Paint questions

[par]

The condition of the paint on the bottom of my Mooney and LG area (wells/doors) needs some work. The rest of the plane is actually in very good shape in terms of paint. I would like to attempt the re-spray myself in the gear wells at the very least but the tough part will be the removal of the old paint. I have been searching for the best method for paint removal and it seems most shops like to use chemical stripper. Is it possible to use a blasting method instead to accomplish this task instead? If not, what is the reason for choosing a chemical stripper over blasting? Blasting seems like it would be much quicker and easier with better results.

Also, once I get the old paint off, will I need to prime and paint or just paint? I will simply be matching the current white paint so its nothing fancy. I'm curious to see what some of you have done in the past. The only shop quote I've received so far was 6-8k just to do the gear wells and fuselage bottom and that's a no go for me.

 

Par

[DonMuncy]

All the sandblasting I have seen used a pressure high enough to push dents in aluminum. I'm no expert.

[carusoam]

There is a video of an interesting chemical stripper made by the TKS people.  You can probably find it around here with a search or two.

When searching, you will find some tank sealant strippers.  Read them both.  One can adversely effect the other...

Best regards,

-a-

[Sabremech]

I'm doing a little landing gear work on mine right now and looking ahead to the wheel wells. I don't want to use chemical stripper as there are too many places for it to not get cleaned out completely and for corrosion to set in. I'm looking at soda blasting the wheel wells, at least those areas other than the wing skin itself. It will be interesting to see what other ideas people come up with or have previously done for the wells.

 David

[isaacpr7]

If you strip to bare metal you must use etching primer. This type of primer will allow good adherence of the following coats and resist corrosion. Surfacer primer absorbs humidity and will cause corrosion but if you're not stripping to bare metal it will not be an issue. The etching primer is normally is pistachio green in color.

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[jetdriven]

I wouldn't put any stripper in the gear wells.  Just clean it very well with mineral spirits then denatured alcohol, scuff with scotch Brite then paint. 

For the rest of the skin, strip it with a neutral stripper such as sp-909 and variprime etching primer and topcoat.  

[par]

Just now, jetdriven said:

I wouldn't put any stripper in the gear wells.  Just clean it very well with mineral spirits then denatured alcohol, scuff with scotch Brite then paint. 

For the rest of the skin, strip it with a neutral stripper such as sp-909 and variprime etching primer and topcoat.  

 

A lot of the old pain inside the gear wells is actually chipping and peeling off down to the bare aluminum. I'm worried about doing all the work of cleaning and painting only to have the same issue shortly thereafter.

[1964-M20E]

soda blasting I've seen them do aluminum drink cans with no damage to the aluminum.  The drawback is the mess and where the soda ends up and sanding by hand in cramped quarters above your head is not my idea of fun.

[MB65E]

Plastic media blasting will be the best. Sand will leave silicon behind and imbed itself in the material. I fear chemical strip in the wells too. 

On mine, one of these days I'll tackle my landing gear buy pulling it out and refinishing everything. Until then it's scotch brite and a rattle can. 

I have had good luck with the "epoxy appliance paint" it's super tough, application/coverage is great, and the white dries really smooth and glossy. 

-Matt

[Yetti]

1 hour ago, isaacpr7 said:

If you strip to bare metal you must use etching primer. This type of primer will allow good adherence of the following coats and resist corrosion. Surfacer primer absorbs humidity and will cause corrosion but if you're not stripping to bare metal it will not be an issue. The etching primer is normally is pistachio green in color.

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I am curious about this...   How does it absorb humidity if coated with an enamel top coat of paint.    Seems like Mooney Factory Paint was automobile paint.  Rustoleum has an aluminum etching primer now.  How does it compare the the traditional green stuff?

 

[Yetti]

The last HF purchase was a soda blaster...   Seems like a slow process, but maybe good for spot blasting places.  I could see Dawn soap to remove wax and oils.  Scuff with scotch pads.  Spot blast with soda blaster, feather with sand paper the place paint is missing.   Prime, then paint.  Rustolem Gloss white is a pretty close match to the original Mooney white

[bradp]

I did my gear well with the following:

Tape and mask everything 

thorough cleaning

more cleaning 

clean with solvent (spirits or isopropyl)

scuff with scotchbrite 

Clean again with solvent 

etching primer

epoxy would be best.  I used rattle can enamel and got great results.   Figured it just needed to hold up.  Not look pretty.  

[jetdriven]

6 hours ago, Yetti said:

The last HF purchase was a soda blaster...   Seems like a slow process, but maybe good for spot blasting places.  I could see Dawn soap to remove wax and oils.  Scuff with scotch pads.  Spot blast with soda blaster, feather with sand paper the place paint is missing.   Prime, then paint.  Rustolem Gloss white is a pretty close match to the original Mooney white

Don't use dawn soap in the wheel wells. It has a Ph of 12 and is corrosive to metaI. I washed my plane with it and it corroded the heck out of two bare spots.  The wheel well is made up of several laminated sections of spar cap and skin and you don't want anything in there that can even think about causing corrosion, because it will certainly total your plane. And it's just a matter of time.  Like that guy using paint stripper in the fuel tank of his Mooney. His plane is totaled he just doesn't know it yet. Or he doesn't believe stripper causes corrosion on lap seams. 

[par]

So how the heck do you clean all the crap that is in the wheel wells? There is oil, dirt, water, and whatever else the tires can kick up in there and it needs to be cleaned before it can be repainted. Soap would be the best choice. Is there a particular type of soap that is acceptable? How about some high end car wash soap?

[mooniac15u]

Dawn dish soap has a pH around 7-8 which is only slightly basic. 

[jetdriven]

46 minutes ago, par said:

So how the heck do you clean all the crap that is in the wheel wells? There is oil, dirt, water, and whatever else the tires can kick up in there and it needs to be cleaned before it can be repainted. Soap would be the best choice. Is there a particular type of soap that is acceptable? How about some high end car wash soap?

How about mineral spirits to kill the grease and follow that with denatured alcohol to cut the film left behind by the mineral spirits.  No water, and no acid or alkaline.
Dawn's info says pH of 9. After the water evaporates it wil;l be that again.  Anyways, aluminum tolerates acid better than  bases but none belong in aluminum seams.

[Andy95W]

9 hours ago, jetdriven said:

I wouldn't put any stripper in the gear wells.  Just clean it very well with mineral spirits then denatured alcohol, scuff with scotch Brite then paint. 

For the rest of the skin, strip it with a neutral stripper such as sp-909 and variprime etching primer and topcoat.  

Byron's advice is safe and effective.  Rubbing with the red Scotch Brite will flake off the peeling paint and smooth the edges nicely, for large areas you can use a flat piece of scrap aluminum as a scraper.  I like lacquer thinner to help soften the old paint and degrease the area, but mineral spirits is a lot cheaper and you won't pass out with your head in the wheel well.

It won't be perfectly smooth like the top of your wing but you will be satisfied and pleased with it.  And if anybody sticks their head in your wheel well, and that person isn't a judge at Oshkosh, tell them to mind their own damn business.

[mooniac15u]

40 minutes ago, jetdriven said:

How about mineral spirits to kill the grease and follow that with denatured alcohol to cut the film left behind by the mineral spirits.  No water, and no acid or alkaline.
Dawn's info says pH of 9. After the water evaporates it wil;l be that again.  Anyways, aluminum tolerates acid better than  bases but none belong in aluminum seams.

That's the pH for the concentrated soap. pH is concentration dependent. 

It is also a logarithmic scale so pH 9 is about 10 times more alkaline than pH 8 and 1,000 times less alkaline than pH 12.

[mooniac15u]

If Dawn is causing a problem with aluminum I would guess it's the presence of the sodium salts rather than the absolute pH. The protective layer of aluminum oxide on the surface is likely being converted to sodium aluminate and leaving unprotected aluminum metal exposed. 

[Yetti]

Depending on who you read.  Dawn is about a 7    Simple green is about a 9 ...   Simple green hurts alot more in a cut than Dawn so that seem about right.

Mineral spirits would cut the crud also

[RLCarter]

The wheel wells are probably the hardest part to prep/paint but luckily one of the few places anyone ever sees. Use several different shaped stiff bristled brushes to get into everywhere you can (corners and seams especially) with lacquer thinner. This will remove most of the grime, oil and flaking paint. Use Red Scotch Brite pads to scuff or fully remove the existing paint. Any bare aluminum will need to be primed, I would use Zink Chromate or just make sure the primer you use is for Aluminum as it requires a conversion coat or the paint wont stick. Wipe the area down one last time with thinner before applying any type of paint. Paints (color and primer) bounds 2 different ways either a chemical bond which is best or a mechanical bond, too long between coats means you have to scuff the previous coat so read the instructions on the paint you are using for times. Light coats are much better than heavy coats which generally will result in runs in the paint plus thick paint chips off easily when dry. To keep runs to a minimum on both the primer and paint the first coat should very light (dusting) and allow to tack up before the second coat which still wont be a full coat (still see through in places), your third (or 4th coat if needed) coat will be your cover coat so watch for runs, any blemishes that pop up during any of the painting will generally get bigger so don't try to hide them with more paint.Be sure to mask off any area you don't want paint on, and remember paint will hang in the air and fall on top of wings, fuse and stab. Common issues with painting are "fish eyes" which is contaminate on the surface, "orange peeling" which is either too much air and/or not enough paint, "dry spots" too little paint,moving to fast and/or too much air, "paint runs", too much paint, too slow, too much air. Hope this helps, just remember don't get rushed

[jetdriven]

27 minutes ago, Yetti said:

Depending on who you read.  Dawn is about a 7    Simple green is about a 9 ...   Simple green hurts alot more in a cut than Dawn so that seem about right.

Mineral spirits would cut the crud also

From their own literature it's 9. That's at 10% concentration. But what's the concentration in a seam when the water all evaporates?

https://www.pg.com/productsafety/msds/Ultra Dawn MSDS - July 2014.pdf

[N201MKTurbo]

Be careful with solvent, compressed air or blasting in the wheel wells. There are a couple of places where you are looking at fuel tank seams. You can blow the sealant out of the tank.

experience talking....

[Bob_Belville]

Ms. Google knows everything. Some of it is true.

http://housekeeping.about.com/od/environment/tp/Ph-Levels-For-Common-Cleaning-Supplies.htm

[isaacpr7]

1 hour ago, isaacpr7 said: If you strip to bare metal you must use etching primer. This type of primer will allow good adherence of the following coats and resist corrosion. Surfacer primer absorbs humidity and will cause corrosion but if you're not stripping to bare metal it will not be an issue. The etching primer is normally is pistachio green in color.

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I am curious about this...   How does it absorb humidity if coated with an enamel top coat of paint.    Seems like Mooney Factory Paint was automobile paint.  Rustoleum has an aluminum etching primer now.  How does it compare the the traditional green stuff?

 

The absorption happens during the curing process due to the type of solvents used to mix in the surfacer primer, not after you coat with paint. You can also trap moisture if you do not wait for proper flash time between coats. There's a lot to cover on this matter and a lot if chemistry involved. If you want to understand it better I suggest reading an auto body paint book but be aware that you will not find all the information in any one book. I have read several and they all have information the others will not cover. Here are some useful links with summarized information:

http://www.how-to-build-hotrods.com/primer.html

http://www.gearheaddiva.com/5397/epoxy-vs-self-etching-primer-for-painting-bare-metal/

PS: The green stuff you are referring to is etching primer which has chromate coating mixed in it.

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