Spraygun Cleaning and Shellac

Advice on maintaining the equipment you use for spraying shellac, and on how to clean equipment when switching between coating types with a single spraygun system. December 1, 2009

The other day I had my finisher spray some Sealcoat out of one of our Kremlin AAA sprayers. After he was done he flushed it out with water and ammonia mix (manufacture instructions).When we went to spray again the next day the sprayer would spray. After diagnosing the problem we discovered the hose was plugged up. Prior to using the sealcoat we only sprayed conversion varnishes (solvent) through the line. Was this a bad idea to spray the Sealcoat through the line?

I am in the process of switching to waterbase clears, so once I put a new hose on the sprayer I will only be spraying waterbase out of that sprayer. Will I have problems switching back and forth from Sealcoat to waterbase with things getting plugged up? I don't want to be buying new hoses all the time. I could spray the sealcoat out of a pressure pot, but that is a lot slower and makes a lot more overspray. Any help would be appreciated.

Forum Responses
(Finishing Forum)
From contributor G:
Use denatured alcohol to clean out the system, not water and ammonia.

From contributor M:
I always keep separate fluid lines for WB or different coatings. When I'm done spraying I do a complete breakdown and cleaning of the pump change back to the compatible fluid line and never have a problem.

From contributor F:
Contributor G is correct the solvent for shellac is alcohol. Some people like to have different guns for waterbase, lacquer, and shellac but I find itís not necessary if you know and follow proper cleaning procedures for your equipment. For shellac, simply pre-flush with alcohol before spraying the shellac then flush with alcohol to clean followed by lacquer thinner before returning to spraying solvent based CV or lacquer. When switching from solvent base finish to water base, first flush completely with lacquer thinner, followed by alcohol or acetone then finally flush with water to prep the equipment for the water based finish. Do the whole thing in reverse to go back to solvent based. The reason for the acetone or alcohol in the middle is that they are miscible in both water and solvent and will help remove residue from the previous flush from the system before flushing with the next.

From the original questioner:
Thanks for the help. I will try the alcohol next time and see how it goes.

From contributor J:
I have to agree with contributor Fís post. Pre-flush with appropriate solvent will go a long way in helping preserve your fluid hoses. I learned the hard way just like you!

From contributor P:
I never spray shellac out of my AAA. It puts out way too much material, and finish quality is not an issue when shooting shellac as a sealer, so why take the chance of gumming up your expensive rig when a throwaway gun will do fine?

From contributor G:
Just get the right nozzle and it will put out as little or as much as you need it to put out. I do understand why you might not want to use the AAA, a standard gun can do it just as well.

From contributor A:
I agree with contributor P. Buy a cheap HVLP two quart pressure pot setup ($200) and use it for Sealcoat and other non important finishes. Having two rigs is usually better than one.

From contributor D:
We spray Sealcoat all the time. Start by cleaning your lines with 4-6 ounces of alcohol. If you have a long line set then use the ammonia and water mix to purge the last remaining shellac before using it for waterbased clears. If you want to go to solvent based varnish flush it with lacquer thinner prior to cat varnish or alcohol only.

From contributor J:
We use sealcoat all the time and have a dedicated pot and gun for it. The cost of the various purge cycles that contributor F mentions (good advice by the way) justified a dedicated rig. In a refinishing environment, we use the Sealcoat as a barrier coat and the quality of those coats is paramount, so we keep the gun in diamond condition - as good as the topcoat rig. It is the sanding sealer or body coat rig that we get a little lax with.

From contributor R:
I work for Kremlin and have changed back and forth many times. The key is a three time flush. If you have a solvent based coating in the system, and are changing to a water based coating, first flush with the recommended solvent for that coating, flushing until it is clear. Then flush with water and soap, and then clear water, then purge the water and bring the water based coating into the system and spray. When reversing, to the opposite three time flush.

I like using the Kremlin Airmix on both produces. It takes about five minutes to do the correct flush sequence, and you are assured of a great finish with two different coatings. It was mentioned by someone that the gun puts on too much material. A typical water based coating has a volume solidís around 33%. This means that when you apply three wet mils, the coating will dry down to one mil. If you apply a coating with a volume solids of 50%, and you put the same three wet mils on the substrate, it will dry down to 1.5 mils, which it too much. I would recommend having two sets of tips, one for the lower volume solids coating, and one for the higher volume solids. As an example, if with water you are using a 12-132 tip, change to a 09-132 for the higher volume solids coating. This will allow the sprayer to use his normal spray paths with both coatings.

From contributor U:
Contributor R - I agree with your steps. As it worked perfectly on a demo we did here recently for a customer. The flush procedure is simple and quick and the airmix works well for this product.

From contributor F:
Contributor S: I have heard of manufactures recommending soapy water as a flush for water base finishes but never saw the need for it. I've also had some concerns about possibly contaminating the system with the wrong soap. The acetone or alcohol mid flush I previously mentioned seems to work fine without having to use soap.

From contributor R:
I have been in this business for a long time. I understand your concern, but switching between waterbased coatings and solvent based coatings needs to be done correctly every time to assure great system up time. Most water based coatings are ammonia based. I really like to add 1% Little Bo Peep ammonia to straight water as a flushing material. This is very little cost, and works great. But, the three step flush is still the key to long and short term system up time.

From contributor M:
I am just a dumb old finisher but I remember back in the mid 80's in LA when all this WB stuff started along with wonderful things like the SCAQMD. The largest millwork shop in LA at that time was Standard Cabinets and they put in a state of the art air-assisted airless system (Kremlin wasn't popular yet, Graco was IN) and they had it hard plumbed in place heaters and all. They were told a lot of the same stories I am reading here about just flushing the system out three times, using ammonia (that is a wonderful experience I have to tell you.) And everything will be right with the world. Switch back and forth between WB and lacquers no problem! To make a long story even longer it was a big problem. All of the lines were full of gunk and they couldn't get it out of the lines well enough to keep from plugging their inline filters all the time. So they had to replace all the lines at huge expense. Anyone who has cleaned enough equipment knows just flushing something out doesn't clean it. The weak link in the flush three times theory are the fluid lines. Coating will build up in there. That is why I use a separate line for any chemically different coating. I don't do it that often so it's not really a big deal. I flush three times, take the damn fluid line off, store it marked clearly with what it is contaminated with and go back to my original line and I have never had a contamination or clogging problem. I did the same thing with my pressure pot system, and worked great on that too. Everything else can be taken apart and scrubbed and that's what I do and why I do it.

From contributor R:
I agree with you if you do not have a high enough flow in the lines. The problem with HVLP and conventional (some are still using it), is the hoses are large, and you cannot get enough velocity in the hoses, which is caused by the laminar flow effect. The main motion is in the center of the hoses, and little movement on the edges where the contamination is at. With AA systems (most), we use 3/16 and 1/8" ID fluid hoses, which overcome the laminar flow problems. That being said, HVLP and conventional should always change hoses. With the high flow rates in AA hoses (small ones only) the laminar flow effect is minimized and the three flush works well. I did see some of the old Graco installations, and they were using 1/4" ID hoses, which have twice the volume of a 3/16" ID hose. There are reasons for everything, and sometimes you need to find out the real causes for problems.

From contributor U:
Well my first guess as to that long ago failed system was the hard plumbing size, my guess it was 1/2'' ID stainless as most hard piped systems were. If flushing was done at low pump pressures, probably with no tip in the guns the flow would indeed be laminar and you would have very little scrubbing action. As the pump runs smoothly at low pressures and fluid flows easily with no tip, the operator is quick to see clean clear lines and assumes he is fully flushed. If feasible, using separate lines is a foolproof solution, but not always a option everyone has when the job arises.

From contributor O:
Interesting! I switch between solvent and water-based in my 10.14 and do a three stage flush, but the middle flush is with alcohol, as I was taught this removes any water or lacquer thinners from the previous flush. I haven't had any major problems, but I do find that some wb manufacturers recommend adding ammonia to the water, others recommend a little soap and some say use lukewarm water only.

From contributor R:
I agree with the alcohol as the middle flush. The reason for the three flush is to eliminate the carrier from the last coating. Alcohol does the same thing, but leaves a waste liquid to depose of after flushing has been completed. Look at smaller ID lines, higher flush flow rates, and the three flush, and you can run any product.

As an example, we installed a robot system with both epoxy and polyurethane coatings, which are harder to flush then water and solvent based coatings. We had a three flush program, and 3/16" ID lines. There were never any problems with clogging. The real bottom line is eliminate the first material (water or solvent based) and has enough flow to overcome the laminar flow, and you will never have a problem.