Ken: Hi, I'm Ken Trimber welcome to the KTA
university podcast.
Our podcasts are designed to tackle relevant
topics in fabrication, construction, cleaning
and painting in both industrial and commercial
fields.
Today's topic is inorganic versus organic
zinc-rich primers.
My guests today are both from KTA, Jim Machen
and Bill Corbett.
Jim I understand you'll be talking about organic
zinc.
Jim: Yes, I will.
Ken: And Bill inorganic zinc.
Bill: Yes.
Ken: Well let's get started.
What makes it-- what is so special about primers
that contain zinc?
Jim: Well similar to hot-dip galvanizing and
zinc metalizing, organic and inorganic zinc
primers provide a zinc rich coating that provides
galvanic protection or sacrificial protection.
It sacrifices itself to protect the steel
and that's the reason why it's very important
in the corrosion protection process.
Ken: Okay so the addition the barrier protection
it gives you this galvanic type protection.
Jim: Correct.
Ken: What makes one type organic and the other
type inorganic; what's the difference between
those two?
Bill: That's an interesting question.
I get that question a lot whenever I'm teaching
classes on coatings.
And the zinc is a component to both the inorganic
and the organic zinc-rich primers.
And the zinc is actually an inorganic material
because it doesn't contain carbon.
So it's not the zinc that determines whether
it's inorganic or organic, it's rather the
vehicle or the resin system.
Inorganic zinc have an inorganic resin system
and the organic zinc have an organic resin
system or vehicle system in them.
SSPC actually has a paint specification it's
called paint 20.
And it describes several different types of
zinc rich primers but they're categorized
as type 1, inorganic or type 2 organic.
And the inorganic zinc which primers are further
categorized as either water-based post cure,
water-based self cure or the ethyl silicate
type self cure.
And those are the most common that are used
in shops and some in the field.
The organic types contain an organic binder
and typically that's the epoxy or your thing,
something like that.
Those resin systems are combined with the
zinc and occasionally years ago they used
vinyl in with the zinc but because of EOC
regulations they have essentially gone by
the wayside.
Jim: We see in the industry right now the
probably the most common use of an organic
zinc primer is the zinc dispersed in epoxy,
two-part epoxy.
Although there is quite a bit of use of moisture
urethanes and to a lesser degree sometimes
zinc are dispersed in - type primers and those
are typically used for touch-up of galvanized
systems.
Ken: Alright so the main difference, the zinc
is the same as what you're saying the difference
is the binder, the glue that holds the zinc
together, is organic or inorganic.
Since zinc gives you this sacrificial or galvanic
protection, which of those two products is
better; organic zinc or inorganic in terms
of that type of protection?
Bill: Well you know that's also an interesting
question.
I'm gonna go back to SSPC paint 20 for just
a minute and talk about levels of zinc and
then I'll talk about why one might be better
than the other.
SSPC paint 20 lists three different levels
of zinc that may be in either an inorganic
or inorganic zinc coating.
You can formulate the different levels of
zinc into either.
But level one is anything greater than 85%
in zinc in the dry film.
And you have level two which is between 77
and 85%.
And then level three is between 65 and 77%.
So you can formulate any of those three levels
in either types and they're all considered
zinc rich but obviously the higher the zinc
loading the better sacrificial protection
that you can have that Jim was talking about.
But really what it comes down to is perhaps
not as much the concentration of zinc but
it's the zinc to zinc contact and it's the
zinc to metal contact.
So with the inorganic zinc because you don't
have as much resin or binder insulating the
zinc particles and insulating the zinc from
the metal itself; you typically will have
theoretically better sacrificial protection
because of that electrical contact with the
steel and with the particles zinc.
Jim: In theory, I agree that inorganic zinc
probably give better galvanic protection than
the organics.
The reason being that you touched on is the
the zinc rich particles are primarily dispersed
in epoxy or moisture cured urethane binders
which have a tendency to envelop the particles
more and prevent that into-- that more intimate
metal to metal contact you need.
That being said they still give great galvanic
protection.
The biggest thing about organic zinc rich
primers is that they have some application
efficiencies over inorganic zinc primers.
They're more user-friendly, they're a little
bit more tolerant of application methods in
limited access areas or in difficult areas
like we commonly run across on bridges.
We can actually brush limited areas with organic
zinc rich primers and that's just to the nature
of the binders that they're dispersed in.
When you disperse a zinc rich primer and an
epoxy binder or a more secured urethane binder,
they take on the application characteristics
of that binder and they don't dry quite as
quickly as do in organics.
So we have the ability to have a little bit
more open window for applying the materials.
Ken: So I think what I'm hearing is you agree
Jim that the inorganic may give you better
protection theoretically.
[yes] I think you're saying the application
challenges of inorganic versus organic might
negate some of that benefit.
[yes] Well Bill in terms of application challenges
of inorganic, you agree that it's tougher
than organic or--?
Bill: Yes, inorganic zinc are more challenging
to apply without question.
Not only they are more challenging to apply
but they're sensitive to-- they're more sensitive
to thickness, they are more sensitive to curing
conditions, they are more challenging to finish
coat for a variety of reasons.
but I think all those challenges if you will,
if they're recognized can be overcome.
We can do applicator training and make sure
that the applicators know what they're dealing
with, know the conditions under which the
product needs to be applied and know its limitations
or some of its challenges.
An example of that is you know for years the
Army Corps of Engineers applied vinyl coatings
to their Tainter gates.
And if you know anything about vinyl coatings,
they are equally challenging to apply; they
dry spray, they cobweb and to overcome some
of those challenges what the Army Corps of
Engineers did is they qualify the applicators
rather than going to a different coding system
arguably one that might provide lesser protection
because of the application challenges.
And I draw that analogy to to inorganic zinc
versus organic zinc because you may sacrifice
some protection just because of application
challenges.
And if we recognize those we can overcome
them.
Ken: Given that, I understand your comments
on the challenges of applying the coatings;
I'm gonna ask you two questions.
The first one is if I apply all three coats,
let's say it's zinc primer, epoxy, - urethane
finish.
I'm gonna play all three coats in the shop,
I'd like to know which of the two primers
you folks will recommend.
Same question after that, if I applied all
three in the field with that change your opinion,
would you suggest a different primer?
Let's go with the shop, three coats in the
shop Jim organic zinc, what do you say?
Jim: Organic zinc in the shop is becoming
very popular right now, primarily due to the
fact that when we have the inorganic zinc
supplied in the shop we have to constantly
monitor the relative humidities.
Because the ethyl silicate binders used in
the organic zinc primers react with - cure.
If we have insufficient moisture, we have
prolonged cure times.
With the organic zinc, because the epoxy zinc
rich coatings are chemically cured they have
a tendency to react faster because of their
more temperature dependent.
The heat that we use in the shop sometimes
isn't there.
We don't have the heating characteristics
but they do have accelerators and faster curing
organic zinc nowadays.
And because because they have accelerators
and they have faster Recoat windows with organic
zinc, they become more popular in the shop.
Ken: For production reasons it sounds like
for production reasons you can recoat it rather
quickly, get the steel out the door.
Jim: And another issue with the organic zinc
in the shop is the inorganic zinc primers
when they're applied too heavily they have
a tendency to mud crack.
Mud cracking but can become a problem for
application of the coatings because we have
to remove the mud cracking if we have extra
extra thick coatings.
Organic zinc are more forgiving in those terms,
they don't have the mud cracking problems
like in organics have.
Therefore if we have a more complex configuration
that we're applying the coatings to we can
have more forgiving properties of the organic
zinc, we don't have near as much mud cracking.
Ken: Alright, Bill?
Bill: And I'm actually a proponent of using
or or even going with tradition if you will
and continuing to use the inorganic zinc for
shop applications.
Because the environment isn't necessarily
controlled that it's controllable.
And what I mean by that is some of the difficulties
or challenges that I was talking about earlier
and Jim talked about as well which included
you know thickness.
Again, training can handle that, applicator
training and certification can handle that.
Overspray, dry spray again those are application
issues that can be overcome.
Outgassing whenever a mid coat is applied
in the shop in the case of total shop painting;
that can be taken care of by mist coating,
applying a mist coat prior to a full coat
over the inorganic zinc.
The lack of relative humidity or humidity
in the shop; that can be overcome by misting
the inorganic zinc down with water after a
couple hours of set time or cure time to accelerate
that or promote that curing process if the
humidity in the shop is low particularly in
the winter months whenever the heat is a little
bit higher.
So all of those can be overcome and you do
have again the greater zinc to zinc contact,
the greater zinc to steel contact.
And in fact inorganic inks are routinely used
today; the Pennsylvania Department of Transportation
for example continues to use inorganic zinc
primers as their shop primer for new steel.
Another argument that you'll occasionally
hear is that with the organic zinc, like an
epoxy zinc or - urethane zinc you can actually
lower the degree of surface cleanliness that is
required.
Inorganic zinc typically they need a near
white blast where the organic zinc you may
be able to get away with the commercial blast.
But for a new steel what we have to remember
is both a near white in the commercial blast
require the removal 100% of the mill scale.
The only difference between the two is the
percentage of staining that's allowed to remain.
So for a new steel, by the time we remove
100% of the mill scale, we’re essentially
going to be at a near white blast.
So where there's a perceived economical benefit
by lowering the degree of service cleanliness,
it's probably not really there.
Ken: Alright so it sounds like you're both
agreeing inorganic is a little more difficult
to apply than organic.
Bill you feel that those challenges can be
overcome and I know that as you both mentioned
the inorganic requires moisture to cure which
could potentially affect the ability to shop
to put a new coat on and a second coat the
next day or maybe 30-40 hours later depending
on the humidity in the air.
But Bill you're saying you can overcome that
by misting water on it, on the zinc to enhance
that cure if you're in the dry climate?
Bill: Certainly and I would add on to that,
that there are even methods now that can be
used, ASTM standard methods for verifying
that you do have a good cure on the zinc which
is really really important.
It's a methyl ethyl ketone solvent rub test.
We don't want to assume that because we've
waited the allotted amount of time or that
we've missed it a zinc down with water that
we have achieved that cure.
So we're going to verify that using a standard
solvent rub test.
Ken: And that test is for inorganic zinc--?
Bill: Inorganics zinc only, yes.
Ken: Okay, alright skimming the application
challenges you've talked about especially
for the inorganic zinc and Bill I know you
say that can be overcome.
Let's assume now that all three coats are
being applied in the field.
So there may be some blend conditions you
know perhaps much more complex shape.
So you have - old bridge, it's got lacing
bars and things compared to the new steel
in the shop, a little more complex configuration.
I'd like to see if that changes your opinions
as to which primer you would apply.
Let's start with you Jim.
Jim: Well by far the most common primer used
in the field is the organic zinc rich primer.
Typically because of the-- for the reasons
you mentioned, when we get on bridges we have
many complex configurations.
We have gussick connections with multiple
verticals and diagonals entering into the
connection.
We have inside of box carters, we have lattice
box beams, we have rivets, we have nuts, we
have bolts; all those things present application
problems.
Because the organic zinc are much more user-friendly
we are able to apply them easier to these
complex configurations.
Whereas with inorganic zinc we're very much
limited because they dry so fast.
We're limited to the application to spray
if and when you do brush it can become problematic.
If you can brush limited area is with an organic
zinc but when you start getting into larger
areas and larger tight configurations, organic
zinc by far have the advantage in the field.
Bill: Yeah and I've you know to answer your
question, it does change my mind.
I would probably yield to using organic zinc
in the field.
Even if the work is done inside containment,
you still don't have very good control over
conditions it's very difficult to to apply
them as Jim indicated.
If you have a simple structure it can be done
but if there's any complexity at all it's
gonna be very very difficult.
You're gonna end up with a lot of mud cracking
issues so I would probably yield to using
more organic zinc in the field.
Jim: And I have seen inorganics used in the
field but like Bill said on those cases, we
had very deep girders on the bridges with
a lot of surface area, not a lot of complex
configurations.
And there are some bridges that are designed
that way but typically what we do not see
inorganics used very much in a field.
Ken: Well let me ask this, now let's go back
to the shop for a second.
Let's say I'm only applying the primer in
the shop, the finish, the intermediate finish
in the field; which prior would you think
is better in that situation?
Bill I’m gonna start with you this.
Bill: Yeah in that case I like to see an organic
zinc used if it's a shop prime only, they're
very durable, you don't have a recode interval
with those.
So for example if the shop steel is primed
and it gets mobilized to the field and it's
not field top coated for several months, it's
all you got to do is pretty much - pressure
wash it to get the zinc salts off it.
It's not gonna be degraded by solar radiation
from the sun and again you're gonna get probably
better protection in the long term.
Jim: Well it depends on the long-term we're
talking about here.
I agree in theory that inorganic zinc are
probably better if you're going to shop prime
they don't leave it sit in the field for a
long time.
However we do see a lot of organic zinc now
that have extended recoat windows.
Ken: Like what’s that mean by extended?
Jim: Extended recoat windows for example up
to a year.
Now, what happens is typically the projects
where were having the steel come out shopp
primed; it's usually erected and the intermediate
and finish coats are usually started within
a year.
On larger projects, I would agree that there's
an advantage to use the inorganic zinc because
of their unlimited recoat windows.
But organic zinc nowadays because they're
highly loaded with zinc and they have a rough
surface texture for physical surface texture
themselves, they do have extended recoat windows.
And we just - see we don't see the problems
that we used to see, With regards to degradation
by solar radiation or a degradation by sunlight;
epoxy binders inherently have the tendency
to chalk when they're exposed to sunlight.
So when you have an organic zinc primer that's
an epoxy binder with the zinc rich in it,
you're going to have a tendency to have some
chalking.
But no matter what you do in organic organic
zinc in the field, if it's a year later they're
typically going to be pressure washed before
they're painted anyhow.
And pressure washing typically takes care
of all those problems of chalking or surface
dirt or even if the zinc salts form on the
inorganic zinc primer.
Ken: Alright so for the epoxy zinc, let's
say that in the field I can in fact prepare
it by pressure washing.
I don't have to go abrade it or anything like
that prior to putting the intermediate on?
Jim: With most of the formulations we have
now, if they have extended recoat versions
yes, we don't have to go abrading the existing
coatings recoat them after an extended time
period.
Ken: Okay, good.
Now Bill you mentioned zinc salts, I know
that the inorganic zinc will get covered with
that the longer it's exposed.
Does every bit of it have to be pressure washer
can I still have some in the porosity of the
zinc so to speak?
Bill: Yeah, I think it's going to be very
difficult to remove 100% of the zinc oxides
and in fact some of that zinc oxides will
help fill those pores and potentially reduce
some of the outgassing issues related to putting
the second coat on.
So removal of the majority of it would be
helpful but a 100% removal wasn’t necessary.
Ken: And let me go to top flanges; many times
for a bridge steel you're gonna put the zinc
on the top flange only and they want to put
shear studs, attach shear studs.
Which primer would you suggest in that case?
Jim?
Jim: Well we see use of both but I believe
if you're going to do shear studs and a lot
of it has to do with the sequencing of the
work.
If they're just exposing the top flanges and
their blast cleaning them and they're going
to shoot shear studs on the top flange with
only those areas exposed only; I would probably
prefer to use the inorganic zinc to prime
the top of this flanges they're going to shoot
shear studs.
Some - of the organic zinc if you keep the
thicknesses at the proper level you can shoot
the shear stud right through the zinc.
But the problem is when we get an application
in the field, we have a tendency to apply
coatings a little bit thicker, inorganic zinc
thicker.
So we have to grind to put the shoot to shear
stud, so we have to grind a bare metal, so
we shoot this your stud into bare metal.
But if the application thickness of the inorganic
zinc is controlled properly, we can shoot
the stud right through the inorganic zinc.
Ken: But typically you would say grinding
is going to be required because--
Jim: Typically grinding will be required because
of the thicknesses, right.
Ken: Well you sort of made the case for inorganic.
Bill, anything to add?
Bill: No, I agree.
I think if the inorganic zinc can be applied
very thinly to the top, top of the top flange
that you could shoot the shear studs right
through there.
But ultimately I like to see the inorganic
zinc ground away to get a little bit better
application of those studs.
Ken: And so Jim we could use organic as long
as we grind them correct?
Jim: We could use organic and in fact we do
use a lot of organic.
But we have to grind it away to make the shear
stud.
Ken: So it's probably a good rule to just
plan on grinding to be safe.
So what about on top coating?
Let's say that I'm only putting one coat on
I'm not worried about aesthetics, let's take
that away for a moment.
Which would you do as a single coat system
given the proper pH and things like that;
I'm not worried about chemical exposure, inorganic
or organic zinc for outdoor exposure?
Bill: Well I guess you know I can make an
argument for using inorganic zinc.
They can be used outdoors as long as you're
not concerned about aesthetics.
Because the zinc is going to begin to oxidize
very quickly but it's not going to oxidize
uniformly across the surface.
You're going to have a streaky appearance.
But again that oxidation will help fill some
of the pores and you know it's just the nature
of the type of coating it is.
Now, one of the things that's important to
remember and you did address you know chemical
exposure and that kind of taking that off
the table.
But we have to remember that zinc is an amphoteric
material and it's very sensitive to low or
high pH.
So if you have either of those conditions
it - be very careful about using on top coated
zinc as the total system.
But if it's a neutral pH environment, it would
work fine.
Ken: Give me the range, you say low to high
- what to what.
Jim: I would say as low as 6 and probably
as high as 8 or 9.
But outside of that range I'd be uncomfortable.
Ken: Jim any thoughts on--?
Jim: Well organic zinc don't have the reactivity
problems with pH like inorganic zinc do.
Inorganic zinc are more reactive with the
environment when the pH varies and even if
the temperature varies a little bit.
Organic zinc because - dispersed in organic
zinc rich binders, they have the tendency
to take on the characteristics of those binders
and they'll actually perform better in a single
coat exposure environment.
The problem with epoxies again is they have
a tendency to chalk and they might have a
tendency to discolor with exterior exposure
alone.
Given the fact that we're going to have a
zinc rich coating and exterior exposure, I
don't think that organic zinc or inorganic
things really make a difference.
They're going they're both going to have their
aesthetic problems after they're exposed for
a while.
Ken: Okay good.
What about repairs, are they easy to repair,
the primer, is it easy to repair, is a challenging
and how do you repair them, damage--?
Bill: I mean for for inorganic zinc you can
repair them with an inorganic zinc.
But the initial application better be pretty
green.
In other words that you know it cannot be
fully cured and then you can do some touch-up
with inorganic zinc.
But if it has gone through a cure, I would
highly recommend going with an organic zinc
for a repair of the materials.
In either case, you know the inorganic zinc
whether it's you know a new application or
repair application they’re spray materials
very very small areas can be touched up with
a brush and pretty much you're looking at
a spray application.
Jim: Well, I prefer the organic zinc for field
touch-up obviously.
they can be cleaned and we can roughen the
area around the touch-up area.
One nice thing is they brush apply better,
if we're gonna do feel touch-up we within
with organic zinc they apply, brush apply
much easier.
A lot of times in the field because of the
brush ability characteristics and the recoating
characteristics of inorganic things, we will
touch up inorganic zinc in the field with
organic zinc.
We get the same essentially equivalent corrosion
protection but we have the ability because
of their applicator friendliness to apply
them.
Ken: Okay so you both agree touch up inorganic
with organic, inorganic is easy to touch up
with organic.
Alright, final question.
There's a lot of talk about Class B slip resistance
for slip critical joints; do these primers
both achieved Class B which is the highest
level?
Jim we start with you.
Jim: Well virtually all the organics that
we see in for example on the NIP code proved
lift of products and a lot of the DOT lists;
they virtually all have an A slip.
There are products and a lot more products
now the organic zinc that do have B slips.
So we have both A and B slips with organic
zinc rich coatings.
Ken: Okay but not all the organic is typically
is good to a B level?
Jim: Not? all organics are typically to a
B level but with your major manufacturers,
due to the need for slip creep resistance
it's driven them to test some of their organics.
And there are organics out there that have
a Class B slip.
Bill: And on the inorganic side, you know
for me to say that 100% of all inorganic zinc
will pass Class B slip coefficient; I don't
have any evidence of that.
But I'll say the majority of inorganic zinc-rich
primers with you know level a 1, 2 or 3 zinc
loading will likely be able to pass Class
B slip coefficient with little difficulty.
Ken: Good, any final questions before we wrap
this up or comments?
Jim: I'm a big organic zinc guy.
The market has driven the organic things to
the point where they're usable in the shop
now.
They don't have the problems with curing that
they used to have, long cure times which may
flow through the shop difficult.
So they flow through the shop better, they
may not provide the same level of galvanic
protection as do inorganic zinc.
But in light of the application characteristics,
I think and the ability to apply them better
once we get out into the field I think that
may be a moot point.
The galvanic protection is still excellent
and the applicator user friendliness of the
product just makes it much more easier to
use.
Bill: Yeah, I guess that's the question is
you know if organic zinc rich primers, the
advantages or their advantages outweigh you
know their limitations; you would think that
we would see a strong trend towards more organic
zinc being used for both shop and field application.
But we still see a lot of inorganic zinc use.
Now that might be because people are reluctant
to change, they have confidence and the performance
of inorganic zinc rich primers; there can
be a variety of reasons.
But both products are still readily available
manufactured by as Jim said you know a lot
of the major manufacturers make of both.
So I think that an argument can be made to
use you know either one depending on owner
preference and ultimately what their goal
is.
If you are painting new steel, the intent
is for that steel to last a long time; you
might want to invest in perhaps a little bit
better galvanic protection that the inorganic
zinc would give you versus the organic zinc.
Jim: With regards to using inorganics or - organics,
we're seeing an increased use of organics
in the field and in the shop for all the reason
we mentioned earlier.
When we talk about the advantages of galvanic
protection of inorganic zinc over organics;
you have to remember that one thing in the
field, that's assuming that we're always going
to have the zinc exposed and it's going to
be reactive.
In the field we're taking the organic zinc
and the inorganic zinc and we're coating over
with a coat of epoxy intermediate and a coat
of a urethane finish which protects the organic
zinc and the inorganic zinc from being exposed
to the environment.
So once we do that and we're protecting the
organic or inorganic zinc rich primer, I think
that the differences between long term corrosion
protection probably do not outweigh the application
characteristics of the organics zinc.
Ken: Jim you just brought up a good point
I want to ask the both of you.
Let's talk about that, you've got all coats
on in the field I agree with what you said.
But now I have a breach in the coating and
a scratch in it; which one do you think is
going to resist undercutting corrosion better,
inorganic or organic?
And I know - coat has different criteria for
undercutting for an organic versus organic.
Bill what do you think, which one do you think
is gonna resist it better?
Jim: Well of course I'm gonna be a proponent
of inorganic zinc in that case because when
you do get a breach in the coating system
you've got exposed metal.
So because you have more zinc, it's probably
going to have a little bit better throwing
power to protect that initially unprotected
area.
Ken: More zinc or more zinc content?
Bill: More zinc to zinc contact and more zinc
to metal contact.
So it'll have the ability to protect that
area.
Nnd it's interesting you did bring up the
fact that - coat does have a tighter undercutting
- undercutting criteria for inorganic zinc
versus organic zinc because I think they recognize
that the inorganic zinc should be capable
of protecting better in that case.
Ken: Alright, well thank you.
I guess to sum it up, it appears there's no
real clear-cut answer one way or the other.
Both products have their advantages and disadvantages
and we've heard that.
It sounds like the inorganic might in theory
give you a better galvanic protection.
But with the application to difficulties you
may not see that in practice.
It sounds like for total shop painting, we're
seeing both systems still being used but for
the field it seems as if organic zinc may
be the better choice because of tough configurations
and more user friendliness.
For a shop primer only, sounds like you can
go with either but it sounds like inorganic
may be fairly common in that regard with the
finished coats in the field.
So it depends on a case-by-case, looks like
either product is gonna be very suitable for
your needs.
Just recognize the advantages of disadvantages
and challenges in using them.
So that's the end of this podcast, thank you
for watching us and please join us again in
the future for our next one.
Thank you.
