BACK to Index
The craziness continues!
My continuing flirtation with Aviation:
I've purchased a 90% complete Mitchell U-2 Flying Wing!
(Which in Aviation math usually means, 90% is left to be done.)
Painting with Water Based House Paint
AUGUST 13, 2016: OK, Norman has shamed me for letting this build-log fall so far behind - so I'm going to jump ahead to discuss what we are currently working on - which is painting the beast. He also wants us to share what we have learned on the topic of painting an aircraft with water based house paints. I'm just getting started and therefore I can not address the important issue concerning the long term viability of using exterior latex house paints on aircraft. We have not done any "test coupons" of any nature. If it doesn't work out I am prepared to pull it off and to start again.
Let me say from the outset: The following is a discussion about my personal project and research. It is NOT A RECOMMENDATION for anyone else to pursue any of these ideas or procedures.
This is NOT a crazy idea. As far as I can tell, people have been using exterior latex/acrylic house paints to paint experimental, homebuilt aircraft since the 1980s; in addition, Stewart Systems has developed a proprietary water based paint system which has STC approval from the FAA. In my humble opinion we simply don't have to continue to subject ourselves to the expenses, inconveniences and health hazards associated with the toxic, solvent based products of the aircraft service industry. Nor do we have to invest in the time and expense of building a temporary "paint booth" or buy a fresh air painter's suit (hood or mask) as the water based systems can be brushed or rolled in addition to being sprayed. (No airless type sprayers, please!!!)
In the fall of 2015 I could see that I was nearly ready to paint the beast so I purchased the supplies and started looking for a hangar or space in which I could install a paint booth for the job. I was unable to find a space as winter closed in and soon I realized that not only did I need a large space, but the space had to be heated. In addition, I would also have to buy my own fresh air suit and I began to worry about the need for spark-free heating and ventilation systems for the booth. Working with volatile solvents is potentially hazardous. I had eliminated the idea of using my garage and or a storage shed because the size of my Aircraft's center section is too large for them and because of the possible penetration of the toxic fumes into adjoining structures. Winter came and went without a solution to the problem being found.
As summer 2016 approached I finally found an auto-painter who was willing to give me a bid on painting my aircraft. He would use my materials and do the work in his climate controlled shop - the price seemed reasonable and I was about to accept the quote when my wife's car's transmission blew up on I-70 up in the mountains. The blown transmission simultaneously blew up my budget and I was once again dead in the water. So I was back to the DIY approach but now a new problem had raised it's ugly head. When I bought the solvent based supplies I was thinking I would get the job done in the fall so I had ordered the low temperature reducer - which will not work with summer temperatures and summer was upon me - finding a temperature controlled space is out of the question.
Approximately 10 months had passed without any progress: I was totally frustrated, angry and hostile - I was on the verge of giving up and burning the project - literally. Then I made the Executive Decision to keep the project and to abandon the toxic solvent based paint schemes! What's left of the Poly Fiber stuff will end up on EBay one of these days but the first coat of water based primer was rolled onto the Aircraft's center section August 13, 2016 and I thought I was a very happy camper!!!
And So We Begin:
While I was able to find a few discussions on the internet, I have relied heavily on the fine work of Drew Fidoe as reported on the following link: http://bowersflybaby.com/tech/latex.html. In addition I attended a session on the Stewart System at Oshkosh-2016; YES, I cleared another bucket list item this year as I finally found my way to our aero-Mecca.
Objectives for painting wood and fabric aircraft projects:
1. To fill the weave of the fabric so it is air-tight;
2. To protect the fabric from the destructive effects of Ultra Violet Radiation and to protect any exposed wood from moisture;
3. To provide a flexible, long lasting and aesthetically pleasing finish to the project;
4. To accomplish the first three items by using thin, light weight coats of paint (Indeed, some all metal skinned projects skip the painting steps entirely!);
5. To avoid the issues associated with any system which requires toxic solvents or spraying - No Spray booths!!!
It seemed at the time as though Latex/Acrylic house paint can successfully achieve all of these objectives:
Selecting the paint:
We found that most of the staffs of the local paint vendors are not very knowledgeable about the contents of their paint products or at least they won't share the information. We needed paints which will remain flexible for years; which can be thinned for light-weight coats; which can be sanded and which contain Titanium Dioxide, Zinc Oxide and/or Carbon black for UV protection. The literature seems to suggest that using latex for the primer and 100% Acrylic for the Color coats will provide a long lasting, flexible surface. The literature also seems to suggest using the flat, satin or semi-gloss sheens but I don't recall the glossy sheen being mentioned often. I noted that the Stewart System's primer is a rather dark gray color. And also, Stewart Systems use a water based Epoxy for a final Top coat which they claim provides a shiny finish, indistinguishable from that of the solvent based systems. We will use a slightly different approach...
Black could be used for a primer color as it would have great UV protection but a black primer can have significant negative effect on the color of the top coats. Also I noted comments indicating that latex paints in the flat, satin or semi-gloss sheens will not buff up to produce a shiny surface.
My Choices: I selected a mid-gray (containing carbon black), multi-purpose Latex primer and a 100% Acrylic top-coat (using a Titanium Dioxide base). I tried using the High Gloss Sheen but I would eventually find that it produces an excessive "orange peel" surface which might take 45 days of wet sanding to produce an acceptable surface. As my first primer coat was applied I became concerned that the gray shade was not as dark as intended but since I'm going with a bright Yellow top coat the light gray was the recommended primer. Since my project will always be hangared or covered, I am confident that it will have sufficient UV protection from the paints selected. I'm using Sherwin-Williams products.
NOTE & UPDATE: In the final analysis I dropped all attempts at using the very labor intensive High Gloss sheen and elected to switch to the FLAT sheen because it reduces the incidence of an "Orange Peel" surface and it wet-sands relatively easily and quickly. (You can look up the sheen charts on the Behr Paints web site to see the correlation between sheen and orange peel.) Tests indicate we should be able to produce a very smooth aerodynamic surface with a single sanding with 1500 grit wet-sand paper. We will finish the surface with a clear-coat of Varathane exterior water-based Spar Urethane to provide a flexible, long lasting, durable finish and to provide a shiny, slightly reflective surface to my project.
Mixing the Paint:
Now that I have selected the paint, I need additives and thinning agents to make the paint more "self-leveling". We are able to brush, roll or spay latex paint without leaving marks in the finish if the paint has been properly thinned and reduced.
Additives - Thinning
agents - reduce the viscosity of the paint:
2. Windex Window Cleaner fluid
3. Automobile Windshield Washer fluid
Surprise! I found that virtually no one recommends the use of water as a thinning agent even though we are using water based paint. But the few comments I found about adding water to thin the paint all seemed to be negative. Windex window cleaner was recommended in one discussion I read because of the Ammonia it contains - the claim is that latex paints contain Ammonia so they are compatible products but I didn't attempt to learn more about it's use. Finally, Automobile windshield washer fluid was almost universally recommended throughout my research. The fluid contains surfactants and alcohol to help the spreading process as well as lowering the paint's viscosity. The manager at Sherwin Williams cautioned about using too much as an excess amount could leave the paint surface "tacky" for "days". My internet research also recommended limiting the amount used.
I elected to use the Windshield Washer fluid.
- Reducing & Flow Agents - promote spreading (self level) & extend drying time:
2. M-1 Latex Paint Extender
Everyone seems to use Floetrol - pretty much it was the only flow agent recommended throughout my research and it seems to be universally available. Sherwin Williams carries Floetrol but they also have a competing product which is less expensive and provides greater coverage. The bottle is simply labeled "M-1" and it states that it will extend the drying time of the paint by about 15 minutes while improving the paint's flow characteristics. The suggested mixture is 2 - 6 oz per gallon of paint.
I elected to use the "M-1" at the maximum suggested ratio but I eventually settled on a higher concentration.
There aren't any formulas to speak of found in the literature - just generalities. No one seems to want to share their formula and I think I found out why. The flow and drying characteristics of paint are effected by a number of factors - ambient temperature and humidity being the two major elephants in the room. Also, the formula should differ depending upon the method of application - surely the formula for spraying will differ somewhat from the formula for rolling.
NOTE & UPDATE: Here is my final formula for using a 4 inch foam roller to apply the paint. The following materials were added to my wife’s ex-food blender.
1. About four cups of paint – Determine the weight!
2. Diluents Mixture = 10% of the weight of the paint.
1 Part "M-1" to 2 Parts Windshield fluid - again I measured everything by weight.
Mix for about 5 minutes using the blender's slowest setting which will mix the paint without entraining air. I found this formula works well in 60 - 70 Degree temperatures.
Higher temperatures may require a higher concentration of diluents as will preparing the paint for spraying. However, the local Sherwin Williams manager strongly advised me to limit the addition of thinning agents to a maximum of 25%!
Filling the Weave:
Latex paint does not bond chemically to the poly-ester fabrics used to cover aircraft but it does bond mechanically to the strands of the fabric by flowing around them in a way which provides a strong and permanent foundation for subsequent coats. The primer coat is thinned in order to be brushed or rolled onto the fabric. Enough pressure is used to ensure that the paint enters the weave without building up or running on the back-side of the fabric. The first primer coat should fill the weave but the weave pattern will be visible in the paint surface for one or two subsequent coats.
Reminder: When I speak of "a coat of paint", I am referring to the application of two crosses coats rolled at 90 degrees to each other without significant wait time between the cross coats. Start at one end of the wing working toward the other end of the wing. When the first pass is completed return to the end where you started and continue painting by rolling at 90 degrees to the first pass. I usually rolled span-wise for the first pass and then chord-wise for the second pass. Wait a day or so before applying additional cross coats. Continue adding cross coats until the paint is uniform and allows no light to pass through to the interior of the wing. Some people apply primer coats until they a 100 watt bulb inside the wing cannot be detected from the outside. Careful, don't set your project on fire!!!
I elected to use 4 inch foam rollers and a good quality, 2 inch brush. After rolling out a small area I would check the area for roller marks which were removed by lightly and gently re-rolling. The brush was only used to paint those tight areas which the roller could not reach.
Do not attempt to get a uniform color coverage or worry about a few pin-holes with the first primer coat. After the coat has dried sand it to a smooth surface in order to remove thick or high spots before adding additional coats of primer.
NOTE & UPDATE: After we applied the first primer coat to the wing's surface in 2016, I was appalled by the workmanship and condition of the wing's construction. The surface was covered with deep waves that traverse the direction of the airflow. In addition the fabric had bridged some of the waves which created huge air pockets beneath the fabric. Both conditions are totally un-acceptable and may have rendered the wing incapable of flying, so we stripped the fabric and spent the next 4 months filling and sanding to remove the waves and gusset humps. We worked on the wing surface like it was a fine show car and then re-applied the fabric one wing section at a time using the Stewart System's water based glue.