Nestor_K

[empip]

Hi, you seem very knowledgeable in the diy/paint arena.
Do you have professional qualifications relative to the subject? Or are you self taught?
It is nice to know these things ... But only if you come clean !

 

[Nestor_Kelebay]

Well, Empip, I'm neither a painter nor a paint retailer, I'm a self taught landlord.

Basically, about 10 years ago, I realized I had a problem in that when tenants would leave nail holes in the walls when they vacated, I was able to do a good job repairing the plaster, but the problem was that the paint I would put on the wall wouldn't match the faded paint that was already there. And, my local paint store was totally useless; they couldn't even come up with any suggestions on what I could do to minimize the amount of difference, and I attribute most of that to the fact that they really don't need to know anything to sell paint since most people TELL THEM what kind of paint they want, what color, what gloss and what brand. It's not up to the paint guy to tell them what kind of paint they really NEED.

So, I ended up going to the Winnipeg Centenial Library and looking up some books on paint, all of which were pretty old, but I happen to find out that our local community college was putting on a course for people wanting to become professional house painters. So I went to that college book store and photocopied the sections out of that book on binders and pigments used in oil based and latex paints. (Much of the rest of it was on what colors went with what other colors.) And, from that book I learned that water based paints are primarily made out of two kinds of plastic, notably polyvinyl acetate (white wood glue) and polymethyl methacrylate (Perspex), and Googling polymethyl methacrylate led me to the Rohm & Haas Company (who are the largest manufacturers of the resins made out of that kind of plastic for use in making water based paints in North America. And, in turn, I found the web site of the Paint Quality Institute, which was established by the Rohm & Haas Company to inform painters, paint retailers and the general public about the advantages in using high quality paints made from Perspex plastic.

http://www.paintquality.com

And, as a result of that, for the past 10 years or so I've been going from DIY forum to DIY forum on the internet explaining water based and oil based paints to people, and helping to dispell a lot of the misunderstanding and misinformation surrounding the subject of paint in general. (Paint is the least well understood technology in the entire home center.)

Anyhow, getting back to the problem at hand, as a result of finding out more about paint, I realized that much of the reason the paint I was using was fading on my walls was because the tint formula called for quite a bit of Hansa Yellow (which is the color of Canary Yellow), but is one of the least colorfast pigments used in house paints. So, what I did was I switched to a paint color that called for only 6 drops of yellow oxide (a MUCH more colorfast pigment) per gallon, and now I can repair nail holes years after tenants vacate, and you can't tell there was every a repair done to the wall. Before, when I'd repair nail holes, the new paint didn't match the faded old paint so half the prospective tenants were asking if I intended to repaint the walls because of the "blotches" on them (referring to the new paint which was lighter than the old paint.

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

I've talked about the difference between the various kinds of emulsion paint so far in my posts, but I haven't really posted too much on the difference between drying oils (like linseed oil and Tung oil) and alkyd resins and polyurethanes. Also, I haven't hardly talked about pigments at all, and I guess that's because no one has asked a question where that was a consideration.

 

[empip]

Cheers for that N.
Questions regarding the oils have cropped up.
I have noticed posts on their usage with regard to exterior woodwork, for example window frames.

 

[gcol]

Well COME ON Nestor! The suspension is killing me. What paint colour only has 6 drops of yellow per gallon?

Hey is that why white gloss goes yellow after a time? Or is that for another reason?

Gcol

 

[Nestor_Kelebay]

Gcol:

No, only oil based paints yellow with age. Most emulsion paints won't yellow with age at all.

And, not all oil based paints yellow as much as others.

You see, all animal fats and vegetable oils are "triglycerides" which means that the fat or oil molecule consists of three hydrocarbon chains called "fatty acids" connected to a glycerine molecule. Different kinds of vegetable oils contain different kinds of fatty acids, and it's the kind of fatty acids there are in the oil that determine how much a coating made from that oil will yellow with age. The most common drying oils used in coatings are Safflower Oil, Tung Oil and Linseed Oil. Of those three, Linseed Oil contains the most of a fatty acid called "linolenic" fatty acids, and linolenic fatty acids produce the most yellowing. As a result, paints and varnishes made from linseed oil yellow more than varnishes made from Tung oil (which contains very few linolenic fatty acids).

Similarily, alkyd resins are made by modifying soy bean oil which wouldn't dry to a film naturally the way linseed oil does. Soy bean oil contains mostly linoleic fatty acids, and they don't cause as much yellowing as the linolenic fatty acids in linseed oil, so alkyd paints yellow less than boiled linseed oil based paints.

Go to this web site:

http://www.seatons-uk.co.uk/home.aspx?d=content&s=62&r=109&p=451#

and click on the link "View typical fatty acid profiles" to see average values for the kinds of fatty acids found in each of the most commonly used oils for making paints and coatings out of.

Linolenic fatty acids are the worst for yellowing, and linseed oil contains the highest amount of those kinds of fatty acids, so linseed oil based paints and varnishes yellow more than other kinds of "oil based" coatings.

But, although it's not common knowledge, the yellowing in oil based coatings is reversible. If you expose the yellowed paint to direct or indirect light from the Sun, that yellowing disappears.

Take a look at this web page:

http://aic.stanford.edu/jaic/articles/jaic24-02-002.html

The yellowing of oil based paints used by artists over the centuries is a problem for museum curators who generally have more oil based paintings in their collection than they can display at any one time. Consequently, many old oil based paintings have to remain stored in boxes for years before they are put on display. But, storing old oil based paint under dim lighting conditions causes the oil based paint to yellow.

The above study showed that the centuries old practice of taking oil based portraits outdoors and exposing them to sunlight is effective in eliminating the yellowing that occurs in oil based paints under dim lighting conditions. And, that elimination of the yellowing by exposure to sunlight can be performed over and over again.

So, if you have any yellowed oil based paint in your house, you can eliminate the yellow from it by positioning a bloody great mirror to reflect sunlight onto that paint. (And, in fact, even indirect sunlight is effective in eliminating the yellowing that occurs in oil based paints with age.)

Anyhow, Gcol, now you know why some oil based coatings yellow more than others, and that you can eliminate that yellowing by exposing the paint to sunlight. But, the sad state of affairs is that by reading these last few paragraphs, you now know more than most people working in paint stores about yellowing in paints and what can be done about it. And, as I've said in previous posts, there's no good reason for that since none of this stuff is complicated or difficult to learn. The real problem is that there's no one teaching it.

 

[gcol]

Thanks Nestor, that's very interesting stuff. So instead of painting the doors in my house I can just take them into my back yard for a few hours. Might be hard with the door casings though.

Hey you still didn't say what colour you picked for its low yellow content.

 

[masona]

Nestor,

Have you heard of Holkham Linseed Paint which may interest you and I believe Oilman on here went on a training course with them will know more about this.

 

[Nestor_Kelebay]

Gcol:
That color really doesn't have a name since it arose by me simply wanting to make a highly colorfast (correct word is actually "lightfast") paint so that I could repair nail holes left by tenants invisibly. I'll let you think of a good name for it.

Masona:
No, I've never hear of this brand of linseed oil based paints, but from what I saw on the web site you linked to is that it's just an ordinary boiled linseed oil based paint, just like everyone was using up until about 20 years ago or so.
I'm sure it's a good paint so far as a boiled linseed oil paint goes, but the reason why alkyd paints have come to dominate the "oil based paint" market is because they dry to a harder film that yellows less faster. That harder film is going to crack and peel earlier on wood outdoors (which swells and shrinks with changes in it's moisture content caused by changes in humidity), but the chemists have a way around that too by making EXTERIOR oil based paints with a higher oil content so that they dry to a softer film which retains it's elasticity for longer. I guess there may still be some people who still want to use a drying oil based paint, but the only place I'd really see a need for it is in restoration work on historical buildings where it's important to use the same materials and techniques that were used by the original builders.

 

[empip]

Nestor could you pop to ..
//www.diynot.com/forums/viewtopic.php?t=42603&start=0&postdays=0&postorder=asc&highlight=

Have an answer from the guy who wrote the pva faq.

 

[Nestor_Kelebay]

Oh ye of little faith...

Will respond to this fellow's response in the "Plasterboard then PVA then skim?" thread.