Discussion in 'Painting Forum' started by SJNServices, Jul 28, 2010.
Anyone have any recommendations for aluminum siding on a mobile home?:beer:
"Rocks are good at being opaque, but they're even better at being old."
By the time you finish reading this post, that sentance will mean something that will help you make better paint color decisions for the rest of your life.
I'm presuming that this aluminum siding is already painted, so you'll be painting over paint, not over aluminum.
Personally, I am partial to oil based paints. I think they are simply better than latex paints because they form harder, stronger films and their film formation mechanism is bullet proof. It's hard to prevent an oil based paint from forming a proper film.
And, if it were me, I would go with a flat oil based paint simply because that saves you the work of sanding down the old paint for better adhesion of the new paint when it comes time to repaint. As long as you keep painting with flat paint, you maintain a "ready-to-paint" surface. That is, a flat paint doesn't need to be sanded to provide for good adhesion of the next coat cuz it's already rough.
And, I'm also partial to INORGANIC pigments, which are basically coloured rocks that have been pulverized into a fine powder and that powder used as a pigment to colour a can of paint. Artists like Da Vinci and Michaelangelo used pulverizing coloured rocks in their famous paintings like the Mona Lisa and the ceiling of the Sistine Chapel.
Paints get their colour from pigments only, wood stains get their colour from dyes only and there are also these things called exterior semi-transparent and opaque house "stains" that use both pigments (that stay on top of the wood and dyes that penetrate into the wood). Pigments can be broken down into two catagories; organic (which are made from chemicals in a laboratory) and inorganic (which are basically coloured rocks that have been pulverized into a fine powder.
And, both organic and inorganic pigments can be broken down into both natural and man made. For example, the natural inorganic pigment "Sienna" (which is a mustard yellow colour) gets it's name from the village of Sienna in Italy where the ground and rocks are mustard yellow in colour. The man made equivalent of "Sienna" is a pigment called "Yellow Oxide". Yellow oxide is chemically the same as Sienna, so it's properties are the same as Sienna, but because it's man made it can be produced in large volumes of consistant colour and particle size. And, because it's man made, it's availability and cost are not affected by political upheaval or natural disasters in the parts of the world that produce Sienna. So, the man made equivalents of inorganic pigments have the same properties as natural inorganic pigments, but they're more consistant in colour and particle size, and the supply is more reliable.
So, the inorganic pigments used in modern house paints can be considered the man made equivalent of pulverized coloured rocks. Now think about this for a minute...
For a rock to be 300 million years old, it must be extremely chemically stable or it would have decomposed by now. In fact, a coloured rock is about the only thing I can think of that can sit outside in the Sun for hundreds of years, and NOT FADE. For that matter, the reason why the planet Mars is red is because of all the iron oxide (Fe2O3, or "rust") in the rocks there, and those rocks on Mars have been rust coloured for billions of years even without an atmosphere (to speak of) to protect them from the intense UV light from the Sun (which our atmosphere protects us from). Rocks are the undisputed intercontinental heavy weight champions when it comes to chemical stability.
Now, if you grind up some rocks from Sienna, Italy into a fine powder, and use that powder to make a mustard yellow paint, the chemical stability of the rock manifests itself in the unparalleled colourfastness of the paint. That paint won't fade from exposure to the Sun any more than the original rock would, and those rocks in Sienna have been the same colour since DaVince and Michaelangelo pulverized them into fine powders.
Also, rocks are pretty good at being opaque. So, if you pulverize an opaque rock into a fine powder, then the powder will have similar optical properties as the original rock. So, inorganic pigments tend to be more opaque than the organic pigments, and so paints that get their colour from inorganic pigments will have better hide than paints that get their colour from organic pigments.
But, which are the organic and inorganic pigments in the paint tinting machine? Well, ask the man at the paint store to show you the colourants in his paint tinting machine, and they'll be easy to spot.
The organic ones are the "colourwheel" colours. That is, your bright reds, yellows and blue are all organic. And, the green and orange (which you could make by mixing blue and yellow and red and yellow) are also organic. And, the magenta colourant will also be organic. Basically, any colour (other than black and white) you're likely to find in a comic book will be an organic pigment.
The inorganic pigments are all the rest, and are commonly called the "earth tones". They're the colours you can imagine a rock being. These are:
1. White - which is titanium dioxide, and it's not a good idea to use titanium dioxide as a white pigment in exterior paints because it acts as a catalyst in the UV degradation of the plastic binders in paints. So, paint companies will often use Zinc Oxide as the white pigment in their EXTERIOR paints to avoid that problem. Also, Zinc Oxide is a natural biocide which prevents fungii growing on the paint in humid climates.
2. Yellow Oxide - which is mustard yellow in colour
3. Red Oxide - which is reddish brown in colour and is the most common form of iron oxide, or rust
4. Brown Oxide - which is chocoloate brown in colour
5. Raw Umber - which is a very dark brown that could be mistaken for black, and
6. Black - which is actually "soot", and is made by burning high purity natural gas in special furnaces with insufficient oxygen. The result is the production of copious quantities of soot.
Black (soot) is not really a pulverized rock, but is included with the inorganic pigments because it shares their extremely high colourfastness, high opacity and the fact that it's not made from chemicals.
So, if it were me, I would go with any single one of the above six inorganic colours or find a colour whose tint formula calls for only colourants made from inorganic pigments (such as yellow oxide, black and red oxide). That will give you the highest hiding and most colourfast paint you can get without paying extra for the name on the can. And, I would go with an exterior oil based FLAT paint to get the least amount of prep work needed for each paint job and the longest lifespan between paint jobs.
And, I'd go with any company's top-of-the-line exterior alkyd paint, but not necessarily a nationally recognized name like Sherwin Williams or Benny Moore. See if there are any local paint manufacturer's listed in your phone book under "Paint, Manufacturers" and support your local economy. It doesn't have to have Benjamin Moore's name on it to be good quality.
Or, at least, that's what I would do.
A ton of great info and I thank you!!:beer::trophy::beer:
Hi Nestor Kelebay,
Very nice information. I've really learned a lot from it. It may be a long post but I must say that it is worth reading.
Amcraftma: Thanks for taking the time to read it.
You can learn more than you need or want to know about latex paints at:
Painting information and resources for home interiors and exteriors - Paint Quality Institute
That's the web site of the Paint Quality Institute, which is an organization that was established by the Rohm & Haas Company, a company few people have ever heard of. The Rohm & Haas Company was founded by Dr. Otto Rohm and Mr. Otto Haas back in the 1900's to sell products to the leather tanning industry. However, Dr. Rohm had done his PhD thesis in the polymerization of acrylates, and remained interested in that subject throughout his life. He was the first one to both find an economic way to make the feed stock for acrylic plastic, and the first one to find a way to cast acrylic plastic into sheets. In 1933, Dr. Otto Rohm patented and marketed cast acrylic plastic sheets under the trade name "Plexiglas".
The Chemistry Chronicles - The Long Road to "Organic Glass"
The Rohm & Haas Company made Plexiglas out of the plastic known as "polymethyl methacrylate", or PMMA. It was used to make airplane windows, canopies and bottom gunner turrets on airplanes during WWII. However, that same plastic can be made into a wide variety of different shapes. If you make polymethyl methacrylate into tiny blobs, each about 0.1 microns in diameter (or about 1/50 of the diameter of a red blood cell) then it is called a "polymer colloid" and can be used to make the "binder" in good quality latex paints, acrylic floor "waxes", acrylic grout/masonary sealers and acrylic nail polishes for women.
The Rohm & Haas Company was the largest producer of polymethyl methacrylate in both sheets and as "polymer colloids" (or "resins" for paints, floor finishes, etc.) in North America until the company was purchased by Dow Chemical in 2009.
A good quality latex paint is in fact a "slurry", which is what you call solids suspended in a liquid. The solids in this case are the polymer colloids, coloured pigments and clear, transluscent or white "extender pigments" all suspended in a solution of water and a low volatility water soluble solvent called a "coalescing agent" or "coalescing solvent".
Polymer colloids are tiny hard "blobs" of plastic that would be transparent and colourless if they were large enough to see. But, because they are so small, a suspension of polymer colloids in water would be milky white in colour. That's because the tiny clear polymer colloids reflect and refract light the same way that water droplets in a clowd do, and your eye sees the resulting mixture of every different colours of light as the colour "white".
When you apply a latex paint to a wall, the first thing that happens is that the water evaporates. The result is that those polymer colloids find themselves immersed in that coalescing solvent at an ever increasing concentration. The coalescing solvent dissolves (kinda) the polymer colloids making them very soft and mushy. The same forces of capillary pressure and surface tension that make small water droplets coalesce to form large rain drops in clowds then come into play and cause each soft mushy polymer colloid to stick to and pull on it's neighbors. The result is a continuous film of soft mushy plastic with the coloured and extender pigments suspended inside it very much like raisins in raisin bread.
As the coalescing solvent subsequently evaporates from the paint film, filling the room with that "freshly painted smell", the plastic film hardens up again to the original hardness of the polymer colloids (when they were still in the paint can), and what you have is a hard film of clear plastic on your wall with tiny coloured pigments and clear, transluscent or white pigments suspended inside that film to give it colour, opacity and (depending on the extender pigments) it's level of gloss. Lots of large extender pigments results in low gloss, and without extender pigments, all paints would dry to a high gloss.
If the paint you applied to your wall was of good quality, that plastic film will be made of polymethyl methacrylate, the same plastic that Plexiglas is made of. (!) (most people don't know that)
And, if you understood that film formation process, you realize that it results in the elimination of all the solid/liquid interfaces that previously reflected and refracted light at the surface of each polymer colloid. So, the darkening of latex paint as it dries is entirely due to the elimination of those solid/liquid interfaces as the polymer colloids coalesce into a solid plastic film.
Typically, however, people refer to the kinds of polymer colloids used to make latex paints as "binder resins". If you hear the word "binder" or "resin", it refers to the plastic blobs in the wet paint that coalesce to form a solid plastic film that everything else is suspended inside. You have to consider the context to know whether they mean the polymer colloids in the wet latex paint or the solid continuous film of plastic in the dry latex paint. They say "paint binder resins" because polymer colloids made of PMMA have many other uses other than for making paints.
There ya go. Most people working in paint stores don't know why latex paints darken as they dry; they just know that they do. Now you know WHY they do, and can explain it to them.
None of this stuff is complicated. It's just that it's not taught anywhere, so there's a widespread lack of knowledge and understanding about this stuff. And, lack of understanding is fertile ground for misconceptions and misinformation to come into existance and spread like wildfire.
The problem with using oil outside is that the paint will dry out and crack. Have you ever seen a house where the trim paint looks like alligator skin? That means it was painted with oil. Many current latex products both block uv rays and are mildew resistant. Oil does neither. Also, they remain flexible and they'll never crack. Also, you don't need to use a flat with latex because latex will stick to latex regardless of sheen as long as it's clean. Oh yeah, it's a million times easier to apply and clean up, and it's much much better for the planet.
Interior oil based paints dry to harder films that don't have the elasticity to stretch and shrink with wood outdoors. Consequently EXTERIOR oil based paints are made so that they don't crosslink as much as interior oil based paints. That means they don't dry as hard, and have sufficient elasticity to stretch and shrink with wood outdoors. If you see an oil based paint outdoors that's all cracked up like aligator skin, it's because someone used an interior oil based paint on wood outdoors.
However, that's all irrelevant because we're talking about painting over aluminum siding which doesn't change it's dimensions depending on it's moisture content. The reason I recommended an exterior oil based paint is because it would be both more UV and mildew resistant, and because my own personal experience (and that of many others) is that oil based paints last longer outdoor than latex paints.
A latex paint will stick better to a glossy latex paint than a glossy oil based paint, but you're saying you can paint over a glossy latex and expect the same adhesion as you'd get if you roughened that latex, and that's simply not true. The improvement in adhesion comes from the increase in surface area between the two paints. The adhesion is the same per square centimeter, but you have more square centimeters of contact area between the two paints if you sand the glossy latex down.
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