# Viscosity vs. Tip Size



## Tony B (Jul 30, 2008)

I never use a viscosity cup but I guess I should. I know how I like to spray and I judge the viscosity of my lacquer by how fast it runs down the shaft of a large screwdriver. Not very scientific, but it works for me. I recently bought an HVLP with a turbine and the technique is slightly different largely because the "look" of the wet surface is different than in conventional spraying. I managed to muddle thorugh it and my finish is just fine but I would also like to go back to the basics. 
So, my question is: Is there a relationship between viscosity and tip size? It seems to me that there would be yet the instructions that come with the gun kit talk about the viscosity and measuring with the included viscosity cup yet mention nothing about the tip size. What am I not understanding here?
The attached link below is the instruction manual and my statements above relate to page 4.
Thanks in advance.

http://www2.woodcraft.com/PDF/HV5000.pdf


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## Rick Mosher (Feb 26, 2009)

The viscosity cup you are using is different from the #2 zahn cup that I use so I can't give you specific times without a conversion chart. However the thicker the material the larger fluid nozzle you will need. Your manual says you have a 1.0, 1.5, 2.0 and 2.5 tip. I would expect the 1.5 would be great for spraying lacquer. The 2.0 and 2.5 would be better for thicker material like latex, oil urethane or water base coatings. The 1.0 would be for spraying stains or very thin shading lacquers. Start with the 1.5 tip thin like you normally do and then check the viscosity. Now when you spray how good is the finish? If there is any orange peel you need a little more thinner, add some and check again. Once you get the gun to spray perfectly write down the viscosity time and now you can duplicate this with that coating everytime by just thinning until you get the same measurement. Keep a record for each tip size and coating that you use and you should have very consistent results every time you spray.


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## Tony B (Jul 30, 2008)

I have been having better results with the 2.0 tip and some thinning. I also recently changed brands of finishing products. The vinyl sealer shoots fine with 2.0 and no thinner but the lacquer is quite a bit thicker and needs thinning. 
What I was curious about was if there was a direct relationship between a viscosity and tip size. It seems like there would be. And if so, why dont the manufacturers say so. If there is a direct relationship, then I would assume that if I went to a 2.5 tip for my lacquer, then I wouldn't need to thin it. Conversely, if i thinned out the lacquer enough, I should be able to shoot it through a 1.0 tip. If this is the case, what purpose does the viscosity cup serve other than repeatability, which I could get from percentages of thinner added?
I also realize that there is a point at which certain finishing products will never really set right if too much thinner is added.


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## Rick Mosher (Feb 26, 2009)

You will have to experiment for yourself on this but I think you'll find that if you use the 2.5 tip for your lacquer with no thinner you will get orange peel. The HVLP will not be able to atomize straight lacquer well enough. It will be better to use the 1.5 or maybe the 2.0 with proper reduction (the manufacturer of your coating will have recommendations for the maximum amount of thinner you can add) Professional spray guns do have recommendations of viscosity range for each fluid nozzle. Maybe if you called the tech department of the manufacturer of your gun they should have that info. Do some experimenting and let us know what you find out. ( One extra tip: a retarder is an excellent thing to add to your lacquer to help get rid of orange peel esp. in cold weather. Most of them are butyl cellosolve or butyl carbitol but I prefer MAK (metyl AMYL ketone) your lacquer supplier should have these in stock.)


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## Tony B (Jul 30, 2008)

I called the manufacturer of my coatings the other day and the tech rep uses an HVLP with a turbine similar to mine. He says he uses 1.8 tip with less than 10% thinner but my 2.0 should work just fine. I tried it that way and it did work pretty good. However I added a little more than 10% thinner and it went on just fine. I havent called the tech rep for the gun yet but I will. And yes, I always add retarder no matter what time of year or weather conditions. I add it and fisheye remover as soon as I open a can of finish. The retarder amounts to about 8 oz /gal which is what they recommend. I have a friend that uses almost 20% retarder and 30% thinner to the same product I use. I seems to work pretty good for him.

I am still experimenting with the gun and getting more comfortable with it. The last few pieces i sprayed on Mon. I acted like it was my old familiar Binks. 

I always wear a cheap Wally World watch and the cheap crystal has been through several days of me spraying and so far not a drop of overspray on the watch or my eye glasses for that matter. 

At first, the heavier than normal coatings I was applying with the HVLP actually worked to my advantage. Although just a slight orange peel, I was building coats anyway on table tops and a buffet top to be sanded for prep of a mirror finish. It was the first time I ever used a buffer and all worked out great. The whole process of mirror finishes is somewhat long and tedious but relatively easy if you follow the rules.

Thanks again for the help.


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## Rick Mosher (Feb 26, 2009)

The amount of thinner you add affects the dry film thickness of your coating. In general about the most you can spray on a vertical surface without a run is 3-4 mils wet film thickness (A quality paint store will have a wet film thickness gauge you can use to measure this for yourself) If your coating is 25% solids and you use no thinner and spray 4 mils wet then your dry film thickness will be 1 mil. If you added 1:1 thinner then you would only be applying 1/2 mil dry film. 

This may seem a little geeky to some but most coatings today, esp catalyzed finishes, have a MAX dry film thickness and exceeding this number can cause catastrophic failure of your finish such as extreme checking. 

Also when buffing out a finish if you are applying a low dry film thickness per coat you stand a real good chance of wet sanding and buffing through a layer of finish and leaving the dreaded "halo" which can only be fixed by spaying another coat and going through the entire process again.(The old nitrocellulose lacquers didn't do this because they are solvent release finishes, each coat melts into the previous coat chemically) That is why most professional finishers doing high gloss use high build, high solids finishes like polyester or 2k urethane which can be built to very high wet film thickness in one coat.


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## Tony B (Jul 30, 2008)

I use pre-cat lacq most of the time. What do you recommend as the minimun DFT before starting the wet sand stage for a mirror finish.


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## JoelMohawk (Nov 28, 2009)

Tony
All coatings mfg's have an optimum "viscosity" this is the recommended balance that allows the coatings to flow and dry properly. High solid products may require a larger tip orifice to allow the product to pass thru the tip at the desired quantity and with the best possible atomization. For most turbine systems that don't possess much fluid or pattern adjustment, its best to spray material at the mfg's recommended viscosity.


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## Rick Mosher (Feb 26, 2009)

Tony, you have to check with your manufacturer. They will have a DFT that you shouldn't exceed in their Product Information sheet. Unfortunately most pre-cat lacquers are anywhere from 2 mils to 4 mils depending on which one you are using. They are also VERY sensitive to temperature and should only be sprayed AND cured at temperatures 65 degrees or over.


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## littlebob (Nov 25, 2009)

I am wondering what brand of finish you are spraying with a 2.0 tip? I spray with a turbine and a 1.0 or 1.5 tip. I spray both water base and solvent base ML Campbell products. I add maybe an ounce of thinner per qt for solvent base and nothing for water base. 
Never use retarder unless it is real humid. Never run into problems with either. I am in Wisconsin, so maybe it is the weather difference? I know Campbell specs a 5 mil wet limit. Just wondering. thanks bob


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## Tony B (Jul 30, 2008)

biggbob said:


> I am wondering what brand of finish you are spraying with a 2.0 tip? I spray with a turbine and a 1.0 or 1.5 tip. I spray both water base and solvent base ML Campbell products. I add maybe an ounce of thinner per qt for solvent base and nothing for water base. ...... thanks bob


I use Gemini / WFS products. I was just looking at ML Campbell and their specs are similar as far as % solids by volume. Lets for a minute just look at tip sizes and ignore whether HVLP or conventional gun. here is what I find and this is just me talking, I dont know about others. 
So here goes: The vinyl sealer is around 15% solids by volume and if I shoot it through a 2.0, i barely have to thin it, if at all. If I shoot it through a 1.5 tip, I thin it about 10%. The pre-cat lacquer is about 20-21% solids by volume. If I shoot it through a 2.0 and dont want a high build with light orange peel, I thin it quite a bit like maybe 20% (just a guess). To get it through a 1.5 tip I have to add approx 30% thinner to get it to flow what I feel is a decent wet coat.


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## Tony B (Jul 30, 2008)

Rick Mosher said:


> Tony, you have to check with your manufacturer. They will have a DFT that you shouldn't exceed in their Product Information sheet. Unfortunately most pre-cat lacquers are anywhere from 2 mils to 4 mils depending on which one you are using. They are also VERY sensitive to temperature and should only be sprayed AND cured at temperatures 65 degrees or over.


The factory rep suggested no more than a total of 5 mils DFT. That should be enough for a flat surface to polish up to a mirror finish. Without actually measuring the DFT, he said that if I follow the normal procedure for a mirror finish ( multiple coatings and sandings between coats) by the time I get that flat surface with absolutely no dips after my final 320 grit dry, I most likely will have between 5 to 6 mils DFT and after the entire wet sandings and buffings, i will probably have between 3 and 5 mils DFT total when finished. 
I dont have the time to experiment and play with it right now but the next time I have a mirror finish job I will get an eddy current gage and actually mil it every step alomng the way just out of curiuosity.


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## Rick Mosher (Feb 26, 2009)

Just as a point of reference 5 mil is about the thickness of a sheet of notebook paper. On open pore woods like oak you will not be able to do a high gloss without exceeding the DFT unless you use a filler of some kind.


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## Tony B (Jul 30, 2008)

Rick Mosher said:


> Just as a point of reference 5 mil is about the thickness of a sheet of notebook paper........


I was doing Ok till you brought that up.
Kinda scarey, ain't it?
Thanks for ruining my day.:laughing:
All your input is greatly appreciated.


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## Rick Mosher (Feb 26, 2009)

As a finisher it is a very important thing to keep in mind. On high gloss jobs I use polyester sealer which can be built to 20 mils or more and then topcoat with a 2k urethane made for wood products (Milesi) Catalyzed finishes cure faster and can be buffed sooner than say lacquer finishes. (Automotive shops bake the urethane at 135 degrees or so overnight and can buff the next day.) Lacquer buffs very nice but it really should cure as long as possible so it is done shrinking before you start your final sanding and buffing. Piano shops used to let lacquer sit for a month before buffing. They pretty much all use polyester or a combination of polyester and 2k urethane these days. A little trick when buffing lacquer also, esp when using the glazing compound is to mist a little water on the buffing pad to help keep it cooler. Very important if you are using the foam buffing pads which create a tremendous amount of heat.


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## Tony B (Jul 30, 2008)

Rick Mosher said:


> ...... On high gloss jobs I use polyester sealer which can be built to 20 mils or more and then topcoat with a 2k urethane made for wood products (Milesi) Catalyzed finishes cure faster and can be buffed sooner than say lacquer finishes. ...... ........A little trick when buffing lacquer also, esp when using the glazing compound is to mist a little water on the buffing pad to help keep it cooler. Very important if you are using the foam buffing pads which create a tremendous amount of heat.


I use a rubbing lube disolved in water and spray from a squirt bottle. I use this for the wet sanding as well as the buffing. It was recommending by the coatings tech rep. After the flattening and wet sanding stage, I start with a wool bonnet and the course compound which I am led to believe has the cutting equivelant of 1,000 to 1,500 grit. Then I use the wool bonnet again for the medium duty compound which is about 1.200 to 2,000 grit equivelant. The final buffing is with the 3M blue foam pad and a finishing glaze.

The first two tops went so well, I am now adicted to mirror finishes. So now you have me wanting to try polyester for a sealer. I called the tech rep while he was on his way home so he will send me the PDS sometime tomorrow. I spray epoxy somewhat regularly (on industrial steel surfaces) so I am familiar with all the things that need to be looked at such as temperature and its relationship to pot life etc. I am also familiar with coating failures due to pushing to the limits and the dreaded "lock-up" of equipment if you wait too long. Aside from that, is there anything I need to know that might be particularly problematic about polyester?
Thanks in advance.


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## Rick Mosher (Feb 26, 2009)

#1. Be VERY careful mixing the catalyst. If you splash MEKP into your eyes it can cause blindness. Use safety glasses.
#2. Polyester will come off in a sheet if sprayed on any oily wood. Every polyester mfg. sells an isolante product, (which is a thin 2k urethane product) Use it.
3. Spray it only in a good spray booth and USE A RESPIRATOR!
4. Most polyester are sprayed by spraying a wet coat and letting it dry enough that when you stick your finger in it you don't pull a string and then you spray on another coat. You just keep doing this until everything is filled. Let dry overnight and sand like crazy the next day.
5. Check with your rep for directions specific to his product.


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## Tony B (Jul 30, 2008)

Rick Mosher said:


> #1. Be VERY careful mixing the catalyst. If you splash MEKP into your eyes it can cause blindness. Use safety glasses.
> #2. Polyester will come off in a sheet if sprayed on any oily wood. Every polyester mfg. sells an isolante product, (which is a thin 2k urethane product) Use it.
> 3. Spray it only in a good spray booth and USE A RESPIRATOR!
> 4. Most polyester are sprayed by spraying a wet coat and letting it dry enough that when you stick your finger in it you don't pull a string and then you spray on another coat. You just keep doing this until everything is filled. Let dry overnight and sand like crazy the next day.
> 5. Check with your rep for directions specific to his product.


Thanks Rick
Sounds like it is just a high quality version of polyester that I use in fiberglass construction and repair. I decided to go sailing today and take a few days off. I havent had a decent day off in months. Anyway, when I got in, I checked my e-mail and didnt get the promised PDS. No problem. I will call them again tomorrow. From my conversation yesterday with the reps, the info for application is pretty much the same as what you said including the 2K poly. They also mentioned that when you apply it, the first coat goes on kinda wavey and should be flattened somewhat before the second (final coat) of polyester. I'm taking off till Sunday and Monday is Jury Duty. I'll be real busy after that. As soon as I get a request for a really deep build, I will order the polyester and just do it.


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