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Gun Filter clogging up quickly with sediment?

Charles Member

This is an issue that has appeared in the last few paint-grade projects we have done. We have narrowed it down little by little. Today I think we may have found the source of the problem, but would like to learn if anyone else has had the same issue.

The product is MLCampbell's High Performance White in Satin. This is a solvent-based product. We are adding a bit of Flow Enhancer #2 so it does not flash off too quickly when it is hot. I know it is December, but we are in Florida and the finishing booth can be over 80F.

The gun is a CAT HVLP with a 2.5 gallon pressure pot. There is an inline filter (100 mesh) just before the gun. In trying to resolve the issue we even purchased a new pressure pot with new hoses without success.

We have cleaned the gun completely, but the issue appears to be somewhere before the gun.

The filter clogs up with a lot of small white particles. We first thought it was paint residue inside the pressure pot pick-up tube and/or the fluid line. When we replaced both, the issue still remained.

If we do not stop, disassemble and clean the filter after spraying about 10-20 square feet of parts, the filter will clog and the spray output decreases tremendously. Some of the particles will be forced through the filter and result in a gritty surface.

We thought that the product (purchased in one gallon containers and placed into the pressure pot still in the gallon container) might not have been mixed completely. We purchased a paint shaker (Harbor Freight air-powered) and shake the gallon can for about 10 minutes. Not sure if the problem remained the same, or even got worse.

During today's spray session, when one of the gallons was depleted, we took a careful look inside the almost empty gallon can. Normal operation with the pressure pot will leave about 1/8" of liquid product at the bottom. This is as far as the pick-up tube reaches. By tilting the can, we noticed that there was a lot of white debris on the bottom of the can.

Is this unmixed flatting agent?

Our next test is to shake the can for 10 minutes, then transfer it to a clean, empty can while straining it with a medium mesh paper filter. We will be curious to see how much, if any, debris is left on the bottom.

One other note about the product. This is a pre-cat product. Our distributor adds the catalyst when we order it. The product is labeled to be good for 120 days. This particular product is at about 100 days. It has been kept out of the extreme heat and cold, typically between 60 and 80 degrees.

This has happened on a few different orders recently. So, it does not seem to be related to just a single manufacturing run. Or, at least I do not think so. I never compared batch numbers from our distributor.

It just really kills production throughput when we have to either a) sand and refinish panels, or b) stop and clean the filter every 5 minutes during an hour spray session.

Has anyone else seen this issue? Any ideas?

By the way, this does not happen with the primer (similar pressure pot set-up, albeit with a different gun). Actually we do not even use a filter on the primer (MagnaClaw White) and have had no problems with debris.

12/6/17       #2: Gun Filter clogging up quickly with ...

Try shooting the same material through a gravity gun (no pot, no hoses) and see what happens. What type of paper strainers are using?

12/6/17       #3: Gun Filter clogging up quickly with ...
Leo G Member

Strain it through a 100 mesh or finer before you spray it.

12/6/17       #4: Gun Filter clogging up quickly with ...
Jim Clark

Flattening agent will do that when it goes bad.
It's usually to small of "seeds" to get
with a strainer.
Pour some of the agent in a coffee filter and
check for particles.
Sometimes panty hose works good.

12/6/17       #5: Gun Filter clogging up quickly with ...
Charles Member


Thank you very much for the replies and suggestions. After reading the suggestions, and giving it some thought, I decided to try a fresher gallon of finish. The catalyst was added to this finish about 37 days ago. Since the official expiration date is 120 days after catalyzation, this is a relatively fresh mixture.

I cleaned the filter. I used the same pressure pot and hoses. I used the same gun.

There was a little bit of debris on the first workpiece. I expected this since I did not tear the gun apart since the filter was catching most of the debris from the older gallon of finish. I only flushed the gun out quickly.

After that, the finish applied virtually perfectly. I only saw a single bit or two of trash while applying the new gallon. I am now about halfway through a second gallon (same newer date) and still achieving great results. There was one speck of debris in the second gallon. And, I am checking each work-piece quite closely. I did not inspect the filter yet for build-up, but the finish is still flowing at full capacity. I expect to find a pretty clean filter when I do check it.

I had the opportunity to speak with my distributor this afternoon and asked if anyone else had ever had this problem. The answer was that it was very rare. They have heard about it once or twice. The explanation was that the catalyzed finish was starting to harden or crystallize as it got older.

One suggested solution was to add some lacquer thinner and put it on the shaker again to mix. The crystals may/should dissolve. The second solution was to return it for an exchange. I have 1.5 gallons left, so I might try adding thinner to the half gallon as an experiment on a first coat. I will probably simply exchange the full gallon.

Our new ordering protocol will be to only purchase what is expected to be used in the next 30 days instead of the 90+ days as we were doing.

Again, thanks for the suggestions. We can now get back to a normal finishing timeline.

12/6/17       #6: Gun Filter clogging up quickly with ...

We strain every ounce through a fine cone paper strainer..... that few minutes of straining is worth gold when your not having to fiddle with flushing lines and scrubbing mesh filters....If you have things clogging filters you essentially have an answer to your problem....having to put extra coats to fix finish defects = $$$ it's more time, more labor and also it effects your finished surface... Are you getting close to being over the dry mil limit on recoats? over millage can result in catastrophic finish failure on a big job. don't depend on your equipment to clean your paint.. if you fine strain it you will see just how much crap is in your paint.... flush the filter with solvent and look close.. you will find solid particles... lint & hair everytime no matter the manufacturer..

12/6/17       #7: Gun Filter clogging up quickly with ...

Yeah, no matter what finish or how much of a hurry I'm in, I always filter the paint before catalyzing or reducing, you never know if anything has fallen in the can, or possible sediment from tons of potential sources.

An ounce of prevention is worth a pound of cure.

12/7/17       #8: Gun Filter clogging up quickly with ...

We never use the inline filters between the gun and the regulator. We mix the fluid strain it with the paper cone filters directly into the spray can.

12/7/17       #9: Gun Filter clogging up quickly with ...

A few thoughts, why are you not stirring the product? If a flattener or pigment is settled on the bottom of the can, it's settled. Shake til the cows come home and I'm pretty sure that material will be firmly on the bottom.

I second everyone in regards to staining material into the put, i have a simple wooden holder that holds my strainer over the pressure pot. Strain, strain, strain!!!

Third, i only use post-cat c/v Valspar. But recently i took delivery of 4 gallons of finish catalyzed by the supplier due to fup by or our purchasing agent. I was able to use it in a smaller project. It was catalyzed right before delivery.

Why are you accepting product that's already 37 days catalyzed on delivery?

12/7/17       #10: Gun Filter clogging up quickly with ...
Charles Member

A few answers to questions posted after we found a resolution. (Well, maybe more than a "few.")

1) We shake every gallon on a shaker for 10 minutes before we set the gallon can inside the pressure pot. If it has been more than a few hours since we started spraying, we open the pressure pot and stir the product again. If it has been setting a day or more, we can remove the gallon container and put it back on the shaker for another 10 minutes.

1a) After shaking the product for 10 minutes, we do check the bottom with a stir stick. There is nothing left on the bottom. Our shaker holds the can sideways, so I think that helps.

2) There two air regulators are mounted on the pressure pot. We have a three inline air filters that are all way before the pressure pot. One is at the output of the air compressor. The second and third ones are located in the finishing room, but still about 25 feet from the pressure pot.

3) The inline fluid filter is mounted at the input (base) of the gun.

4) This is a pre-cat product. This is NOT a post-cat product. It is catalyzed usually on the day I pick it up at my distributor. The product is then good for 120 days from that date according to the manufacturer. The distributor clearly marks the top of the can with the date and instructions. Theoretically the product should be fine for the full 120 days. Product that is 37 days old is still pretty fresh. This 37 day old product is performing flawlessly. It was the 100+ day old product that had issues. This was still in date according to the specifications, but had started to crystallize.

5) We typically spray 1-4 gallons per day. There may be several days between projects. We have not had any issue with lint, hair, etc. in the gallon cans from the manufacturer. We simply shake the gallon, open it, set it in the pressure pot, add flow enhancer and stir (if required), then close the pressure pot. We prefer to place the cans directly into the pot rather than pouring the fluid into the pot, then needing to clean the inside of the pot after usage. This also makes color changes very easy.

6) When we used gravity feed cup guns, we paper-strained everything, every time. We have not found the need to paper-strain with the pressure pots. If there is any potential foreign material, the inline filter should catch it. And, it did until the filter got clogged. Then, the fluid pressure build-up forced some of the debris through. That is when we knew we had a problem to solve. Prior to this issue our methods had been working quite well. I know that others may disagree with this, but our protocol, with the exception of this older product, works very, very well. But, we will keep those comments in mind. Thank you.

7) Please refer back to my original post to see what steps were taken to trouble-shoot the problem.

8) As I posted in the UPDATE post above, we have now changed our ordering protocol to only purchase what will be used in 30 days instead of 90+ days. We have also learned, from our distributor, that if this problem arises again with older product, we can add some lacquer thinner and re-shake the product. This is supposed to break up the particles. However, I prefer to avoid the issue with our new ordering protocol.

I do appreciate the comments and suggestions. They did help in our thought process to resolve this issue. I hope that posting this may help someone else in the future as well. That is why I felt it imperative that I take the time to respond with the updates. THANKS!

12/7/17       #11: Gun Filter clogging up quickly with ...
Charles Member

Quick follow-up to my NOTE #4 in the previous post.

The 100+ day old product and the 37 day old product were from two different deliveries. Both orders were catalyzed the day we received them. This probably was not clear in the previous posts.

We were trying to save a few $ by ordering larger quantities to get the price break. In theory this would have worked since we were using the first order within the 120 day window. In reality, it caused problems. Our distributor did credit us for the bad product, but it took us some time to trouble-shoot and solve the issue.

12/9/17       #12: Gun Filter clogging up quickly with ...
DanShaf Member

Shaking vs. Stirring

The idea behind both operations are to:

1. Place particles into suspension within your finish.

2. Maintain particles in suspension within your finish; help keep particles "wetted out" (this means that each particle must be completely surrounded by the liquid finish in order that they are part of the dry film that knits itself together when the finish sets up);

3. Mix into an even solution any materials that were intended to dissolve into the finish, such as solvents, additives, dyes, and so on.

Shaking can introduce bubbles, though these are supposed to settle out and with time they usually do.

Stirring is often accomplished with a paint paddle or a stick.Instead of twirling the stick around the can and grinding away at the bottom, the better method to stir is to take the paddle and create a motion like what one hand does when swimming the dog paddle, a windmill action that pushes the finish material from the top to the bottom.

The best way to stir is with one of those paint twirlers, I don't know what they are actually called. These devices actually "grind in" the particles and also whatever solvents might be swimming about, and they do this better than any other motion, better than shaking, and better than paint mixing sticks.

Ultimately, that's what you are wanting to achieve, the motions and forces that "grind in", and by doing so, getting your best mix and your best suspension of your finish material.

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