Epoxy School Blog

Epoxy troubleshooting - pigment pot problems

I think the idea of a pigment pot is great, however you’d be surprised how many headaches I’ve seen them cause contractors over the years.

For those not familiar with pigment pots, or pigment packs as they’re also known, they are small tubs of pre-dispersed pigment stirred into suitable products to add colour. They’re very handy for both manufacturers and contractors mainly because they allow these products to be coloured as needed and, therefore, can make the task of managing stock much easier.

While they’re very handy and straight forward to use in theory, there are a few things you might want to be wary of to make sure you don’t run into any trouble.

In epoxy for solventless epoxies

If you work with solventless epoxies like I do, you really want a pigment dispersed in an epoxy resin and nothing else. Some pigments are dispersed in solvents or plasticisers, both of which might be compatible, but they can also give you grief.

Personally I don't like working with solvents for a number of reasons I've already spoken about at length, so I try to minimise their use in any shape or form. As for plasticisers, which are typically compounds called phthalates, my problem with them relates more to the fact they can stop an epoxy from fully crosslinking and this can have a negative impact on performance.

Beware the pigment

On a similar note, be aware of the actual pigments used in the pigment pot. For the contractors who value safety and eco-friendly practices, the pigment pot can be an unexpected hazard – cadmium, cobalt and, amazing as it may seem, lead-based pigments are still used by some manufacturers today.

It actually reminds me of an unfortunate instance where a contractor promoting the use of safer coatings unwittingly used pigment pots containing toxic substances that severely compromised the green objectives of a high-profile project. Not all pigments are safe and not all pigment pots are equal, so it pays to know exactly what goes into them.

Old pigment pots

Freshly manufactured pigment pots usually mix easily enough, however over time they can have a tendency to thicken and settle, which can lead to problems like clumping. Prevention is certainly better than the cure in this case, so if you have an old pigment pot there are a few things you might want to consider before application.

Firstly, you can warm the pigment to loosen it up and get it back to more like its original viscosity for easier dispersion. Secondly, mixing the pigment pot into a fraction of Part A rather than the whole bucket can be effective because the higher concentration gives the mixer a better chance of breaking up the clumps. Finally, you might look to strain the mixed product through a fine sock to make sure the clumps are separated out before you apply.

Clumps of undispersed pigment pot visible in solventless epoxy film.

Batch-to-batch colour consistency

Some manufacturers are very good with their colour consistency from batch to batch, others might not be. If possible, only use the same batch across the job to ensure that there’s no chance of inconsistency. If you can’t do that, use the same batch for each coat. If that's not possible either, you can record the weight of one pigment pot, mix as many as you need together in a separate container and re-fill each pot once again. This will blend all of the inconsistencies into a uniform colour.

To finish off, I’ve separated out and left a very common pigment pot issue to last because it’s more a factor of how they’re used rather than any problem with the pigment pots themselves. The problem I speak of is colour separation and I actually covered this topic in a previous post a while ago (read it here) so I won’t go into great detail here. Just as a quick summary, the greatest risk of experiencing colour separation occurs when putting a pigment pot into a low-viscosity, clear epoxy because the blended pigments are free to move around and settle at different rates. The best way to avoid it is to use coatings that are formulated to be tintable (rather than clear) and apply during the afternoon; both of which help restrict the mobility of these pigments.

What other pigment pot problems have you encountered?

Take care and talk to you later,


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Epoxy clean up - are you a folder or a scruncher?

I used to be a scruncher, but I saw the light and I'm now a proud folder. Ok, before your mind goes into the gutter let me just make it clear I'm talking about cleaning up epoxy resins here and nothing else!

Believe it or not there are clear advantages to using a folding technique when cleaning up epoxies and, seeing as my recent posts have wandered into the field of handy practical tips, I may as well highlight some of these while I’m at it.

Now, I know some are happy to sit over a bucket of solvent with an old brush when cleaning tools, however if you want a long career in the epoxy industry I strongly believe you should minimise your exposure to harsh chemicals at every opportunity. The headaches, solvent highs and skin irritations will catch up with you eventually!

If you want a less hazardous way of cleaning up epoxies that’s also neat and efficient, here’s how I go about things.

No need to get aggressive when cleaning up epoxies

The first point is to always use gloves and make sure they can handle the solvent being used. Some solvents can disintegrate even the highest quality gloves and, therefore, aren’t really suitable as general purpose cleaners in my opinion. Those of you familiar with methylene chloride will know what I’m talking about! I tend to stick with methylated spirits (or denatured alcohol) where possible and only turn to more powerful solvents like acetone or methyl ethyl ketone (MEK) for cleaning up epoxies that have partially cured. There’s really no need to use anything more aggressive than that.

The “squirt and fold” approach for cleaning up epoxies

Those of you who do work with a bucket of solvent are probably wondering how I go about cleaning tools. Well, I find a squirter bottle and rag to be a great combination. You could use an ironing spray bottle on the mist setting as well, but I’d prefer not to as there’s greater chance of inhaling the stuff. If you need to get into nooks and crannies, a quick blast from the nozzle at close range normally does the trick. Other than that, I simply squirt onto a folded rag and start wiping, re-folding as required to create another clean patch.

A squirter bottle and folded rag are effective at cleaning up epoxies.

The big advantages with folding are neatness and efficiency. Firstly, folding means I have a smooth, flat surface to wipe with far less chance of smearing. Secondly, I have a small contained area where the mess sits in the rag. I can fold to lock it inside and go again with a new, clean surface. If you scrunch, you tend to lose track of the dirty areas and this often leads to goop getting everywhere. Have you ever tried to clean a liquid pigment like phthalo blue or signal red using a scrunched rag? It’s a nightmare!

Finally, I can use the back of the rag when folding because the solvent soaks through the layers and allows me to pick up even more resin. This means you're using a lot more surface area when folding, which greatly reduces the number of rags needed.

For those unwilling to give up the bucket and brush method, I suggest at least switching to white vinegar instead. It will remove the majority of waste off your tools and a quick wipe of methylated spirits/denatured alcohol at the end will bring them up as good as new.

Dry your rags before disposal

There’s one last tip I have with relation to cleaning up epoxies and it’s also a pretty important piece of safety advice: let solvent-soaked rags dry out in the open before you throw them in the bin. Solvents give off a lot of vapour and a heap of soaked rags stuffed into a bin can quickly build up to become a serious fire hazard.

If you still doubt the benefit of being a folder after reading all of this then I can only suggest that you try it. It is one of those habits things that people seem to adopt for good as soon as they try it because it is so much more effective. I guarantee that you'll use much less solvent, rags, time and energy when you next clean up.

What are your nifty clean up tricks? Do you have a method that works well and doesn’t create a mess or involve nasty solvents?

Take care and talk to you later,


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Epoxy application - is masking tape the answer to clean, sharp lines?

It’s no secret I'm a big fan of taping. Clean, sharp lines make a huge difference to the finish of a floor, however there are a few things that can catch you out if you're not careful.

To start with, getting the right tape is not as easy as it seems. As you may know, there are countless types and it can all be a little overwhelming. They all theoretically serve the same purpose, but as they say in the classics “oils ain’t oils”, and, in this case, “tapes ain’t tapes”.

What’s the best tape to use?

When trying to select the best tape to use, I normally make the following comments –

  • Masking tape is a popular choice in the coating industry but in reality it is a weak paper-based tape with ordinary adhesion. It’s designed this way so it doesn’t pull off house paint when removed. This type of tape is cheap and commonly used, but it's not the right choice in all circumstances.
  • If you want to take a step up from masking tape, look for a tape known as “14-day tape”, manufactured by 3M. It's essentially the same thing, however it's more durable and sticks better.
  • If you want a really sharp edge on concrete, you must use tape with better adhesion still. I prefer using a cloth tape (aka “Gaffa” tape) as the adhesion is much better and there’s less chance of bleeding underneath.

  • Getting the best out of your tape

    With the right tape in hand, better results can be turned into fantastic results if used correctly. Here are the tips I usually pass on in this area –

  • Pull the tape as soon as you can and while wet. Some contractors are happy to let the epoxy harden and use a Stanley knife to cut the tape off, but my preference is to pull straight away so I have a neat, straight line and less chance of bleeding underneath. The only time you should hold off is for thicker films that can self-level. In that case you want the coating to have at least gelled before pulling the tape to avoid it smoothing out and flowing past the tape line.
  • For contractors that don't like re-taping walls, you can be smart by using a two-step or “double tape” system. Apply tape and plastic/paper film starting 10mm/0.4” up from the floor, then apply a second round of tape along the bottom, a few millimetres off the floor. The idea being that you pull the bottom line of tape as you go and leave the taped plastic in place. This way, you have sharp edges where you need them and constant wall protection throughout the entire job.
  • Even if you’re using a cloth tape you can still struggle to get a sharp line if the profile of the surface is too rough, e.g. a house brick. With these surfaces you’re almost guaranteed to see bleeding underneath because the tape simply can't get into all the crevices. In these circumstances you’re probably better off carefully cutting in with a brush.

      Bleeding of epoxy underneath a tape line on bricks.

      I think proper taping practices can be neglected sometimes because it’s the sort of thing that goes unnoticed on most jobs. One thing is for sure though, an ugly edge will draw attention and can cause a whole lot of grief. I was reminded of this on a recent floor where an otherwise beautiful finish was rejected because of some slopping taping and the contractor was forced to re-do the whole thing again.

      What are your thoughts on taping? What tapes work best for you? Do you pull straight away or cut later on? Have you heard of messy edges leading to customer call-backs?

      Take care and talk to you later,


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Epoxy application - good application habits

There’s nothing I love more than simple stuff that makes a big difference. You know, those warm and fuzzy moments when you think to yourself, “Wow, that’s gonna make things a whole lot easier!”

In the previous post, Epoxy application - bad application habits, I gave you some of the worst pound-for-pound application habits going around; the stuff that bobs up time and again as the cause for very avoidable problems. As promised, here is the other side of the coin. The following are all pretty simple application habits that may not sound particularly ground-breaking, however they’re guaranteed to give you those moments I speak of and make your life as an epoxy contractor a whole lot easier. Enjoy!

Use cotton "inners"

I always insist on wearing disposable gloves, typically latex because they are cheap and readily available. There are a couple of things I don’t like about them though – 

  1. Sweat – a big problem with these gloves is the sweat, which can do a couple of bad things: it can run down your arm and onto a wet film, and, it can react with the powder in the gloves to cause skin sensitivity. I buy powder-free gloves to avoid the sensitivity issue, but these are near impossible to put on with sweaty hands. 
  2. Padding – the other problem is they are no good for holding onto tools because they offer no padding or protection. 

Here is a great tip to overcome both of those pains: use thin cotton gloves underneath. You won’t realise how much of a difference it makes in both of these departments until you give it a shot!

Putting on cotton "inner" gloves for easier application.

Wear an apron over work clothes

I actually started wearing an apron as a bit of fun for my decorative flooring range, Floorchef, but the more I used them the more I liked the idea. Not only did they protect my work clothes, but the pockets were very handy for storing rags, gloves etc., and I no longer needed to walk off the floor to replace the consumable items because I carried them with me. While you’re at it, you might also want to grab yourself some sweat bands and even head bands. Items like these are a blessing when you’re at full throttle in hot, humid conditions and trying to stop sweat dripping all over the floor.

On clothing, I’d like to quickly comment on the broader topic of presentation. Work clothes are always going to cop a bit of punishment, but it isn’t a good look to have finger prints all over and smears everywhere. The client will probably be thinking, “If they can’t keep their work clothes clean, what will they do to my walls?” My suggestion is to have a nice, clean set for meetings and inspections because it will set you apart from others turning up in their soiled gear.

Squirter bottles for clean up

Here’s a great little tip for contractors wanting to take their cleanliness and safety to the next level: put your solvent in a squirter bottle. It gives you so much more control over the amount used and is far better for your health than slouching over an open bucket. The pointed nozzle also gets into all the hard-to-reach places for a thorough clean of your tools!

Roll out the carpet!

Contractors who like to work clean will use some form of dropsheet, with most being made of plastic that can be slippery, light and flimsy. If you’re after something more robust and easier to control, I’ve known a few contractors that carry around a roll of old carpet instead. The carpet is simply rolled out at the start over a plastic dropsheet and back up again after they’re done. All the little drops and drips are absorbed into the pile and there’s nothing to dispose of. Brilliant!

Get your diamonds right

One of the best tips to save you time, money, and perhaps even your sanity, is to develop a better understanding of your grinder and be willing to invest in the right set up. The fact is there can be a big difference in how concrete grinds from one slab to the next. For instance, hard concrete tends to produce ultra fine dust, which doesn’t abrade well and can result in hard discs glazing over and losing their efficiency. With this in mind, hitting every slab with the same grinding disc because you don’t want to fork out on multiple sets of diamonds will only end up costing you more in extra labour and perhaps even coating failures.

One last bonus tip...

Just to finish off I thought I’d hand over one last tip mainly because it’s such a simple fix for a rather costly mistake. If you use a drill mixer and you’re not able to release the mixing paddle each time, tape up your chuck so that when you lay the drill down the resins don’t run along the shaft and into the chuck. Funnily enough, this tip actually came from one of my more experienced contractors who had to replace two drill chucks within a very short space of time and was desperate to avoid a third!

So, there we go. Five very simple, yet very effective application habits I know you’ll love if you give them a try. What other simple, good application habits do you have? I’m sure we’d all love to hear more!

Take care and talk to you later,


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Epoxy application - bad application habits

I talk a lot about the right habits, but what about the bad ones? Identifying the things you do that aren’t particularly helpful is a logical first step on the road to better practices, so let’s take a quick look at these.

First of all, I believe good habits come from proper education and strong mentoring right from day one. If no one shows you how to do something properly and set the right standard, you’ll naturally do what you think is the easiest, quickest or cheapest. If you get away with it, you’ll probably just repeat it until you inevitably pay the price (and it’s often a hefty one at that).

With that in mind, I thought I’d play my part and pass on some pearls of wisdom to help you avoid the pain bad application habits can lead to. The items below are what can be seen as the pound-for-pound champions of bad habits – five simple things I feel don’t get enough attention and lead to very common, very avoidable problems. Cut these out of your business and I guarantee you’ll notice the difference!

No sampleboard

Sampleboards are the ultimate application tool, yet in my experience very few contractors ever get into the very rewarding habit of doing them.

Why are they so valuable?

For starters, they represent the perfect proving ground for the products you use. To be honest, I’m still amazed at the willingness of contractors to learn on the job and I get calls all the time from guys in the field looking for advice because they’re in trouble. They’ve been handed a new product and jumped straight into application without testing it for themselves; without proving what the manufacturer told them; without getting a feel for how it behaves in the pot or on the floor; without making sure the system they’ve put together actually works. It’s such a big gamble!

Once a sampleboard has been done and confidence in the product established, the next phase of their value kicks in. This time, it’s all about the client. While it sounds obvious, I’ve learnt the hard way that your average Joe is not an expert and you can’t expect them to know exactly what the finish will look like. If they don’t get a chance to see a sampleboard before work begins, they could easily have some unrealistic vision in their mind and that can spell trouble. This also includes industrial work because although these jobs are fundamentally about performance, you can’t assume aesthetics won’t be an issue if they don’t meet expectations.

Budget roller covers

I understand that cutting costs in business is often a good thing, but in my opinion contractors simply can’t afford to be skimping when it comes to roller covers. I’ve lost count of how many floors I’ve seen ruined by loose fibres and the poor contractor has had no choice but to put down an extra coat in order to rectify it. Such a costly exercise could’ve easily been avoided if they’d been prepared to pay for roller covers with much better fibre retention. It’s such a small cost in the overall scheme of things!

If using budget roller covers can’t be avoided, consider only using them for basecoats and de-lint thoroughly by wrapping the roller in masking tape and removing. Repeat this process, fluffing the roller cover in between until there are no fibres visible on the back of the tape. If that sounds like hard work, you can give them a wash in a washing machine instead (with no detergent of course).

Roller cover lint ruining a beautiful, high-gloss epoxy floor.

No preparation

Sanding concrete is not what I would call preparation; neither is sweeping or hosing. You may be lucky and get away with poor preparation in some instances because the conditions are favourable, but statistically the odds are against you. The ironic thing is that you actually don't save any time or money by taking shortcuts with preparation. Most people quote to do a job once, so if your preparation isn’t up to scratch you’ll just end up blowing your profits in call backs.

Adding solvent to extend coverage

Trying to save a few dollars by diluting your product and stretching out a “skinny” coat isn't a good idea. There might be situations that genuinely benefit from adding solvent, such as better penetration for sealing applications or easier handling in the cold, however adding solvent just because you’re trying to make it go 10-20% further is crazy. Quote to do the job once, with the right products applied at the right film thicknesses, and you'll reap the rewards.

Starting early and rushing

This is pet peeve of mine because no matter how many times I say it, I still get ignored! Put simply, if you want the best possible finish on your job then you should aim to be applying in the afternoon and not the morning. If you apply in the morning when the concrete is starting to warm and the air is starting to expand, you’re increasing the risk of developing bubbles and blow holes in the film. I get that busy schedules and access issues don’t always allow this to happen, but if you’ve only got one job on for the day then you probably don’t have an excuse.

On a similar note to the scheduling of your work is rushing. With flooring in particular, the exit point is the most critical because it’s usually the spot your client sees first. If you have rushed it, spread it thin or not taken care in other ways, it will show and leave a very poor first impression. Take your time and be sure you have enough product and patience to get out the door with a great finish.

I hope the majority of these bad application habits don't apply to you. If they do then take heart that it's never too late to make a change for the better. In the next post I’ll deal with the other side of the coin – some of the best simple habits I believe have a big impact.

Take care and talk to you later,


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Epoxy application - the epoxy contractor rut

Having worked with hundreds of epoxy contractors over the years, I’ve seen quite a large number stuck in what I’ve come to call the “epoxy contractor rut”.

This condition can present itself in a number of ways, however, just like any other rut these people share an over-riding feeling of dissatisfaction. They no longer find any excitement or reward in their epoxy work and it seems every job is a big pain in the you-know-what. They’re tired, unhappy and often unhealthy; their epoxy businesses are literally making them sick!

Peter is one such epoxy contractor I met quite a few years ago. His story always sticks in my mind not only because he was a classic example of a contractor in a rut, but because he was able to drastically turn things around and unearth the secrets to doing so at the same time.

Peter’s epoxy contractor rut

When Peter first contacted my company he was clearly fed up with the type of work he had fallen in to – using hazardous, solvent-borne coatings on the same domestic garage floor jobs, day in and day out. He was becoming conscious of his health with headaches, sore throats and mood swings a daily battle. His motivation was also beginning to suffer, which he knew would inevitably spell trouble for his epoxy business. He obviously needed a change; a better way of doing things that would allow him to re-discover some spark and boost his well-being.

Unfortunately this kind of situation is typically not a quick fix. The problem Peter had, like many epoxy contractors, was that he had been taught HOW things were done and not WHY. The important theory needed to understand his craft and help steer his business in the right direction was sorely lacking. Because he had no one he could ask to get the answers he needed, his confidence remained low and he was never able to break out of the doldrums.

The turnaround begins

After some effort, we convinced Peter to undertake our decorative epoxy training program. While he later confessed to doing it only because of the generous discount we offered, something must have clicked inside as a change in attitude gradually became more apparent every time we dealt with him.

In the beginning, his main focus was pretty much on finding cheaper products and cheaper ways of doing floors so he could compete in the industry’s race to the bottom. On every job he would get in, get out and never look back. Over time, however, we saw a totally different Peter in operation.

No longer was domestic flake flooring the one and only string to his bow – he was now installing outstanding commercial decorative finishes and starting to branch out into the industrial field. No longer was low pricing the be all and end all – he was focussing on the greater value he could offer clients rather than simply undercutting the competition. He was even starting to feel more comfortable taking phone calls and handling the tricky questions because he continued to develop his understanding of the coatings he used. He was becoming a more complete epoxy contractor, running his own race and his confidence was sky-rocketing!

Peter used epoxy training to create decorative floors like the one in this garage.

A better epoxy business awaits!

To cut a long story short, in the end Peter did what many epoxy contractors never do and successfully worked his way out of the rut. The keys for him and anyone else in his position were willingness to change and a desire to learn. By investing in epoxy education and opening his mind, he was able to learn new skills and explore new paths that could take his epoxy business in more fulfilling directions.

The wonderful thing about this story is that this kind of transformation can be achieved by anyone. It takes time and will power, but the end result can also be life-changing. If you’re a contractor in a rut, I strongly believe a better future is possible if you spend some time thinking about the type of epoxy work you really want to do and the skills you need to learn in order to do it.

If you’d like to hear more on my thoughts about the contractor rut and how to escape through epoxy education, please contact me at any time.

Take care and talk to you later,


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Epoxy application - solventless epoxies and cold temperatures

When the cooler months roll around and temperatures drop, application can start to become a bit of a headache for contractors.

As a manufacturer of solventless epoxies, I can always bank on being asked two questions during these periods – 

  1. How can I make solventless epoxies easier to apply? 
  2. How can I speed up the cure? 

Obviously the answers can depend on the products being used, but there are a couple of things that help regardless.

Cold temperatures and epoxy handling

Firstly, let's take a look at making epoxy handling easier.

Step one involves getting the product out of the bucket and in single digit temperatures (1-10oC/34-50oF) the thick viscosity can make that a task in itself. With this in mind, storing the product on the floor in a cold shed is not going to help your cause. Instead, look to store the product in a warmer space, somewhere indoors away from the extremes and closer to 25oC/77oF. It doesn't have to be in your bed, although that would be perfect!

Keeping the product at moderate temperatures this way will also stop the products from turning into a gluggy semi-solid, which can happen with some epoxies in cold temperatures. Crystallisation, as it’s known, can be reversed by slowly heating and stirring the product, however you certainly don’t want to be doing that every time!

If storage at a reasonable temperature isn’t possible, some contractors make special “hot boxes” to warm the epoxy directly before use. These devices are essentially timber boxes that house a few kits of product and are heated via an electric fan-forced heater. There are also submersible heaters available that can keep certain volumes at a constant temperature, however I’m not too sure how practical they are in the field.

An example of a hot box used to warm epoxies before application in cold temperatures.

Cold temperatures and epoxy application

These little tricks might work well for getting the product up to a nice mixing temperature before use, but even that may not help you if the slab itself is extremely cold. A cold slab will tend to act like a big heat sink and this means even if your pre-heated product is 30oC/86oF when it hits the floor, it’ll quickly drop to the temperature of the slab once applied and drag you back to square one.

This cold substrate issue can be eased by heating the room, however if you're using a gas heater and your epoxy has a problem with amine blushing you’ll need to be extra careful. These heaters increase the levels of carbon dioxide when operating, which is one of the key ingredients needed for blushing to occur. This warning can actually be extended to any heater that doesn’t burn clean and therefore could potentially interfere with the flooring, e.g. kerosene heaters have been linked to adhesion problems.

Apart from heating, there’s also a school of thought out there that suggests using a thin epoxy to seal the surface first can make epoxy application easier because it protects the thicker basecoat from the icy slab. Such an approach may be worth trying if you can work in the additional cost and time of an extra coat.

Cool temperature and accelerating cure

Finally, cold temperatures also mean slower reaction times. If your epoxy isn’t adversely affected by heating as already discussed then continuing to heat the room after application can be a good way to achieve a shorter turnaround. Besides that, the answer to speeding things up is the use of a stir-in epoxy accelerator. Be aware these additives can affect the UV and chemical resistance of the product, so never use them in quantities greater than recommended and never in the final coat if possible.

I’ll finish off by adding that introducing a small amount of solvent to a solventless epoxy is also a popular way of reducing viscosity and making epoxy application easier. Unlike the other options given here, however, adding solvents won’t cut cure times in cool conditions and some solvents like acetone will drag it out even further!

Take care and talk to you later,


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Epoxy troubleshooting - concrete additives and coating adhesion

Like most people I suspect, there was a time when I thought concrete was just concrete and all slabs were the same. How wrong I was!

With a little more experience under my belt, I know how flawed this thinking is; in fact, I would now go as far as to say that NO two concrete slabs are exactly the same. It might sound like a big statement, but when you consider all the variables of modern concreting practices, it’s quite possible that even the same batch can end up looking and performing differently if applied in two separate locations.

Concrete slabs aren’t concrete slabs!

Why is this so? When you talk about different locations, you’re also talking about the potential for different weather (temperature, humidity, wind, sun light), different handling, different application, different finishing etc. All of these factors can have a big say in characteristics of a concrete slab and we haven’t even touched on the content of the concrete itself. Water and the aggregate composition are obvious variables here, but concrete has come a long way and these days all sorts of concrete additives can be used to speed up, slow down, harden and even slow corrosion depending on job demands. Imagining every slab as at least slightly different perhaps doesn’t seem so absurd after all!

Ok, concrete is ever-changing and unpredictable, so what? Well, for coating contractors it can actually be a bit of a problem because it challenges the age-old assumption that sticking to concrete is a sure thing. Some modifications can indeed interfere with coating adhesion and it was something I learnt the hard way several years ago.

The concrete additives lesson

The painful, yet extremely valuable lesson came through on a project involving a tilt slab construction coated with epoxy for protection and waterproofing.

For those unfamiliar with tilt slabs, these are slabs that are poured horizontally in moulds then cracked and erected to form the walls of whatever building is being constructed. A "mould release" is used to make it easier for concrete to break away and is generally added in controlled amounts to the moulds themselves and in between the concrete layers.

On this particular project however, there was a rush on the high-profile job (which happens more often than not these days) and the construction company needed the slabs to cure quicker. Conventional concrete accelerators were ruled out because the slabs were being poured on top of each other, so they figured the next best thing was to use greater quantities of mould release to allow successive pours to be done sooner.

Unfortunately, as it was later discovered, the excess mould release was absorbed by the slabs as they cured – not a problem if the panels were left as is, but a major snag when you plan to put a coating on them!

Because of the extreme levels of mould release used, the normal tilt wash detergents were no longer effective. They seemed to be doing their job on the surface, however the stuff that had soaked into the concrete was playing havoc with coating adhesion. After some desperate scrambling and frantic tensile adhesion tests, the solution ended up being multiple washes with the detergent and a deep grind to remove several millimetres of contaminated concrete before coating adhesion was restored. It was an intense experience and a huge sigh of relief was breathed by all I can tell you!

Samples of epoxy showing the difference in coating adhesion on concrete contaminated with mould release.

Be wary of concrete assumptions

I think the take-home message from this near disaster is you need to be wary of all concrete slabs, not just tilt slabs. Every slab is different and you need to ask questions of what you see before you rather than make assumptions. What is the composition of the slab? What else may have been added? What could it have been exposed to?

A similar scenario to the one above that I know catches many people out happens in residential garages. Instead of mould release, the contaminants in this case are the tyre shine products that are usually a type of silicon spray. Being invisible to the naked eye, it’s very easy to assume the concrete is clean and washing isn’t necessary. They give the floor a light grind and think it’s all gone well; only to watch in dismay a short time later as their beautiful new garage floor quickly peels off (read the post on Hot Tyre Pick-up).

Take care and talk to you later,


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Epoxy troubleshooting - hydrostatic pressure and moisture tolerance

What is hydrostatic pressure and how is it related to moisture tolerance?

If you’re a regular visitor to this blog, you would’ve previously read about the benefits of choosing moisture tolerant epoxy hardeners when it comes to avoiding amine blush (Epoxy troubleshooting – amine blush).

But, does a moisture tolerant product mean I don’t have to be concerned by hydrostatic pressure? I’ve heard these terms creep into the same conversation many times and feel as though it could end up down a dangerous path if one starts getting confused as the answer to the other. The answer is: no, they are two different issues really.

The difference between hydrostatic pressure and moisture tolerance

Hydrostatic pressure is arguably the most complex, poorly understood of all preparation issues and a great example of why flooring can be a tough gig. Not only is the issue itself a bit of a mystery, there also seems to be vagueness around the products used to fix it, and, as we’re highlighting here, some related concepts such as moisture tolerance.

In brief, being moisture tolerant means the product doesn’t react badly to moisture during application, which is a very handy property because you typically don’t have to worry about humidity in the air etc.

Hydrostatic pressure, on the other hand, is a powerful, destructive force that acts on a coating through the movement of water or water vapour in the slab. Typically this pressure is caused by a moisture source close to the bottom of the slab, which, in the absence of an effective moisture barrier below, sees water rise through the pores in the concrete. This migration becomes a problem in a coating sense when it becomes trapped beneath an impermeable film sitting on the surface, at which point the build up of pressure can be sufficient to blow sections off or cause other forms of damage like blisters.

You can probably see the relationship between moisture tolerance and hydrostatic pressure more clearly now; a moisture tolerant product might be able to handle application onto a slab with excess moisture, however this capability certainly doesn’t mean it will be safe from the hydrostatic pressure acting on it once it hardens.

Hydrostatic pressure affecting concrete in a basement.

Hydrostatic pressure warning signs

If moisture tolerant products aren’t the answer to hydrostatic pressure, what is? Before we get into that, let’s take a look at how you can diagnose such problems in the first place. Luckily, there are a few simple tests that can be used to spot hydrostatic pressure issues before you go and put a coating down.

To start with, grinding a spot and seeing what colour it turns can be quite informative. If it starts to darken soon after, this is a classic warning sign that hydrostatic forces are at play. In this case you should also keep an eye out for efflorescence, which are visible marks that result from water coming to the surface and depositing silt-like substances as it dries.

A step up on those basic visual tests is to tape a 60cm x 60cm/2ft x 2ft plastic sheet to the concrete with duct tape and leave it for 24 hours. If water droplets appear on the underside of the plastic, or if the concrete appears darker in this area, your slab could have a problem.

For those after a more scientific approach, moisture meters can also be purchased to measure the levels at points on a slab and alert you to any potential problems. With this equipment, most people talk about 5-6% as being the maximum acceptable moisture content of concrete for flooring before hydrostatic issues are raised.

Personally, I’d never count on just one of these when assessing a slab. I’d look for multiple signs of a problem first and use that to guide my judgement on any action that needs to be taken.

Dealing with hydrostatic pressure

If your checks all point in the same direction and you do have a hydrostatic pressure issue, there are two common ways of dealing with it – both of which look to create some form of water barrier to block it as it moves up through the slab.

Water-based epoxies are the first and probably the most common option here. These are typically 40-50% solids products that are applied onto a pre-wet slab. As the epoxy is water-based, it thins down very quickly and penetrates deeply before crosslinking to form a barrier. Other than that, there are also some colloidal silicate solutions that promote the ability to penetrate into the slab, reacting with the residual lime and cement to form a gel barrier instead.

A couple of quick side notes about these treatments – 

  1. Be careful when dealing with cracks as they may not consistently close off with these moisture barriers
  2. In basements or other below-grade spaces, hydrostatic pressure can also be an issue on the walls and should be dealt with in the same way if they’re to be coated.

In closing, I just wanted to make the point this post should only be taken as a broad overview to raise awareness of hydrostatic pressure and how it relates to moisture tolerance. As mentioned previously, hydrostatic pressure is a very technical, complex issue and further reading is recommended for a full understanding.

Take care and talk to you later,


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Surface preparation - can I sand concrete?

Is sanding an option for preparing new concrete slabs? I guess so, but not if you want the coating to stick!

This is very much “Floor Preparation 101” and I don’t want to spend too much time on it, but I still hear of contractors using coarse sandpaper on a Polivac machine to prepare new slabs and thought I’d explain why it’s not a great idea once and for all.

(Note: For those unfamiliar with the term, Polivac is a particular brand of machines used for buffing and sanding.)

Sanding concrete doesn't remove laitance

I think this bad habit can creep in when contractors come across a fresh, clean slab and underestimate the work that still needs to be done to make a coating stick. The slab might be brand new and a quick sand may seem good enough, but the problem with doing that is it fails to remove all the laitance and that means you can be headed for big trouble. The fact is sanding in this manner might only remove around 5-10% of the stuff sitting on top, which means the coating will floating on a bed of weak powder rather than anchored to a solid surface. It won’t be bonded well and will probably peel off as soon as it’s put under any stress, such as a car parked on top of it.

While preparing a new slab is generally a much easier task than a damaged, contaminated slab, you still need to do it properly. In most cases, this all boils down to laitance and getting the job done there. If you don’t, expect a call to come back and fix it!

A Polivac machine with sandpaper is not the right machine to prepare concrete.

When can I use a Polivac?

While using sandpaper on a Polivac doesn’t adequately remove laitance, you can get attachments that do the job well. As I mentioned in a previous post, Decorative epoxies – the polished concrete and warehouse looks, an example of this type of thing is something called Diamabrush, which uses diamonds on flexible brushes to prepare the concrete. As discussed in that post, it’s actually a good option for decorative resin flooring because it follows the contours of the slab rather than flatten it completely and that can have a number of advantages in that field.

Like I said, this topic is well documented and I didn’t want to go too far in this particular post. I simply wanted to highlight this common problem once again and ensure that you don’t feel tempted to sand the floor. There are many ways to remove laitance, however sanding is NOT one of them.

Take care and talk to you later,


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