Frank Wentzel
10-22-2002, 04:11 PM
thechemist
posted 08-14-2001 02:49 PM
Note that Gougeon has constructed a test which shows a dramatic difference in some property between their product and their competitor's. Anyone favoring or disfavoring one company or another can use such data as evidence of something being better or worse.
This easily becomes the Argument by False Analogy that we occasionally play with, or fail to recognize.
Referencing What the Product May Actually Do by actual test or testimony of users is the most valid thing one can say about any product.
The fact that a product does some task poorly does not mean it is a bad product, be it West, CPES, antifreeze or any other. Each product does some things better than any other. Put West or CPES in your car radiator and you will be in big trouble, for antifreeze is the best of those as an engine coolant.
Where firefights can start is where a manufacturer or their representative promotes a product for a use which is not appropriate, which does more harm than good, or just plain does not work very well.
The test of water-barrier-properties of West's properties versus Smith's CPES is not a valid one because that does not seem to be the primary purpose of that product, meaning the two products do not share a common purpose.
From Smith's company web site, http://www.smithandcompany.org
"The original Clear Penetrating Epoxy Sealer™ was ...... [developed for restoration of wood in the marine marketplace,]... the highly aggressive marine conditions proved the acid test for this new technology. It gave paint and varnish that actually stuck, and sealants and adhesives that did not tear or crack where all other products readily failed. Some boat owners were also painting contractors, architects or similar, and began to use these products in the architectural field, for restoration as well as an adhesion-promoting primer for paint on new wood buildings. It proved far more workable than any other practice for "restoration" of deteriorated wood, and it soon became apparent that enamel or latex house paints applied to wood treated with this product did not readily fail, where without this treatment failure of paints typically occurred in half the time and rot soon started up again behind a wood repair with a filler. "
This does not seem to be an intentional application area of Gougeon's products , from what I have seen of their literature.
Further, from page two of that web site, http://www.smithandcompany.org/more.htm
"The new technology departs from old wood treatment practices, even with epoxy products, with the discovery that the fungi that cause decay in wood actually penetrate into wood far beyond the visible region of total decay, and that the extent of this penetration is not obvious and may be many inches. The old-technology practice of removing visibly decayed wood leaves an infected region below the "repair" and any water intrusion or diffusion that brings the humidity above roughly fifteen percent triggers germination of fungal spores in the infected region, and rot begins anew.
The genesis of the new technology was the development of a product that would selectively impregnate the entire infected region of wood with a water-repellent resin system derived in large part originally from wood, to bring about restored mechanical properties similar to wood and a water-repellent characteristic, while leaving a natural porosity in the treated wood so it could "breathe" as does natural wood. This prevents the accumulation or condensation of liquid water in the wood behind old-technology filler repairs, a leading cause of failure of such repairs. "
It should be clear that one manufacturer is promoting a product for one purpose while another manufacturer is testing it for a different purpose, finding it lacking, and drawing a [false] conclusion.
As for a real water barrier, from that same site,
"In about 1975 Steve Smith discovered what caused the gelcoat blisters and laminate decomposition that was suddenly prevalent on glass-reinforced polyester (GRP) boats ("fiberglass" boats). He invented then the barrier-coat technology which is now in common use everywhere in the world for the repair of such damage and prevention of its occurrence.
That same barrier coating, when applied to the bottom of a wood boat, made possible the end result of a wood boat with a dry bilge, normally an unheard-of condition. Two additional factors were vital in achieving that result. One was the caulking of every seam and joint with a flexible, high-adhesion sealant. This absorbed small relative movements while maintaining a water tight seal. The second was the use of Clear Penetrating Epoxy Sealer, which allowed these products to adhere to the wood, whether dry or slightly damp."
If Gougeon were interested in comparing a moisture-diffusion barrier of their own with one of Smith's, or Interlux's or anyone else who makes such products , they could have done so directly, as most paint manufacturers, even Smith, make such things. To my knowledge no one has done direct comparisions of these products, although I expect the mineral-filled paints will do better than the unfilled resin coatings.
In any test of completely sealed wood samples, measuring weight gain, one may still not be measuring what is useful in the real world, as all will ultimately reach equilibrium as fully saturated specimens.
Where coatings are applied to wood hulls, it is the water-evaporation-rate off the inner surface, balanced against the water-diffusion-rate through whatever barrier coating, if anything, which may be on the outside, which determines equilibrium moisture content in the wood.
If the inner water evaporation rate is high enough, any external coating [or antifouling paint alone, if perhaps ten years build-up] will give wood with moisture below perhaps 15-20%. If the inner water-evaporation-rate is low enough, the best external water barrier will be inadequate, and the wood hull will eventually be fully waterlogged, with a moisture content far beyond the fiber-saturation-point.
thechemist
posted 12-21-2000 09:25 PM
--------------------------------------------------------------------------------
Er......guys......some epoxy does grow on trees....sort of.
Epoxy resin such as you are familiar with is a petrochemical-based product, although it did come from trees, although long dead.
The "epoxy" of epoxy resin and the "resin" part are two different parts. The epoxy part is two carbon atoms and an oxygen atom in a ring. The resin part can be any sort of petrochemical poo or biodegradeable organic goo. Put them together and what have you got? Stickety glippety gloppety goo. Only that takes too long to say which is why we made life easier for you guys and gave you the simple name of epoxy resin. It ain't technically precise, so you can't be too literal with it. It's a generality.
The amine curing agents do come from natural gas, petroleum, and ammonia.
There are a host of resins and oils derived from natural sources, such as walnuts, cashew nut shells, walnut shells or walnuts, tung berries, linseed oil, castor oil, and various oils, and gums from trees, menhadden oil from some sort of fish thing, animal oils, and probably they will even find some sort of oil in something else one day. All of these things can be modified with a few simple chemicals to add an epoxide group or an amine group to them.
When that is done, you have (either before or after curing, depending on your nomenclatural preferences) epoxy from trees. or walnuts. or fish. It can be done.
posted 08-16-2001 02:56 PM
Sounds as if there are a few business owners or employees here, as well as the idle rich.
Those of us who have to actually work for a living, or help supervise others doing the same thing, may or may not see the checkbook and accounting side of things, depending on the size of their company and who else is taking care of that area.
Setting the price of a product nowadays has less to do with the cost of raw materials than it used to.
In some states such as California, the spiraling cost of health care and insurance is driving up those overhead costs by about ten to fifteen percent a year for large businesses, and twenty to thirty percent a year for a small business. Federal environmental regulations everywhere, while sorely needed in some circumstances but not in most, further force costs up. The Plaintiff's Attorney who specializes in out-of-court settlements [meaning extortion] has further increased the costs of all manufactured goods.
The increasing cost of living due to [whatever social factors] has required companies to increase employee pay at double the "inflation" rate, just to barely keep their employees' standards of living about the same. Otherwise, the skilled ones go elsewhere and they have to hire new [cheaper] ones, and cannot see the training costs.
Costs that were once not a significant part of a business overhead have now grown to where they are the previous year's profit. Costs of complying with new government regulations such as controlling where rainwater goes or what it touches have cost small paint companies many year's profits, and increasingly onerous micromanagement by city and county agencies [for example] drove the De Soto paint company out of Berkeley and into the Mojave desert where land was cheap, even though they were a clean manufacturer and had a nice manufacturing facility. United Parcel service moved their administrative service and billing center out of Modesto a few years ago , to Texas, because it was just too expensive to exist and employ people in California, and their bottom line motivation was keeping the company profitable while avoiding more strikes due to wage demands of their Teamster drivers.
Anyone who does any sort of marketing knows the skills required to produce promotional literature or labels or maintain a web site. It used to require only a draftsman and a local printing company. Now it requires Information Specialists who speak HTML and cost double what a production worker does, and computers, printers, scanners, software, all of which costs a bunch and is obsolete two years later.
Some guy in his back yard fifty or even twenty years ago probably could have made any simple chemical product and marketed it successfully. Now, no one can do that. The cost of regulation compliance, the county fees [now up to six or seven hundred just because you MIGHT generate any hazardous waste] all these things add up to overhead costs that are actually more than the cost of raw materials and more than profits for small businesses, and are comparable to profit margins for mid-size or large businesses. I think the bottom line is that our society is changing, and the increasingly service-oriented and communications/information orientation of society is responsible. I think this change will continue in the next ten years, possibly at a greater rate.
The cost of any product reflects not only labor and material and "overhead" and profit, but all the costs of keeping a company IN EXISTENCE . Today's costs are not tomorrow's costs and if you do not anticipate tomorrows costs you will never sell today's product at a price that guarantees survival. In our society today, it has become surprisingly expensive to do just that.
But, I digress.
Surely someone has a rational question about a simple chemical matter, instead of stating with absolute certitude that someone's formula cannot possibly contain wood-derived resins becasue there is no such thing.
There ARE such things.
Triglycerides [walnut oil, tung, castor or other drying oils used in varnish] are articles of commerce, common as cat hair, and easily modified from their olefin --chemistry to either epoxy or amine by a chemical manufacturing company. For example, water can be added to any double--bond. This gives a secondary alcohol for any unsaturated triglyceride. Epichlorohydrin can be reacted with such an alcohol to give an glycidyl ether, which is an epoxide. Ammonia can be added to such a double--bond to give primary amines, or to any acid to give amides.
The same can be done with any wood-derived resin which has any hydroxyl or unsaturation. They can all be modified in this manner. This sort of chemistry has been in practice on an industrial scale for over a hundred years.
Anyone with a chemical background can see this. It is obvious from the foregoing chemical discussion. Such things exist, and can be EASILY made.
Cardolite [a chemical manufacturer], for instance, makes a variety of phenalkamines and epoxides derived from cashew nuts or the oils of their shells.
I cannot tell you what any epoxy company is using in their products unless they publish their formula, but claims of wood-derived resins are assuredly possible and easily feasable.
As for what ingredients are listed on a MSDS, the OSHA hazard communications standard requires the consumer be informed of the hazards. If a relatively non-hazardous material is dissolved in a hazardous material, the manufacturer need not disclose any but the hazardous ones. If a material is hazardous at a high concentration but present in sufficient dilution, its hazard may disappear compared to other ingredients.
That, in a nutshell, is why you will often not find all of a product's ingredients on a MSDS in the U. S. A. In Europe, different rules apply, but there are many similarities to the foregoing.
thechemist
posted 08-24-2001 01:23 PM
A minor clarification....CPES as referred to by the Practical Sailor [which they have occasionally called CEPS] is actually two different products used together as a "system", namely the single product Clear Penetrating Epoxy Sealer, which Smith refers to as CPES, and that followed by a fairly thick topcoat of their clear polyurethane topcoat.
Maybe 6 years ago Practical Sailor did a test of Smith's CPES epoxy product with a varnish applied on top. Perhaps someone has a back issue and can see what they said about it...I think it was pretty good.
The application of varnish on top is what Scott is talking about, I believe.
The application of the polyurethane on top is what ROWE is talking about, I believe.
That said, the issue of adhesion is what I wish to address here. There are different adhesion mechanisms, depending on what molecular groups are present in either the topcoat or the varnish.
An adhesion-promoting primer may promote adhesion better if the topcoat is applied before that primer has fully cured. The manufacturer of the primer is usually rather specific about this "window of opportunity". The reason the "window of opportunity" exists is that there is a region between "wet-liquid" and "fully cured with all amine blush fully developed and all benzyl alcohol and other plasticizers fully exuded onto the surface", where the surface of the primer not only has no interfering contaminants but actually has various molecular groups present, not yet reacted, and those are capable of grabbing something applied on top.
Those molecular groups may or may not go away, getting used up in the primer curing reaction.
That is one mechanism of adhesion.
Some [epoxy or other] primers leave a film of chemical fishhooks [or chemical Velcro, if you wish] even after they cure, and those are capable of grabbing certain other kinds of topcoats, depending on the chemical makeup of the topcoat.
That is another adhesion mechanism.
Some topcoats may be capable of aligning their reactive chemical groups with not only each other, for the topcoat curing mechanism, but also with the chemical groups that are left over after the underlying primer has cured, assuming that "primer" exudes no interfering surface contamination.
That is another adhesion mechanism.
Some manufacturers of either primer products or topcoat prodcuts are more-or-less clear on what is "compatible" with what. Usually the compatibility issue revolves around what one guy thinks another guy is using in their stuff, if you have different manufacturers.
Varnishes made from oilseed resins ["traditional" varnish, perhaps with various cooked resins (alkyd) or completely synthetic(e., g., polyurethane) resins added] chemically cure by a reaction of double-bonds with the oxygen in the air, catalyzed by a metalllic soap, a "dryer". So do oil-base enamel paints. I have discussed this in the past, in a few threads which can be found with a search, for those who wish to know more. Searching the Text, in Building/Repair, for words such as double, bond, drier, [or dryer...] should turn them up.
Some epoxy products are capable of reacting with the "double-bond" molecular structure, in various ways. I cannot tell you what manufacturer has what exact chemicals in their formulation. Some of these resins are essentially non-hazardous, compared to other resins or solvents that may be in a formulation, and thus would not even be listed on the MSDS, thus offering no clue as to what is in their stuff. The fact that only solvents are listed on a MSDS tells you nothing except that a particular manufacturer may be a bit more than average paranoid, notwithstanding the recent flap and contradictory posts about this in other threads.
I know what sorts of chemicals are in the Industry, as articles of commerce, and there is pretty much any kind of reactive chemical group you might want on most kinds of resins. Thus, most things can react with most other things, based on the artistry of the manufacturer.
Evaluation of any product should be based on what the manufacturer says [pretty reliable for military-industrial products] or word-of-mouth for consumer/commercial-grade [usually more reliable, since consumer product manufacturers and distributors all-too-often employ people in their Marketing Departments who are not interested in the meanings of words and keep their dictionaries on a shelf in the closet, beside the jar containing their conscience].
The bottom line is, try following the manufacturer's instructions, but with a healthy dose of suspicion. Remember , Joe may say Bill's stuff will stick just fine to Joe's stuff, but Joe did not make Bill's stuff, does not know for sure what is in it, and Bill may change his formula once in a while and not tell anyone.
posted 08-14-2001 02:49 PM
Note that Gougeon has constructed a test which shows a dramatic difference in some property between their product and their competitor's. Anyone favoring or disfavoring one company or another can use such data as evidence of something being better or worse.
This easily becomes the Argument by False Analogy that we occasionally play with, or fail to recognize.
Referencing What the Product May Actually Do by actual test or testimony of users is the most valid thing one can say about any product.
The fact that a product does some task poorly does not mean it is a bad product, be it West, CPES, antifreeze or any other. Each product does some things better than any other. Put West or CPES in your car radiator and you will be in big trouble, for antifreeze is the best of those as an engine coolant.
Where firefights can start is where a manufacturer or their representative promotes a product for a use which is not appropriate, which does more harm than good, or just plain does not work very well.
The test of water-barrier-properties of West's properties versus Smith's CPES is not a valid one because that does not seem to be the primary purpose of that product, meaning the two products do not share a common purpose.
From Smith's company web site, http://www.smithandcompany.org
"The original Clear Penetrating Epoxy Sealer™ was ...... [developed for restoration of wood in the marine marketplace,]... the highly aggressive marine conditions proved the acid test for this new technology. It gave paint and varnish that actually stuck, and sealants and adhesives that did not tear or crack where all other products readily failed. Some boat owners were also painting contractors, architects or similar, and began to use these products in the architectural field, for restoration as well as an adhesion-promoting primer for paint on new wood buildings. It proved far more workable than any other practice for "restoration" of deteriorated wood, and it soon became apparent that enamel or latex house paints applied to wood treated with this product did not readily fail, where without this treatment failure of paints typically occurred in half the time and rot soon started up again behind a wood repair with a filler. "
This does not seem to be an intentional application area of Gougeon's products , from what I have seen of their literature.
Further, from page two of that web site, http://www.smithandcompany.org/more.htm
"The new technology departs from old wood treatment practices, even with epoxy products, with the discovery that the fungi that cause decay in wood actually penetrate into wood far beyond the visible region of total decay, and that the extent of this penetration is not obvious and may be many inches. The old-technology practice of removing visibly decayed wood leaves an infected region below the "repair" and any water intrusion or diffusion that brings the humidity above roughly fifteen percent triggers germination of fungal spores in the infected region, and rot begins anew.
The genesis of the new technology was the development of a product that would selectively impregnate the entire infected region of wood with a water-repellent resin system derived in large part originally from wood, to bring about restored mechanical properties similar to wood and a water-repellent characteristic, while leaving a natural porosity in the treated wood so it could "breathe" as does natural wood. This prevents the accumulation or condensation of liquid water in the wood behind old-technology filler repairs, a leading cause of failure of such repairs. "
It should be clear that one manufacturer is promoting a product for one purpose while another manufacturer is testing it for a different purpose, finding it lacking, and drawing a [false] conclusion.
As for a real water barrier, from that same site,
"In about 1975 Steve Smith discovered what caused the gelcoat blisters and laminate decomposition that was suddenly prevalent on glass-reinforced polyester (GRP) boats ("fiberglass" boats). He invented then the barrier-coat technology which is now in common use everywhere in the world for the repair of such damage and prevention of its occurrence.
That same barrier coating, when applied to the bottom of a wood boat, made possible the end result of a wood boat with a dry bilge, normally an unheard-of condition. Two additional factors were vital in achieving that result. One was the caulking of every seam and joint with a flexible, high-adhesion sealant. This absorbed small relative movements while maintaining a water tight seal. The second was the use of Clear Penetrating Epoxy Sealer, which allowed these products to adhere to the wood, whether dry or slightly damp."
If Gougeon were interested in comparing a moisture-diffusion barrier of their own with one of Smith's, or Interlux's or anyone else who makes such products , they could have done so directly, as most paint manufacturers, even Smith, make such things. To my knowledge no one has done direct comparisions of these products, although I expect the mineral-filled paints will do better than the unfilled resin coatings.
In any test of completely sealed wood samples, measuring weight gain, one may still not be measuring what is useful in the real world, as all will ultimately reach equilibrium as fully saturated specimens.
Where coatings are applied to wood hulls, it is the water-evaporation-rate off the inner surface, balanced against the water-diffusion-rate through whatever barrier coating, if anything, which may be on the outside, which determines equilibrium moisture content in the wood.
If the inner water evaporation rate is high enough, any external coating [or antifouling paint alone, if perhaps ten years build-up] will give wood with moisture below perhaps 15-20%. If the inner water-evaporation-rate is low enough, the best external water barrier will be inadequate, and the wood hull will eventually be fully waterlogged, with a moisture content far beyond the fiber-saturation-point.
thechemist
posted 12-21-2000 09:25 PM
--------------------------------------------------------------------------------
Er......guys......some epoxy does grow on trees....sort of.
Epoxy resin such as you are familiar with is a petrochemical-based product, although it did come from trees, although long dead.
The "epoxy" of epoxy resin and the "resin" part are two different parts. The epoxy part is two carbon atoms and an oxygen atom in a ring. The resin part can be any sort of petrochemical poo or biodegradeable organic goo. Put them together and what have you got? Stickety glippety gloppety goo. Only that takes too long to say which is why we made life easier for you guys and gave you the simple name of epoxy resin. It ain't technically precise, so you can't be too literal with it. It's a generality.
The amine curing agents do come from natural gas, petroleum, and ammonia.
There are a host of resins and oils derived from natural sources, such as walnuts, cashew nut shells, walnut shells or walnuts, tung berries, linseed oil, castor oil, and various oils, and gums from trees, menhadden oil from some sort of fish thing, animal oils, and probably they will even find some sort of oil in something else one day. All of these things can be modified with a few simple chemicals to add an epoxide group or an amine group to them.
When that is done, you have (either before or after curing, depending on your nomenclatural preferences) epoxy from trees. or walnuts. or fish. It can be done.
posted 08-16-2001 02:56 PM
Sounds as if there are a few business owners or employees here, as well as the idle rich.
Those of us who have to actually work for a living, or help supervise others doing the same thing, may or may not see the checkbook and accounting side of things, depending on the size of their company and who else is taking care of that area.
Setting the price of a product nowadays has less to do with the cost of raw materials than it used to.
In some states such as California, the spiraling cost of health care and insurance is driving up those overhead costs by about ten to fifteen percent a year for large businesses, and twenty to thirty percent a year for a small business. Federal environmental regulations everywhere, while sorely needed in some circumstances but not in most, further force costs up. The Plaintiff's Attorney who specializes in out-of-court settlements [meaning extortion] has further increased the costs of all manufactured goods.
The increasing cost of living due to [whatever social factors] has required companies to increase employee pay at double the "inflation" rate, just to barely keep their employees' standards of living about the same. Otherwise, the skilled ones go elsewhere and they have to hire new [cheaper] ones, and cannot see the training costs.
Costs that were once not a significant part of a business overhead have now grown to where they are the previous year's profit. Costs of complying with new government regulations such as controlling where rainwater goes or what it touches have cost small paint companies many year's profits, and increasingly onerous micromanagement by city and county agencies [for example] drove the De Soto paint company out of Berkeley and into the Mojave desert where land was cheap, even though they were a clean manufacturer and had a nice manufacturing facility. United Parcel service moved their administrative service and billing center out of Modesto a few years ago , to Texas, because it was just too expensive to exist and employ people in California, and their bottom line motivation was keeping the company profitable while avoiding more strikes due to wage demands of their Teamster drivers.
Anyone who does any sort of marketing knows the skills required to produce promotional literature or labels or maintain a web site. It used to require only a draftsman and a local printing company. Now it requires Information Specialists who speak HTML and cost double what a production worker does, and computers, printers, scanners, software, all of which costs a bunch and is obsolete two years later.
Some guy in his back yard fifty or even twenty years ago probably could have made any simple chemical product and marketed it successfully. Now, no one can do that. The cost of regulation compliance, the county fees [now up to six or seven hundred just because you MIGHT generate any hazardous waste] all these things add up to overhead costs that are actually more than the cost of raw materials and more than profits for small businesses, and are comparable to profit margins for mid-size or large businesses. I think the bottom line is that our society is changing, and the increasingly service-oriented and communications/information orientation of society is responsible. I think this change will continue in the next ten years, possibly at a greater rate.
The cost of any product reflects not only labor and material and "overhead" and profit, but all the costs of keeping a company IN EXISTENCE . Today's costs are not tomorrow's costs and if you do not anticipate tomorrows costs you will never sell today's product at a price that guarantees survival. In our society today, it has become surprisingly expensive to do just that.
But, I digress.
Surely someone has a rational question about a simple chemical matter, instead of stating with absolute certitude that someone's formula cannot possibly contain wood-derived resins becasue there is no such thing.
There ARE such things.
Triglycerides [walnut oil, tung, castor or other drying oils used in varnish] are articles of commerce, common as cat hair, and easily modified from their olefin --chemistry to either epoxy or amine by a chemical manufacturing company. For example, water can be added to any double--bond. This gives a secondary alcohol for any unsaturated triglyceride. Epichlorohydrin can be reacted with such an alcohol to give an glycidyl ether, which is an epoxide. Ammonia can be added to such a double--bond to give primary amines, or to any acid to give amides.
The same can be done with any wood-derived resin which has any hydroxyl or unsaturation. They can all be modified in this manner. This sort of chemistry has been in practice on an industrial scale for over a hundred years.
Anyone with a chemical background can see this. It is obvious from the foregoing chemical discussion. Such things exist, and can be EASILY made.
Cardolite [a chemical manufacturer], for instance, makes a variety of phenalkamines and epoxides derived from cashew nuts or the oils of their shells.
I cannot tell you what any epoxy company is using in their products unless they publish their formula, but claims of wood-derived resins are assuredly possible and easily feasable.
As for what ingredients are listed on a MSDS, the OSHA hazard communications standard requires the consumer be informed of the hazards. If a relatively non-hazardous material is dissolved in a hazardous material, the manufacturer need not disclose any but the hazardous ones. If a material is hazardous at a high concentration but present in sufficient dilution, its hazard may disappear compared to other ingredients.
That, in a nutshell, is why you will often not find all of a product's ingredients on a MSDS in the U. S. A. In Europe, different rules apply, but there are many similarities to the foregoing.
thechemist
posted 08-24-2001 01:23 PM
A minor clarification....CPES as referred to by the Practical Sailor [which they have occasionally called CEPS] is actually two different products used together as a "system", namely the single product Clear Penetrating Epoxy Sealer, which Smith refers to as CPES, and that followed by a fairly thick topcoat of their clear polyurethane topcoat.
Maybe 6 years ago Practical Sailor did a test of Smith's CPES epoxy product with a varnish applied on top. Perhaps someone has a back issue and can see what they said about it...I think it was pretty good.
The application of varnish on top is what Scott is talking about, I believe.
The application of the polyurethane on top is what ROWE is talking about, I believe.
That said, the issue of adhesion is what I wish to address here. There are different adhesion mechanisms, depending on what molecular groups are present in either the topcoat or the varnish.
An adhesion-promoting primer may promote adhesion better if the topcoat is applied before that primer has fully cured. The manufacturer of the primer is usually rather specific about this "window of opportunity". The reason the "window of opportunity" exists is that there is a region between "wet-liquid" and "fully cured with all amine blush fully developed and all benzyl alcohol and other plasticizers fully exuded onto the surface", where the surface of the primer not only has no interfering contaminants but actually has various molecular groups present, not yet reacted, and those are capable of grabbing something applied on top.
Those molecular groups may or may not go away, getting used up in the primer curing reaction.
That is one mechanism of adhesion.
Some [epoxy or other] primers leave a film of chemical fishhooks [or chemical Velcro, if you wish] even after they cure, and those are capable of grabbing certain other kinds of topcoats, depending on the chemical makeup of the topcoat.
That is another adhesion mechanism.
Some topcoats may be capable of aligning their reactive chemical groups with not only each other, for the topcoat curing mechanism, but also with the chemical groups that are left over after the underlying primer has cured, assuming that "primer" exudes no interfering surface contamination.
That is another adhesion mechanism.
Some manufacturers of either primer products or topcoat prodcuts are more-or-less clear on what is "compatible" with what. Usually the compatibility issue revolves around what one guy thinks another guy is using in their stuff, if you have different manufacturers.
Varnishes made from oilseed resins ["traditional" varnish, perhaps with various cooked resins (alkyd) or completely synthetic(e., g., polyurethane) resins added] chemically cure by a reaction of double-bonds with the oxygen in the air, catalyzed by a metalllic soap, a "dryer". So do oil-base enamel paints. I have discussed this in the past, in a few threads which can be found with a search, for those who wish to know more. Searching the Text, in Building/Repair, for words such as double, bond, drier, [or dryer...] should turn them up.
Some epoxy products are capable of reacting with the "double-bond" molecular structure, in various ways. I cannot tell you what manufacturer has what exact chemicals in their formulation. Some of these resins are essentially non-hazardous, compared to other resins or solvents that may be in a formulation, and thus would not even be listed on the MSDS, thus offering no clue as to what is in their stuff. The fact that only solvents are listed on a MSDS tells you nothing except that a particular manufacturer may be a bit more than average paranoid, notwithstanding the recent flap and contradictory posts about this in other threads.
I know what sorts of chemicals are in the Industry, as articles of commerce, and there is pretty much any kind of reactive chemical group you might want on most kinds of resins. Thus, most things can react with most other things, based on the artistry of the manufacturer.
Evaluation of any product should be based on what the manufacturer says [pretty reliable for military-industrial products] or word-of-mouth for consumer/commercial-grade [usually more reliable, since consumer product manufacturers and distributors all-too-often employ people in their Marketing Departments who are not interested in the meanings of words and keep their dictionaries on a shelf in the closet, beside the jar containing their conscience].
The bottom line is, try following the manufacturer's instructions, but with a healthy dose of suspicion. Remember , Joe may say Bill's stuff will stick just fine to Joe's stuff, but Joe did not make Bill's stuff, does not know for sure what is in it, and Bill may change his formula once in a while and not tell anyone.