Paint Stripping Procedure:

 

1. Preparation for Paint stripping & Repainting

While it is not always essential; generally the best, most consistent results are obtained if the aircraft is cleaned before stripping. Although any good aircraft exterior cleaner may be used, our best recommendation is to use TURCO 5948 DPM at 10-25% in water, applied by spray, brush or mop, followed by a thorough water rinse. A warm to hot water rinse will insure that the skin temperature of the aircraft is high enough for ideal stripping. After the aircraft is completely clean and dry, it is ready for taping and masking.

Although Turco's benzyl alcohol based Environmentally Advantaged (EA) paint strippers are generally much less aggressive than methylene chloride based products on most substrates, it is still absolutely necessary to protect sensitive aircraft parts from any contact with these products during the stripping operation. Basically, these sensitive parts are the same as would be protected in a methylene chloride stripping process. These would include windows, composite structures, pitot tubes, some high strength steel fasteners (especially if an acid product is being used), doors and access ports, tires, landing gear and struts, wheel well areas, any areas that might allow access to the aircraft interior or to engines, etc.

During the time the aircraft is being readied for stripping, all the necessary equipment and chemicals should be assembled in the stripping area. The hangar temperature should be checked to verify that it is on or above 25°C. The containers of stripper should have been stored in a warm environment so that the stripper temperature is also on or above 25°C.

 

2. Paint Stripping

Using a 10:1 barrel pump with Teflon lined, stainless steel braided solvent resistant hose fitted with a stainless steel spray wand with a 6520 to 9520 non-atomizing spray tip; apply the stripper to the aircraft. The first application should be a very light film, only slightly heavier than a mist coat. If the belly is painted, start at the lowest point of the keel line and work in both directions, to the nose and to the tail. If the undersides of the wings are painted, apply the stripper to the crown and sides of the fuselage and the wingtips. The last areas to be coated should be the empennage. The mist coat s hould be allowed to dwell for thirty to sixty minutes before application of the first stripping coat. The purpose of the mist coat is to provide an initial softening and swelling of the paint, allowing the next heavier coat to cling better. It provides "tooth" and helps minimize sliding. It also acts to dissolve and dilute any residual greasy or oily soils from the surface, which also helps minimize sliding. Usually, by the end of the application time of the mist coat, the areas that were coated first have had sufficient dwell time and the application of the first stripping coat can proceed immediately. This should be a full even coat. The thickness should be such that the underlying paint can still be just seen. Too heavy an application will promote running or sliding. The application schedule should be the same as that used for the mist coat.

The first stripping coat should be allowed to dwell three to four hours for conventional EA strippers, longer for Extended Dwell (ED) products. These latter products should be allowed to dwell for at least six to eight hours, or even overnight. Beginning about an hour before the end of the dwell time, the entire painted surface of the aircraft should be agitated with stiff bristle brushes. This helps break loose the loosely adherent stripped paint and provides mechanical acceleration to the stripping process. At the end of the dwell time, the spent stripper and stripped paint should be squeegeed off the aircraft onto the floor. If, at this time, the aircraft is not completely stripped, the entire process is repeated, skipping the application of the mist coat. This may be repeated, as required, until the aircraft is essentially stripped.

When essentially all of the paint has been stripped, spot stripping is done to remove any remaining residual paint. Masks are removed from painted areas that must be stripped and these are done by hand. This is usually accomplished by brush application, followed by scrubbing with abrasive pads, such as TURCO Abrade-A-Pads or Scotch-Brite.

Once stripping is complete, the aircraft should be squeegeed again to remove spent stripper residue and loose paint chips. These are pushed onto the floor, where they are gathered together in open-top sealable drums for disposal as hazardous waste. Collecting the concentrated waste for disposal before it is diluted with water helps minimize waste disposal and waste treatment costs. Finally the aircraft is washed again with a 10-25% solution of TURCO 5948 DPM, thoroughly rinsed and allowed to dry (if it is not going to be painted immediately). This wash step is more critical than the initial wash, and should be done very carefully so that a surface suitable for painting is obtained.

 

3. After-strip Cleaning

The aircraft should be divided into overlapping sections for cleaning. Typically, each section might be about 6 meters long, although this would depend on the manpowered and equipment available. The critical point is that the section should be such that the cleaning solution is never allowed to dry on the surface. Application should be with a 2:1 to a 5:1 barrel pump, fitted with a chemically resistant, braided hose and an application wand. The wand should be equipped with a wide-fan, non-atomizing tip (60-100°). Application should be from the keel to the crown, on both sides of the aircraft.

After application is complete, the entire section being cleaned should be agitated, with heavy duty TURCO Abrade-A-Pads or Scotch-Brite pads, being sure that the entire surface is scrubbed, with no areas missed. After scrubbing, the area being cleaned should be thoroughly rinsed with good quality high pressure, high volume warm water. The rinsing should begin at the bottom of the section being cleaned, working up to the top, and down again. This sequence should be repeated until all cleaner, stripper residue and stripped paint is rinsed from the surface. Particular attention should be paid to seams, door openings, etc., where cleaner or stripper residue could be trapped.

For maximum efficiency, the next areas to be cleaned may be processed, one step behind. That is to say, while one area is being scrubbed, cleaner solution may be applied to the next; while one area is being rinsed, the next may be scrubbed. Cleaning should continue in this staggered fashion until the entire aircraft fuselage has been thoroughly cleaned and is water-break free.

If the aircraft is not to be painted immediately, it is allowed to dry at this point. If it is to be repainted, it should be etched immediately, before it is allowed to dry. The purpose of etching is to remove any existing corrosion products, and to provide a highly active aluminum surface for maximum corrosion resistance and paint adhesion.

 

4. Etching (Corrosion removal)

Prepare a 50% by volume solution of TURCO Metal Glo #6 (formerly TURCO 3003 - TWA) by mixing equal volumes of the concentrated etchant and good quality potable water. To assure uniformity, the solution should be thoroughly mixed, but air entrapment, or foam generation should be avoided. To assure uniformity of etch, the entire surface to be etched should still be uniformly wet. To be sure of this, the area to be etched should be sprayed with water so that a continuous uniform water film wets the surface.

Just as it was for cleaning, the aircraft should be divided into overlapping sections for etching. Typically, each section might be about 6 meters long, although this would depend on the manpower and equipment available. The critical pint is that the section should be such that the etchant solution is never allowed to dry on the surface. This is extremely important to ensure a uniform etch. The etchant solution is applied to the wet surface using a 2:1 to a 5:1 barrel pump, fitted with a chemically resistant, braided hose and an application wand. The wand should be equipped with a wide-fan, non-atomizing tip (60-100°). Application should be from the keel to the crown, on both sides of the aircraft.

After the etchant solution has been allowed to dwell on the aluminum surface for a few minutes, a vigorous etching action should be noted, this should be evident by the appearance of small bubbles over the entire surface, giving the appearance of foam. If this does not appear, or is not uniform, the etching step will probably have to be repeated to obtain a satisfactory result.

After the etchant solution has been allowed to dwell on the surface for 10-20 minutes, the entire section being etched should be agitated, with heavy duty Abrade-A-Pads or Scotch-Brite pads, being sure that the entire surface is scrubbed, bottom to top, front to back, with no areas missed. After scrubbing, the area being etched should be thoroughly rinsed with good quality high pressure, high volumewarm water. The rinsing should begin at the bottom of the section being etched, working up to the to, and down again. The rinsing should begin at the bottom of the section being etched, working up to the top, and down again. This sequence should be repeated until all of the etchant solution is rinsed from the surface. Particular attention should be paid to seams, door openings, etc., where cleaner or stripper residue could be trapped. Rinsing should continue until the rinse water uniformly sheets from the aircraft surface, without bubbles or foam. When rinsing is stopped, the residual water film should be continuous and free of foam. The aluminum surface visible through the water film should have a uniform soft luster. The water film should dry uniformly from the top down. If any of these conditions are not apparent, it is advisable to etch the surface a second time.

For maximum efficiency, the next areas to be etched may be processed, one step behind. That is to say, while one area is being scrubbed, etchant solution may be applied to the next; while one area is being rinsed, the adjacent area may be scrubbed. Etching should continue in this staggered fashion until the entire aircraft fuselage has been cleaned and it has been observed to be water-break free.

If it is included as part of the paint schedule, a conversion coating may now be applied. The conversion coating should be applied before the surface has had a chance to dry from the etching step. Of conversion coating is not included, the surface should be allowed to thoroughly dry and then should be painted immediately. For best results, it is usually recommended that a solvent wipe should precede the painting step to insure that all water residues is removed. If the surface is to be conversion coated, the solvent wipe is omitted.

 

5. Conversion Coating

Although the evidence for the added value of conversion coating the aircraft is mixed, many facilities include this step as a precautionary measure. Others feel that a properly cleaned and etched surface provides equivalent paint adhesion and corrosion control. If the surface is to be conversion coated, that should be done immediately after the final rinse in the etch procedure, before the surface has had time to dry. If necessary, the surface should be kept wet with a water spray until conversion coating can be started.

Conversion coating is accomplished using either ALODINE 600 Brush as received, or a 25% accomplishes conversion coating by volume solution of Turcoat Liquid Alumigold Concentrate. This latter solution must be prepared using good quality potable water. The reservoir tank must be of stainless steel or acid resistant plastic (PE or PP) and it must be clean and dry. Charge the reservoir with water to about half the final volume, add the required amount of Turcoat Liquid Alumigold Concentrate while mixing, and finally add sufficient water to bring it to the final volume while mixing. The pH must then be checked with a reliable pH-meter, or narrow range pH paper (sensitive to within 0.1-0.2 pH units). If the pH is not within the range 1.5-1.9, adjust it to be within that range by small additions of nitric acid to lower it or ammonium hydroxide to raise it, mixing thoroughly after each addition[1]. A low pH will result in a heavy powdery coating. A high pH will result in a very light, thin coating or no coating at all.

The conversion coating solution is applied using the same equipment as used for the etching process. The application equipment must be thoroughly flushed with water before use. All accessible exterior surfaces of the pump must also be cleaned with water before use.

Just as it was for cleaning and etching, the aircraft should be divided into overlapping sections for conversion coating. Typically, each section might be about 6 meters long, although this would depend on the manpower and equipment available. The critical pint is that the section should be such that the conversion coating solution is never allowed to dry on the surface. This is extremely important to ensure a satisfactory conversion coating. The coating solution is applied to the wet surface using a 2:1 to a 5:1 barrel pump, fitted with a chemically resistant, braided hose and an application wand. The wand should be equipped with a wide-fan, non-atomizing tip (60-100°). Application should be from the keel to the crown, on both sides of the aircraft. Application should be continuous, throughout the dwell period, so that a heavy wet film of solution is continuously present over the entire surface being treated.

After the conversion coating solution has been allowed to dwell on the aluminum surface for the desired time, which may be as little as 15 seconds, or as long as several minutes (up to about 5 minutes), the conversion coating should have formed on the surface. Because of the dark color of the solution, it will be difficult to see, however. If necessary, the progress of coating formation may be judged by rinsing a small area so that the coating may be seen. The thickness of the coating may be judged by the intensity of its color. The quality, by its shade. A good coating will have a light to deep golden yellow color. As the thickness increases, this will change to a yellow brown color. If the coating is not thick enough, or is not apparent, discontinue rinsing and continue application.

After the coating has formed, the area being treated should be thoroughly rinsed with good quality low pressure, high volume room temperature water. (Hot water will remove the color from the coating). The rinsing should begin at the bottom of the section being treated, working up to the top, and down again.  This sequence should be repeated until all of the solution is rinsed from the surface. Particular attention should be paid to seams, door openings, etc., where residual solution could be trapped. Rinsing should continue until the rinse water uniformly sheets from the aircraft surface, with no trace of color. When rinsing is stopped, the residual water film should be continuous. The aluminum surface visible through the water film should have a uniform yellow gold appearance. The water film should dry uniformly from the top down. As it dries, a slight iridescence should be apparent. The conversion coating at that point will have a soft, gelatinous structure and may be susceptible to mechanical damage, such as smearing. As it dries, it will harden. If the color is a dull brown, it may have been allowed to dwell too long, and may be powdery. If the quality of the coating is not acceptable, the entire etching, rinsing and coating process must be repeated.

For maximum efficiency, the next areas to be treated may be processes, on step behind. That is to say, while one area is being rinsed, conversion coating solution may be applied to the next; while one area is being rinsed, the adjacent area may be allowed to dry and be evaluated. Treatment should continue in this staggered fashion until the entire aircraft fuselage has been conversion coated and it has been observed to be of acceptable quality.


 





 

Paint Strippers