FINISHING OPTIONS FOR MUSICAL INSTRUMENTS
With personal health and environmental concerns (and regulations) ever increasing, the manufacturers of finishing materials have seen that the long term trend is moving away from solvent based finishes and toward less hazardous, less toxic products. In response, many manufacturers set the goal to manufacture a finish with all of the positive characteristics of current solvent based lacquers but without the hazardous, toxic solvent base.
There have been steady improvements in water based products intended to eventually replace the solvent based products for all applications. There have been hits and misses, but the currently available water based products are finally close enough to this goal to be used for guitar finishing. These products are now as easy to apply and work with as solvent based lacquers and give great results - especially considering the obvious advantages of using a less toxic water based system. Guitar builders using these products claim that they are achieving finishes that are comparable with those of the solvent based product.
As with the solvent based lacquer system, there are many good products available for pore filling, color shading, sanding, and buffing that are compatible with this water based urethane. Although most builders are spraying the water based urethane, this product also works well as a brush-on finish.
The advantages of using this water based urethanes are tremendous for all woodworkers. The health risks and environmental harm are diminished to almost nothing. Cleanup is easy with warm water. The vapors are not harmful or toxic so no breathing protection or strong ventilation is required. The water based urethane has very high solid content so less material is used to finish each instrument, and there is no need for lacquer thinner during spraying or cleanup. Any required thinning is accomplished with distilled water or a compatible reducer. This makes the water based system far more economical (guitars per gallon) than using solvent based lacquer. Because of its less toxic nature it can also be shipped without restriction - unlike hazardous/toxic materials.
We presently offer the KTM9 water based finish and are confident that it is a great water based finish to compete with nitrocellulose lacquers. It is clear, hard, repairable, economical, does not require a cross-linker or other additives, and shows no blue tint on the finished instrument. It is the finish that we recommend most highly to beginning and professional luthiers.
Other materials used with water-based lacquer:
• Staining raw wood - Use either our Alcohol Soluble Aniline Dyes, FSB or Water Soluble Aniline Dyes, FSBW or dye concentrate, FMDY (Water-Soluble or MEK-Soluble).
• Shading color mixed into finish - Use either Water Soluble Aniline Dyes, FSBW or Water Soluble dye concentrate , FMDYWF.
• Pore filler - LMI Pore Filler works fine but for best results, use our System 3 clear epoxy filler ( FSB1.5K or FCC1.5K) with the silica thickener (FST1Q)
• Sealer –Use the finish itself as a sealer or one of our shellacs.
Some Frequently Asked KTM9 Questions
Are there instructions for how to apply this finish?
Yes, see articles below.
Does the KTM9 require a cross-linker?
No, this was only required on the previous KTM product, the KTM4
Does the KTM9 require a sealer?
No, you can use the finish itself as a sealer
How does it differ from previous water-based finishes?
The KTM9 is by far the best waterbased finish available. It is relatively problem free, is clearer than other products on the market and is harder.
Most Waterbased finishes have a blue cast when you turn the instrument in the light. Is this true for the KTM9?
No! The clarity of the KTM9 is substantially clearer than other waterbased finishes on the market.
How does it differ from Nitrocellulose lacquer?
Only the most experienced builders will notice a difference visually (assuming the finish was applied correctly). It is very clear and transparent and can be applied thin so as not to inhibit the tone of the instrument. It is much harder than any other waterbased lacqer, and almost as hard as Nitrocellulose. It is similarly easy to repair.
One great advantage over lacquer that the KTM9 has is that it is much, much safer to use. You do not need to buy a spray booth to apply it and it can be shipped anywhere. It is also better for your health (lacquer can cause respiratory and other problems with prolonged inhalation or exposure) and is much kinder to the environment as well.
I have applied the finish and am having trouble achieving a flat surface. What did I do wrong?
Achieving a good finish is always challenging but KTM9 is relatively easy to use and immune to many common problems. Still, finish work is never simple and you must take care to make sure the finish comes out perfect. If you are having troubles chances are that the finish is not at fault! The most common culprits are:
- Applying the finish too thick
- Not having a flat, smooth surface beneath the finish
- Poor pore filling
- Using with incompatible products
- Unclean spray equipment
- KTM9 is fairly forgiving when it comes to the ambient humidity in your shop, but this can be factor as well
Can I apply the KTM9 over an oil finish, shellac or a solvent based sealer?
KTM9 adheres well to shellac, but it is probably best to avoid applying it over oil, varnish, or other solvent based products such as nitrocellulose lacquer or sealer. The only products that we know for sure to be safe are flake shellac (like we carry, avoid the pre-mixed hardware store variety) our Microbead filler, the System 3 epoxy filler and the previous KTM product, KTM4. It's possible that it may be compatible with other waterbased products available, but we can not be sure.
Do I need to use a spray booth when finishing with KTM9?
A spray booth helps with ventilation (which is absolutely essential with a nitrocellulose finish) and helps to eliminate dust in the air. Since ventilation is not so critical with the waterbased finish (you can finish next to a fan near an open window) you can do without a spray booth if you have adequate dust control in your finishing area.
Can I brush on the KTM9 finish?
Spraying this (or any other) finish is best because the coats can be applied thinly and evenly –but you can use a brush with excellent results.
How do I get the best results when using a brush?
Use a fine cell foam brush (available at any paint or hardware store). Use the flat portion of the brush near the edge and avoid using the point of the brush. Do not over-saturate the brush with finish. Practice applying the finish as thin and even as possible before applying the finish to your instrument. As with any finish, it is best to work in a dry, humidity controlled environment.
How many instruments can I finish with a quart of KTM9?
Approximately 4 to 6 instruments. Compared with Nitrocellulose lacquer it is a very economical product.
Are there compatibility issues with other products?
We have heard that it is best to use our FGX yellow glue since regular Titebond tends to cause sinking around binding and purfling joints. It can accept our Waterbased Metal Acid dyes and our Water based Aniline dyes. If you are dying the wood directly (as opposed to adding it to the finish) be sure to use the alcohol or MEK based dyes to keep the colors from running.
Are there shipping restrictions with this product?
Unlike Nitrocellulose lacquers, the KTM9 can be shipped overseas or by air delivery.
What pore fillers can I use?
The clear System 3 epoxy filler we carry will give you the best results. It enhances the appearance of depth and the durability of the resulting finish. Our microbead fillers work well if you must use a colored filler.
Can it be buffed or polished?
Yes, it can be machine buffed or hand polished just like Nitrocellulose finishes.
KTM WATER-BASED LACQUER COMPLETE FINISHING PROCESS
KTM-9 successfully creates a nitro-lacquer like finish, but with the environmental and health advantages of water based chemistry. It is simple and safe to use, very forgiving in the application process, has all of the desirable physical and visual properties of the solvent base finishes, and saves time. KTM-9 is a self-cross-linking urethane/acrylic co-polymer which cures to hard in one week. The application process takes two days, spraying 4-6 coats per day and sanding lightly between every other coat (as necessary). Because the flow out is so good, there is very little leveling necessary and runs are rare, even with heavy application. Here is John Greven's method of applying KTM-9 which maximizes its lacquer-like look and durability.
PREPARATION OF WOOD BEFORE FINISHING
- Sand surfaces smooth and scratch-free. On the hardwood sides, back, and neck, sand with the TRI-M-ITE papers. Use progressively finer grit papers from 120 grit through 220 grit - sanding with the direction of the grain. To maintain flat surfaces always use sanding blocks or rubber sanding pads to support the paper. Each progressively finer grit must remove the scratches from the previous sanding. Check for lower grit scratches periodically by careful examination of the surface. This close examination of the surface (and your sanding progress) can be enhanced by wiping the surface with Naphtha or lighter fluid and closely examining the surface while wet with fluid. While wet it will appear as it will under finish and even small scratches will be apparent.
- Repeat this sanding process on the softwood top, but you may need to proceed through the finer 320 grit paper for a perfectly smooth, scratch-free surface.
- Mask off the fingerboard and cover the soundhole as required. The instrument is ready for filler/finishing.
- Fill open pores in hardwood: Most of the hardwoods used for guitar bodies and necks - e.g. all rosewoods, Koa, Walnut, Mahogany, and more - have very open pore structure. These open pores show as a multitude of tiny depressions throughout the smoothly sanded surface of these hardwoods. It is essential to fill these tiny depressions to achieve a flat and smooth surface. This is the most important step in the finishing process to achieving a perfect glass smooth final finish. Committing the time and keen attention toward filling the pores effectively, and thoroughly, at this stage will reduce the time and effort used in spraying and sanding the clear lacquer coats later in the process.
Silica thickening powder can be added to System 3 epoxies to thicken them if necessary. It will not compromise the clarity of the epoxy and makes it easier to sand. I suggest starting with one part silica powder to 3 parts epoxy mix to bring the mix to the thickness of whipping cream. Many people prefer to make the epoxy thicker for the back and sides and thinner for the top. Squeegee the Clear Coat System Three epoxy material over the entire surface to be finished, making every effort to push the epoxy into the pores while maintaining a thin, flat film. Don't worry about dust or other blemishes, as this coat will be sanded later. Allow to cure overnight until hard. A grocery store variety window squeegee cut down to approximately 4 inches works great to apply the epoxy filler.
Dry sand lightly with 320 (I use a random orbital sander for this). Recoat with a second application of the epoxy and allow to set-up overnight.
The next day, sand the epoxy level and free of pores with 320 or 400 grit paper. It is important not to sand through the epoxy film to bare wood as this will show up under the finish as color changes. If you are able to produce a dead flat, level, pore-free surface at this point, you are ready for the KTM-9 top coats. If there are still pores showing, repeat the epoxy step.
FINISHING WITH KTM-9
- Starting the finishing process. When the epoxy coats have been sanded flat with no pores and no sand-throughs, it is time to start the KTM-9 top coating. The finish may be brushed on or sprayed with any of the same kinds of equipment as one would use for lacquer. I use a conventional compressed air gun at 45-50 pounds pressure. I would also recommend thinning the KTM with 1 TBS of denatured alcohol per cup of finish to improve the film deposition when spraying. No thinning is required when brushing.
- Spray 4-6 coats per day waiting one hour between coats (or until the previous coat is hard to the touch). Because this finish flows out so well, there is rarely need for sanding between coats.
- Allow the finish to set up overnight.
- Day two, the first coats will be hard enough to sand back with 320-400 grit paper. This allows for a better mechanical bonding with the succeeding coats. It should not be necessary to sand heavily as the initial film should be very flat. It is a good idea to sand out any small runs or other blemishes before doing the final coats.
- Four to six coats sprayed at one hour intervals should be plenty of finish. Hang the instrument up in a warm place for a week to cure out.
- To prepare for final buffing, fine sand with 1000 or 1200 grit paper, followed by 2000 grit Abralon. I continue to 4000 grit Abralon, but this is not absolutely necessary. It saves a little buffing time. When the finish is flat and smooth from sanding, it's onto buffing.
- Machine buff with medium compound on a 12 inch buffing wheel running between 650 and 1200 RPM. I like the slower speed for greater control, Mike Doolin prefers the higher speed. Change pads and buff with the fine compound to a high gloss. The entire buffing process takes about 20 minutes per body, less for a neck.
The resulting finish will dazzle. It is totally transparent, warm and crystalline like nitrocellulose lacquer. It looks deep without being thick. The film is tough and hard as well as very resistant to solvents and sweat. Repairs are easy as well. A light sanding and recoating will bring back the finish to original perfection.
One last note: the KTM-9 is backward compatible with other water base finishes should you need to overtop an older film with the new material. Light sanding of the old finish should allow for minimal witness lines and excellent adhesion.
Following are two articles on finishing with KTM-9 water-based lacquer by Keith Rhodes and Mike Doolin
HAND BRUSHED APPLICATION AND FINISHING PROCESSES
by Keith Rhodes
KTM-9 is a waterborne finish which creates a finish similar to a nitro-cellulose lacquer finish. It is a self-cross-linking urethane acrylic co-polymer. Applying this finish can be completed in approximately one week. The finish is applied directly from the can with no thinning required. It has good flow characteristics, so that not much sanding is required between coats. The final buffed finish is extremely clear.
I have built classical guitars for several years, always using a hand applied French polish finish to the entire guitar. (The results have always been pleasing but I have often been disappointed when people have played my guitars and have returned them with scratches-a result of somewhat careless handling and the softness of the French polish.) With this in mind, I decided to apply KTM-9, a hard wearing finish to the back and sides of my instruments. All of my soundboards for the present time, however, will still be hand finished with shellac.
Having a small workshop and not wishing to purchase expensive spraying equipment or build a spray booth, I decided to try hand brushing the finish coats of KTM-9. I read both Mike Doolin’s and John Greven’s articles about spray finishing with KTM-9. I found the articles to be well written and very informative and I followed many of their recommendations. I was not able, however, to track down any information in these two articles or indeed anywhere about hand brushing this finish, so I basically used a method similar to applying a brushed traditional violin varnish finish and followed my intuition.
Here is the way I hand brushed and finished a classical guitar. I hope that you will find the description useful for finishing your own instruments.
I finish sanded the instrument as I normally do. This particular wood required a pore filler, so I applied two thin coats of Z-poxy. Working with a small area at a time, I used an angled credit card to force the epoxy into the pores. The card was then used to remove as much of the still liquid epoxy as possible. A safety razor works equally well for this task. The idea is to apply very thin and even coats of epoxy. A strong back light is essential to judge what is happening with the epoxy. Backlighting is also important later on, both when working with the KTM-9 and during the buffing operation.
The epoxy coats were applied 24 hours apart, sanding between coats using 320 grit wet/dry paper. As you would with any sanding operation, be sure to use a good quality fine particle filtering face mask when sanding the dried epoxy. Water was used as a lubricant, as it keeps the dust down and creates a slurry which speeds the cutting action. It is important not to sand through the epoxy to bare wood because this will show through the final finish. In most cases, after two coats of epoxy, I ended up with a flat, even surface free of pores. If I was not happy with the result, I would continue to apply more coats of epoxy, following the same 24 hour time schedule.
A varnish brush is not suitable for KTM-9 finish because the bristle soaks up water and the finish is water based. For about $4, I bought a 2" polyester “Shortcut” brush by Wooster Co. at Home Depot. The brush is easy to handle and has splayed bristle ends which help the finish coats to flow well. This brush does not absorb water.
I began by heating the can of KTM-9 by placing it in a large pan of hot water for 10 minutes, which I think helped the finish to flow from the brush more easily. While this was cooking, I spread clean paper on the work bench and gathered some paper towels.
To charge the dry brush, I dipped lower quarter of the bristles into the finish for about 3 or 4 seconds, then I withdrew the brush to just clear of the surface and allowed it to drip gently into the can until no more drips fell from the brush.
The instrument was set horizontally on the covered bench with the back facing upwards. I quickly and smoothly applied the finish, starting at the top about two inches in from the side of the upper bout. The first stroke was extended from about two inches from the top to two inches from the bottom. This column of finish was then brushed out to cover the two inch uncovered strips. This procedure was adopted to prevent the finish from flowing over the binding running down the sides.
The second stroke was started two inches from the top and continued down to two inches from the bottom. This stroke was made to slightly overlap the first stroke. The uncovered areas at the top and the bottom of this second stroke were then brushed in. Subsequent strokes followed this procedure until the top was covered completely. Please note that the brush should always move from a wetted surface to a dry area-the same as if you were painting an interior house wall.
As the finish was applied, I kept recharging the brush by dipping the end of the bristles into the can for a couple of seconds and allowing the excess to drip off the brush back into the can. Using this method, I avoided creating bubbles by working the brush too much.
It is very important to use a strong back light to see where the finish is going, and one has to be careful not to miss a spot. It is also important to charge the brush with the correct amount of finish. This comes with experience.
I did not brush back and forth but laid down the finish as smoothly as possible, trying to have the finish flow onto the surface. If I missed a spot, I did not try to rebrush it.
When I finished coating the back of the guitar, I moved to the sides. I held the guitar by its neck and coated the sides by working down from the heel of the neck to the butt of the guitar-first one side and then the other. The guitar was held vertically and the strokes were made from the center of the sides to the back and from the center of the sides to the front at about a 45 degree angle.
It was important to work quickly and smoothly. I did not to try to touch up any area because this would have resulted in a streaked finish. The surface was covered once, then was allowed to dry.
I applied three coats of finish each day for two successive days and allowed the finish to dry for a minimum of two hours between coats. An infra red lamp can speed up the drying process if you have one. If there were any gross drips, I sanded them off with 400 wet/dry sandpaper before I applied the next coat.
After the final coat was applied, I allowed the finish to dry for a couple of hours, then I sanded. The instrument was then allowed to harden for four weeks before final sanding, buffing and polishing.
The instrument was wet sanded with successive grades of sandpaper starting with 400 grit Mirka wet/dry paper using a flexible rubber block as a backing. When I was satisfied with the overall appearance of this layer, I moved through finer grits of wet/dry Mirka. I used 600 grit, 1000 grit, then 2000 grit successively. As the water was applied to the surface during the sanding operation, the beauty of the wood grain started to jump out at me and I began to have a feel for what could be expected in the completed instrument.
Finally, although not strictly necessary, I used a dry 4000 micro abrasive because I thought that it would save me some time during the buffing operation. This followed John Greven’s recommendation.
I had to build my own buffing machine. I bought a buffing arbor, two 12" diameter muslin buffing wheels, two 12" diameter cotton (Domet) buffing wheels and two large steel washers to support the center of the Domet wheels from LMI. I also bought a 1 inch diameter pulley to mount on the motor shaft. In addition, I bought a stick each of Menzerna brown course (600 grit) and white fine abrasive. From Brazil Electric, I bought a 1 1/3 HP, 1725 RPM electric motor. All of this stuff was assembled on a plywood base, which was clamped to a heavy wooden stand that I move outdoors for the buffing operation. The center of the muslin wheels were flooded with cyano acrylate, and after the glue had dried, power sanded to ¾” diameter to fit the arbor shaft. The glue causes some smoke when dropped onto the cotton. The pulley ratios gave me a buffing speed of about 1100 RPM, which is about the upper limit for buffing, but gave me no problems.
Buffing was a fairly easy operation and only took about 15 minutes. The Domet wheel was charged with the brown coarse compound and the Muslin wheel, with the white fine compound. Each wheel was dedicated to each compound. A strong light was used to keep a beady eye on things.
Important note: A buffing machine is an efficient transportation system, which will move your new guitar, in the blink of an eye, by air, from one end of your shop to the other, so be sure to have a firm grip on the your instrument before you start to buff.
The buffing wheel will rotate toward you, so hold the instrument slightly below the level of the axle. I gradually brought the instrument surface to bear on the wheel charged with the coarse compound. I worked down the spine of the instrument out towards the edges of the bout. The back was buffed this way. I repeated at 90 degrees, then again at 45 degrees. Do not present the edge of the instrument directly into the buffer because you will burn the finish off the edge Do not use a lot of pressure on the wheel, a somewhat light touch is all that is required. The back of the neck and the sides were buffed next.
The same procedure was followed using the fine buffing wheel.
You may hand polish or you can power polish using Abralon sanding disks. These are available from LMI.
I rate this first attempt as highly successful and I am pleased with this finish, which came out very clear and transparent. Application was far easier than I had thought and, with more practice, I expect to become very proficient at using the brush to apply this finish. The two most difficult parts of the process were judging the correct amount of finish to charge the brush with, and the method of brushing out the finish onto the instrument. This was, however, a matter of experience and I quickly found way of handling this finish.
I suggest that before trying to finish an actual instrument you practice on some scrap plywood to get your feet wet and refine your technique.
Give it a whirl! You will be delighted.
Waterborne Finishing with Grafted Coatings "KTM-9"
by Mike Doolin
Please note: As of January 2006, I have switched to catalyzed polyester and am no longer using waterborne finishes on my guitars. I have not used a waterborne product since then, so I'm sure my knowledge of them is hopelessly out of date. I will not be updating these instructions any further, nor will I answer email questions about them. Such as they are, these instructions contain everything I know (or rather, knew) about waterborne finishing.
Why did I switch? Hardness, and speed. Polyester is pretty much the standard finish on factory guitars, and it provides the durability to which most steel-string players are accustomed. And since it's basically 100% solids and cures by catalyzation instead of evaporation of solvents, it doesn't shrink back over time. I can rub out a finish after 5 days cure and know that a year later it will look just as good.
But those qualities come at a price, and that price is toxicity and flammability. I spent about $2000 on a commercial spray booth, built an explosion proof room around it, and vented the booth out through an unused utility chimney. Plus, I bought a supplied-air full-face respirator. With solvents like acetone and MEK and with MEKP as the catalyst, this stuff is not to be trifled with. Besides, it stinks to high heaven until it's cured.
And so, I still recommend waterborne finishes to small-production and hobbyist luthiers, and anyone unwilling or unable to make this kind of investment in finishing equipment. But I would recommend asking around about waterborne products which have come out in recent years, it's likely that improvements have been made, and I haven't kept up on the technology.
Finishing is the Achilles Heel of lutherie. Lacquer, the standard by which all others are judged, is clear and tough but toxic and flammable. Waterborne finishes try to solve the problems of toxicity and flammability, but never seem to be really clear and really tough. We've all tried the waterborne products offered for musical instruments and found them wanting.
When I decided to build guitars full-time I knew I'd have to find a waterborne finish which really did the job. I wanted to work from my home, which meant working in the basement next to my gas water heater and furnace, which meant that highly flammable finishes were not an option. So I bought a little of every waterborne finish I could find, from hardware-store hobbyist products to commercial acid-catalyzed cabinetmaker's finishes. Overall, the quality was shockingly low, and the best of the bunch were mostly those already offered to luthiers.
But in recent years, waterborne technology has advanced tremendously, and I've tested and sometimes used new products as they've come out. The latest of these is Grafted Coatings "KTM-9". It dries hard and clear, can accept water- or alcohol-based dyes for tinting and colors, and rubs out to a high gloss. It builds, self-levels and burns into itself well. It has low shrinkage after curing and leveling, and is resistant to sweat. The resulting finish is the closest I've seen to traditional lacquers and varnishes.
I spray in my small shop wearing a mask, near a 12" fan blowing out a window. I wear a glove on my left hand since I hold the guitar with it while spraying with my right, to avoid spraying my skin. I don't have a spray booth, I'm spraying in a corner of my main shop space, so I run my air filters for a few minutes before and all day during spraying, to keep the wood dust out of the air. The space has no humidity control and not much temperature control either, so actual spraying conditions vary from about 60 to 90 degrees Fahrenheit, and 35% to 85% relative humidity, depending on the time of year. However, I have a humidity controlled storage room where I put all works in progress; the humidity is always 45% in there, while the temperature varies from about 75 to 85 degrees. I hang pieces in there immediately after spraying each coat, so they dry under controlled humidity conditions. Then after all spraying is complete, I leave the sprayed pieces in that room while they cure.
I've developed a method for applying waterbornes which has been giving me very good results. I commonly hear luthiers tell me that they assumed my finishes were lacquer! This stuff works, if you play by its rules. So here's my method as of this writing...
KTM-9 is water clear with no tint whatsoever. Though not necessary, a little tint can give a nice warm lacquerish tint to the finish if you want it. I like the Color Tone tints. These tints don't seem to affect the curing properties at all - I've done very intense transparent and opaque color finishes on solid body instruments with no difficulties. For a basic amber tint, I put 2 drops of Vintage Amber and 1 drop of Red Mahogany in a cup of finish, and spraying 2-3 coats of this adds up to a nice even tint. It's best to keep the color light enough that it takes several sprayed coats to achieve the final color - that will help you keep the color even. But it's best to only tint the first few of a day's coats, and spray a couple of clear coats over that. Then when you level you'll be sanding away just the top clear coats and leaving the tinted coats undisturbed. After spraying the second day's coats you'll have a full day's coats of untinted finish. This will prevent the color from bleeding onto the player's hands and clothes!
You can also spray Color Tone tints directly on the epoxy or the first few coats of finish. I add Color Tone to straight alcohol and spray that onto the finish. The tint actually soaks into the finish, and then I seal it in with more clear coats. This is a good way to create a sunburst. I spray my sunbursts during the first day of spraying KTM-9. After getting the epoxy perfectly level, I spray two coats of KTM-9 to provide a base for the sunburst. After that has dried for an hour, I spray many, many coats of the tinted alcohol, gradually building the color and creating a very even, subtle fade from the center to the edges without building any finish. Then I seal the sunburst in with straight KTM-9, spraying enough coats that I know I won't sand through to the sunburst when I level the next day.
Mike Doolin, Luthier