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Old 11-12-2019, 01:23 PM   #1
Ian1932
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Default Painting Over Water !!!!!!!!!!!

Painting Over Water

Im trying to contribute to this site with things i know about. I thank everyone for helping with my projects!

Most would have never put any though into this. This is 100% true always!



Helpful painting tips... I have found over the years of painting there are simple things you can do to make sure things go as planned. I have painted professionally architectural mill-work and steel components for 25 years. Hopefully this can help someone.

My friend is restoring a 60's mack truck. He took the frame and had it sand blasted. He had the raw frame in his dark cool garage. The following day after blasting he wheeled it outside and epoxy primed it, then Y2K, waited then 2 days and top coated with a black chassis paint. When he was done it was really nice for a heavy truck frame. He started to assemble. About 2 months later little brown dots started to appear, kind of like it was bleeding. This is because he painted over water!

If you have ever taken a cold pop outside, or beer for most, and shortly after the can had beads of water on the outside. If you take a slightly warmer beer outside, it will get condensation as well but just not as bad. If you take a ever so slightly cold beer outside you may not be able to see or fell the water, but it is there! This is caused by the can being colder than the surrounding air temperature. Just like a fresh sandblasted pc of steel, this will also do the same thing!

IF METAL IS COLDER THAN THE IR TEMPERATURE IN THE ENVIRONMENT YOU ARE PAINTING IN, THE METAL IS WET!

The tip is to make sure that the metal you are painting is always WARMER than the air outside or in your shop. Out west, in Las Vegas this might not be an issue because the humidity is so low out of the gate. In places like TN or PA the humidity is generally pretty high even though on a 70 degrees and feels so nice. There is still plenty of water in the air to screw up your painting.

The solution is to "hot box" before you paint. If you are painting a frame you can build a cardboard hut around it and run a heater in side all night the day before (picture below). Or, you can put things in the oven, even heat them with a propane torch or ? I don’t mean to paint them while they a blazing hot but 5 or 10 degrees warmer than outside.

There have at least 5 times where i myself saw a frame in primer with rust poking all through it.

Some think a self etching primer is the key, this is not true. The idea is to hurry up and paint a 100% dry pc of metal and seal of with an epoxy that will lock out moisture and air completely! If there is no moisture and oxygen, rust cant happen, you need both components for rust.

I really hope this helps someone getting ready to paint!
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Old 11-12-2019, 01:40 PM   #2
rockfla
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Default Re: Painting Over Water !!!!!!!!!!!

Here in FLA where the humidity is ALWAYS high, even in "winter" months we can see 70+ degree days with 50's% to 60's% humidity, what are your thoughts/opinions on leaving items in our pant room to achieve "ambient" temp before both priming and painting???
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Old 11-12-2019, 01:43 PM   #3
34pickup
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Default Re: Painting Over Water !!!!!!!!!!!

My first paint job was when I was a kid and I painted my dad's 51 pickup in October. It was supposed to be bright red. And it was bright red for a few months. After that he found himself driving around in a pink truck. I was told it was because the weather was too cool to paint in October. I don't know if that was the reason, but I never painted in the fall or winter again.
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Old 11-12-2019, 01:46 PM   #4
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Default Re: Painting Over Water !!!!!!!!!!!

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Originally Posted by rockfla View Post
Here in FLA where the humidity is ALWAYS high, even in "winter" months we can see 70+ degree days with 50's% to 60's% humidity, what are your thoughts/opinions on leaving items in our pant room to achieve "ambient" temp before both priming and painting???
The higher the humidity the more important this is. In Floridia i would always have my metal warmer that the air you are painting in. The box is the easiest solution...Hope this helps you!
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Old 11-12-2019, 01:48 PM   #5
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Default Re: Painting Over Water !!!!!!!!!!!

You can also use a conversion coating before priming. On steel I use Ospho. I always wipe my stuff down with prep sol before I shoot it and have never had a problem with condense. I don't completely agree that there will be differences in temperatures of materials due to different compositions. So if you move a project from the shade out into the sun, then it might condense a bit before it equalizes in temperature but it doesn't take long to heat up down here in south Texas. If you use a paint booth then stuff should stay at equal temps.

Capillary action can hold moisture in the joints between pieces of overlapping metal but it will dry out if a person hits it with compressed air several times and allows a dwell time before prepping to shoot the primer. I have never shot material over something that was wet with water before wiping or spraying it down again with prep sol and letting it dry out.
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Old 11-12-2019, 01:48 PM   #6
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Default Re: Painting Over Water !!!!!!!!!!!

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Originally Posted by 34pickup View Post
My first paint job was when I was a kid and I painted my dad's 51 pickup in October. It was supposed to be bright red. And it was bright red for a few months. After that he found himself driving around in a pink truck. I was told it was because the weather was too cool to paint in October. I don't know if that was the reason, but I never painted in the fall or winter again.
Some low quality paints like rustoleum will fade fast in direct sunlight. Could have been poor quality paint or too cold. Hard to say though...
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Old 11-12-2019, 02:05 PM   #7
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Default Re: Painting Over Water !!!!!!!!!!!

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You can also use a conversion coating before priming. On steel I use Ospho. I always wipe my stuff down with prep sol before I shoot it and have never had a problem with condense. I don't completely agree that there will be differences in temperatures of materials due to different compositions. So if you move a project from the shade out into the sun, then it might condense a bit before it equalizes in temperature but it doesn't take long to heat up down here in south Texas. If you use a paint booth then stuff should stay at equal temps.

Capillary action can hold moisture in the joints between pieces of overlapping metal but it will dry out if a person hits it with compressed air several times and allows a dwell time before prepping to shoot the primer. I have never shot material over something that was wet with water before wiping or spraying it down again with prep sol and letting it dry out.
Prep sol is a great product especially for removing oils and contaminates. Also, the region on where one is painting will be the largest factor. Mostly it comes down to if your metal is colder than the air moving across it, it is wet!
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Old 11-12-2019, 02:14 PM   #8
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Default Re: Painting Over Water !!!!!!!!!!!

Rust is iron oxide, IE oxidation of iron. Actually only O2 is needed. There is more free oxygen in air then water. However as soon as ferrous metal is exposed to air, it starts oxidizing due to mainly the O2 but there is H20 there also, that is why you need to "etch" it to stop the rust that has begun that you cannot see, but also seals the metal from the air with a thin coat of iron sulfate.
After I get anything sandblasted like a frame, I DA sand it to remove the sharp points left by the blasting material that removes the rust, immediately etch then shoot a catalyzed sealer (available now thankfully) on the parts for later primers and topcoats. Haven't had any come backs of rust yet and I have been doing this since the 1970s before the catalyzed paints were available. The etch is the key. I pay attention to the relative humidity as much as I do the temps before painting. My 2 cents.
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Old 11-12-2019, 02:49 PM   #9
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Default Re: Painting Over Water !!!!!!!!!!!

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Originally Posted by deuce_roadster View Post
Rust is iron oxide, IE oxidation of iron. Actually only O2 is needed. There is more free oxygen in air then water. However as soon as ferrous metal is exposed to air, it starts oxidizing due to mainly the O2 but there is H20 there also, that is why you need to "etch" it to stop the rust that has begun that you cannot see, but also seals the metal from the air with a thin coat of iron sulfate.
After I get anything sandblasted like a frame, I DA sand it to remove the sharp points left by the blasting material that removes the rust, immediately etch then shoot a catalyzed sealer (available now thankfully) on the parts for later primers and topcoats. Haven't had any come backs of rust yet and I have been doing this since the 1970s before the catalyzed paints were available. The etch is the key. I pay attention to the relative humidity as much as I do the temps before painting. My 2 cents.
Etching primers are great for metal that has been stripped chemically. The etching primer has a light acid and zinc to "etch" or enhance adhesion by making a chemical bond to the steel. Modern epoxy primers are such great product for locking out moisture. Etching primers must be sealed by another primer, especially if it would ever be stored outside. The etching primer will put a hold on light flash rust from humidity. Still, a wet pc of metal needs to be dry regardless of primers and topcoats. I have found that an etching primer isnt necessary on sand blasted metal. And, everyone is going to have their preference and what works for them now and in the past. Most people have little experience painting raw metal and getting a beautiful topcoat. I just hope this helps someone not paint over moisture they dont believe exist on their raw steel parts. I always, on raw metal use epoxy, then while its still wet (1 hour dry time) apply 2 coats of Y2K, then after cutting dry Y2K, topcoat with paint of choice. This creates a fantastic wet on wet bond that is extremely durable and locks out moisture.
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Old 11-12-2019, 04:30 PM   #10
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Default Re: Painting Over Water !!!!!!!!!!!

If you ever want to test the moisture theory take a propane torch and heat a cool piece of metal. Water droplets will form.
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Old 11-12-2019, 05:57 PM   #11
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Default Re: Painting Over Water !!!!!!!!!!!

To be clearer, I don't use etching primer, I use gloves, phosphoric acid and and aggressive stainless steel wool and follow instructions.
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Old 11-12-2019, 06:03 PM   #12
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Default Re: Painting Over Water !!!!!!!!!!!

RalphM, one of the main combustion products from burning natural gas or propane is water as well as heat. That is partly why you can vent a 95+% gas furnace like a dryer with plastic pipe.
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Old 11-12-2019, 06:24 PM   #13
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Default Re: Painting Over Water !!!!!!!!!!!

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To be clearer, I don't use etching primer, I use gloves, phosphoric acid and and aggressive stainless steel wool and follow instructions.

Oh, i see. Is it a product like "after blast"? If used that before as well.
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Old 11-12-2019, 06:39 PM   #14
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Default Re: Painting Over Water !!!!!!!!!!!

It gets humid as hell down here when the coastal breezes are coming up from the south. If it's too humid, I can't spray. I would have to have an air conditioned booth and I don't. Once it heats up in the summer time I can spray in the morning but it has to be before it gets too hot. Paints have information from the manufacture that informs a person on whats a go and what's a no-go and some brands are real picky.

I use the Ospho as a conversion coating pretty much like deuce roadster but I rinse it off before it dries so it's not like a primer. It will still convert the surface to a phosphate finish. I don't use etching primers. I still use zinc chromate primer now and then just to add some further corrosion protection in some places but it's mostly for aluminum parts and I use a different mix for the conversion coating on it so that it gets pickled with alodine.

It rains a lot down here in the cooler months so things have to be ready for the corrosion battle.
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Old 11-12-2019, 11:19 PM   #15
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Default Re: Painting Over Water !!!!!!!!!!!

Fascinating subject. I've always had an interest in a home done professional quality paint job but I know nothing about paint on metal. I did however refinish pianos for several years in a professional shop. To include wood repair, stripping, wood grain fill and stain on pianos roughly 70 to 90 years old. There are many similarites to repainting a car. We used nitro cellulose laquer and scraped, sanded and polished the finish with outstanding results. Wood is so much easier than metal to me.
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Old 11-13-2019, 06:36 AM   #16
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Default Re: Painting Over Water !!!!!!!!!!!

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Originally Posted by deuce_roadster View Post
Rust is iron oxide, IE oxidation of iron. Actually only O2 is needed. There is more free oxygen in air then water.

Deuce, Rusting cannot occur without both "water and oxygen". oxidation needs both components. Rust cant happen with just oxygen.
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Old 11-13-2019, 08:29 AM   #17
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Default Re: Painting Over Water !!!!!!!!!!!

All air holds some moisture. If water was forming on the metal due to change in temperature, I'm surprised he did not notice the paint or primer not laying down properly. Just to be clear when the weather gives you the dew point that is the temperature when moisture from the air starts to condense. The higher the humidity the higher the dew point. Air dryer's performance is measured by the dew point of the air. So -40 air means you will not see moisture until the air temp is below -40. If the dew point is 50 and the temp of the metal is 50 then the metal will cool the air around it and result in moisture.
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Old 11-13-2019, 08:40 AM   #18
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Default Re: Painting Over Water !!!!!!!!!!!

What kind of prep is needed for water based paint? is it ok to shoot water base on blasted (wet) metal after cleaning without creating adhesion problems? would prepping with Methyl Ethel Ketone solve any moisture entrapment issues? it seemed to me that M.E.K may be somewhat water soluble and dries quickly .
what about using flex agents for frames? I had problems with a frame primed with an etching primer when put into service the top coat began to crack and peel. the PPG rep said I should have used a flex agent. I never heard of such till this happened . are there paints formulated for frame/metal flex without using such additives?
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Old 11-13-2019, 09:33 AM   #19
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Default Re: Painting Over Water !!!!!!!!!!!

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What kind of prep is needed for water based paint? is it ok to shoot water base on blasted (wet) metal after cleaning without creating adhesion problems? would prepping with Methyl Ethel Ketone solve any moisture entrapment issues? it seemed to me that M.E.K may be somewhat water soluble and dries quickly .
what about using flex agents for frames? I had problems with a frame primed with an etching primer when put into service the top coat began to crack and peel. the PPG rep said I should have used a flex agent. I never heard of such till this happened . are there paints formulated for frame/metal flex without using such additives?

Honestly, i know nothing of water based finishes. I will never use them unless they quit making others. You should not have to use a flex agent on a frame. I know they flex but paint should have good enough adhesion to "go with the flow" of a bend.

Stick with epoxy, then a nice workable/sandable 2K primer, then top coat with a single stage urethane or base coat / clear coat. These products in my opinion, together, create such a fantastic durable finish...I have sprayed hundreds of gallons of this combo and seldom ever had a problem (this isnt an exaggeration). If i did it was an oil contamination, from what exactly, i cant pinpoint. Ever see a car with a huge dent in the door and the paint doesnt have even a crack or even begin to fail? Good prep and quality paint is the answer to great adhesion. Avoid wiping parts with lacquer thinner or acetone before painting. Use something like prepsol.

Cracked catalyzed top coats normally are from over thinning. Use the mfg.'s recommendations. Some people have a gun that cant break down a paint so they thin it more to make it "flow". Over thinning traps solvent and as the paint dries it shrinks but shrinks after the surface of the finish has started to cure.

These (pictures) were sandblasted and primed the same day with epoxy, they 2 coats of 2K. Dried then sanded smooth with 500 without water, just dry paper. Then 2 coats of single stage urethane, wet on wet. The gun is an EURO FLG-5, I have several spray guns, some were $1000 or more. This gun is the best out all of them in "my" opinion. These are all 2 coats off the gun. No sanding between or buffing.

The truck i painted about 10 years ago. It needed a lot of body work. I primed the truck with 1 coat of epoxy then the urban camo was done with base coat clear coat, no flex agents. About a year after paint someone hit it at the grocery store. You can see how far metal can bend before the paint pops with good adhesion. It hard to tell but the dent is about 3" deep. It also is holding back rust well as this truck sees salty winter roads...
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Last edited by Ian1932; 11-13-2019 at 10:19 AM.
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Old 11-13-2019, 10:38 AM   #20
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Default Re: Painting Over Water !!!!!!!!!!!

MEK is not as good as plain old methanol at drying a wet surface. Blow the surface off with compressed air and us a prep sol or wax & grease remover product. It will be dry of all solvents after 15 minutes or so. Blow it off again to remove any other contaminants. MEK drys fast but it's too expensive to use as a solvent for anything other than fiberglass resin or sealants where nothing else will work as well. Lacquer thinner is also good for removing water and crud since it also has some alcohol in it but breathing any of these more volatile fluids will knock you down. They absorb through the skin faster too so wear gloves or limit your exposure.

Just to add. I looked up several wax & grease removers and most all of them contain from light to heavy hydrotreated Naphtha as the main ingredient. From there, the lesser ingredients vary but isopropyl alcohol, mixed xylenes, toluene, ethyl benzene, cumene, and 1,2,4- Trimethyl benzene in trace quantities could be in there.

Prep-sol 3919S was a trade product of Dupont but is now under the Axalta banner so it's till out there but there are a lot of others. Most all go under wax and grease remover description. I just call them all prep-sol.

Last edited by rotorwrench; 11-13-2019 at 11:33 AM.
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