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Removing old paint

Before applying a new paint job the old paint has to come off. My shop says it can be done chemically or by sanding. So far I do not understand the implications of each. Any painting experts on this forum who can help?

Then after painting all those stickers have to be renewed. How is this usually done? Do you go to any local store and design them all yourself or is there anybody selling complete sets for different airframes?

www.ing-golze.de
EDAZ

The usual sheet metal in aircraft is Alclad – high-strength aluminium alloy sheets plated with soft pure aluminium for corrosion resistance. This is the reason why chemical stripping is usually the preferred method for metal, as sanding may damage the aluminium plating. However, on bonded structures like Grumman AA-1 and AA-5 the paint stripper may damage the bondlines, so they have to be masked with impervious tape (usually sticky aluminium foil) before applying the stripper to the rest of the airframe. The remaining narrow strips of paint are then carefully sanded. On the other hand, “sanding” may actually mean abrasive blasting, which can be done with a fairly gentle abrasive (e.g. walnut shell powder), but I am not sure it’s cost-effective on big surfaces.

LKBU (near Prague), Czech Republic

I have had a couple of aircraft painted. Chemical processes were used on both, the really important thing is that the aggressive stripping chemical is thoroughly removed before re-painting. I think this sort of attention to detail is the reason it is important to pick a reputable paint shop.

The paint shop has always re-painted (or stickered) stripes and letters etc for me. In one case I just “designed” a colour scheme by looking at pictures of the same model of aircraft on the internet and picking a design we liked, then chose the colours. The paint shop worked from photographs.

It is sometimes possible to get current paint scheme designs from the aircraft manufacturer if the type is still in production, and this is what I did for the second aircraft.

Things like the manufacturers logos etc were sourced by the paint shop.

Darley Moor, Gamston (UK)

Thank you for the details. Did anybody here have any issues with chemical paint stripper causing leaks to wet wing tanks?

Last Edited by Sebastian_G at 31 Oct 15:58
www.ing-golze.de
EDAZ

Sebastian,
You should especially watch the paint stripper on the windows (as a/c is pressurised), an aquaintance several years ago had to
replace all of the windows on his Cheyenne due to incorrect proceedure by the paint shop!

You have to consider also that Boeings and Airbus’es are designed specifically to be stripped and re-painted over and over. A small GA aircraft is not. Chemical stripping and acid etching may do more harm than decades of corrosion will do. The painters may do all kinds of crazy things too. An inspector at SAS (Scandinavian Airlines System) told me a very scary story done by so called professional painters. This was on a DC-9. He was to inspect it after it has been stripped for re-painting. They always inspect the fuselage for cracks etc. They know the usual places for cracks and it all looked good. When finished he looked at it from a distance, and saw a few marks in the fuselage, looking like someone had taken a sharp object cutting the surface. He then looked at different angles to get the light from different positions, and he could see several marks along the surface. At a certain angle he could see them all, and it said “SCANDINAVIAN” in a several years old livery font.

What the painters had done was to use a knife or some sharp object to somehow cut/carve out the edges of the letters straight onto the fuselage for some odd reason. The DC-9 if of course pressurized and had several compressions and decompressions per day over a long service life, and any cutting of the surface of the fuselage skin is a strict NO NO. Luckily it ended well, after thorough checking none of them were deep enough to not being fixed by sanding and polishing.

This was professional painters painting airline aircraft for a living, just think about what low paid personnel painting GA aircraft might do

The elephant is the circulation
ENVA ENOP ENMO, Norway

There was a similair thread on here just a couple of weeks ago:
Link

Chemically or sanding can both be done, see the link as well. On aluminium aircraft chemical paint stripper is common. Fabric and Fiber aircraft are sanded.

Normally the painter will also reinstall all placards and stickers. On the larger ones you can often choose to have the spray painted, or vinyl. I would suggest you leave this work to the aircraft painter. There a different kinds of vinyl, depending on the application, size etc.

“sanding” may actually mean abrasive blasting

I agree largely with Ultranomad, just like the bonding, your sealed edges of the fuel tanks will also be masked, during paint stripping, to prevent stripper getting in contact with the fuel tank sealing. These small edges are done by hand sanding by a good painter. Same is true around the windows. A good aircraft painter will go for quality. And remove all these small bits by hand, just like around the rivit heads, without damaging the windows. I have seen some aircraft which where blasted, I wasn’t impressed, as all skin panels on these aircraft seem to be slightly dented in in the unsupported area’s. Remember the aluminium skin is really thin, so easy to disform.

Get a good aircraft painter is the most important. Trying to save money on suchs a project might degrade the quality of work, with corrosion as a first risk, or a paint job with a lot of dust in it, which just doesn’t look good. Feel free to contact me should you require contact information for a quality aircraft painter.

JP-Avionics
EHMZ

One of the aircraft we had done had wet wings, one had bladder tanks. Both had windows. Neither aircraft had problems with fuel tanks or windows..

Darley Moor, Gamston (UK)

Thank you for the good comments. So my bottom line is that chemical stripping is no problem as long as all windows and other non metallic parts like composite, tank seals etc. are masked properly. Such masking should be done that a safety border of metal is left untouched which will get hand sanded later.

How about rivets? Is there any risk the stripper gets into the rivets and stays there causing problems? I ask because my paint shop says they might prefer not to use chemical stripper at all. And I am a little afraid that too much sanding might be no good idea either, especially when sanding bigger surfaces some more agressive mechinery will have to be used…

Another question on paint preparation. On many planes and ours also the front windows are fixed with many screws. Usually these screws are painted together with the airframe. On some pictures of brand new planes I can not make out the screws. Are they too small on the pictures or is it possible / wise to fill the screw heads with some filler? Gettings the windows out is a major job anyway which, I hope will never happen. So the extra work to get out the filler would probably not matter much compared to the total work required.

Then we have a surface damage to the front of our radar pod. I think our paint shop is not really familiar with that. Is it ok to use normal non metallic non carbon composite materials for repair? Or are there any special materials whch should be used?

And a last one. Some paint shop advertise they apply a primer/filler which is then sanded down for a better finish. I know this is done on cars but is it wise on planes considering weight?

www.ing-golze.de
EDAZ

How about rivets? Is there any risk the stripper gets into the rivets and stays there causing problems? I ask because my paint shop says they might prefer not to use chemical stripper at all.

Rivets which have been riveted correctly should be closed, so no stripper would get between it. After chemical stripping the aircraft should be washed with lots of water and eye to detail. A good paintshop will also repack your wheel bearings, as water might enter due to the amount of water used. A good paintshop will also check the drainholes in your aircraft (yes they even excist on a pressured aircraft)

And I am a little afraid that too much sanding might be no good idea either, especially when sanding bigger surfaces some more agressive mechinery will have to be used…

That is possible, and done sometimes as well, great care must be taken not to damage protruding rivet heads. They are easily sanded away / damaged when done incorrectly.

Another question on paint preparation. On many planes and ours also the front windows are fixed with many screws. Usually these screws are painted together with the airframe. On some pictures of brand new planes I can not make out the screws. Are they too small on the pictures or is it possible / wise to fill the screw heads with some filler? Gettings the windows out is a major job anyway which, I hope will never happen. So the extra work to get out the filler would probably not matter much compared to the total work required.

These screws that stay in place forever are often spray painted. You don’t want to use filler in them, that might break out, and if it doesn’t it is very hard to locate the screws. These screws are hard to get out anyway, as all paint in them have to be removed using pick tools, before your screwdriver will have a firm grip.

Then we have a surface damage to the front of our radar pod. I think our paint shop is not really familiar with that. Is it ok to use normal non metallic non carbon composite materials for repair? Or are there any special materials whch should be used?

On large aircraft these are often painted with special paint and filler. Basically it determines a lot on the behaviour. A good avionics shop would be able to assist you and measure the effect of the used products.

JP-Avionics
EHMZ
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