Description
Learn about the different types of cracks that can occur in concrete, why they happen, and how to prevent them.
For more information about cracking, see this article.
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Transcript
Jeff Girard (00:02):
Here we go.
Caleb Lawson (00:03):
Morning everybody. Welcome to the Maker in the Mix podcast. It is April 26th, Wednesday, 8:00 AM So today we kind of wanted to address the topic of cracking in general. I think we’re going to zoom in on one or two different types of cracking that we’ve had experience with or whatever and why those things happened. So I wanted to just quickly list off the types of cracking and then what we’re going to zoom in on. So shrinkage, settling, premature drying, thermal heaving, which would be a root or something coming up from underneath. And flexural cracking. So the ones that kind of matter to us are going to certainly be shrinkage, premature drying, thermal and flexural. So I think from a description, they’re pretty self scripting descriptors. So shrinkage, cracking, obviously it’s shrinking. And for us, that tends to appear in, if we’re doing a non-structural face coat, shrinkage, cracking would appear for us in the face coat cause it’s not reinforced often.
Caleb Lawson (01:20):
Premature drying can happen for a number of reasons. Failing to cover your concrete, I think a lack of curing polymer could potentially be a possibility. There’s a number of reasons why premature drying could happen. Thermal cracking heat, A lot of us are using rapid set. I’ve had thermal cracking from letting it get too hot, so not using it tarter and kind of pulling that heat curve down. And then certainly flexural cracking, which we’ve all probably dealt with in some form or fashion. So that’s a broad brief 30,000 foot overview of what we’re going to be talking about today. I do think we’ll probably end up zooming in on map cracking, which is a function of premature drying for the most part. So yeah, Jeff, I’ll let you take it from there, but that’s kind of the introduction. Welcome to everybody who is already on and anybody who will join and watch later. So
Jeff Girard (02:18):
Fantastic. So as Caleb mentioned, there’s a bunch of different
Caleb Lawson (02:23):
Background
Jeff Girard (02:24):
Noise and when you look at your concrete, when we’re making something for a customer, whether it’s a piece of furniture or a countertop or wall panel or whatever, we can’t tolerate cracks. And it’s not that we can’t tolerate them, our customers generally don’t tolerate cracks. They see anything that looks like a crack no matter what it is as a flaw. And the hard reality that we face is we’ve set the bar for the aesthetics of our product. So high compared to other kinds of concrete in the world, there’s no room in general. There are specific examples where you want cracks in the concrete because that’s part of the aesthetic design that you’ve created. But by and large, our customers will not tolerate a crack in our concrete, in their concrete. It’s not our concrete, it’s their concrete. And there’s really no way to fix that.
Jeff Girard (03:29):
There are certain special circumstances if you really clever or have spent a lot of time trying to figure that out, how to make a crack disappear. But the general state of things is if you got a crack, the only way to fix it is to redo it. And that’s a harsh reality. So the moral of this whole topic is how to cracks happen and really how to prevent them because there’s no real fix. You well rub a cement paste into a crack and hope that it goes away. It’s not like a TV DIY fix where you see the quick five second little thing because that crack is still there. You’ve just filled it in. It’s not glue
Caleb Lawson (04:16):
Well. And one thing that I think some of us could embrace is there can be beauty in imperfection. So I would say too that while we as a general rule can’t tolerate cracks, there are aesthetic ways to, the Japanese art of Kintsugi comes to mind, mending things with gold or a gold resin or whatever. So I do think that there is room in the artistic world for doing something like that intentionally. What we’re really going to be zeroing in on is unintentional cracking. And
Jeff Girard (04:57):
That’s a good point because I know some of our colleagues, Baylor, part of their aesthetic is actually intentionally creating a cracked face coat.
Caleb Lawson (05:10):
Yeah. I mean I did it in my own kitchen on purpose, different color, and it’s awesome.
Jeff Girard (05:14):
Just like a crackle glaze on ceramic, that’s a specific look. Yeah. We’re talking about things that are unexpected. Absolutely. So we’re going to ultimately head to and focus in on map cracking or some people call it crazing. But I want to step through some of the other cracks types first to get ’em out of the way. So we generally don’t worry about things like frost heave cracking our sidewalks cause we’re not making sidewalk. But if you do a quick internet search on map cracking or what causes crazy or things like that, you’ll, you’ll generate a bunch of different articles written by a lot of different organizations. ACI, the American Concrete Institute, Concrete Contractor Magazine, a bunch of other places that summarize things. And they focus largely and logically on what I consider regular concrete sidewalks, floor slabs, walls, that sort of thing, construction grade concrete.
Jeff Girard (06:19):
And what we do as artisans, as makers, as producers, tends to be a little bit more esoteric, a little bit more refined. And our mix designs tend to be a little more complex and oftentimes quite different from conventional concrete. So some of the things you’re going to read about in an article about, well, you have to worry about bleed water and this and that, by and large, we don’t deal with that because our concrete mixes don’t have that kind of water. We don’t deal with that. And it’s just like we don’t have to worry about frost heat cracking or root growing under our countertop. I mean, it’s possible. I’ve had a house break my concrete, and I think we have an article on the CCI website about that where I did a kitchen in a house where they added onto the kitchen and the kitchen was added onto land that was filled in. They had extended the backyard and built it up, but they didn’t do a great job at compacting things, which is really important. And the house settled. And in the settling of the house, you could see the crack in the drywall and then the crack through the countertop where the house broke the countertop. It wasn’t fault of the countertop. My concrete’s job is not to hold your house together. So that’s a fundamental flaw. That’s a clear external source. So that’s a very different kind of crack. Now again, one of your,
Caleb Lawson (07:49):
Well, and I want to interject and define, a lot of us talk about hairline cracking, defining that. I think something you’ve always told me, Jeff, is that a hairline crack can be defined as if you cannot stick a piece of paper into it.
Jeff Girard (08:04):
One of those
Caleb Lawson (08:05):
Crack that and smaller. Now aesthetically for us, unless that’s intentional, even something like that is unacceptable. Absolutely. I mean, you can sometimes get away with map cracking because sometimes the sealer won’t show it, but sometimes it will. And so that’s why I think know that I have gone through various iterations of my business where I’ve used different mixed designs or I’ve used different ingredients or I’ve used different curing processes or whatever the case may be. And I’ve had experiences with map cracking over the years. I’m not having those issues right now. I think I’m using good practices and that’s great. But I think it’s good to draw on the experiences that we’ve had. And so that’s definitely, I’ve had experiences where certain color, let’s say it’s in a dark color, well unfortunately they’re going to get darker with sealer. And so you’re going to see that crazing with white, you’re less likely to see it. And so maybe have been for the last six months doing largely white concrete and you don’t see ’em, but maybe you just did a gray or a black piece and you’re like, oh crap, now I see it. And maybe it’s been happening for six months. And so I think it’s worth really paying attention to, if you notice it today or tomorrow or in a month, look at what you’ve been doing and see if anything’s changed over the, well, we
Jeff Girard (09:34):
Can we’ll dive more into that when we actually get to map cracking. But talking about hairline cracks and how you define it, that’s largely up to you to define it. There isn’t an industry standard as far as I’m concerned about what, again, construction concrete
Caleb Lawson (09:53):
Is assuming it’s not structural cause that’s as well.
Jeff Girard (09:58):
And usually hairline cracks occur for a variety of different reasons. And again, it’s creating that definition. And this is going to, excuse me, topic for a future podcast is setting expectations
Caleb Lawson (10:16):
Sure are
Jeff Girard (10:17):
Incredibly important. So this is one of those subsets of setting expectations is what can you expect from your concrete as a customer? What can you expect to happen when it’s delivered, when you live with it? And over time, because concrete is not a static material that never changes, it undergoes changes internally and it undergoes external changes because of its environment. And we can get into that a little bit later. But again, getting back to the basics of cracking all cracks, no matter what they are, electro cracks, hairline cracks, heaving cracks, whatever our even plastic shrinkage cracks are tension failures. This is where the concrete itself is being pulled apart and it can’t hold itself together. So
Caleb Lawson (11:18):
Because ultimately with or without reinforcement, concrete is still a hard and brittle material. So even if you’ve got, I mean like GFRC has wildly more flexural strength than conventional concrete. But still, if you bend it, it will crack.
Jeff Girard (11:34):
Correct. So
Caleb Lawson (11:37):
Stress it, I should
Jeff Girard (11:38):
Say you stress it. Yeah. When concrete, every material in the universe has some stretchiness to it. Rubber is very, very stretchy carbon like carbon fiber is very, very stiff, very non-st stretchy. But it’s still stretchy too, a little bit. And that’s called modulus. Every material has a degree of stretchiness, even concrete. It’s very, very small. And when you exceed that, when you stretch it too much, it fails. It fails. Brittle, as you just mentioned. And we all know that. And the job of reinforcement, whether it’s fibers or rebar, is not,
Caleb Lawson (12:22):
Is to take the load off the concrete
Jeff Girard (12:24):
It. It’s to take the load off the concrete, but even more so, it’s st it the, you’re putting something stiffer and not and less stretchy in the concrete and enough of it to stop the concrete from stretching to the point where it won’t crack. It’s still within, it’s called elastic limit. It’s still within its stretchy range, which is tiny, tiny, tiny, very small amount. So if you exceed that, you get a crack. And now all the different kinds of concretes that happen, all the different cracks that happen happen for different reasons. Of course we’re leaning toward map cracking, which is all surficial. And it all happens at a certain time and generally for certain reasons. But there are other manifestations of that. Let’s talk about flexural, crack bending, cracking. You’ve got a big long slab. What’s the big piece, biggest piece you’ve made recently?
Caleb Lawson (13:21):
Recently I did a 21 foot hearth about a year.
Jeff Girard (13:25):
So a long 21 foot hearth, very easy to bend. You pick it up at the wrong end in it’s wobbly, it’s floppy, right? You bend it enough. When you bend something, you’re stretching it. When you’re stretching it, you’re creating a lot of tension on that side that’s stretching more. And if you bend it too much, you get a crack, you get flexural cracks and flexural cracks tend to occur. This is the theme. They run perpendicular to the scope of bending. So they’re going to run this way. So if you see a whole bunch of lines together in kind of parallel, especially toward the middle, those tend to be flexural cracks. If you see one deep crack that runs all the way across and down the face,
Caleb Lawson (14:13):
That would be a brutal
Jeff Girard (14:13):
Pathway. That’s a brittle failure. That’s a very deep, that’s a structural failure right there. Hairline cracks, flexural cracks can show up. Hairline cracks are merely a description of the size of the crack, right? Again, my personal definition for my customers, because it’s easy because most customers have a piece of copied paper. It’s like if you can’t get the piece of copy, copy paper in the crack, I’m calling that a hairline crack. That’s just my definition. That’s part of me setting those expectations to the customer. It’s just an easy rule of thumb because who’s going to have, and maybe you have one, because if you work on cars, maybe you do or
Caleb Lawson (14:55):
Fielder gauge,
Jeff Girard (14:55):
You got a fielder gauge, you got a 1000th of an inch, which would be what.
Caleb Lawson (15:01):
But even still, I mean to my eyes, if I’ve got something I can fit anything into, I’ve got a problem.
Jeff Girard (15:07):
If you can see it, that’s the more critical stages. If you can see it, it’s there. It’s real. And if it’s there and they don’t
Caleb Lawson (15:16):
Want, and to your point of it’s there, it’s real. If you can’t see it, it isn’t real. Exactly. Cause everything is what it looks like. And
Jeff Girard (15:24):
A long, long time ago, I did a demonstration. This was like, I think 2003, this is pre GFRC days, and this is kind of when PVA fibers were starting to come on the market. And I made an eight foot long, basically an eight foot two by six. So it was eight foot long inch and half thick, six inch wide beam. And there might be pictures on the c c a website in an article about it. Steel reinforced, by the way, had to be supported at each end. And I had 500 pounds of sand on it, impressive on itself. And I had the president of ACI standing on it with me at a conference. And so that was pretty cool. The thing is, there were no visible cracks in it. Now were there cracks in it? Absolutely. There were thousands of them. And that was the function of the PVA fibers not to hold the beam together because they can’t do that. What their job was to distribute the cracks. So you didn’t have one giant big crack that was obvious. You had thousands of microscopic cracks that you couldn’t see.
Caleb Lawson (16:33):
Which I was talking to you Jeff the other day, and we were talking about ECC as a, and it what’s stand for Engineered Composite Composite, that’s right. Yeah. So you know, were telling me that the origins of that are pretty fascinating, but there, it’s a seismic material. So it is intended to, in a seismic event, in a structural event, crack and fail. But the idea is it will hold itself together long enough to keep people safe and get people out of the building. So to that point, on the concrete pers on the countertop perspective, it’s the PVA’s job are to
Jeff Girard (17:09):
Distribute those,
Caleb Lawson (17:10):
Distribute the cracking so that you don’t spread it, fail brittle, but also in our niche industry so that you don’t see them.
Jeff Girard (17:19):
And if a client can’t see a crack, it’s not there. And that’s really the moral of that story. So you could argue very reasonably that incorporating those kinds of fibers into your face mixes might be a way to control cracking, flex cracking or other kinds of cracking if you have them.
Caleb Lawson (17:47):
Something like that is not, I don’t think, should be used as a structural fiber. And we can get into that debate
Jeff Girard (17:53):
That that’s another topic.
Caleb Lawson (17:54):
I know some guys are using these little HD fibers, little tiny glass fibers apparently don’t show up. I’ve never used them, but I’ve heard
Jeff Girard (18:03):
I have ’em three millimeter long, 18 micron, I think I could be wrong. Glass fibers, AR glass fibers. And the fantastic thing about ’em is they’re absolutely invisible. They’re not. It’s
Caleb Lawson (18:20):
Scrambled.
Jeff Girard (18:22):
Yeah. Yeah. So when you machine them, if you hone your concrete and do a salt and pepper finish, you physically cannot see them, nor can you feel them. And a half a percent dose in a mist coat sprays beautifully. So I’m just putting that out. There is, it’s their great way to do that kind of control, but I think it’s more of if you need that. Right.
Caleb Lawson (18:48):
Well, and so really we should move into the subject of this situation, which is map cracking specifically.
Jeff Girard (18:56):
So what is map cracking? And it’s basically the surface skin of your concrete. And it’s usually an eight only extends about an eighth of an inch deep three millimeters. You’re going to read that. That’s a number that’s out there on the internet. I never cut, taken a tile saw and cut through one and actually measured it. But experience have said it’s shallow. They’re shallow surficial cracks and they tend to happen very quickly after casting. So within a few days, I’ve even personally seen it happen within a few hours. And they typically manifest themselves as a random crackle of ru interconnected cracks that form like little rough, random, geometric shapes that all connected. So it’s not like a linear flex crack, which is pretty easy to identify as a flex crack map. Crack is just kind of random everywhere it might start, I
Caleb Lawson (20:09):
Think it, I don’t know this is the case, but it could be getting the map name from what it
Jeff Girard (20:14):
Looks like. Yeah, it looks like a map. Yeah. I’ve even heard the term spider cracks. So it’s like a spider web. And the main cause of that in most concrete situations is poor curing conditions. Basically you’re taking your concrete out and it’s drying too fast. It’s in an environment that’s too dry and the surface of your concrete is drying out and shrinking and it’s shrinking and can’t withstand the shrinked forces. So what cracks are caused by tension? What’s causing the tension? So when water evaporates, that movement of water creates a lot of capillary suction forces, which can be quite strong. That’s how water can go up, freeze and can go up hundreds of feet into a tree. It’s drawn up by capillary action through the tree and the respiration that there’s more than just that. But capillary action on its own is quite powerful. And if you’ve ever washed dishes and use the sponge and you done washing the dishes that night, you squeeze out the sponge, you put the damp sponge on the countertop in the morning when you come in and look at it, it’s all curled and dried because the top surface that’s exposed to the open air has dried more than the underside that’s touching the countertop.
Caleb Lawson (21:47):
Oh sure. Yeah.
Jeff Girard (21:47):
Water evaporating has caused the sponge structure, which is not very strong to shrink, to collapse. Right. And that’s the driving force of curling, which on its own is another topic, but it’s that drying action that is so harmful and that’s what causes the tension that co creates the map cracking.
Caleb Lawson (22:10):
Yeah. So we’ve defined it. So
Jeff Girard (22:13):
How do you stop it?
Caleb Lawson (22:14):
How do you stop it? Yeah, well how do you stop it for our particular industry? What types of practices are causing that? And then certainly how do you stop it would be along those. So
Jeff Girard (22:28):
My first state is if you have a mix design that allows moisture to leave the concrete rapidly, that’s a problem. So that’s the first thing is change that the easiest, there’s two easy ways to change that. One is less desirable than the other one is to use a proper curing polymer. We’ve mentioned this in the past, and that’s the function of a curing polymer G F R C. The entire commercial industry that’s been in use globally for the last 50 years is incredibly dependent on curing polymers for everything to work to be economically feasible. Because if you didn’t use a curing polymer, you had better be wet curing your concrete long enough so that the structure of that concrete, especially the surface, can withstand the drying suction forces that create map cracking. Because if you don’t, you get map cracking. So map cracks are a symptom of some things that’s not being done right either. There’s an ingredient that should be under your concrete that’s not because you’re choosing to do certain curing situations or you’re not curing the pro concrete properly. And that means now
Caleb Lawson (23:46):
I will, I’ll add one, I’ll add one thing to that is I have seen over the years that I’ve determined that there is an ingredient in whatever mixed design I’m using that is causing something even though there is a curing power, I
Jeff Girard (24:04):
Dunno if it is. And that’s another possibility. That’s another aspect of it. And I’ve witnessed it and gone from elation of seeing this four meter long beautiful piece of concrete I just made to after a few hours going, well it’s going in the dumpster because you can visibly see cracks happen on the surface and it’s not from drying.
Caleb Lawson (24:31):
And I don’t know the answer to that one
Jeff Girard (24:32):
And that that’s a material and ingredient thing. There’s incompatibilities with things and I can only knowing some of the other things that cause cracking in concrete, take educated guesses, it’s not really guesses my hypothesis on why that cracking happened. Sure. And we’ll get to that. We’ll get that. But let’s get back to the main causes of map cracking. Let’s say you have a a brand new piece of concrete. You’re using this mix that you’ve used for years and all of a sudden this one piece, you take it out of the mold and it looks great. And as you’re doing whatever you’re going to do to it over the course of the next few hours or couple days, you notice wow at you get to the point where you’re, you’re going to go what? Clean the piece off, ready to seal it, like clean the oh no ceiling is absolutely good practice. And all of a sudden you notice there’s mat cracks everywhere and they only show up when it’s wet. What happened? Well, sometimes it’s hard to figure out what happened, but in this instance, in this case, it turns out that maybe you were not the one who did the casting. Maybe you had an employee do the casting.
Jeff Girard (26:07):
And it turns out from talking to them that they sprayed their mist coat and then they got a phone call or something and instead of have to wait for half an hour getting on it right away and getting that backer on it right away when it’s just at the right consistency, it’s still moist, it’s still pliable, et cetera, et cetera. That mis coat dried out and became it actually under underwent, not necessarily plastic shrinking cracking, but because it started to dry out and it’s so thin, it created a lot of internal stresses that manifested themselves after the P 50 molded. I’ve been on consulting jobs in Nevada, in Oakland, California in a very, very big, very well respected company. And that was the reason why they were having these problems is pieces were being sprayed and the mist coat was just being left open to the open air. And that’s an easy fix. That’s just, okay, you got to change how you do things.
Jeff Girard (27:17):
In the Nevada case, it was 6% humidity and the shop was a hundred degrees. So you’re basically, there you go, concrete in an oven and concrete. And this is something that I see, especially with folks who don’t really know concrete that well. They’re not in the concrete industry and you say, oh well I got to wait for my concrete to dry. Everybody thinks your experience with things that get hard paint or glue when you’re a kid is you wait for the to dry. Well, these are chemical reactions. So you actually don’t want it to dry. Water is the fuel. It’s like the most important ingredient. And so that it
Caleb Lawson (27:58):
Reminds me of a time before I bought my company that I believe my predecessor tried to consult with you on a process that ended up being, I mean just not a great idea to begin with because he wanted to I think kiln, cure it or something. Yeah,
Jeff Girard (28:12):
Yeah. Put it, no, no, it’s like no, no drying is bad for concrete and that’s kind of K, the root cause of map cracking is drying of some
Caleb Lawson (28:24):
Premature
Jeff Girard (28:25):
Premature drying. And if you have your piece of concrete and it comes out of the mold, you dul it the next day. I don’t care what mix you’re using when you dul it very early in its age and it’s life, it is a lot weaker than it will be when it’s fully cured. Now those of us who use rapid set where it gains strength, 28 day strength and 24 hours for real, its chemistry happens so fast that it’s unusual to see map cracking from drying. But you can get map cracking from thermal issues where it’s thermally drying itself.
Caleb Lawson (29:09):
It’s so hot.
Jeff Girard (29:09):
Yeah, it’s so hot. You’ll burn yourself if you touch it. It’s basically drying itself out. So that’s accelerated drying. It’s accelerated curing, but it’s also accelerated drying. We’re talking about regular concrete here, our regular concrete. But the point is still valid is that keeping that concrete moist. And the important thing is to keep it continuously moist, not intermittently. You don’t just sloshed water on it in the morning and then come back in the afternoon. That’s actually bad. And there are lots of articles written about that, how that actually can exacerbate things. But when I say it, keep it moist, that means keeping the internal humidity levels the moisture content within the concrete high enough so that you don’t have those suction forces trying to collapse everything and B, waters the fuel that makes it stronger. And you want that concrete strong enough so that it can dry out and still remain as a strong crack free skeleton.
Caleb Lawson (30:13):
And so a lot of those methods would be, the dogs about to bark Boone, please stop. There’s a runner going back. Shop Boone just can’t handle it. So there are a couple of ways you can do that. A use curing polymer and that will keep the moisture in the concrete B, you could cover it in plastic and put a heat blanket and put a steam unit. I mean you could steam cure it, you could full on white cure. It seems to me the easiest and most economic and least path least resistance to a quality material would be to use, use curing polymer
Jeff Girard (30:47):
That that’s the logical thing because that’s what the GFRC industry as a whole shows half a century ago as the better solution because the
Caleb Lawson (31:00):
Century go Jeff, isn’t that, I mean, are there technologies that could circumvent that need or is that something that’s just, it’s the best because, or it’s still in use because it’s the best?
Jeff Girard (31:15):
Well, there is no such thing as the best that applies to everything. Anytime you’re working with a material, whether it’s wood, whether it’s steel, whether it’s concrete, whether it’s plastic, it’s always a balance. And this is really what engineering is. And a lot of people don’t understand this. It’s not finding the best solution at the cost that is acceptable. I can make titanium carbon fiber, whatever, paperclips, and they’re going to be the best paperclip. But if they cost a hundred dollars a piece, 99.99% of the people will simply say, that’s ridiculous. I don’t need that. Right. So it’s always a balance. Now is there some esoteric exotic technology out there that can prevent all map cracking? I don’t know. But is it so expensive that 99.999% of the concrete industry simply says it’s not worth it Because there’s many things that are cheaper that do exactly the same thing?
Caleb Lawson (32:27):
Yeah, I think what I’m getting at is if there was a better option, the industry at large that we are kind of a subset of would be using it. Absolutely. And maybe there will be a better option. But it’s like I look at things like I, I’m an Apple guy, Jeff’s an Android guy, and I would put it out there that Android tends to adopt certain technology earlier and in certain applications, I mean maybe Samsung’s figure it out, but maybe HTC hasn’t. And so in certain applications those things are buggy upfront. That’s right. Whereas Apple is going to wait on it and when they put their phone out, it’s going to do exactly what they say it’s going to do, no more, no less. And so I think that what I’m looking at this as is the Apple approach. I want to use something that is reliable now and we’ll do exactly what it says no more, no less. And when something else takes that place, totally happy to switch to it.
Jeff Girard (33:26):
And that’s a really good perspective to apply to this situation is, and I want to again go back to the GFRC to really drive this point home. And I’m using the G F R industry because, well, it’s outside of us, it’s in fact we’re
Caleb Lawson (33:45):
A derivative of it in
Jeff Girard (33:45):
Theory. We’re not just in theory. Literally. I mean you, I know that some of the people who used to be in the GFRC industry back pre 2006, 2007, and they left and came into our industry and brought a lot of this, I mean, Hram Ball, who’s, man, I don’t have the textbook with me. He’s one of the people who authored and a lot of the code written for the commercial GFRC industry. He’s the one who taught me how to do this. And he’s, he taught a lot of people how to do this. And
Caleb Lawson (34:20):
This being GFRC, this
Jeff Girard (34:21):
Being GFRC and the GRC industry as a whole and have a lot of technical papers on this going back to the eighties and even before that, polymer made it possible, made it economically feasible. Again, going back to just because you know could do something, but if it’s cost too much to do, is it worth doing? So before the days of polymer existed, the way they had to make GFRC and we’re, we’re not talking about little planters and doo-dads that we make, not doo-dads, but the stuff we make is tiny. When you’re dealing with a two or three story building panel and you’re doing cladding for an entire building where you’re maybe making several thousand square feet of panels a day every day of the week, you got to cure those. And so they have to be wet cured, continuously wet cured in a fully 95 plus percent humidity environment for seven continuous days. So imagine the size of the facility and the infrastructure it need needed to keep these things really, really damp. That’s expensive. That’s really expensive. And it was so expensive even in the seventies that many people said, Hey, this is a great idea, but it just costs too much to do.
Caleb Lawson (35:37):
And with the advent of polymer, now they can cast and strip ’em and throw ’em outside.
Jeff Girard (35:43):
Now you don’t need that expensive facility. That expensive facility can make more product. And like you said, it can just be stored outside. And it is, it’s colloquially termed to air curing, but the function of a curing polymer is to hold a moisture in, right? That’s its job. Its only job is to hold the moisture in.
Caleb Lawson (36:03):
It’s kind of funny that we started on map cracking, we ended up back on polymer. And I think that’s all related.
Jeff Girard (36:09):
It’s all related. Everything about concrete is related to everyth. Every choice you make, every ingredient you put in it, everything you do before, during and after casting absolutely makes a difference. And again, this is kind of to drive home when you make really good concrete that is well designed and well thought out, that has everything it needs in it and nothing it doesn’t, you generally don’t have any problems with it. Now,
Caleb Lawson (36:38):
And I used this analogy, the Android analogy, and I used the vehicle analogy a couple of weeks ago, but I think it holds true. There’s nothing wrong with new technology. There’s nothing wrong with changing, there’s nothing wrong with being open-minded. I think those are all super valuable and asset producing traits. But if you look at a company like Mercedes, great car, but they tend to have technology that’s a bit ahead of its time. I mean, Mercedes-Benz had the whole auto cruise control 10, 15 years before anybody else did it. And there were issues, there were issues of it veering off the road. There were issues of it not working properly or whatever because the kinks hadn’t been ironed out. And frankly, I think Mercedes knows that their customer base would rather have the new technology than have the perfective tech technology. And I think that’s a totally fair thing to say, right? I think it’s totally fair to say, listen, you’re allowed to prefer new over proof it totally fine, but know that that’s what you’re referring.
Jeff Girard (37:46):
And except the choices of, wow, it’s going to cost me a lot of money to fix that new piece of technology that other cars don’t have yet. And the new, and
Caleb Lawson (37:57):
Now Honda has it and you can bet, well a Honda that’s got it, it’s going to work. The
Jeff Girard (38:05):
GRFC industry wouldn’t exist if somebody didn’t say, Hey, let’s look at different polymers in the concrete and see what that does. Now, there are a lot of reasons why, and again, I’m straying away from the main issue, put it all ties together, put it all ties together, is I have a dry curing polymer. There are a bunch of dry curing polymers in the market. Why do people look at dry curing polymers over the liquid commercial GFRC polymers that were used and that still are being used is when you ship them, you’re not shipping water and B, they can freeze and it doesn’t hurt them. So it doesn’t cost you as much to ship in the winter and you can buy and bulk and they don’t go bad and things like that. There’s a lot of positive reasons, but that doesn’t make ’em all the same. And just to come back to the topic at hand, I have personally seen map cracking happen and you have two Caleb in concrete that has a curing polymer in it. And in a certain situation you saw map cracking when you normally didn’t. And there are other
Caleb Lawson (39:17):
Reasons. No, I mean I had a piece that I used two separate mix designs in just I was marbling something and it doesn’t really matter why, but there was map, you could tell there was map map cracking in the sections of the marbling that had that one mix design and there wasn’t in the sections that didn’t. So that was a really fascinating side by side. And it is kind of an aside, but you’re back to the other week. You extent
Jeff Girard (39:44):
The matter. Yeah, it it’s relevant because it goes back to what I said. Sometimes a mix has something in it that,
Caleb Lawson (39:53):
And I don’t know how to answer that question. I mean you can make guesses, but unless you’re looking at the ingredient list
Jeff Girard (39:59):
And
Caleb Lawson (40:00):
Blended mix design,
Jeff Girard (40:01):
When you are using a mix design that you didn’t make, go to the grocery store, you buy a box of cake mix, you’re trusting that the ingredients that are in the cake mix are all good for you and will help you make the best cake that you can. Right, right. So there’s a trust level there. Sure. And this is also well known in the construction industry in the concord industry as a whole is if you, and this has to do with superplasticizer, it’s known that if you use very high doses of some superplasticizer that can lead to map cracking. Now I don’t know if that’s a direct cause too much is a direct cause or is an indirect cause, meaning a lot of superplasticizer when you use a high dose have retarding characteristics. Now these are not super plasticizers that intentionally have retarding characteristics for you it’s
Caleb Lawson (41:04):
Like super red (pigment) is a retarder, but that’s not as
Jeff Girard (41:05):
Exactly, but if you use a lot of a superplasticizer because you really want to make that concrete really fluid or you’ve made a big batch of concrete and it’s sitting there and it’s kind of stiffening up over time and it’s not as fluid as you likes. So you keep dumping more in more superplasticizer into loosen it back up. There’s a point, and I don’t know what the point is because it’s dependent on the chemistry, it’s dependent on the brand, et cetera, et cetera. But there’s a point where there’s so much superplasticizer in there, it starts to have a retarding characteristic, meaning the strength gain is slowed down and one of the cause of map cracking is the concrete is not strong enough to resist the shrinkage forces caused by drying. And if you are retarder, if you have something that’s slowing your strength gain down in your concrete, then you might be seeing map cracking because of that.
Caleb Lawson (42:01):
Sure.
Jeff Girard (42:02):
So that’s another possibility. Even it could happen even if you do follow good curing practices where you keep your piece covered using curing polymer, et cetera, et cetera. So I don’t want to point everything to one cause, but there is a very common cause, especially in the concrete world that has to do with premature drying and you’re not using curing polymer. Now most concrete doesn’t use curing polymers because it’s too expensive for ordinary concrete. We need it for a lot of good reasons. And
Caleb Lawson (42:39):
I think so I think that would be a good time. Cause it’s 8 45 and I want to make sure that we’re respecting people’s time listening, but to answer any questions that might be in the peanut gallery and wrap it up. But I think the bottom line is, I think the most concise way to say it is map cracking can most of the time be traced to premature drying and there are ways to prevent that, which we’ve kind of gone over in this podcast.
Jeff Girard (43:10):
Yeah, I think that’s a great summary. During polymers are not going to stop flexural cracking. They’re not going to cause they’re not going to stop thermal cracking. They will or they will stop or minimize premature drying because that’s their function is to slow drying. So to wrap this up, yeah, Mount cracking mostly caused by early drying and excessive drying.
Caleb Lawson (43:43):
Absolutely. There’s one gentleman in the chat, do you have any questions, sir? Or
Jeff Girard (43:53):
If you do, go ahead and unmute yourself. Yeah.
Caleb Lawson (44:00):
Oh, hang on. He’s still muted.
Jeff Girard (44:04):
Hang on, let me, okay, I can only, there
Caleb Lawson (44:16):
Should be a way to unmute yourself there in the audio section.
Jeff Girard (44:21):
Yeah.
Caleb Lawson (44:23):
Oh, I think I heard something. No, he’s still muted. I still see a red microphone next to his
Jeff Girard (44:28):
Participant’s name. Buddy had the same issue the other day we talked. Yeah, if you can, on the very left side of your screen, there should be a little microphone symbol that you should be able
Caleb Lawson (44:42):
To Oh, okay. There you go. Hello.
Jeff Girard (44:45):
Good
Speaker 3 (44:45):
Morning. The wet one, the liquid one.
Jeff Girard (44:57):
The liquid one, does it have issue? The same issue? It can, yeah. Oh yeah. Liquid polymers tend to be used at a higher dose than dry polymers and that tends to compensate for that. But you can still have map cracking in extreme circumstances. So let’s say you cast a piece of concrete and you’re using a liquid curing polymer and you’re using the correct amount, but it happens to be very hot. Maybe it’s 35 C, maybe it’s 40 C really, really hot. And then maybe it’s very dry or maybe it’s very windy. You know, you’re doing a piece outside or you’ve got air a fan in your shop and it’s blowing air and it’s causing a lot of rapid evaporation of that surface. It is possible.
Caleb Lawson (45:53):
But then there again, good practices cover your concrete and then that would not be an issue.
Jeff Girard (45:57):
Correct. Correct. And you can get map cracking. It can occur after you dul it. So you can do all the proper curing practices of covering it in plastic overnight, which is all that’s necessary with it. Oh, a curing polymer because it’s, it’s starts to do its thing once it coalesces and forms that internal, you call it a curing memory, even though it’s more of a matrix that generally happens within the first 24 hours.
Caleb Lawson (46:27):
I think the general, the general answer though is that generally speaking with a polymer, this is not a major issue. Correct. If it is an issue, then there are other causes that are probably not the polymer. Right. If that makes sense. So in the instance that we spoke of earlier in the podcast where okay, there was an issue with a polymer with a mix that had a polymer, it was another ingredient that we have to diagnose. But generally speaking, if you have a Keurig polymer and our, your curing practices are good, you’re covering your concrete, you’re waiting 24 hours or 12 hours or whatever it is not going to be Right. I would think that the polymer then would not be the cause of the issue at that point.
Jeff Girard (47:11):
Right. Maybe you, you’ve dumped in far too much superplasticizer in your mix, then maybe that’s that’s the cause, but it’s far more likely that you’re going to get map cracking in a mix that doesn’t have polymer in it. Yes,
Caleb Lawson (47:27):
Exactly.
Jeff Girard (47:27):
Cause that’s its job is to hold moisture in. And if you’re not using that, then what’s keeping the moisture in? No. And that’s even exacerbated even more with mixes that have low water cement ratios because there’s not as big buffer of moisture inside. And the flip side of that is if you have a very high water cement ratio, concrete now making a concrete really porous, so it’s very easy for the water to escape. So it’s a delicate balance. That’s another topic, but I’m just trying to, not a complex picture, it’s just a picture, it’s a clear picture that has a lot of little details around the edge. So
Caleb Lawson (48:08):
Keep tuning in.
Jeff Girard (48:09):
Yeah. So keep tuning in. Good question though. Good question.
Caleb Lawson (48:13):
Yeah, absolutely. Well, I think we probably ought to wrap it up for today. Absolutely. If that’s cool. And I really enjoyed exploring this topic and I also look forward to hopefully some other people have questions as time goes on. And this gets posted to Facebook and the website and YouTube and all of that. So look
Jeff Girard (48:33):
Forward and I think one last thing is if you have something you want us to talk about, let us know.
Caleb Lawson (48:39):
Yeah, absolutely.
Jeff Girard (48:40):
What’s on your mind, because
Caleb Lawson (48:44):
If you want I’m, we can have it linked in the podcast, but if you have questions that you want us to answer, if you have topics you want us to cover, email me. My email is Caleb, [email protected], and there’s no.com or anything like that. And we can link that in the video description and the website and all of that. But shoot me an email at that email address if you have things that you want us to cover or questions you have. Again, that’s [email protected]. Cool. I think that’s a good way for people to chime in. And again, join us live too. I mean, not everybody can be here at Wednesday at 8:00 AM but we love having people involved,
Jeff Girard (49:30):
So. Absolutely. Well, thanks for stopping by and we’ll see you next time.
Caleb Lawson (49:35):
Sounds great. See you. Bye.