UV Cure Finish Experiment (DIY)

[Mike.Mara]

OK... Partially through my own impatience I have decided to experiment with making a DIY UV (Sun-cure) finish that we can all use.

I have the goal to be able to make it available to everyone here, so hopefully that means even those of you without a compressor and HVLP could use it through a Preval or similar home spray gadget. This might not be possible as getting it thin enough to spray through a Preval might be problematic... But I'll try my best.

Anyways... On to the goals:

• To have a sun cure finish we can all have access to.
• Not need expensive UV light systems.
• Preferably with no expensive spray equipment.
• Cost-effective. (Less than £20 a litre.)
• Recipe available here for free. (I'm not trying to make any money off this.)

The UV cure systems on the market at the moment mostly seem to be made of a polyester base with styrene as the thinner. As any of us who have looked into polyester resins know, you can get an additive to cure it via UV light. So the resin, styrene and UV additive are readily available to all of us in small quantities. This means we can all make these fancy UV cure finishes manufacturers charge in excess of $100 for and without the need for a few hundred pound/dollars of UV light equipment. (Plus the cost of safety gear when using said lights.)

A low viscosity polyester resin is my starting point, that way we can avoid the use of too much styrene that would prolong flashing times. (The average seeming to be 15 minutes between coats.) That meaning that with an average (On MSDS and TDS sheets) of three coats, you can have your guitar or other project ready for level sanding and buffing in about an hour. Sounds good right?

Now on to the issues I foresee... UV light from the sun on average will only penetrate wood about 80um (0.08MM). So that means unless you feel like the addition of MEKP, we need a sealer. I've toyed with the idea of a seal coat just using polyester resin and MEKP since we know polyester is compatible with itself... This would serve two functions, a grain filler and sealer. It's downfall being that there will be a lot of sanding before you can top coat, and anyone that's sanded polyester knows it's not fun. I'm completely open to ideas on other ways to fill and seal the wood here but with the preference of it curing/drying quickly.

So far the starting point will be polyester resin + UV catalyst and around 7% styrene. My research has suggested that 7% is the maximum before we start to affect the polyesters properties when cured. This may make the already low viscosity resin too thin, but I'll adjust it as I go to get the right balance between spray-ability and runs. Although a few minutes in the sun and the runs can be sanded off, so worst case scenario it still beats lacquer. The addition of wax in styrene may be needed to make the final coat cure tack free, but that's a problem for future me.

Anyone out there care to chime in? It may be a few weeks before I can buy the supplies to start the experiment so there's a while to discuss possible pitfalls or improvements.

Mike.

[ScottR]

I've got no wisdom for you, but I'll be watching this closely.

SR

[Mike.Mara]

On 2017-6-11 at 3:02 PM, ScottR said:

I've got no wisdom for you, but I'll be watching this closely.

SR

Thanks Scott, Hopefully all will go well!

[pan_kara]

hah, this would be something. Does this potentially have the "coats melt together" properties like nitro? i.e. no witness lines?

I'd guess for coats sprayed in succession maybe yes, for touch-ups or coats sprayed after curing maybe no, but I have no knowledge about this type of finishes ...

[Mike.Mara]

5 minutes ago, pan_kara said:

hah, this would be something. Does this potentially have the "coats melt together" properties like nitro? i.e. no witness lines?

I'd guess for coats sprayed in succession maybe yes, for touch-ups or coats sprayed after curing maybe no, but I have no knowledge about this type of finishes ...

You're exactly right. The idea is indeed to spray multiple thin coats in succession and then cure. If any more are required a good level sand will be needed to try to avoid sanding through with successive coats after the previous layers have been cured. This is the same process needed to be followed even when using the "professional" UV cured finishes as they are all polyester or vinyl ester based.

If I were a chemist I'd go ahead and develop a formula for one that would have the ability to "melt" to the coats underneath as it is possible... But the chances of normal people like us even being able to get a hold of those kind of chemicals is extremely low.

Either that or if I were rich... Or at least had enough money to burn, I'd contact Morrells and grab a 20L tub of their UV cure lacquer and split it into smaller batches for regular people to buy.

[Prostheta]

I would suspect that the best person to ask would be @StratsRdivine as this is right up his street. It is also possible that Chris (@verhoevenc) might have something to add from his personal experience.

[StratsRdivine]

On 6/10/2017 at 6:42 AM, Mike.Mara said:

Mike.

Cool stuff to work with, and the sand to powder after 30 seconds of cure is quite addicting.  I was a UV chemist for four years or so formulating sprayable UV coatings back in its infancy, 20 years ago, and developed buffable topcoats (unheard of then, due to stratification of the cured film).  Although I have a couple patents in polymer science, I have been out of the coating formulation world for nearly 20 years, so I am certain that the working/curing/shrinkage/buffing properties of todays UV coatings are well advanced, so take my views with a grain of salt as to their accuracy (test and verify). 

If I ever get into the guitar building business, I am considering dusting off my 20,000 watt UV system (the ballast weighs more than motorcycle and pulls 100 amps upon ignition - you get bonus testosterone when its firing) just for instant finishes, but my current system is cheap, and effective (PE gelcoat sealer topped with 2K auto urethane).    

See my responses below in Red:

To have a sun cure finish we can all have access to.

Not need expensive UV light systems.  Evidently true, but I am skeptical of "hot" UV finishes that might not fully extinguish the photoinitiator, especially in shaded areas not getting the full dose of UV, in which UV lights are a perfect choice.  Meaning, that some areas of the guitar body like inside cutaways may not fully cure (extinguishing the PI) and will leave some unreacted PI in the film, causing migration, stickiness, not enough crosslink to cut and buff, etc.  This may not be a problem nowdays.      

Preferably with no expensive spray equipment.  Dipping is a neat idea - messy but I have done it, but adequate spray equipment is cheap, and worth it.   

Cost-effective. (Less than £20 a litre.)  The savings on time covers the cost.  

Recipe available here for free. (I'm not trying to make any money off this.)

The UV cure systems on the market at the moment mostly seem to be made of a polyester base with styrene as the thinner. As any of us who have looked into polyester resins know, you can get an additive to cure it via UV light. So the resin, styrene and UV additive are readily available to all of us in small quantities. This means we can all make these fancy UV cure finishes manufacturers charge in excess of $100 for and without the need for a few hundred pound/dollars of UV light equipment. (Plus the cost of safety gear when using said lights.)

A low viscosity polyester resin is my starting point, that way we can avoid the use of too much styrene that would prolong flashing times. (The average seeming to be 15 minutes between coats.) That meaning that with an average (On MSDS and TDS sheets) of three coats, you can have your guitar or other project ready for level sanding and buffing in about an hour. Sounds good right?

Now on to the issues I foresee... UV light from the sun on average will only penetrate wood about 80um (0.08MM). So that means unless you feel like the addition of MEKP, we need a sealer. I've toyed with the idea of a seal coat just using polyester resin and MEKP since we know polyester is compatible with itself... This would serve two functions, a grain filler and sealer. It's downfall being that there will be a lot of sanding before you can top coat, and anyone that's sanded polyester knows it's not fun. I'm completely open to ideas on other ways to fill and seal the wood here but with the preference of it curing/drying quickly.

So far the starting point will be polyester resin + UV catalyst and around 7% styrene. My research has suggested that 7% is the maximum before we start to affect the polyesters properties when cured. This may make the already low viscosity resin too thin, but I'll adjust it as I go to get the right balance between spray-ability and runs. Although a few minutes in the sun and the runs can be sanded off, so worst case scenario it still beats lacquer. The addition of wax in styrene may be needed to make the final coat cure tack free, but that's a problem for future me.

Anyone out there care to chime in? It may be a few weeks before I can buy the supplies to start the experiment so there's a while to discuss possible pitfalls or improvements.

OK, now pay close attention at this point - gonna drop some science on ya.  Personally, I would never use UV cure as the sealer, only the topcoats, and here are several major reasons:

1. End grain will soak the resin in deeper than the UV will be able to penetrate and cure, therefore leaving "wet" resin inside the wood, which will then later dissolve the cured top film due to the "solvency" of the wet resin.  Surface may feel dry after UV cure, but its a ticking time bomb.  I have had this happen several times when sealing MDF edges with UV sealers.  Months later, the film began wrinkling.  When I cut the edge on a tablesaw, I saw and smelled the wetted UV binder had soaked in waaaayyyy beyond the point of UV penetration (like 3mm).  This is the primary reason not to use UV cured sealers, unless quick coats are sprayed into end grain, and cured immediately, which I would never do on porous mahogany - will soak deep beyond UV depth within seconds.  
2. PE gelocats are sooooo cheap, (I pay about $50.00 per gallon) and soooo easy to coat and sand.  Believe it or not, you still have a similar issue as above, with MEKP cured PE gelcoats, but for a different reason.  The PE resin can actually soak in to end grain, and leave much of the sanding aids on the surface, but my tests have shown great adhesion.  PE gelocat is awesome for several reasons:  It thins to sprayable viscosity quite easily with a combination of up to 9% styrene, and 10% acetone.  Flow is great, and the acetone flashes immediately.  Styrene is recommended because it is a REACTIVE diluent, meaning that it actually crosslinks INTO the final polymer, rather than flashing off.  
3. PE gelcoats have two primary wonderful additives that make your life easier - Thixotropes and sanding fillers.  The primary thixotrope is ultra fine silica called Cab-O-sil.  Thixotropy is a reology term that means it is shear thinning.  Meaning that when the coating is flowing, it flows with low viscosity, but once stationary, it "gels" and resists runs and sags.  Cab-O-sil is common in ALL sealers but is really evident in thick PE gelcoats.  You can spray 15 - 20 mils vertical, with tons of "hang time".   Then Gelcoat has calcium carbonate, talc and sometimes microspheres as sanding aids.    

So there is my reason for using MEKP cure PE for sealer, on opaque coated guitars, but clear is a little different.  You may not get the sanding aids but clear PE with Cab-O-sil additive, and you have a nice sealer - still better than UV cure clear sealer due to the end grain soak-in problem, and clear, pure PE resin is even less expensive than PE gelcoats.   

Now, once sealed - whatever method you like - UV is king of topcoats now.  Full cure is expected, and sanding is easy for multi coat builds.  The big issue is the ability to buff.  This is where I am no help, as I have not researched which UV's will buff, but imagine that they all will..  I would personally use a high solids UV cured aliphatic urethane, rather than PE to decrease post cure shrinkage which will telegraph grain after your mirror buff job.      

[Mike.Mara]

16 hours ago, StratsRdivine said:

OK, now pay close attention at this point - gonna drop some science on ya.  Personally, I would never use UV cure as the sealer, only the topcoats, and here are several major reasons:

I agree with this and I did say so in the post lol... I mentioned unless you want the addition of MEKP we'll need a sealer of a different type. Maybe the way I worded it wasn't clear? Thanks for the warning of why though... I just assumed you'd be left with un-cured resin under the cured film, not that it would slowly dissolve it... That would not be pretty.

The issues with buffing aren't as prominent as it seems they once were. You can buff (to my knowledge) all of them nowadays... My desk buffed up a treat. And almost all projects I've seen with UV cured polyester have been buffed. So hopefully that means it won't be a problem... But until it's in the testing phase who knows?

16 hours ago, StratsRdivine said:

It thins to sprayable viscosity quite easily with a combination of up to 9% styrene, and 10% acetone.  Flow is great, and the acetone flashes immediately.  Styrene is recommended because it is a REACTIVE diluent, meaning that it actually crosslinks INTO the final polymer, rather than flashing off. 

So you can thin with acetone? I spoke to so many people in the resin industry who told me it wasn't possible since the resin would never cure or they just plain didn't know... Is that some kind of reaction with the MEKP as a catalyst or are they just talking out of their ass?

My bad about the flashing off... I know it's a reactive thinner, I just assumed, wrongly it seems, that some would evaporate, hence the manufacturers saying leave it 15-30 minutes between coats. Do you know the reason? 

Regarding the issue with shaded areas... I'm also not sure if this is a problem. I know you'll have to expose all areas and be careful not to miss any. So far I've not had any problems with the projects I used UV cure resins on, but saying that none have been as complex a shape as a guitar... Maybe a cheap MDF box covered in foil and a couple tanning bulbs could be an option for a booth for all-round even curing?

With the UV cured aliphatic urethane, is that something we can make at home and cure with the sun as a worst case UV source?

Failing that, your experience has shown acetone to be a good enough thinner? I'd prefer not to interfere with the chemistry of the resin too much (A bit is fine) just in case it changes the properties of the cured film. If we could thin purely with acetone that would be great... You could just buy a pre-packed UV cure resin and just thin. Is that an option?

Would the telegraphing of the grain really still be a problem even with a seal coat of resin+MEKP and sanded down smooth?  I hope not...

Anything else you care to add? I could really use all the help I can get. (Clearly ).

Mike.

[StratsRdivine]

Hi Mike,

You are definitely on the right track, and I see nothing you mention that would not work, and the only questionable part is the shaded areas, and how to get enough light to it.  If Sunlight (which is a great source of UV, but sadly not always there in UK) then I would imagine a front surface mirror to focus on cutaways or just aim the guitar best as possible for those areas.  A great source for high powered UV is the hand held 1500 watt system from American Ultraviolet, or similar source in UK.  The smaller hand helds can be aimed directly where you want, and even the whole guitar if you make lawn mower passes.  

The reason chemist say to NOT use acetone in PE is because they are assuming traditional heavy build use of PE like boat hulls where its up t0 100 + mils thick.  At 20 mils per coat, the acetone can evaporate out easily.  

Regarding additional tanning bed bulbs, you need to be certain that the UV coating you use specifies the wavelength of tanning bulbs, because that is long wavelength UV, whereas most UV coatings react to shorter, more intense UV waves.  If the sun cures it, then tanning bed bulbs should.  Back when I was a chemist, the sunlight reactive coatings had excessive amounts of photoinitiator to get full cure, and even then the surface was still tacky from oxygen inhibition.  Then the coating would continue to crosslink and shrink over time due to the excessive PI that went unextinguished.  I imagine that not to be the case much now, but I am skeptical compared to a good 2K urethane.  

BTW - when I mentioned cabosil added to PE for sealer coat in clear coats, the cabosil acts like a flatting agent a little, but mixes crystal clear, so no worry on clear coats.  

If you were to use UV as sealer, then I would coat only the end grain areas first, then cure as fast as you can before it soaks in too deep, then sand and coat whole guitar again with same UV sealer.  This is the beauty of UV - multiple thick coats within minutes.  

[MiKro]

Well I am not a chemist, but with some years experience in finishes.. The thing that stood out to me in the OPs post was the base /sealer coats or color coats. Now I am most likely way off base as I have been drinking heavily the past 6 or so hours. What my long time experience has been is this. Dewaxed Shellac has always allowed almost every finish  be applied over it, whether it is a melting,,film or penetrating type of finish. Would this not apply in this scenario??? A blonde 1/8 to 1/4 pound cut using a pure 180% alcohol (Think everclear) with color tint or used as a sealer would make since in my opinion but what the Fuck do I know. I've only used this under nitro, poly, acrylic, 2 part cat, 2 part auto, oil, and water base. ???

my drunken 0.02cents worth???

mk

 

 

[Prostheta]

I just read, "2 parts auto oil" and cast my eyes back to the six hours of drinking then 180 proof/90% ABV.

Mike, this is definitely how to get things done. What those things are, not sure yet. Good or bad, things will get done.

[Mike.Mara]

On 2017-6-20 at 6:53 PM, StratsRdivine said:

Hi Mike,

You are definitely on the right track, and I see nothing you mention that would not work, and the only questionable part is the shaded areas, and how to get enough light to it.  If Sunlight (which is a great source of UV, but sadly not always there in UK) then I would imagine a front surface mirror to focus on cutaways or just aim the guitar best as possible for those areas.

Awesome news! I've got some supplies arriving today so I can start experimenting. I decided to try a pre-packed UV resin first just because it already has everything in the right proportions so if we can just buy that and thin, literally anyone can make it up. Failing that I'll be ordering the separate ingredients to mix my own.

Great idea about the mirror! Funny you should mention the sun here in the UK... The last week has been ridiculously sunny and we've been having a heat-wave... Supplies arriving today and... Overcast. I do have an OSRAM full spectrum bulb which does work for curing resin, so worst case scenario I have that but it's blindingly bright, even with goggles.

I'll be trying a few different sealers I have laying around to see what works. I'm hoping shellac will since I love what it does to wood but I'm not going to hold my breath.

On a side note... Do you know the shelf life of MEKP? I have some laying around but it's pretty old.

On 2017-6-21 at 5:51 AM, MiKro said:

What my long time experience has been is this. Dewaxed Shellac has always allowed almost every finish  be applied over it, whether it is a melting,,film or penetrating type of finish. Would this not apply in this scenario???

I'm hoping that shellac will work, I love the chatoyance of shellac and it does beautiful things to wood. I'll give it a test and let you know.

[Mike.Mara]

21 hours ago, Prostheta said:

I just read, "2 parts auto oil" and cast my eyes back to the six hours of drinking then 180 proof/90% ABV.

Mike, this is definitely how to get things done. What those things are, not sure yet. Good or bad, things will get done.

I read that the same way lol... That would be a stinky finish huh.

I would love it if we could get 180 proof here, then I wouldn't have to worry about the methanol in methylated spirits. I don't drink alcohol and since the cure for methanol poisoning is ethanol... That would not be a fun day for me.

Mike.

[MiKro]

On 6/21/2017 at 7:46 AM, Prostheta said:

I just read, "2 parts auto oil" and cast my eyes back to the six hours of drinking then 180 proof/90% ABV.

Mike, this is definitely how to get things done. What those things are, not sure yet. Good or bad, things will get done.

Supposed to be a comma between many of those LMAO!!! Like I said I was in an intoxicated state..

[Mike.Mara]

And we have results... It works!!!

I haven't sprayed it yet but thinned it to a definitely sprayable state following @StratsRdivine's suggestion of 10% acetone. (Give or take).

It cured without any issues what-so-ever. (Even with my area having been over-cast.)

I decided to do a less-than-ideal-test... Basically I was trying to see if I could screw it up. If you can easily mess it up then it's not really a home finish for everyone.

I sealed the wood with a sealer (shellac) that I wasn't sure was compatible, Less than ideal sealing at that too... Then after letting it dry just a few hours, gave it a scuff sand with 320grit. I then proceeded to mix roughly 10% (I was using a pipette) of acetone into the resin, shoved it on and spread it around with said pipette, then immediately into the sun (within a few minutes) and left to cure. To my surprise it worked. I stress tested it by bending the maple (fretboard blank I messed up before CNC'ing one) to the point I felt comfortable without it snapping... No lifting or separation of the resin. Shellac is compatible so far.

I then proceeded to level with 320, followed by 2500 ... Then a bit of stropping compound on a piece of kitchen towel to buff, followed by cotton waste with the same compound as before. Not ideal at all since it's still relatively coarse.

And the result...

Not bad huh? Considering I was intentionally doing everything rushed to see if I could ruin it. (I know this resin works, I've used it before, I needed to see if the "average joe" with no experience with finishing could easily apply it without many issues.)

 

So... Next will be proper tests with spraying since I know acetone, even with little time to evaporate, isn't going to affect the resin.

Looks like the shop bought resin with acetone is the way to go rather than mixing it ourselves since it exceeded my expectations in how well it thinned and buffed. Plus it saves people who really don't want to store the left over chemicals (Styrene, wax in styrene, excess resin ect.) from having to find a place to store them.

So yeah... Apart from more thorough testing with spray equipment looks like we have ourselves a sprayable UV cure finish!

And thanks to StratsRdivine it ended up being easier than I thought it would be.

The resin is Solarez Gloss Polyester and just a bottle of pure acetone from a nail supply store. (Plus MEKP if using as a sealer.)

Nice and simple. Over-went my estimate at £20 a litre, ended up being £36.

I'll get to spray testing next week with more accurate measurements since this being the UK, Just when you want it, the sun goes away. It can cure on non-sunny days with extra time... But not on days when it's going to rain, so I'll have to wait.

At least we know that if you do it badly, the result is acceptable, so done correctly it should be awesome!

[Woden]

Thanks for posting your experiments on here. So many articles I read about finishing with lacquers are US-based where the humidity/UV levels are totally different to Blighty, so I look forward to seeing what your conclusions are once you've spray tested.

[Mike.Mara]

1 hour ago, Woden said:

Thanks for posting your experiments on here. So many articles I read about finishing with lacquers are US-based where the humidity/UV levels are totally different to Blighty, so I look forward to seeing what your conclusions are once you've spray tested.

It's no problem! Spray testing may not be for a while as I'm sure you know, the sun has gone and won't be showing up again any time soon!

With the way the tests went, as long as you stick to 10% acetone, it'll spray a dream through a HVLP or touch up system.

I did some further tests with more acetone in the mix, varying from 20%-50% and as expected, the resin didn't cure beyond a flexible jelly (jello for you guys in the US) like substance. Maybe I didn't let it evaporate long enough, but even after an hour in the bright summer sun it never cured.

At this point I'm hesitant to say if a Preval will work or not as the mix was still just a tad thick but until I get one and test it out I'm still not 100% sure.

A suitable spraying area is still what's holding me back a bit on further testing since out of the sun it will never cure unless you add MEKP and I'm still a bit concerned about mixing too many flammable liquids in one batch. Plus I still need to do some more research on how acetone and MEKP will interact. I'm thinking a collapsible booth that I can fold out and lay in the sun to cure any overspray.

And just in case anyone is interested, I have come across a possible UV source in the form of a Exo Terra Repti Glo 10.0 Desert Terrarium Lamp. Seems to have the right wavelengths covered and isn't expensive either. I may get one in so I can do some winter testing on the resin.

[Woden]

I was going to say, yeah, don't wait for the sun to return and just make a DIY UV oven for winter curing! Great idea. Let me know how you get on because I think this is one of the best options around. I know all the big factories use UV curing and it sounds like the time saved would be a  big bonus for the one man shops like many of us have.