yellowing resins indoors - PODCAST

This podcast video episode came from a discussion I had with an installer this week. He wanted to understand how resins were discolouring indoors and what he could do about it. I was able to find some photos to go with the discussion that can be seen on the video.

I would love to hear your experience on the topic?

PS. All ResinJack podcasts are available to listen on Spotify and many other podcast platforms.

As always...

Take care and keep smiling 


Video Transcription: 

Welcome to the Resin Jack Podcast. Today I thought we would dive into a topic that was asked of me this week and I thought it was a really good topic. What we're talking about is UV or degradation of coatings indoors.

The question was posed to me by a contractor with regard to metallic resins and his concern was in looking at different types of decorative resins out there. He'd noted that some of them tended to yellow off quicker over time than others.

He's right, that is what takes place. But this podcast is going to be more about why that's happening, not so much assessing different types of resins. 

What are the Sources of UV light Indoors

The starting point in all of this is that there are sources of UV light inside of a building. It's not always to do with the sun.

So firstly, on the inside of glass, it's pretty obvious that if the glass is clear and the sun is blaring through the glass, well then that's a source of UV. The ways to counteract that, if we're in the resin flooring field, we talk about whether they have tinted glass, whether they have curtains, covering glass, and so forth.

Now those measures will assist in preventing some of the UV degradation, but even curtains might stop the primary area of the floor being affected, but they're not going to stop all of it.

Tinted glass certainly is better, but not everybody wants tinted glass in their environment, whether that's a home or a retail store or whatever it may be.

In bathrooms as an example, there are heat lamps that are used and they too can give out some form of UV light. Now, I'm not sure to what the intensity is, but it is notable in plastic fixtures and so forth in bathrooms that where the towel rail as an example, where the towel hangs underneath the towel, it is less discolored than on the outside of the towel. And that's a sign also of this UV degradation.

Other sources inside are to do with fluorescent lighting as an example. So fluorescent lighting itself when the tubes are new. The powder that sits on the inside of the fluoro tubes is there to get excited by UV that is emitted from the tube. I'm sure there's a very technical explanation for it, but that powder gets excited by the UV and that's part of the glow that fluorescent tubes provide.

The problem with UV transmitting through that powder is over time, that powder is weakened to some degree, maybe it's used in the catalytic process and UV is able to transmit through. So UV sources seems to be more prevalent or UV degradation seems to be more prevalent with old fluoro tubes than new ones.

The other obvious source of UV light is not so much in residential retail, but overhead and more traditional are those sodium vapor lights and those types of industrial lights, I think they're also mercury vapor lights, they also will put out certain amounts of UV. In our warehouse, we have those lights still, they call them high bay lights and they'll still put out a degree of UV. How much is a different matter. But they're all sources of UV light in side.

Other Floorings and Discouloration - are there Warranties? 

The other point around that, I should just make the point on flooring, is that although we're talking about resin flooring, if you read any technical data sheet or any warranty statements with regard to other floor coverings, whether that's vinyl or timber carpets, they too will talk about being affected by weathering and they won't provide a warranty for discoloration because of UV, whether that's indirect or direct.

So that's what I've noted in the warranty statements that I've read. So I realize that as a flooring alternative to those mainstream flooring, we are not that different, but there are things we can do and should be aware of.

Examples of Discoloured Resin Flooring

I want to look at a couple of projects that we were called in on to have a look at, because they reflect UV degradation inside the building.  In this first particular photo, which you can see, you can see that it's a flake floor, the majority of the floor is a very light-coloured flake.

There's a lot of sealer on it and I'll explain why in a moment. But you can see that what's taken place here is that there's a strip, a thin narrow strip that has gone yellow in amongst what still looks quite white around it.

How Specification can affect Discolouration

And what has actually taken place here is that the client has specified a very smooth flake floor. They want it particularly smooth and that's why you can see the amount of topcoat on here. And in order to achieve that, the installer was advised by his manufacturer to install a solventless epoxy first to fill in all the hollows, all the voids of the flake before they then put on the urethane.

And all of that is good in theory, particularly on flat areas if the floor is level. In practice though, that's not that easy to do, because what you end up doing is because the specification was for gloss, you end up trying to apply a gloss clear coat over a gloss clear coat.

So this is a section of floor that doesn't have the urethane and it's only the epoxy that is showing and in fact is yellowing. Now you might say, "Well, why is the epoxy yellowing inside?" And we've talked about sources of light.

This happened quite quickly within a number of months, less than 12 months. And so, you can see that the urethane with its absorbers in it has protected the epoxy from discoloring throughout most of the floor.

But in this section, it's missed. You can talk about whether that's a problem of installation or whether it's a problem with specification or problem with epoxy or whatever it might be.

I think there's a combination of factors in there, and I'll show you why it's not quite as simple as you think.

So this isn't particularly a smooth floor. Here is the actual floor and this is a section of cove. And then, this is the coated wall. Now, this is where the specification comes into play, because the idea of putting a clear solvent as epoxy down thick over the flake on the horizontal is okay, but when the specification calls for a cove, it becomes very difficult to apply a thick, solvent and self-smoothing epoxy on a vertical or on a cove.

And even more difficult is the concept of putting a thick enough urethane on there.  And you're applying gloss on gloss and this wasn't a big open area. This was lots of tight spaces where you're working in and around equipment and benches and things.

So there has to be a certain amount of leniency in there for installers.  But it's still yellowing, because of the fact that there's no PU over protecting it. And there is an internal source of UV light. 

Doing flake on coving is difficult and it's even more difficult to get at the same degree of consistency on the horizontal as it is on the cove.

Now this floor should perhaps never have been specified to be smooth, because of that fact that you can't get it consistent.  You can see two sections of cove where they're intersecting and on one section, even though it's pretty ratty-looking cove, you can see that it's still not discolored and yet the other is, so they may well have got the PU onto this area better than on this area.

I don't actually know if this is a fixed bench and they physically couldn't get in there and coat it well, but you can see that UV has still managed to impact the epoxy in that area and discolor it. This is a totally different project and it was a installer who was asked to go out and take a look at a floor that they wanted to rejuvenate to freshen up.

And when you look at the floor, you can see that it looks like a tan-based flake system.

And so, the installer was thinking that this is a tan base until he moved some things around. And in this particular area you can see a very definitive line where the original color you can see is actually more like a light grey color with its flake in amongst it.

And yet in the area that wasn't covered by boxes, it was, you can see that it's discolored a fair bit. All indoors again, I don't actually know if there was a urethane on here or not. My guess, it was just sealed with a solventless epoxy. I don't know how old that floor is either.

But again, it's just good to be aware that there is discoloration indoors and you need to have that discussion with your client at that time of quoting so that they understand everything weathers, all resins will weather like this, it's just a matter of how fast do they weather.

Discolouration in Residential Projects

In residential applications, people will want to renovate or redecorate before you wear through the coating.  So they'll get tired of it and want a change of colour before they will actually wear out the coating.

You don't get many homeowners that say, "Have a look at my 20 year old carpet," or, "Have a look at my 20 year old tiles, how awesome do they look?" Most people want to look to renovate that.

Do Different Types of Epoxy affect Discolouration? 

The topic I just wanted to touch on quickly was to be aware of when it came to looking at different types of epoxies. So the conversation I had with the contractor was, every resin has positives and negatives.

So you'll see when it comes to choosing decorative resins, a lot of manufacturers will go down the path of as clear as they can and they'll choose cycloaliphatic amines.

And most are happy to go down the path of a isophorone diamine, an IPD or IPDA, IPDM. The reason why is it's very clear, it's actually quite stable when it comes to UV. So it has decent performance because of its aliphatic properties. It's cheap as far as a curing agent, it's very reactive.

So you can add a lot of diluent with it to keep the cost of the overall resin down.

So a lot of manufacturers go down that path. The problem that I have with using IPD curing agents for finish coats and in particular for metallics, for decorative finishes, is that they tend to have susceptibility to moisture.

So when you're doing a high build product, you don't want to see it blush, you don't want to see haziness or inconsistent of haziness is even worse, where in some areas it's full gloss and in other areas it's hazed off. It becomes really obvious what's going on.

And that is a form of blushing, even though many people, many installers have never even understood that, that's what they were seeing.

And I just find that that is pretty tough, going to do a beautiful metallic floor and it could be a couple of hundred meters, even 2,000 square feet, and then have it hazing in different places.

Which is the Best Type of Epoxy to prevent Discolouration? 

So my preference when it comes to epoxies is not to use IPD in my finish coats. I tend to use a different form of cycloaliphatic amine that is far more moisture tolerant.

It's not an underwater product by any means, but it's far more moisture tolerant.

Now, does it have slightly less performance on UV? Well, yes it does, but keep in mind that the most susceptible component of the part of the epoxy is actually in the part A, because it has this aromatic ring, it's not aliphatic, the double bonds of carbons that break easier with UV compared to aliphatic that only has single carbon bond.

So sorry about the chemistry talk there. So no matter which part B you use, the thing that's going to have the most impact on yellowing is actually to do with Part A.

But again, my preference is to choose something that has less haziness, less defects on the surface, because of moisture intolerances.

We've got the scenario where indoors we still have UV and we know that epoxies when exposed to UV, whether indoor, outdoor will still discolour over time and we just don't know how quickly.

So what do we do about that? And some will jump straight on the polyaspartic bandwagon and say, 'Well, I'll do all my metallic coats in polyaspartic'. And that certainly is an option.

The difficulty with using polyaspartics for metallic finishes is that polyaspartics are very quick to gel, very quick to set once you get them out on the surface, and particularly if you have high relative humidity.

So it means that the pigments don't get a chance to settle and soften the blend patterns. It means that the actual polyaspartic may not get a chance to settle as well either, unless it's a very thick coat.

And it also does mean that people will try to use solvents in the polyaspartic to give them more wet edge, more open time, more levelling time.

And I guess, that comes down to preferences. I like solventless where I can, so that tends to be my preference.

What topcoats can I use over the top of the epoxy?

And for me, they serve a couple of purposes. So we've talked about UV, but the other key purpose for me is if I use a good quality solventless urethane over the top that has UV absorbers in it, like an optimum level of UV absorbers in it, then I end up having a sunscreen on top of my epoxy.

I'm trying to block whatever UVs are coming from indoors or through glass, whatever it may be onto my epoxy. I'm trying to block them before they even get it. And because the amount of UV coming indoors should be less than direct sun, that sunscreen mentality should work longer than if it was out in direct sun.

So that tends to be my preference when it comes to indoors. The other big benefit is if you choose a really good urethane topcoat, then with absorbers in it, then you also improve the scratching and scuffing resistance.

And that is exactly what the client will always want. It's what you always want. You want to go back after a period of time and see that it's looking great still and the client is having an easy time maintaining it.

One quick point there, the reason why I didn't talk about using a polyaspartic topcoat to protect the epoxy is because I don't hear of too many polyaspartics that have UV absorbers in them.

If there is a polyaspartic that has UV absorbers in it, and then of course, it can serve that same purpose of a sunscreen and try to deal with blocking the UV before it hits the epoxy.

But again, I don't see too many polyaspartics with UV absorbers.

So that's why I head down the path of solventless urethanes instead.

So that's the topic of UV indoors. I hope that's been of use to you. If you have questions, I encourage you to send them in or write them in the comments because that's how we see what else is going on out there.

What else can we learn?

My aim of this podcast is to share what I know and share what I learned so that we can keep evolving our industry. We can keep stepping up what we are doing. I hope you've enjoyed that.

As always, I'm Resin Jack, take care and keep smiling.