish sparingly – especially near corners. Once you’ve applied one coat, you can either let it dry on its own or you can use an accelerator. If you use accelerator, be careful not to drip any on the work piece, which would turn that area white.
To remove any imperfections, I use wet/dry sandpaper wrapped around a sanding block and lubricated with mineral oil. Before the second-to-last coat, I use 320-grit then I wipe the surface clean and apply a coat of finish. Then I sand with 400-grit before applying the final coat. Once the final coat has dried, some quick work with 600-grit should be enough to get a pristine surface.
Rub Out the Finish
At this stage your finish should be glossy and smooth. By buffing it with tripoli and white diamond compound applied to cotton rags or soft buffing wheels, you can slightly increase the gloss. Or, by scuffing the surface with 0000 steel wool and diffusing the reflected light, you can make the finish look almost as flat as unfinished wood. Should you rub through the finish, simply apply some more CA to that area and try again. Once you’ve achieved the sheen you like, you’re done. The best part about finishing with CA is that it is virtually maintenance-free – just keep it clean and it will continue to look as good as it did on day one.