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I made a post about 6 weeks ago regarding my thoughts on finishes. At that time, I was experimenting with a 2k Urethane. I thought I would provide an update.

Here's a reminder of my particular scenario and goals:

• Very small workshop (attached garage) with no room for permanent spray booth.
• Created a spray booth that I can disassemble and store when not in use.
• Need a high-quality finish. Something that rivals and/or surpasses the finish quality of a company like Collings.
• Need a finish that won't negatively affect tone. Polyester finishes (even super thin ones) tend to kill the tone.
• Need a finish that I can apply safely.

Nitrocellulose lacquer tends to be king for the simple reason is that it is relatively easy to apply and get fantastic results with. It just works as a guitar finish. However, the off-gassing was just something I couldn't deal with in an attached guitar and workshop. Also, the cold checking and deterioration of the finish over time as well as its fragility to certain chemicals is something that I wanted to avoid, if possible. I struggled to get the results I wanted from oil varnish -- and shellac is delicate. Tonally, both those options are superb. Aesthetically, I didn't like the yellowing effect of the varnish or darker shellac (anything other than platinum blonder flakes).

I chose a 2k Urethane because it is a quality finish and is something that while very toxic - doesn't remain that way for very long. I have been able to make a homemade spray booth that is more than adequate to keep me safe. My biggest concern was whether my shop and setup would yield professional results and whether it would hurt the sound of my guitars. I am very happy to report that the 2k urethane worked splendidly. It's a beautiful finish and I was able to apply a 3mil finish on the soundboard. There is a very slight detriment to tone but it is just barely perceptible. Without question, this is a superior option to polyester if you build a responsive guitar. I believe if I could knock the film thickness down to below 2 mil, there would be absolutely no difference between my guitars pre and post finish. Tonally, I am completely satisfied with the Urethane finish at 3mils. It has come so incredibly close to the results I've gotten with French Polish and oil varnish and I think they edged out the urethane because their film thickness was between 1-2 mils.

In terms of quality, the finish I've produced is as close to perfection as I've ever seen. This is my 2nd time using a spray gun. If I can do it, anybody can with the proper mindset and patience.

Here's my setup:

• Homemade spray booth. Air is pulled from inside and evacuated out a window in my shop. Good lighting is essential. I went out and both a couple decent LED fixtures that will shine light from behind me so that I could see my spray pattern easily. Be mindful of make up/return air -- I made sure windows inside my house were open to allow air movement into and out of my shop. The spray booth materials and blower cost me a few hundred dollars to make but I bought the blower new from Amazon.
• I'm using the Fuji Mini Mite 4 HVLP with 3M PPS system. This works great and allows me to minimize exposure to chemicals. I was concerned about the VOC's and isocyanates and didn't want to risk any exposure. I'm decked out in full face respirator and a disposable spray suit and latex gloves.
• The turbine HVLP makes applying the urethane a bit challenging. I think compressors work a bit better (tail solvents and air expansion/cooling and all that jazz). That said, I was able to figure out how to apply an even, wet film with minimal texture. This was by far, the hardest aspect of this whole process.
• I'm using the Kovax papers for leveling. I had a machinist make me a really nice buffer with 14" wheels. I'm using the StewMac buffing compounds but just because I have them. Will likely switch to Menzerna but the color tone stuff works well. The Kovax system is absolutely brilliant. It is a dry sanding system and leaves behind very even scratch pattern.

I was actually a bit surprised at how much I like the urethane. It feels great on the neck. The clarity of the finish is outstanding and this combined with a very thin finish -- yields a decidedly, non-plastic looking finish. I had a urethane finish on my guitars years ago (outsourced) and it was a bit thicker and looked a bit plasticky. Keep the urethane finish thin and it looks fantastic. In conclusion, I can heartily recommend using this finish for your guitars. If you can manage the spray booth and have a decent spray setup - I think it is one of the best finish options available to you. It has noticeable advantages over nitro. It is relatively easy to apply, level, and buff. And with the proper safety precautions, it is doable for those of us with very limited shop space.

I had planned on taking photos of my spray setup but forgot. My setup is nothing special. I used the following fan from Amazon and made a "Science Fair Project" style booth that rests on my bench. The fan exhausts directly out a window via a hose I made out of clear tarp material. I made an insert for the window that connects to the tarp and prevents any exhaust from returning back into my shop. The blower was only $200 when I bought it. Anything similar will do but try and ensure that it is explosion proof.

https://www.amazon.com/gp/product/B0816 ... UTF8&psc=1

As I mentioned earlier, make sure you have return air coming into your shop. I would run the blower for 10 minutes after each spraying session. 3 sessions in one day -- then I would periodically exhaust my shop air after the last session. My house is poorly sealed but by doing this, I could barely detect any VOC except right near my shop door. By nighttime, all smell was gone from house and the smell in the workshop was also fairly minimal. I did not bring my guitars into my house until the following day.

This 2k urethane stuff is quite toxic. Use fresh cartridges and cover every inch of your body.

The Kovax system is not cheap but is excellent. The US distributor is Eagle Abrasives but you can buy direct from Japan via eBay.

I start the final leveling with their K-800 paper. Then K-1200, K-2000, and K-3000. They have several different "products" but you can mix and match according to their K number. Basically, their K number is equivalent to the European P grit (FEPA). I use a sanding block for flat surfaces during the initial leveling. This gives you good control and ensures you don't round over and burn through finish on any edges. However, I also employ use of their foam sanding block during the initial leveling. This thing is absolutely amazing. It removes texture and flattens but does so with while conforming to non-flat surfaces (it works great for the neck, sides, back, and top !!!). Once the initial leveling is done, I use this foam block for the second grit (K-1200). After this grit, I want the surface to be perfect - no shiny spots at all. Follow up with the 2000 and 3000 and it's off to the buffing wheel.


Their system can be confusing as hell - partly because they have stick on or psa products and velcro products. Lots of different ways to use their product that are intended for different applications. IF you want to try this stuff out, here is what you want to use. In my opinion, this stuff is game-changing. You won't find anything out there that is superior at this current time.

Start with their stick on sheets for the lower grits. This works with your own sanding blocks or their supplied sanding blocks. Look at the Tolecut line for the K-800 and K-1200 grits. This is to remove texture from the finish. Also, the small ToleBlocks are incredible - especially, the curved one. These blocks works great on the headstock and neck. The larger two tone pad is for the barrel of the neck and the body of the guitar. Use the soft side or the hard pink side if you need something rigid. The soft side will eliminate texture while also flattening and conforming to the shape. The right sanding block makes all the difference in the world and this thing is fantastic. I get the full sheets and you can just cut the material into smaller pieces if you need to.

https://eagleabrasives.com/en/hand-sand ... e-hand-pad

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Once you're done with the 1200, then you move to their Buflex product. Use the 2000 and then the 3000. At this point, you can move right to the buffer. You need their foam hand block and and a super assilex interface pad. Confusing, I know and their site doesn't explain it very well.

https://eagleabrasives.com/en/hand-sand ... hand-block

https://eagleabrasives.com/en/interface ... erface-pad

And lastly, regarding HVLP turbines and 2k Urethane. Spraying finishes can be very challenging and this stuff doesn't lay down as easily as nitro or varnish. You have to experiment and a lot of folks tend to have trouble with turbines and automotive clears - mostly, the issue is a lot of orange peel. Not the end of the world but it does add time/labor and it can also mess up your ability to dial in the film thickness. I spent about a week and $75 worth of finish material - trying everything I could. I found out something that works for me and my system but more than likely, this would not extend to you. However, if you have an HVLP turbine and you need help with this stuff -- then I can probably point you in the right direction. So feel free to contact me and I can share my process for figuring out how to get the finish to lay down properly.


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If anybody has any questions, I'll do my best to answer them. I've detailed a lot of what I think is helpful above. In terms of finish schedule - the best thing is to follow the guidelines from your supplier. However, here are a few things to consider:

1). Apply isolante sealer before pore filling. After you've pore filled - sand back flat and apply another coat of the isolante sealer. Don't rush this stuff. Give the sealer and pore filler the proper time to dry.

2). 3 wet coats of urethane clear. Try to aim for around 1mil of dry film thickness per coat. So after the 1st clear session, you'll have 3 mils of finish.

3). Level sand with 320 grit and use frisket tape to help determine film thickness. Frisket tape is the stuff you use to mask of the bridge and fretboard beforehand. I get the finish level with the frisket tape and then I keep on sanding the top. Ideally, I want the top to be 1 mil after I've leveled the finish.

4). Spray another 3 coats of finish. If you are awesome at spraying, then do only 2 coats on the top.

5). It is important to wait between coats as long as you can. If the supplier says 15 minutes to 3 hours (min, max recoat times) - then wait a couple hours. This helps the finish to off gas. But don't wait too long or you will have adhesion problems.

6). Technique is important, you can lay down 1 dry mil of film thickness with each coat or several mils. Meaning you can end up with 3 mils like I do -- or 12 mils if you lay it down too thick.

Great to hear. Can you share which brand, and which specific products, you are using for the 2k urethane finish?

Also, if you have time to share photos of your knock down spray booth, I would love to see what you came up with. I documented mine here:

http://www.luthiersforum.com/forum/view ... pray+booth

Sounds like you got something figured out, that's great. I'd love to see pics too. Also do you have a link to the actual 2k Urethane? When I Google "2k Urethane" it comes up with all kinds of stuff.

Don,
Your booth is much nicer than mine. I don't have a top for mine but I get very little overspray with the FUJI turbine. I'll try and snap some photos for this thread as my design may be a bit easier for some folks to implement than yours.

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Regarding the urethane, I'm essentially using an automotive clear which is commonly referred to as a 2k urethane - or two component urethane. There are lots of different brands. I used the Cardinal Paint product called LuthierThane and their Isolante sealer. Both are two component. I also used their Rosewood oil based pore filler. I use this for the necks and I use West Systems for my epoxy pore fill. A Rosewood pore filler on mahogany necks looks really, really good. Mahogany needs a bit of contrast in the grain and it makes a huge difference over using a clear pore filler. I actually did one application of Rosewood pore filler - waited 3 days and then an application of epoxy. What is so awesome about epoxy pore fillers is that it is very stable and keeps everything nice and flat even after buffing. I normally use epoxy pore filler for the bodies. Again, this goes over the isolante sealer - you don't need to scuff sand the sealer before applying the pore filler since the pores have enough edges to ensure mechanical adhesion. But I do sand back to the sealer after the pore filling.

I believe you can mix and match sealer with clear coat. Most of these formulations are going to be similar. However, be careful if you need to tint your clear -- make sure you contact the supplier to ensure you are using something compatible. A lot of folks are using products from House of Kolor. This stuff does often needs to be reduced/thinned - make sure you are using the suppliers reducer. These formulations can be finicky and some can be quite accommodating - just make sure you follow the supplier instructions.

The Cardinal product took several weeks before it was ready to buff. Part of this was due to my house being relatively cold (around 70F). It's a good product but I am looking at trying either the SimTec urethane or the Ilva urethane as a comparison. Tim McKnight, who helped me out a great deal, uses McFadden's product. The McFadden product has a large minimum order. If anyone uses the Cardinal LuthierThane, contact me and I will provide my finish schedule and instructions (% reduction, etc.).

SimTec
57x1 Urethane
58x1 Sealer

I'll probably try out the SimTec product next. The company has great customer support which is very important. A number of large guitar mfgs are using the SimTec products - both their urethane and polyester.

Cool. Thanks!

Do you have the air intake source independent of your main shop where you are building and storing wood? I have found that running my exhaust fan in winter or humid summer days changes the RH very quickly and recovery is slow.

I remember that Hans Brentrup who used to post here had his spray booth in a separate room in his basement with a sealed door and an elaborate duct system to bring in air from the outside. It had a built in heating unit for spraying in our MN winters.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

My shop is an attached garage. The air intake is coming from my air conditioned home. The amount of air I'm moving should remove the entire contents of my shop every few minutes. I just open several windows from inside my house to ensure proper flow and that I'm not pulling any carbon monoxide down any flues.

I normally condition my workshop space with a dehumidifier. I've done my best to seal my garage over the years and it doesn't take a lot to drop the humidity down to reasonable levels. My wood room is in a separate location and that is also were I do my important glue-ups (bracing and plates to the sides).

My FUJI turbine is located inside my house. If you use a turbine, it is very important that your intake air for the turbine is conditioned air. Spraying doesn't take very long at all - 5 minutes and I'm done applying 1 coat to 2 bodies and 2 necks. I'm taking my air conditioned "home" air and dumping it outside. Expensive but it is what I have to do. I live in Florida, so weather is fairly mild during the winter. All that you have to worry about is the quality of the air while spraying. Once the finish is on the guitar, you can "relax" your climate a bit if need be. If you are pulling air from the outside, then you will need a way to condition the air somewhat. I think temperature is more important than humidity tho'. As long as the air coming out of your gun is good, clean air - you aren't going to be trapping a lot of humidity in the finish (assuming you aren't working in an extreme climate).

Additionally, you can play around with the reducers. You will often have a choice between fast, medium, and slow reducers. The 2k urethane industry is automotive - and their customers spray paint in a lot of different climates. So you can shoot this stuff even if your shop is in the 60's. Ideally tho', I think 70 to 80 degrees is the sweet spot and you will want to use a medium reducer.

BTW, reducer is the same as a thinner. For whatever reason, you "reduce" urethane and "thin" lacquer.

I also pull my make-up air from my house and I also live in a humid climate. Works out well for me. I have mentioned this before, but the final obstacle was long term off-gassing of nitro that built up and leaked back into the house. A small bathroom exhaust fan mounted in my spray booth solved that problem. I let it run for 3 or 4 days after spraying.

HI Barry,
Glad to hear this worked out for you. I considered doing something similar but ultimately, went with the urethane due to my Florida home being so permeable.

I thought the beauty of the turbine was that you didn't have to worry about conditioning the air...

Hi Ed,
I may be wrong but I don't think the turbine changes the need for appropriate shop conditions. The turbine certainly does eliminate the hassle of conditioning the air line and making sure you've eliminated contaminants.

I use a Fuji turbine too. I run mine in a conditioned shop situation, although I don't know whether or not that is necessary. My shop is in the same conditioned atmosphere as my house, with an added gas heater for this time of year. I'm running a humidifier now, but run a dehumidifier in the summer.

I like the Fuji quite a bit. The only negatives I've experienced are that it's loud and the big hose is clumsier than a small diameter air hose. It sprays great. The Fuji guns are nice.

Dave

Toonces, based on your recommendations in a previous thread I tried the Super Assilex sandpapers. I had already used Tolecut and knew that these were great abrasives. The Super Assilex and Buflex don't disappoint either. A better way to sand finishes that I have been looking for, for awhile.

those 2 products are excellent for prepping finishes particularly in use for FP an final buffing out. I watched stephen falk on youtube explain the use of these japanese papers Barry.

3M supposedly has some good papers that go by the name of "Flex Abrasives". The Mirka Abralon pads are also pretty nice and 3M has a similar product in their 3M Trizact line. I've used the Abralon but never the 3M stuff; however, the general consensus online from reviews tends to be that the Kovax stuff is currently without peer.

I've used the 3M Flex Abrasives and they do work very well.

Dave

I sprayed the Simtec urethane once when I was crunched for time getting ready for a show (on Chris Ensor's recommend). It worked great, no issues at all. I would have been tempted to use it again if I had a spray booth. I had to borrow time in a very generous past employer's booth to use it that time.

I'm still using the varnish and satisfied with my results, but I like the color it imparts

Thanks for sharing your experience!

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Burton
http://www.legeytinstruments.com
Brookline, MA.

Burton, I agree - the oil varnish really complements your aesthetic. I actually really enjoyed the "varnish process" but I just struggled with drying issues, especially on the sharp edges and bevels of my headstock - and I use Rosewood a ton. I think spraying the varnish on in two thin coat increments would have worked out better for me. What I loved about the oil varnish the most was how it felt - it's the best feeling finish, IMO.

I picked up some of the Assilex in the 220 grit range to level UV porefill. I ordered 4 “sheets” but what I got was 4 half sheets perforated to split into 1/4 sheets. I also ordered their sanding block.

Barry / Simon, do you use their block / sponge as a backer? I like to use a block that is basically 1/16th sheet that is cork on wood. I’m using it on ukuleles. Anything I should be aware of or just treat it like any other paper?

Brad


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Hi Brad,
I would only use the Kovax stuff for the final leveling/buffing. Not worth the added expense until you get to the end. Additionally, the consistent scratch pattern is really only useful for when you are in the buffing stage.

I'm currently using 3M stik-it P320 to level between finish applications. I use a hard rubber sanding block for this. I've heard Mirka gold is also pretty decent. But I would avoid the Kovax stuff for the lower grits and only use it for the end process. I like psa sandpaper for the leveling because it is easy to place on your sanding block. If you are going for an ultra thin finish it is very important to have the finish perfectly level before your final top coat application. (with the urethane, you do the final topcoat as 3 coats which blend together chemically). This helps avoid witness lines as you level and polish away most of your final topcoat.


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For your 1st leveling once your finish has been applied -- you need something rigid enough to eliminate any texture and imperfections but that also has just a bit of give. I use a relatively hard rubber block that is about 2x2.5" in size. I use the sticky/psa Tolecut k-800 for the initial leveling. I then follow up with the k-1200. I also use their special sanding blocks (their small hard rubber blocks and their two tone sand block with a hard and soft size) with the Tolecut papers - but I make sure to use my hard rubber sanding block for the 1st sanding of a lot of areas onto guitar (top, headstock face, heelcap, etc.). I then follow up with the buflex paper -- which is similar to the assilex in how you use (their sanding block, interface pads, etc.).

In my 3rd post, I did a pretty thorough job of explaining how I use the Kovax stuff but if anyone wants to talk to me about this stuff -- feel free to give mea call (my number is on my fayguitars website). Leave a message because I don't answer the 1st call because of telemarketers.

Thanks, Simon.

I’m building some hardwood topped ukes that need porefill on the top but I’m trying to make sure the porefill is as thin as possible. I was thinking this could help me get it level without going through and without the need for anything thicker than was absolutely needed.

I will try them on leveling finish too.

Thanks for the help and pointers to these products.

Brad


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