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Re: Paint exterior bare metal door

Another trade name for Perspex/Plexiglas was "Lucite" (wasn't that DuPont's version?) and that was also the trademark of a paint. very crappy latex paint that stunk of ammonia worse than any other latex, but what a coincidence.

Re: Paint exterior bare metal door

Yes, that's right.

If polymethyl methacrylate is cast into solid sheets by Rohm & Haas, the plastic sheets are sold under the trade name "Plexiglas".

If DuPont makes the same thing from the same plastic, they sell it as sheets of "Lucite".

If Imperial Chemical Industries (ICI) Ltd. of Britain does it, they sell it as sheets of "Perspex".

(It could be that if DuPont made the resins for that "Lucite" latex paint (never heard of it myself), they may have chosen to call it Lucite simply to signify that it was made of the same plastic as their Lucite plastic sheets. Dunno.)

But, at least people know what Plexiglas is. When you tell them that top quality latex paint is made of polymethyl methacrylate, it doesn't mean a thing to them, and just the experience of hearing a chemical name as long as a shoelace is traumatic.

But, if you tell them that top quality latex paints are made of Plexiglas, they're skeptical, but are willing to be convinced. You just need to explain that the Plexiglas consists of microscopically small blobs that fuse together to form a continuous solid film. But, that film is made of exactly the same stuff as Plexiglas.

Truth be known, most people don't know that latex paints are made of different kinds of plastics. And, of course, different kinds of plastics have different characteristics, thereby making some kinds of latex paint better or worse suited to different applications than others. The observation that some paints "stick together when surfaces meet" is because the plastic in that paint makes for a better adhesive than it does a paint. It's cheap, so people also use it to make inexpensive paints and general purpose primers, but it really only shines when it's forumulated to bring out that adhesive quality and used as a wood glue. To get good results you'll be happy with, you gotta use the plastic that's best suited for the job, and that means you gotta know a little bit about the plastics that primers and paints are made of.

Re: Paint exterior bare metal door


I have been subscribed to the Paint Quality Institute's E-Mail newsletter for several years.I actually keep a folder of printouts of articles as reference material. I find it good, practical information that does overwhelm the consumer with too much technical material.

I am probably somewhat more aware of Rohm and Hass because my wife was born and raised a couple kilometers downwind from its factory in Darmstadt, Germany, where Plexiglas was invented. Rohm and Hass and Merck are the two major industries in Darmstadt. I lived in Darmstadt for several years and have driven by these facilities many times.

There is hardly an area where the phrase "pennywise and pound foolish" is more appropriate than by paint. Lesser quality resins and pigments make for really poor performance and require more coats to get acceptable coverage. However, price alone is not always a determinate of better performance. Some of the major national manufacturers market paints in the $50 to $60 range which ,when tested by independent testing labs, rate significantly lower than paints costing fully a third less. As in other areas, you pay somewhat a premium for that big name.

Further, the majors all produce a full line of paint from "contractor's crap" to really fine paints. I always caution those getting bids from contractors to have the contractor state exactly which paints he intends to use, not just Ben. Moore, Sherwin-Williams, etc. Then call your local paint store and ask just what quality that paint is on the spectrum. What the contractor is using is indicative of his work!

The paint industry tried a few years ago to wean itself from the term "latex" paint in favor of the term "water borne". Alas, latex is now to water soluble paints as Kleenex is to facial tissue. It has become a generic term which is not very descriptive. To my knowledge, there has not been actual latex in paints for decades. I well remember having boxed different "latex" paints back in the late 50's, early 60's and ending up with cottage cheese in the pot!

I do read your posts with interest. You are either quite knowledgeable about paint chemistry, or a master at googling and copy and paste! :)

Anyway, this has been quite a topic drift from how to paint a front door! :)

Re: Paint exterior bare metal door

You are either quite knowledgeable about paint chemistry, or a master at googling and copy and paste!

Perhaps I should explain myself.

I own a small apartment block in Winnipeg, Manitoba, Canada:


Years ago, when I first acquired the building from my father, I had a problem with the fact that every time I would repair nail holes left by previous tenants, the repairs would show because the new paint wouldn't exactly match the old paint.

At the time, I was convinced that the cause of the problem was fading of the paint due to exposure to sunlight, but I had no idea what to do about it. I came into the knowledge (and I don't even remember from where) that our local trade school was adding courses to their curriculum, and would be offering a course in painting for students who wanted to become professional painters. I realized that if they were going to offer a course in painting, there might be a textbook for the course available from the book store at Red River College. I went down there and sure enough, there was a thick hardcover textbook for the course. But, I was told that I couldn't buy it unless and until it went on sale to the general public, and most of it was really about interior design and colour theory, so I wasn't keen on dishing out over $100 for it. Luckily, the bookstore had a photocopier, and I photocopied as much as I could see dealt with paint itself, and anything I thought could help me with my problem in getting paint not to fade. Some of what I photocopied was truly excellent, and some was pretty useless, but it did have a good section on drying oils, and how alkyds and urethane modified alkyds (polyurethanes) are derived from drying oils and are therefore still referred to as "oil based".

I always liked chemistry in high school, and I graduated from the U of Manitoba with a degree in mechanical engineering only because the U of M didn't offer chemical engineering, but I went to the U of Calgary to get my masters in chemical engineering (which I never did complete, and that's a story in itself). Still, I found the subject of paint (especially oil based paints) very interesting.

I got my $40 worth out of that book. With information that I had gotten from that book as well as from other sources, I was seriously thinking of making my own paint, but in a way that was simple enough that I probably wouldn't screw up too bad or waste too much money. My gameplan was to buy a high quality tint base at any paint store and tint it with colourfast pigments I knew I could still buy at artists supply stores. Paint companies were no longer allowed to use pigments like lead carbonate (lead white), cadmium yellow, cadmium red and cobalt blue in their paints, but there wasn't anything preventing an individual from putting those pigments in their own home made paint. I figured I would purchase the pigments at artist's supply stores, put them in the tint base, and then take that concoction to any hardware store to be shaken, thereby distributing the pigments throughout the tint base, and giving it colour.

Well, I never did do that. I've since learned that I can make an equally fade resistant paint simply by using a tint formula that calls only for inorganic pigments. (I'll be posting about paint pigments in here too.) But, I realized that even though I could make an extremely fade resistant paint by using only inorganic pigments in it's tint formula, I still couldn't solve my problem.

That's cuz, where I live, the winters can be extremely cold, and under those conditions airborne dirt will stick to cold walls as a result of something called "Brownian Motion", which basically says that as dirt particles become smaller and smaller and smaller, they less and less follow the laws of Newtonian Physics, and more follow the laws of quantum mechanics.

That is, in Newtonian Physics, if you bounce a ball against a wall, the temperature of that wall has NO EFFECT on what the ball does. But, in quantum mechanics, the ball loses energy to a cold wall and gains energy from a warm wall. In the winter, my airborne dirt particles weren't bouncing off the walls. They would strike the exterior walls of the apartments, lose all their energy, and remain in contact with the cold wall without any hope of obtaining the energy needed to bounce off the wall. And, it was this accumulation of microscopically tiny particles of dirt on my walls during the winter that was causing the paint on the walls to gradually darken with time.

As a result, I no longer rent to smokers or allow the burning of candles, incense or anything that creates smoke in my building, and tenants are quite happy to comply. And, doing that has very greatly reduced the problem I had. When tenants don't burn candles or incense, the amount of airborne dirt in their apartment and in the whole building is reduced, and that reduces the amount of dirt that accumulates on the walls in winter.

So, I started taking an interest in paint well over 15 years ago to solve a practical problem, and even thought I've gotten close, I never entirely solved it. But, since I've been on the internet answering questions on these DIY Q&A forums, a lot of what I've learned comes out in my posts, and people do notice that I understand the subject quite well. At least it wasn't a waste of my time to have made those photocopies so many years ago.

So, that's my story and I'm sticking to it.

I'm pleased to have met you Ordjen.

Re: Paint exterior bare metal door

I painted our metal doors with an interior/exterior semi-gloss from one of the chain stores. The front door did okay, but wasn't happy with the two others. Went back to the store and found out should have used a metal primer first (the doors had been painted a horrible brown dull color). Went back and re did the other two doors. Should have done that first as it made a world of difference. The ivory color I used went on great and is easy to clean rain and weather dirt.

Re: Paint exterior bare metal door


You are over analyzing why walls get dirty in in colder climates. Newtonian physics? Suffice it to say that especially in colder climates, exterior walls and ceilings under roof are colder than interior walls. There is always slight condensation on them and airborne dirt sticks to it. Further, there are always convection currents moving the warm air up and cold air down. To balance this, for comforts sake, the heat vents or radiators are always placed against the outside walls, so as to somewhat neutralize that radiant heat coming off the colder walls.

In the worse case, where less than optimum insulation exists, you can see every stud location and even the location of drywall screws, this due to the relative coldness of the studs and metal drywall screws/nails .

I don't blame you for banning polution sources such as smoking and candles in your rental units. I have had to clean up the mess they make many times for customers who used them.

Complicating this accumulation of schmutz on cold walls, is that we, again for comforts sake, humidify the air in our homes. Too much humidity helps create more dirt accumulation on walls. It is a trade off between dried nasal passages and getting shocked when we touch grounded items, and having a somewhat dirtier house. One of the worse places for damge form too much humidity, is in the bath/shower room. How many times have I witnessed nicotine stains running down the bath wall!

Having grown up in Chicago, where the whole town was burning coal in the 40's and 50's, I appreciate the effects of cold brick walls and airborne dirt. Annual spring wall washing was the norm. Fortunately, in those days, most walls had good oil based, washable paints on hard, plastered walls.

Re: Paint exterior bare metal door


Why would a tiny particle of dirt stick to a droplet of water?

Why wouldn't it just bounce off the surface of the droplet?

Re: Paint exterior bare metal door

Nestor, damned if I know! I just relate a lifetime of observation that cold walls get dirtier. Walls in high humidity areas get dirtier and, indeed,begin to run down the wall making dirty streaks. The amount of available schmutz, be it nicotine,candles, burning of coal, or just general gray household dust, etc. increases how dirty those cool, slightly damp walls get.

I leave it to you to agonize about the pertinent laws of physics! :)

Re: Paint exterior bare metal door

"Why wouldn't it just bounce off the surface of the droplet?"

Easy. They are fellow travelers and arrive at the same moment. The water vapor and the dust particles are in the atmosphere together at the same time, and unless I am recalling my HS and college Earth Science incorrectly, water vapor needs a dust particle to condense around to as it coalesces to become liquid again.

Re: Paint exterior bare metal door

So, the dust particle causes a tiny droplet of water to form around it out of the humidity in the air.

But, wouldn't you get more of that happening where the air is warmer and has more humidity in it?

That is, why don't you get more dirt accumulation between the studs on the warmer parts of the wall cuz the air is warmer there and can hold more water molecules in suspension?


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