Plasterboard then PVA then skim???

[gcol]

No, when I walk into a pub, I try to get a conversation going by innocently asking someone "Why is the head on your beer white if nothing inside it is white in color?

Touche.

And when your fingers grow back to their normal length (after typing all of the above) maybe you could enlighten us as to why the head of beer is white. I was quite happy with my life until you posed that question. Now it's bugging me. So spill.

 

[empip]

Not once does he mention styrene acrylate, the common acrylic binder for paints. Acrylics *do* block, but there are tricks to combat this, often
a wax dispersion added to the paint. As for that hayseed New Zealand
site he quotes, cold air contains *less* water than warm, hence
condensation, rain and snow. Like, duh. The problem with low
temperatures is activation energy rather than water vapour
concentration. As for the evaporation of the coalescing solvent, they
are normally used as a double-edged sword both as coalescer and
plasticiser, so they are selected for low volatility/fugacity. Should he
chose to look at a decent chemistry book on multi-phase systems a
solid-in-liquid system is a suspension or colloid. A Liquid-in-liquid
system is called an emulsion. What bit of that does he fail to
understand? Paint acrylics almost invariably are of the crosslinking
type so that as they dry, the polymer chains actually form a
three-dimensional matrix. There is normally an organometallic compound
somewhere in the system to catalyse the crosslinking. This stuff about
plastic particles is misleading. Perhaps the poster might like to
examine an acrylic or PVA emulsion under a microscope. Pressing the
cover slip will reveal the liquid nature of the polymer globules.

RGDS,

John Schmitt

Feel like I am standing in the midst of something here.

I am sure you two would have a fair amount in common if you just spoke to one another
Nestor ... Call John S and be nice to each other -- You are only here once !!
[email protected]

Jeez... This has stirred the old paint section up from it's slumbers !!

 

[Nestor_Kelebay]

Gcol:

Scroll back on this thread and read my third post. (I think it is the third one.) In that post I explain why a water based "varnish" will be milky white in the can and dry clear, why blue jeans are darker when they're wet and why wet cotton is more transparent than dry cotton.
If you read that post, and still don't understand why the head on a beer is white, post again and I'll "spill".

Empip:
Perhaps John Schmitt knows more about paints than I presumed.

1. Styrene acrylics ARE used as a paint binder, and are mentioned in that file I referred to entitled "The Ingredients of Paint and their Impact on Paint Properties. But, over here in North America, the amount of paint made with a styrenated acrylic binder is quite small. I really don't know if that's the case in Britain, tho.

(and I have every intention to be civil to Mr. Schmitt. I consider this a technical discussion)

2. I am in agreement with John Schmitt's statement that what controls the evaporation of the coalescing solvent is "fugacity".
There's a principle of thermodynamics that says that where you have a multicomponent two phase system (such as a distillation tower in a refinery) equilibrium between the liquid and vapour phases is reached when the "fugacity" of each component in the liquid phase is the same as the fugacity of that component in the vapour phase. Fugacity can be thought of as a "partial pressure" of a component (like ethane or propane) in a liquid or in the vapour.
In the case of paint on a cold day, there simply won't be any coalescing solvent in the air, so in order to reach equilibrium, the coalescing solvent will want to evaporate from the wet paint into the air above it. And, if the relative humidity on that cold day is high, it could evaporate from the paint more rapidly than the water. And what Resene paints is saying is that if that happens there won't be enough coalescing solvent in the paint for it to form a film properly. Also, exactly the same thing can happen on a hot day if the relative humidity is very high.

3. Lots of acrylic resins do crosslink. I expect that every water based FLOOR paint is made with a crosslinking acrylic resin. But, it's completely false to say that they all do. What he's saying is true for floor finishes tho. FLOOR FINISHES do use a metalic compound (it's a zinc compound) to crosslink, and that crosslinking results in greater hardness in the film. However, the reason why zinc is used is because it's a highly reactive metal, and that allows you to make a floor wax stripper which can break up that floor wax by reacting with the zinc atoms in the crosslinks. That is, the stripper contains something that the zinc has a higher affinity for, so that the zinc atom comes out of the crosslink, thereby severing the link holding the resins together.
But, it's important to be able to strip off floor finishes easily because they get embedded with dirt and need to be replaced. There isn't that same need in paints.

4. He says "The stuff about plastic particles is misleading."
The Rohm & Haas Company is a chemical company just like ICI Ltd. and they make the resins that paint companies buy to make their paint from. The Rohm & Haas Company established the Paint Quality Institute to inform painters, paint retailers, architects and the general public about paint, and particularily about "latex" paints. The technical articles on the Paint Quality Institute's web site most certainly would have been written with the input of the polymer scientists working for Rohm & Haas. And, those articles say that the binder in a water based paint is a solid particle.
Resene is a company in New Zealand that makes paint. If they were to put a bunch of incorrect information about paint on their web site it would wreck their credibility and very possibly affect their business. I trust they would realize that it's better not to say anything at all than to put a bunch of incorrect information on the internet that would undermine people's trust in their competance to make a good quality paint.

 

[empip]

....Perhaps John Schmitt knows more about paints than I presumed.

I have a feeling you may be correct there Nestor.
But 'tis all grist to the mill, and a welcome discussion.

John S contributes to http://www.diyfaq.org.uk/contents.html

Loads of stuff down there, or is it up there?

 

[Nestor_Kelebay]

I agree that John knows much more than most people.
Most people aren't aware that styrene acrylic resins are one type of binder used in paint.
Most people aren't even aware that there's a word "fugacity", and the fact that he mentioned it in regards to the solvent evaporation from paint convinces me that he has a chemistry or chemical engineering background.
Also, he was correct that acrylic resins DO use metal atoms in their crosslinks, and that's a well known fact that can be verified by phoning up your local S. C. Johnson Wax sales rep or anyone working for a Janitorial Supply store that sells floor finishes. But, so far as I know, that's only true for floor finishes because of the need to be able to easily strip that floor finish off. (But I don't believe that's true for paints.)

 

[gcol]

You can hardly blame me for missing that post Nestor - there's been a huge increase in the amount of reading needed on this forum recently.

I'll be staring at my pint tonight in a different light. Get it? Get it! I kill me!

Don't suppose you know why those nucleated beer glasses create better head in the pub than they do at home with canned lager do you? Yes the glasses are the same.

Gcol

 

[Thermo]

one small thing Nestor.



US marines may very well make some such noise as Hoaahh, as may your fellow countrymen in your version of the marines, how ever i can assure you Her Braitanic Majestys Royal marines do NOT!

[/quote]a great big Royal Marines HOOAHHH!

 

[Nestor_Kelebay]

Gcol:

I've sometimes been criticized for my posts being too long. However, when it comes to technical stuff, I very much feel that most DIY'ers want to understand the reasoning behind the answers they get, and it's the explaining that makes my posts so long. Some people like to know those explanations, and some apparantly don't. I guess I just have to leave it to the individual to decide for themselves if reading my posts is worth the extra effort.

Thermo: What kind of noise to Her Majesty's Royal Marines make when the occasion calls for a great big HOOOAHHHH from all present?

 

[gcol]

Oh come on Nestor me owd china, I certainly meant no offense by what I wrote. You have enriched this forum no end in the last few weeks. Long may you still have an internet connection!!!
If you can be arsed writing as much as you do then the least we/I can do is to read it.
Cheers,
Gcol

 

[gcol]

And just so you know, our forces say "good show old bean" instead of HOORAH!

 

[Nestor_Kelebay]

Gcol:

Oh, heavens no. No offense was taken. I'm simply pointing out that in other forums I used to post on both in Canada and the US, there were people that thought my posts were TOO long. By the same token, there were lots of people who said they liked knowing the reasons behind statements I was making. So, I've tried to accomodate everyone by stating my answer first, and then following up with the reasoning, or lots of time I'll give reasons in point form and stuff like that to keep everyone happy.

I think to some extent I happen to luck out in this particular forum simply because when I first came on this site there was a paint drying question that had people stumped, and the answer I wrote seemed to make sense to people, so I guess they gave me the benefit of the doubt right away. Most times, getting to the point where people give you the benefit of the doubt is a long hard slog.

I took typing as an elective in high school, and I've been typing 40 to 50 wpm ever since. So, even though it seems like a lot of writing, it doesn't seem like it to me because basically my fingers can keep up with my thinking, so the words go down pretty fast.

Anyhow, it's good to know that someone's reading my posts. It'd be a waste of time to type them if no one read them.

Anyhow, glad to be welcome here.

 

[noodlz]

So much knowledge of paints...do you also do strippers?
Sorry, Nestor, it's the Carry On in me...good ol' British tradition.
Keep up the good work.
Very interesting learnin' make no mistake

 

[Nestor_Kelebay]

Thanks, Noodlz.

Paint seems to be the least understood technology in the whole home center, and there's just no good reason for that. Nothing about it is very complicated. I expect people in this forum are already starting to realize that.

 

[noodlz]

Ah...the art of a good teacher...to make the difficult easy

 

[empip]

Yep, keep it coming Nestor.

Interesting reading ....
Especially when you have put things into practice.
An apartment block must be a great area for experimentation and results appraisal.
pip