Primer Prep Problems

So I am getting what appears to be areas where grease was not properly removed from the aluminum and was hoping someone can't spot my problem area.

Each primer prep session goes something like this
1. Scuff parts using a maroon scotchbrite pad in a tub filled with warm water and Dawn dish soap.
2. Rinse parts and wipe them with a wet rag in a second tub filled with clean water.
3. While wearing nitrile non-powder coated gloves move parts from tub #2 to a third tub of clean water for a final rinse
4. Set parts aside to dry
5. Move parts into the paint booth (also while wearing nitrile gloves) and wipe with denatured alcohol and a clean lint free rag
6. Spray prime with SW Wash Primer or Alodine 1132 pen
7. Dry in the paint booth

For each skin sized piece of aluminum and especially on the interior corners of the ribs, the primer is beading like the aluminum hasn't been cleaned / degreased. All the parts are thoroughly scuffed which tells me I am getting those corners with the dish soap and I can't see any water breaks during the 3rd and final rinse, but I worry that it just isn't cutting the grease. The spots aren't real bad as it seems more cosmetic (the parts are holding the primer but it doesn't appear real uniform). I do however want to figure out the issue before I get to paint since the interior primer cosmetic issues don't matter, but the exterior paint will.

Does anyone see something glaring that I am doing wrong here, or have a better recommendation for a grease cutting agent than Dawn dish soap?

I only washed just few parts with Dawn. I decided to take another tact which worked for the Akzo primer I used.

While handling parts I tried, for the most part, to make it a point to wear gloves during drilling, deburring, ect. to minimize hand oils from adding contamination to the parts.

Prior to scuffing with ScotchBrite pads, I made it a point to clean the parts really well with Acetone using inexpensive general purpose white terry cloth towels. Then after scuffing the parts with maroon Scotch-Brite pads the parts were cleaned again repeatedly with Acetone and a towel until the towel was mostly clean. You want to use white towels so you can see how much gray from the aluminum is getting onto the towels. When it is just a tiny bit move onto the next part.

Spray the primer same day the parts are cleaned preferably within an hour or so.

I've also used the same method to spray SEM primer and have not had any issues.

P60G2

A photo would help diagnose. P60G2 can spray blobs if mixed too thick. Your cleaning should be adequate if the surface is water break free. If so, there's no need for an additional wipe. Try Bon Ami cleanser instead of Dawn.

After seeing Larry (and others) recommend Bon Ami in the past, I decided to give it a try and I like it better than anything else I've tried so far. It seems to take less scrubbing than anything else I've used to get the aluminum to a point where water doesn't bead up on it.

Although, I've done several small parts with Dawn in the past and haven't had any trouble with it so I think it's unlikely to be the problem.

cleaning

I don't believe it to be the wash primer since I am having the same issue while using the Alodine 1132 pen. Also, I am using Sherwin Williams CM0484684 Chromated Wash Primer (similar but different if it matters). I had one issue early on that was similar which was that I used Acetone instead of Denatured Alcohol for the final wipe down. The Acetone leaves a residue which caused a lot of variation in the primer application. At the blog link below on 4-5-19 you can see what acetone did to the empennage primer spray (don't mind the extra primer on the rivets, that's just me spot priming after setting the rivets). While the variation due to the acetone was significantly more than what I am getting now, it is a similar type issue.

I will switch from Dawn to Bon Ami and see if that fixes the issue. Otherwise it sounds like it just may be not scrubbing long enough (which stinks because my fingers already get chewed up pretty bad from the scotchbrite pad during these cleaning sessions).

Kleenstrip Prep-All is a relatively cheap wax remover and degreaser.
It’s much cheaper than DX-330 or other commercial paint prep cleaners and does just as good of a job. You won’t have issues with your parts being clean.

I recommend for any supplies like Scotchbrite substitutes, paint prep products, tapes, label removers, etc... go to your local auto body supply store. These folks sell to the professionals and they won’t use stuff that doesn’t work. They can’t afford it.
I have used dawn dish soap and water.
It’s fine, but a good degreaser wipes clean and evaporates. No secondary rinses required. I have had no comparability issues.
Good luck.

Kleenstrip Prep-All is a relatively cheap wax remover and degreaser.
It?s much cheaper than DX-330 or other commercial paint prep cleaners and does just as good of a job. You won?t have issues with your parts being clean.

I recommend for any supplies like Scotchbrite substitutes, paint prep products, tapes, label removers, etc... go to your local auto body supply store. These folks sell to the professionals and they won?t use stuff that doesn?t work. They can?t afford it.
I have used dawn dish soap and water.
It?s fine, but a good degreaser wipes clean and evaporates. No secondary rinses required.
Good luck.

No pictures, so just throwing out some basic advice:
Use paper towels, not rags.
Silicone is prevalent in laundry softeners, and many other products like auto waxes. Banish anything the even "might" have been around silicone from your paint and prep areas.
Similarly, don't use syringes for measuring paint.

I did a quick google search about whether denatured alcohol leaves a residue and it looks like it can depending on what was mixed with the alcohol to denature it. The pictures on your blog make it look like the spots in the primer are following a long streaking pattern so it seems possible that it could be a result of wiping the parts down before you spray them.

The blog picture was definitely residue from using acetone. I have since changed to denatured alcohol, but didn?t realize that could streak as well. I?ll have to do some tests to see when the problem appears, but plan to start by switching from Dawn to Bon ami for degreasing.

Your step 4. "set parts aside to dry"

I noticed that when I use to let parts air dry, I sometimes ended up with small areas that were slightly "discolored" looking. I assumed the areas were water spots left over from the air dry process. I don't recall any adhesion issues, but something was different when priming those areas. I now use a blow dryer to dry all parts after final rinse. I no longer use rags or paper towels because of the possibility for contamination. Also, I discovered when using paper towels that occasionally very small pieces of the paper towel were left sticking to the aluminum.

I'm using the Akzo primer but I've also had great results with the bon ami. I also use Southern Polyurethanes waterborne wax and grease remover after rinsing and drying the part. I use wypall x80 cloths since they are durable and (mostly) non-linting.

The bon ami is fast too. I scuffed each of the HS skins on my 10 in under 10 minutes. I only needed to touch up a couple of small places.

I don't use any solvents beforehand; that just takes more time. The bon ami instantly takes off any residual red lettering and sharpie. Most solvents just smear wax and grease around and then evaporate. Using a product designed to clean the surface works significantly better.

Surface prep

Pardon while I step on my soap box.
The culprit is aluminum oxide (Al2O3). It's only a few mils thick but it's the enemy of adhesion. Solvents won't remove it. Paint doesn't stick very well to it. Paint also sticks best to an abraded surface. Maroon Scotchbrite does a nice job of scuffing and with the addition of Bon Ami or even Comet or Ajax, the Al203 layer is removed along with any traces of contaminants. Comet and Ajax have bleach so you want to rinse them really well. The Al203 begins reforming immediately in the presence of O2 so you want to shoot primer as soon as possible.
If you want to save the hands, a scotch brite pad works well on a random orbital sander. It's fast. Only a light pass is needed to scuff. However, the wash step is still required. I use gray scotch brite and Bon Ami.
Test your prep method by applying black Gorilla tape to the cured surface. Rip it off.

All water based washing should be before you final scuff, otherwise you are pushing the grease deeper into the crevices and all the water exposure is accelerating the corrosion. Post scuff, use a wax and grease remover before applying paint. This also helps to remove the debris caused by scuffing. Paint should go on within 2 hours of abrasion.

I often use a scuff pad while cleaning with detergent. However, I also do a final scuff and clean with W&G remover right before paint application. You need compressed air and a good amount of drying time after the detergent treatment. Water finds its way into crevices and you don't want to paint over that. No real issue with small parts, but a big problem for assemblies.

Larry

next steps

So here is what I am thinking I'll try next.

1. Wipe / clean with Prep-All cleaner / degreaser
2. Scuff with maroon scotchbrite pad in Bon Ami / water solution
3. rinse and wipe in clean water
4. blow dry and move into paint booth
5. Spray prime or apply Alodine 1132

We'll see how it works. The good part about the Alodine pen is that you can clearly see if you have any remaining grease marks while applying. Much easier to correct if you do have marks than when spray priming.

I noticed that the Akzo primer actually absorbed water when I painted to late in the day.

I was living 1-2 miles from the ocean at the time though.

Could you be having similar problems?

az_gila said:

I noticed that the Akzo primer actually absorbed water when I painted to late in the day.

I was living 1-2 miles from the ocean at the time though.

Could you be having similar problems?

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What did that look like? The only time I've seen water in primer is when my separator filled and it started spitting water drops. I've never seen paint or primer pull it out of the air

jacoby said:

What did that look like? The only time I've seen water in primer is when my separator filled and it started spitting water drops. I've never seen paint or primer pull it out of the air

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Essentially that is what it did in the high humidity before it cured.

It may have been not dry enough and it didn't stick...

Prep

mulde35d said:

So here is what I am thinking I'll try next.

1. Wipe / clean with Prep-All cleaner / degreaser
2. Scuff with maroon scotchbrite pad in Bon Ami / water solution
3. rinse and wipe in clean water
4. blow dry and move into paint booth
5. Spray prime or apply Alodine 1132

We'll see how it works. The good part about the Alodine pen is that you can clearly see if you have any remaining grease marks while applying. Much easier to correct if you do have marks than when spray priming.

Click to expand...

I recommend using a hair dryer to blow dry just in case. Compressor air can have contaminants. I actually use clean shop paper towels to dry. It also removes residue from the water. Especially important if your water has a lot of minerals. Save the paper towels for other uses in the shop. You got this.
Also, just in case, I mix P60G2 1 part primer to 2 parts catalyst. Very thin. Spray till only a hint of color can be seen. Usually two passes at 90°.

mulde35d said:

So here is what I am thinking I'll try next.

1. Wipe / clean with Prep-All cleaner / degreaser
2. Scuff with maroon scotchbrite pad in Bon Ami / water solution
3. rinse and wipe in clean water
4. blow dry and move into paint booth
5. Spray prime or apply Alodine 1132

We'll see how it works. The good part about the Alodine pen is that you can clearly see if you have any remaining grease marks while applying. Much easier to correct if you do have marks than when spray priming.

Click to expand...

All-Prep is used as a ?final wipe?. You don?t want to introduce water after. Water is the last thing I want on the surface of my part even with a thorough drying. Unless youre using distilled water, you will leave trace minerals and maybe even chemicals behind. Many get away with it, but it simply isn?t necessary to go through the process.
You will go through a lot of clean rags but Scotchbrite and then Prep-All is all that is needed. I am sorry, but Scotchbrite isn?t going to embed contaminates in the scratches. If your aluminum is so greasy and dirty that there is a concern, you could clean it, dry it, and then Scotchbrite, but I never do. Fingerprints, human oils, silicon, etc.... the Prep-All will take care of it after you Scotchbrite. Follow the directions on the Prep-All label. Simple.
You are not in a production environment so if you want to add steps you can, but the pros don?t. That?s why these products where developed. Prep and priming take a long time in the build process. Why not make it simple and easier with the right products? Your not washing dirty greasy dishes.

By the way, Dawn isn?t the same it used to be. They still make Classic Dawn, but it still is different and may have added scents and other chemicals. Also, it is much more concentrated than before. Not the same which could be why folks may have trouble using it like they did back in the day. Just a guess.

wirejock said:

Also, just in case, I mix P60G2 1 part primer to 2 parts catalyst. Very thin. Spray till only a hint of color can be seen. Usually two passes at 90°.

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It works and I have done the same without any noticeable ill effects, adhesion issues etc... not 2:1, but certainly thinner. However....

I hate the thought of reducing the product solids and not following the manufacturers recommendations for mixing.

I found my Sharpe Platinum gun nozzle was the culprit. It is a fine nozzle and the thick primer was causing spattering and uneven solids dispersal. I changed over to a Sharpe Cobalt Primer gun and all was well. I could keep the specified 1:1 ration. However, if the can was opened, it may need thinned a bit down the line. I reserve the Platinun gun for top coating now.

Absolutely apply the coating as a “fog”’coat as you describe. 4 mils I believe is all it wants to be. I would have to read up on it again to be sure.

JonJay said:

Absolutely apply the coating as a “fog”’coat as you describe. 4 mils I believe is all it wants to be. I would have to read up on it again to be sure.

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4 mils per coat is on the heavy side (approaching dripping and sagging) for most paints and primers that I've sprayed. Dry film thickness for the Akzo (which goes on thicker than the P60G2) at total opaque is around 0.5-0.75 mils. Wet is going to be closer to 1.5-2 mils.

I just looked at the TDS for the p60G2 and it should be sprayed at 1.3-2.6 mils wet. Dry is 0.2-0.4.

az_gila said:

Essentially that is what it did in the high humidity before it cured.

It may have been not dry enough and it didn't stick...

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That's wild! I wonder if the aluminum was acting as a heat sink and letting water condense on it? I've sprayed in some pretty humid conditions and never had water pull out of the air.

Final decision (maybe)

JonJay said:

All-Prep is used as a ?final wipe?. You don?t want to introduce water after. Water is the last thing I want on the surface of my part even with a thorough drying. Unless youre using distilled water, you will leave trace minerals and maybe even chemicals behind. Many get away with it, but it simply isn?t necessary to go through the process.
You will go through a lot of clean rags but Scotchbrite and then Prep-All is all that is needed. I am sorry, but Scotchbrite isn?t going to embed contaminates in the scratches. If your aluminum is so greasy and dirty that there is a concern, you could clean it, dry it, and then Scotchbrite, but I never do. Fingerprints, human oils, silicon, etc.... the Prep-All will take care of it after you Scotchbrite. Follow the directions on the Prep-All label. Simple.
You are not in a production environment so if you want to add steps you can, but the pros don?t. That?s why these products where developed. Prep and priming take a long time in the build process. Why not make it simple and easier with the right products? Your not washing dirty greasy dishes.

By the way, Dawn isn?t the same it used to be. They still make Classic Dawn, but it still is different and may have added scents and other chemicals. Also, it is much more concentrated than before. Not the same which could be why folks may have trouble using it like they did back in the day. Just a guess.

Click to expand...

I am thinking a combination of the two methods may work best depending on the part. For the small parts I prefer to clean them in a water solution since I can keep them submerged and clean them all before removing the first one from the water and starting the oxidation process. Also, from a dust and inhalation hazard aspect I prefer to scuff them wet.

For these smaller parts I am thinking
1. Scuff with maroon scotchbrite pad in Bon Ami / water solution
2. rinse and wipe in clean water
3. blow dry and move into paint booth
4. Wipe / clean with Prep-All cleaner / degreaser

For larger parts that are more difficult to submerge I am going to try the following
1. Scuff with maroon scotchbrite pad on orbital sander (while wearing a respirator)
2. move into paint booth
3. Wipe / clean with Prep-All cleaner / degreaser (lots of paper towels and rags)

Kind of a hybrid of all the methods presented in the post. I look forward to seeing how the next spray session goes. I'll try to remember to take some pictures of the results and post them here.

That will work just fine. Show us your results!

After reviewing your steps......

I had the same first reaction as Wirejock in post #13. He basically pointed out that one of the most common cause of lack of adhesion is failure to adequately remove the alclad layer, and if that is not the culprit, some other form of contamination or improper primer mix or weather (humidity) issue is usually to blame as others have discussed. I have experienced all of these.

Like John-G from post #2, I am an acetone guy, and it works well for me. What I noticed in your original post is that it seems that you were starting the scuffing process with the part already in the water solution at the very beginning of your process. If that is correct I don't think that you are removing enough of the alclad in some of those harder to reach/scuff areas on certain parts.

So, my process is to scuff it quite a bit while "dry," with the part on my bench or on a table. It makes a mess, but that's where the washing comes in. Then I wash the part in warm water with original Dawn formula detergent and a sponge to get rid of the visible scuffing residue as much as possible, and then I also rinse the parts in another bucket or two to ensure the detergent is removed. Then the part is air dried or sometimes I will "help" it with a paper towel or cloth - always being mindful of not touching the now-scuffed-and-washed part, except on extreme edges as necessary. Then I start the acetone cleaning process - usually with a clean microfiber rag, put on some rubber gloves, and I will reapply the acetone and keep going over all areas of the part as many times as necessary, checking that the amount of residual aluminum material on the rag starts to diminish, as reported by John-G.

Then, when the acetone cleaning is done, I prepare to prime the parts as soon as possible afterward. This has served me well when applying a number of different types of primer products on my airplane parts.

I will also add this - every time I engage in this process for a batch of various airplane parts that I need to prime, my hands and arms, and even my back end up quite sore much of the time because I also use a lot of elbow grease during this entire process. From my experience, I figure that if I am not sore from it then it probably that means I did not scuff or clean it enough.

Anyway, the point is to make certain you are scuffing enough of the alclad aluminum away, especially in those corners and under the flanges, etc., that are very easy to miss.

That's my experience and advice. Good luck and let us know how it turns out.

fl-mike said:

Similarly, don't use syringes for measuring paint.

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Hi Mike,

I have been using syringes to suck up the Stewart Systems primer for my parts and haven?t seen any issues as yet. Is the issue that the syringes may have silicone in the rubber part?

You got me wondering now if I?ve just been lucky...

Syringes

TASEsq said:

Hi Mike,

I have been using syringes to suck up the Stewart Systems primer for my parts and haven?t seen any issues as yet. Is the issue that the syringes may have silicone in the rubber part?

You got me wondering now if I?ve just been lucky...

Click to expand...

Yes, some feel the rubber is contaminated with silicone.

I've been using syringes for the entire build. 1 gallon P60G2, 1-1/2 quarts Jet Flex.
I did read posts early on about syringes and switched to rubberless for a while but neither has been an issue. I do clean them with lacquer thinner before first use if that makes any difference. I also label the inside plunger and outside so they can't get mixed up.

For these smaller parts I am thinking
1. Scuff with maroon scotchbrite pad in Bon Ami / water solution
2. rinse and wipe in clean water
3. blow dry and move into paint booth
4. Wipe / clean with Prep-All cleaner / degreaser

For larger parts that are more difficult to submerge I am going to try the following
1. Scuff with maroon scotchbrite pad on orbital sander (while wearing a respirator)
2. move into paint booth
3. Wipe / clean with Prep-All cleaner / degreaser (lots of paper towels and rags)

Click to expand...

But then what? You've prepped the parts. What is the next step. (Pretend you're talking to some one with absolutely no idea of how to do this...)

Water is not just H2O. It has dissolved solids, so unless you are rinsing with de-ionized water, you could be leaving solid deposits there.


I have yet to see a picture of what your issues are. The log picture resolution is not good enough to see.

Water is not just H2O. It has dissolved solids, so unless you are rinsing with de-ionized water, you could be leaving solid deposits there.


I have yet to see a picture of what )precisely) your issues are. The low picture resolution is not good enough to see.

me too

benjam said:

But then what? You've prepped the parts. What is the next step. (Pretend you're talking to some one with absolutely no idea of how to do this...)

Click to expand...

Don't worry, I felt that way not too long ago as well. I decided on a chromated wash primer as the next step. Sherwin Williams CM0484646 wash primer. This will be followed by their General Aviation Urethane Primer System.

https://www.swaerospace.com/products/paint-systems/general-aviation-paint-systems

While the Wash primer, according to Sherwin Williams, is supposed to be covered by the CM0486707 next for "corrosion protection", I can say with confidence that since it is a chromated wash primer that it has corrosion resistant properties. It is similar to the primer we use on the inside of army aircraft. Now anywhere I plan to paint I will cover with the CM0486707 on top of the 646 wash primer before applying the paint. I also liked this urethane primer system because the regular primer and sanding surfacer for fiberglass are the same liquid, therefore less types of primer that I need to purchase (I hate having half empty cans laying around). Also, this 707 primer is meant to take either the Jetglo series of paint or the new Skyscapes series which are different in that jetglo is intended to be a paint / topcoat where skyscapes has paint for a basecoat with a clearcoat that goes on afterwards.

The biggest reason I went with Sherwin Williams was because I had to educate myself from scratch and they had the easiest website for me to figure out all this aerospace paint stuff. Unfortunately their pretty expensive. I figure about 5-6K in materials to wash prime the entire aircraft inside and out, then prime and paint the cabin and exterior myself.

Thanks for that Mulde.

You?re right, their website is easy to read and digest.

I will keep reading.

Good luck with the build

Update

I think I determined the issue. The problem seems to be letting the parts sit too long between scuffing/cleaning and applying the primer/alodine. I didn't get the prep-all yet so I cleaned a small batch of fuel tank parts in soapy water with a double rinse just like before. The only different was I immediately dried them with paper towel and applied the Alodine 1132. Even in the creases where I was having problems the Alodine went on smooth with no imperfections. I think the root of the problem was the areas where I may have not scuffed all the way through the alclad likely oxidized before I applied primer. By applying it quickly, even the poorly scuffed areas had good adhesion.

Thanks to all those that provided input.



For those that couldn't see the issue in the smaller images, here was the original issue. You can see the problem on the flanges

mulde35d said:

SNIP.... I think the root of the problem was the areas where I may have not scuffed all the way through the alclad likely oxidized before I applied primer.

Click to expand...

Recommend you never do this. There is no reason to remove alclad to prime and some reason to leave it.

I?ve done three RVs, all slow builds and all 100% primed before assembly. I have never had anything like all the issues listed on this thread - perhaps I?ve just been lucky. So in short here is what I do:
- Fit as many parts as possible and then put then in the priming stack.
- Use PPG Alumiprep and a maroon scotch brite pad to clean and lightly scuff the aluminum. Use a lot of water to rinse (right out of the hose - not DI or such). You know you are done when the water sheets off.
- Let dry and shoot a single coat of PPG DP-40LF primer.
- I never use Alodine. The primer provides superior protection.

For the exterior I do the same but add a wipe down of all the aluminum using something like Coleman fuel and a shop towel to make sure all residue is gone before shooting the primer.

The PPG primer is amazingly durable.

Carl

Splotches

The splotches on the flanges look like areas where aluminum oxide was not scrubbed off. It's only a few mils thick but alodine won't convert. One of the many suggestions posted should work fine.
Previous post about Alumiprep works. I used it on the exterior when it was Alodined. I couldn't wash with Bon Ami in the garage and it's far too cold in the Winter up here to wash outside.

Clarify

Just wanted to clarify for everyone, I have either used alodine or used wash primer on various parts, not both on the same part. The alodine 1132 pen is great for touch ups and fuel tank parts while the spray wash primer is easiest for large spray jobs. Both provide a suitable substrate for follow on coats.

Carl Froehlich said:

Recommend you never do this. There is no reason to remove alclad to prime and some reason to leave it.

I’ve done three RVs, all slow builds and all 100% primed before assembly. I have never had anything like all the issues listed on this thread - perhaps I’ve just been lucky. So in short here is what I do:
- Fit as many parts as possible and then put then in the priming stack.
- Use PPG Alumiprep and a maroon scotch brite pad to clean and lightly scuff the aluminum. Use a lot of water to rinse (right out of the hose - not DI or such). You know you are done when the water sheets off.
- Let dry and shoot a single coat of PPG DP-40LF primer.
- I never use Alodine. The primer provides superior protection.

For the exterior I do the same but add a wipe down of all the aluminum using something like Coleman fuel and a shop towel to make sure all residue is gone before shooting the primer.

The PPG primer is amazingly durable.

Carl

Click to expand...

I think he means that he is scuffing through the oxidation layer. It took me a lot of work to get through the alclad laye with 100 grit on a DA when I tested. Your arm would fall off before you could go through it with a scuff pad. The maroon ones are 400 grit equivalent.

WHen he didn't mechanically remove the oxidation layer, he got adhesion failure, which is expected.

Larry