Plasterboard then PVA then skim???

[Darran]

I'm worried. I've recently heard that you shouldn't PVA plastered walls when planning to tile. Fair enough, I wont add PVA to our newly plastered walls. However, before the plastering, I did add PVA to the one plasterboard wall, which our plasterer has now skim-plastered over. I need to tile on this wall, and am now worried that his plaster may fall off the plasterboard...resulting in tiles coming down! Any ideas?

 

[jbonding]

the point of pva is to control suction and adhesion, the skim will be sound , theres other products to seal before tiling, BAL is one, pva is another. even though most people are terrified because of a couple of posts its been used for years, so make your own decision.

 

[Nestor_Kelebay]

Darran:

You said: "I'm worried. I've recently heard that you shouldn't PVA plastered walls when planning to tile."

I'm not familiar with your usage of some words and phrases. Can you tell me what someone would actually do if they were to "PVA a plastered wall".

The reason why I ask is that here in North America, the letters PVA stand for "polyvinyl acetate". Polyvinyl acetate is used to make quite a few different products, but you probably know it best as "white wood glue" or "carpenter's glue". Different kinds of PVA resins are also use to make emulsion paints and primers.

Because they're all made from the same kind of plastic, primers and paints made from PVA resins have some things in common with white wood glue. First off, paints made from PVA resins have a much greater propensity to remain slightly sticky even when dry. (Adhesion is a hard thing to engineer out of a PVA molecule.) In the paint industry, that characteristic is called "blocking" and it's the cause of most complaints about doors and windows tending to "stick" closed after being painted with inexpensive emulsion paints. Better quality paints made from Perspex plastic (which I call "Plexiglass") have excellent blocking resistance, which means the dry paint film has NO residual stickiness.

Another way that PVA based paints and primers are similar to white wood glue is in their poor resistance to moisture. Just in the same way that white wood glue will come apart if it gets wet and stays wet for some time (even after it's been fully dry for years), paints and primers made from PVA plastic will both soften up and loose their adhesion to the substrate their sticking to if they get wet or are exposed to moisture for more than a short period.

But, for a plastic made from PVA resins to soften up, it has to get wet and stay wet for a while. As long as it remains dry, it'll hold fast. Lots of high quality furniture is assembled using PVA glue to hold the joints together. If this "PVA coating" you put on went over top of plasterboard which isn't waterproof anyhow, where is the harm?

That is, what difference does it make if there's PVA on the plasterboard if the plasterboard will loose it's rigidity if it gets wet and stays wet for a while? If the plasterboard on which everything is built up on gets wet and loses it's rigidity, then the tiled wall can move back and forth, and that would mean that the grout lines between the tiles would crack, letting in more shower spray water into the wall, which would result in more softening of the plasterboard, therefore more movement of the tiling, more cracking of the grout lines, more water getting in and we have what amounts to a snowball rolling down hill because the plasterboard itself isn't waterproof. What difference does it make in that circumstance if the PVA over top of the plasterboard isn't waterproof either? You'd have to replace all the tiling and plasterboard in any event wouldn't you?

Where I live, most wall tiles in wet areas like showers is put up on waterproof panels like Wonderboard, Durock or Dens-Shield to prevent that snowball from rolling downhill.

 

[empip]

This PVA FAQ may be of use ...
http://www.axp.mdx.ac.uk/~john49/pvafaq.htm
A starting point for further research perhaps.

Other FAQ's via index at page end.

 

[Nestor_Kelebay]

Question posed by the author in that previous link:

"When PVA dries will it redissolve, and why does it turn white?"

And, I'm not sure if he's intending to explain it, but he writes as follows:

"As the water dries off the polymer forms a continuous film, which does not tend to redisperse. Most of these polymers tend to reabsorb water, which makes them whiten and reduces their strength to some degree."

The author of that web page doesn't seem to have a clue why acrylic emulsions go from a white opaque liquid to a clear colorless film as they dry. If he understood why, he could explain it clearly (no pun intended), because it's not at all hard to understand.

A great big US Marine Corp HOOAHHH!! to the first person who can explain why acrylic and PVA emulsions will be a milky white opaque liquid in the can, but will dry to a clear and colorless solid.

And, not to push the subject too far, another big Canadian Armed Forces HOOAHHH! to the first person who can explain why my blue jeans are darker when they're wet!

And, I suppose, taking the answer to the blue jean question one step further, a great big Royal Marines HOOAHHH! to the first person who can explain why wet cotton is more transparent than dry cotton, thereby laying down the optical principles underlying a wet t-shirt contest for us.

If anyone wants to know the answers to those question, post and I'll explain why all those things happen. But, I'd be interested in hearing prople's guesses tho.

None of this stuff is hard or difficult to understand. It just needs to be explained properly. And, I don't think the guy who wrote that bit about
PVA knew the explanation at all. Otherwise he woulda explained it, right?

HOOAHHH!

 

[Nestor_Kelebay]

Thought I should post the answers to those questions posed in the last post, just in case anyone was interested:

1. Why do acrylic "emulsions" go from a white opaque liquid when wet to a clear colorless solid when dry?

In a nutshell, it's because the liquid consists of clear solid plastic particles suspended in the liquid (which is mostly water) which each reflect and refract light exactly like the water droplets in a clowd do. This reflection and refraction breaks up the incident light into all of the different colors of the rainbow and scatters it all over the place. What your eye sees is a mixture of all different colors of light coming from all different places of the liquid, and you see that mixture of colors as the color "white". And, because any light ray trying to go through that liquid is going to get shredded by the reflection and refraction, you can't see anything on the other side of the liquid, so it's opaque.

The liquid itself is a dilute solution of a low volatility water soluble solvent called a "coalescing solvent" (diluted with water, I mean). As the water evaporates, each plastic blob finds itself surrounded by this water soluble solvent at ever increasing concentration. The coalescing solvent "dissolves" (kinda) the clear plastic blobs, making them soft and easy to deform. Capillary pressure and surface tension then work together to cause each soft plastic blob to pull itself closer to each of it's neighbors, and the result is that all the blobs deform into interlocking shapes with no voids between them, much like the bubbles in a head of beer. Over the next few days, the coalescing solvent evaporates from the now solid film, and the now distorted plastic blobs each harden back up to their original hardness as the coalescing solvent escapes from the film.

Since there are now no longer any phase boundaries in the film to both reflect and refract light, the whiteness disappears and the plastic film becomes the same color as the plastic from which it's made, which is clear and colorless.

So, acrylic emulsions are white and opaque when wet for the same reason that clouds and snowbanks are white and opaque; because the phase boundaries inside them scatter light, and you see that scattered light as "white" light. Acrylic emulsions dry clear and colorless because without the scattering of the light, you see the true color of the plastic which is causing the scattering, and it's a clear colorless solid.

(Exactly the same thing happens in emulsion paints, and for a full description of the process by which emulsion paints dry, read my most recent post in the thread entitled "Crown Solo 1 coat guarantee".)

2. Why are my blue jeans darker when they're wet?

It's because the refractive index of cotton is more similar to that of water than it is of air.

Consequently, when a light ray enters dry cotton fabric, it is reflected and refracted MORE at the cotton/air interface than it would be at a cotton/water interface. So, more incident light hitting dry cotton will be reflected and refracted through a 180 degree angle back to your eye. And, of course, as it's refracted it's broken up into all different colors, and your eye sees that mixture of different colors coming from the cotton as the color "white". Whenever you mix white with any other color, you get a lighter version of that same color. Consequently, the TRUE color of my blue jeans is the dark blue they are when they're wet. The lighter color I see is really an optical illusion caused by the scattering of incident light by the dry cotton.

When the cotton is wet, then because of the greater similarity of the refractive indices of cotton and water, both less light is reflected at every cotton/water interface and the angle through which the incident light is refracted at cotton/water interfaces is smaller. Consequently, an incident light ray entering wet cotton travels in a straight-ER line into the fabric where the light is absorbed. Since less of the light is reflected and refracted back to your eye, you see less light coming from the jeans (that white light coming from the dry jeans would be absent), and so the color you see is darker.

3. How do wet t-shirt contests work?

Since light travels in a straighter line through wet cotton than it does in dry cotton, it behaves more similar to the way it would behave in air, or the way it would behave if the cotton wasn't even there. That is, because wet cotton affects the path of light LESS than dry cotton, wet cotton is more transparent than dry cotton.

AND, you can prove what I'm saying is true by doing a simple experiment:

Take a piece of paper with some printing on one side, and lay it printed side down on a table or whatever. Initially, you won't be able to see the printing very well, if at all.

Now, put a drop of water onto the top of that paper. As the water wicks into the paper, the spot where the water is will become progressively darker and more transparent. That's because the refractive index of the cellulose fibers the paper is made from is more similar to that of water than air. So, as the water surrounds those cellulose fibers, incident light hitting that wet spot won't be reflected or refracted as much at the water/cellulose interfaces, and the result will be that the light will travel in a much straighter line through the wet paper than dry paper. Consequently, it travels in a straighter line through the wet paperto the printed side and in a straighter line back through the wet paper to the unprinted side. As a result, light behaves more similarily to the way it would if the wet paper weren't there, and that's why wet paper is more transparent. And, you can prove that last point by reading the printing through the wet paper, or by holding the paper up to a light. What was a dark spot when the paper was wet will now be the brightest spot when the paper is held up to the light. Again, it's because wet paper is more transparent because of the greater similarity of the refractive indices of water and cellulose.

If anyone wants me to explain any of this better, lemme know.

PS:
Speaking of paper, the simple sugar molecule is what connects all living things. Just in the same way that polyethylene is what you get when you connect ethane molecules end-to-end, cellulose is what you get when you connect sugar (glucose) molecules end-to-end. Water from the roots, CO2 from the air and energy from the Sun combine in a tree's leaves to produce glucose molecules. The tree then stacks those glucose molecules up like bricks in different ways to make cellulose, and something called "hemicellulose" and something else called "lignin". Wood is made of cellulos, hemicellulose and lignin. And, when wood rots, the wood rot fungus (Mr. Serpula Lacrymans) is simply practicing good ecology by recycling those cellulose molecules back into glucose for use in it's own metabolic processes. So, the simple sugar molecule is what ties us all together, plants and animals and man and even the fungii, too.

 

[empip]

Question posed by the author in that previous link:

"When PVA dries will it redissolve, and why does it turn white?"

And, I'm not sure if he's intending to explain it, but he writes as follows:

"As the water dries off the polymer forms a continuous film, which does not tend to redisperse. Most of these polymers tend to reabsorb water, which makes them whiten and reduces their strength to some degree."

The author of that web page doesn't seem to have a clue why acrylic emulsions go from a white opaque liquid to a clear colorless film as they dry. If he understood why, he could explain it clearly (no pun intended), because it's not at all hard to understand.........

I contacted the author of 'the previous link'.
The link being http://www.axp.mdx.ac.uk/~john49/pvafaq.htm
via [email protected]
Middlesex University I think.. but not too sure.

He graciously replied :-

Subject: RE: The PVA FAQ

I am a little puzzled by his use of the term "plastic" instead of
"polymer" to describe PVA, and the use of "particle" instead of
"globule". To me this indicates a less than complete understanding of
the subject, probably gleaned from manufacturers' factsheets rather
than any real knowledge of the subject. He also attests that
coalescing solvents are water soluble. In general this is not true,
the coalescing solvent goes into the discontinuous (polymer) phase due

to the favorable partition coefficient. As for perspex paints, they do
not exist. You may draw your own conclusions. Try calling his bluff on
that.

RGDS,
JS

So, where do we stand?
Are you actually both saying the same thing, diametrically opposed or just slightly at odds ?

 

[Nestor_Kelebay]

No, I think there are some minor points that don't really matter, but some major points that are fundamental to the understanding of film formation in "emulsion" paints.

Lemme start with what I see as the major points:

My computer has been freezing lately, so I will address each issue in a separate post so as not to loose too much typing if it freezes.

I am a little puzzled by his use of the term... ..."particle" instead of
"globule". To me this indicates a less than complete understanding of
the subject, probably gleaned from manufacturers' factsheets rather
than any real knowledge of the subject.

To me, the word "globule" suggests that the binder is a liquid droplet suspended in water. IT IS NOT. It is a hard, clear plastic particle. The notion that the binder exists as a liquid is a popular misconception perpetuated by the use of the word "emulsion" to describe water based paints in Britain. In North America, we refer to the same paints as "latex" paints, but there is absolutely no rubber tree sap in them. Both terms are extremely misleading.

What people need to understand is the following:
1. The binder in "emulsion" paints consists of a hard clear plastic particles
2. As the water evaporates from the paint film, the coalescing solvent softens these particles.
3. When the particles are sufficiently soft, then the forces of capillary pressure and surface tension cause the particles to pull together forming a solid continuous film (with any colored pigments suspended inside that solid plastic film much like raisins in raisin bread).
4. After the plastic particles have fused together into a solid film, the coalescing solvent evaporates from the film, and as it does the plastic returns to it's original hardness.

Now lemme PROVE that what I'm saying is correct.

Go to www.paintquality.com
This is the web site of the Paint Quality Institute which was established by the Rohm & Haas Company who are the largest manufacturers of the acrylic plastic resins used to make "emulsion" paints here in North America.

At that web site, click on the "For the Seller and Specifier" link

On the page you get to, click on "PQI Architect Modules" which is a set of three articles that the people at the Paint Quality Institute prepared for an architectural publication.

When you see the three articles, click on and download the one entitled "The Ingredients of Paint and their Impact on Paint Properties"

Then, scroll down to the 3rd page where the heading is: "Film Formation" and go a bit further to where it says "Latex Based Binders" and says:

"Most water based paints are "latex" paint. THE BINDER IN A LATEX PAINT IS A SOLID PLASTIC-LIKE MATERIAL DISPERSED AS MICROSCOPIC PARTICLES IN WATER. This dispersion is a milky white liquid which is called latex in the paint industry in that it is reminiscent of the natural latex from the rubber tree. Latex is also called emulsion, and in some countries, such as Englad, latex paints ar referred to as emulsion paints."

So, the binder in an emulsion paint is a solid plastic particle that would be clear in color (just like Perspex) if it were big enough to see. The reflection and refraction of light by these tiny solid particles is what makes a deep tint base "emulsion paint" white. There is nothing that's white in color inside the can.

Lemme continue on with the next post.

 

[Nestor_Kelebay]

And, in fact, the reason why paint companies will specify a minimum temperature for applying emulsion paints is because plastics get stiffer at colder temperatures.

If the plastic is too cold, then the coalescing solvent won't be able to soften up the SOLID plastic particles sufficiently so that the forces of capillary pressure and surface tension can cause them to deform enough to form a solid continuous film rather than a mass of blobs sticking to each other (like a pot of cooked rice).

In that same article "The Ingredients of Paint and their Impact on Paint Properties" continue to the next page where you'll find the following paragraph:

"The mechanism of latex paint film formation has some limitations. Because the binder particles are thermoplastic (tending to get softer at higher temperatures and vice versa), they will get too hard to fuse into a continuous, durable film when applied at too low a temperature. This is the main reason paint manufacturers specify a minimum application temperature (typically 50 deg. F) for latex paint products."

And, this makes common sense if the binder consists of solid plastic particles.

But doesn't if the plastic binder consisted of droplets of liquid suspended in water. Cold liquids will flow, too.

Will continue in next post.

 

[gcol]

Nestor I mean this in jest but, when you walk into your local pub, do the guys at the bar turn to each other and mutter "don't say anything about paint to this guy!"

Only teasing, I respect knowledge.

 

[Nestor_Kelebay]

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?"

And, if they know the answer, then I realize I've encountered another paint person, and we usually get along famously.

Empip:

Getting back to JS's comments, let's take the next one:

"As for perspex paints, they do not exist. You may draw your own conclusions."

Gosh.

If JS had bothered to check, he probably would have tried doing an internet search for web sites that contain both the words "Perspex" and "paint" and he would have found this one:

http://www.answers.com/topic/polymethyl-methacrylate-2

which says that Perspex, Plexiglass and Lucite are all trade names for clear plastic sheets made from the same plastic, polymethyl methacrylate. That is, if Rohm and Haas makes a sheet of clear plastic out of polymethyl methacrylate, they sell it as a sheet of "Plexiglass". If DuPont makes a sheet of clear plastic out of polymethyl methacrylate, they sell it as a sheet of "Lucite". And if ICI on your side of the pond makes a sheet of clear plastic out of polymethy methacrylate, they sell it as a sheet of "Perspex". Apart from what they're called, they're all clear sheets of the same plastic, polymethyl methacrylate, or PMMA for short.

And, that same web site goes on to say:

"Acrylic paint essentially consists of PMMA suspended in water; however since PMMA is hydrophobic, a substance with both hydrophobic and hydrophilic groups needs to be added to facilitate the suspension."

And the good professors of polymer science at the University of Missouri agree with me. If you go to this page:

http://pslc.ws/mactest/level2.htm

and click on "Poly(methyl methacrylate) on the left, you'll get an entertaining discussion of that plastic which includes the following statement:

"PMMA is also found in paint. The painting on your right, Acrylic Elf was painted by Pete Halverson with acrylic paints. Acrylic "latex" paints often contain PMMA suspended in water. PMMA doesn't dissolve in water, so dispersing PMMA in water requires we use another polymer to make water and PMMA compatible with each other. To see how we do this, go visit the poly(vinyl acetate) page."

And, from the book entitled:

"Painting & Decorating", "Skills and Techniques for Success"
by E. Kieth Blankenbaker, Associate Professor Emeritus, Technology Education, The Ohio State University, Columbus, Ohio on page 123:

"Acrylic resins are available in a family of copolymers that combine acrylic acid with ethyl acetate and methyl acrylate. Ethyl acrylate gives the resin resistance to heat, ultraviolet light, and weathering. It improves color stability, flexability and strength. Methyl methacrylate imparts hardness and toughness.
A range of high quality resins can be produced by varying the amount of each ingredient of the copolymer. These resins resist yellowing, retain flexibility, are durable, and withstand temperature extremes. Cured acrylic films are resistant to oil and grease and can be cleaned more rapidly than other types of emulsion coatings. Acrylic resins have exceptional color and gloss retention."

What the good prof is saying is that the properties of an acrylic resin can be modified by varying the proportion of ethyl acrylate and methyl methacrylate monomer in the polymer, and this allows companies like Rohm & Haas to make a wide variety of different acrylic resins for paints intended for different applications.

I will concede this point to JS: Anyone not familiar with emulsion paints would not have guessed that they're made from the same plastic that Perspex is. It's not at all intuitive that the paint on your wall and the plastic sandwiched between layers of glass in the front windshield of your car are made of the same stuff.

But, a paint person would have known that.

However, I consider this point to be of medium importance because there are probably few acrylic resins that are made from PURE polymethyl methacrylate. Most, as Blankenbaker says, are a mixture of ethyl acrylate and methyl methacrylate. Still, I consider it of some importance because I find it easiest to think of emulsion paints as falling into two broad catagories:

1. the better quality ones made of Perspex, and

2. the lesser quality ones made from PVA which share many of the same properties as white wood glue (which is also made of PVA).

will continue in next post

 

[Nestor_Kelebay]

Carrying on...

"He also attests that coalescing solvents are water soluble. In general this is not true, the coalescing solvent goes into the discontinuous (polymer) phase due to the favorable partition coefficient."

What JS is saying is not what Dow Chemical is saying on this web site:

http://www.dow.com/ucarlatex/coatingsconnection/archive/0311.htm

Dow is one of North America's largest manufacturers of vinyl acrylic resins with it's UCAR line of resins. The Ucar line also includes some 100% acrylic resins.

That Dow web site states as follows under the paragraph entitled: "Solvents for Industrial and Architectural Latex Coatings":

"Coalescing solvents are used in architectural and industrial latex coatings to promote film formation, and selection of the proper coalescing solvent is a key to the formulation of superior latex coatings. A coalescent is often used in water-based systems as a fugitive plasticizer to soften the resin particles, enabling them to fuse into a continuous film. During the drying process, most or all of the coalescent evaporates, allowing the film to achieve the desired hardness.

Physical properties of the coalescing solvent determine its efficacy in a particular formulation. Among the most important coalescent properties are its distribution coefficient in the latex, its plasticizing efficiency for the latex, and its rate of evaporation. The distribution coefficient, D, is the concentration of the solvent in the aqueous phase divided by the concentration of the solvent in the polymer phase, Eq.1. Large values of D mean there is not much of the solvent in the polymer phase to help with film formation.

D=Cw/Cp (Eq. 1)"

Now, I'm not a paint chemist, but it seems to me that if there is some concentration of the coalescing solvent in the water phase (Cw), then as that water evaporates, the concentration of coalescing agent in the water phase will increase. In order for this distribution coefficient, D, to remain constant, then as the water evaporates, the concentration of the coalescing solvent in the polymer phase would also have to increase to maintain the same distribution coefficient. Thus, as the water evaporates, the resulting elevation in concentration of coalescing solvent in the water phase causes migration of coalescing solvent into the polymer phase to maintain equilibrium, and perhaps it's the influx of coalescing solvent into the polymer during water evaporation that results in the softening of the polymer.

Whether the portion of the coalescing solvent that's in the water phase is dissolved in that water, emulsified in that water, suspended in that water or contained inside the water in some other manner really doesn't matter. What's important to understand here is that it's the coalescing solvent that SOFTENS the polymer particles so that they become soft enough to deform due to the force of capillary pressure and surface tension, not how the coalescing solvent is contained in the water phase.

(Although I would like to hear JS's explanation for how the coalescing solvent exists in the water phase if it is not in solution.)

Take a look at this web page from Resene paints in New Zealand:

http://www.resene.co.nz/homeown/probsolv/Whatsinacanofpaint.pdf

In it, you'll find the following paragraphs:

START QUOTE
"The Process of Latex Paint Coalescing

If enamel or two pack paints (by enamel and "two pack", I think he means oil based and epoxy, respectively) are applied in cold weather nothing happens. That is to saythat the drying or curing process is simply postponed until the temperatures rise. Until this happens these coatings are obviously prone to physical damage by rain, dust or foot traffic etc. but if they survive these possible disasters and temperatures return to normal these paints will restart their drying process as if nothing had happened. This is not the case with latex paints. It is not so much the cold conditions that are the problem but the high level of moisture in the air that nearly always accompanies cold conditions. When there is a lot of water in the air the water in a latex paint cannot evaporate off. There is no room for it in the air.

The latex binder is made up of millions of tiny little spheres of solid acrylic resins suspended in water. Each particle is in the range of 0.1 to 1 µms depending on the type of latex. Each individual latex particle is made up of a core containing long chains of carbonatoms up to 50,000 long. Each particle can also be imagined as being covered in tiny hair-like mini bumper bars, which act to keep each particle separated from its neighbour. These restrict the solids content for acrylic binders to a maximum of 60% and often much lower. As water evaporates from the film the latex particles are deformed until they are pressed against each other. As this happens the coalescing solvent is left in close contact with the Latex and acts to dissolve it and fuse it to its neighbours. As the last water leaves the film all air pockets are removed and a uniform film of paint is formed. The last stage of the drying process is the fusing together of the latex particles and the evaporation of the last of the coalescing solvent.

Coalescing Solvent

Unfortunately, there is another key player involved, the coalescing solvent. This is a vital part of the drying process for latex paints. The coalescing solvent is needed to soften the solid suspended acrylic binder particles in order for them to fuse or stick together in one unified mass. The coalescing solvent is a lot slower to evaporate than water in normal conditions. Normally the water evaporates quickly and the drying paint becomes quite thick making it difficult for the coalescing solvent to escape. In cold conditions this is not the case. The paint remains quite liquid (because the water is not evaporating) and the coalescingsolvent is given much more freedom with which to escape the paint film. There is never any coalescing solvent vapour in the air (unless you live in a paint factory) so in time all the coalescing solvent will evaporate from the coating leaving the water behind. It may take about 3-5 hours for this to happen. As a result the latex particles are left surrounded by only water. When the weather eventually warms up the water will evaporate leaving behind a poorly coalesced acrylic paint. The severity of this poor coalescence on the paints physical properties varies depending on time and temperatures. The worst that can happen is that the paint dries as a powder. In real life this may not be the case and the actual result will be something in between a powder and a normal paint film. The visible results may be a patchy appearance with possible loss of gloss and adhesion. The next rain may result in blistering, or the entire coating could be washed off."
END QUOTE

What those paragraphs are saying is that if the relative humidity in the air is high, then the water won't evaporate from the paint for a long time. But, during this long time, the coalescing solvent will be evaporating from the paint because there is no coalescing solvent vapour in that humid air. As a result, during cold or humid conditions, the coalescing solvent can evaporate from the paint before the water does. And the result will be that there won't be enough coalescing solvent in the paint to soften the acrylic resins enough so that they deform to fuse together into a solid film. Instead, what you'll get will be un-deformed acrylic resins sticking to each other much like the grains of rice in a pot of cooked rice, or worse, not even sticking to each other and the paint drying as a powder that is easily rubbed off.

Anyhow, what both web sites are saying is that as the water evaporates, then the coalescing solvent acts to soften the plastic resins so that the forces of capillar pressure and surface tension are sufficient to deform the resins so that they fuse together into a continuous film. That requires that the coalescing solvent be strong enough to soften the plastic resins enough that they deform easily.

If what JS seems to be saying is that the coalescing solvent is not dissolved in the water, but remains inside the non-continuous plastic phase. If that were the case, then that plastic would remain soft all the time the paint is in the can, and only harden up once as the solvent evaporates once the paint is applied. This is not the case. The resins are hard UNTIL the paint is applied, and then soften during film formation. Then the resins harden up again after the coalescing solvent evaporates, with the result that the whole paint film becomes as hard as the plastic.

Regardless, it is a minor point as to how the coalescing solvent is contained in the water. Still, if Dow Chemical says that there is a concentration of this coalescing solvent in both the water and polymer phases, I'd like to hear JS's explanation as to how the coalescing solvent exists in the water phase if NOT by being dissolved in it.

will continue in next post

 

[Nestor_Kelebay]

and finally...

JS says: "You may draw your own conclusions. Try calling his bluff on
that."

I agree that it's good practice to "call someone's bluff" when you think they may be BS'ing.

But, all of the web pages I cited in these past few posts have reitterated my explanation of what emulsion paint is and how it forms a film.

So, that must mean that either I read much of this stuff and understood it before I posted in this forum, or I just got lucky and found lots of web pages on the internet that agree with what I'm saying.

Here's what I think people should consider:
If someone understands something, then they should be able to explain it to someone else. If they cannot explain it to someone else so that the other person ALSO understand it equally well, then that's more likely to mean that they don't really understand it rather than the other equally intelligent person can't understand their explanation.
That is, it's easier to understand an explanation that makes sense than it is to make sense of something you don't understand, so the onus is on the explainer to make sense of it, if in fact it is reality.
Nature is not complicated. If something makes sense, that's a clear indication that it's probably true.

And, I'd like to hear JS's comments on that last paragraph. That's because during my life I've found that everything I've come to understand has ALSO made sense once I understood it. And, by understanding it, I was therefore able to explain it to other people, who, for the most part, were as intelligent in every respect as I.

And, I await JS's reply to my observations.

 

[empip]

Ok, Nestor ....... could you repeat that please?

Only joking !

 

[Nestor_Kelebay]

Empip:

This JS person might be very knowledgeable about plastics, but what concerns me is primarily two things:

1. If he wrote that web page about PVA which mentions that it turns white when wet, but wasn't able to explain why (in terms of light reflection and refraction), then I'd question whether he understood that the PVA consisted of tiny plastic particles. Anyone knowledgeable about paint will know why a water based "varnish" will be a white liquid in the can but dry clear merely by analogy with a clowd or a snowbank.

2. If he's wondering why I used the word "particle" instead of globule, it's because using the word "globule" suggests that the binder is a droplet. It's a solid particle. And, if the JS lives in England, where you call your water based paints "emulsion" paints, then that suggests to me that the reason why he believes the binder is a liquid is merely because he's being misled by that word. A paint person would know that the word "emulsion" which you use in England is as misleading as the word "latex" that we use here in North America and that in both cases the binder is a solid, even when it's at it's softest. It's more correct to call "emulsion paint" a "slurry".

The JS may be very knowledgeable in his field of expertise, but those two points make me sceptical that he's knowledgeable about paints.