100% Solids Explained

When you consider epoxy floor coatings you may need to do a little math to figure out exactly what it is you’rebeing sold. This is because although the can may be full of a liquid, when you’re done coating your floor a lot of that liquid you bought may have disappeared into thin air. Epoxies can have two types of liquids – “solids,” which are good, and extenders, which are usually not good. If the coating is chemically 100% solids, what you pay for is what you’ll end up with. BUT if the product is only 50% solids material... then 1/2 of it is going to evaporate! Put another way, if a 100% solids coating costs twice as much as a 50% solids coating in the end you’ll come out exactly the same, because it takes 2 gallons of 50% solids to coat your floor to the same depth of protective coating that you’d get from a 100% solids epoxy!


How does that work? Here’s the key… One gallon of ANY liquid will cover 1,604 square feet to a depth of 1 mil. That means, if you spread ONE gallon of water on a surface at 1 mil thick, you would cover 1,604 square feet. If you spread one gallon of paint at one mil thick on the same surface you will cover... 1,604 square feet. How many square feet will a gallon of milk, root beer, or even crocodile tears cover at 1 mil thickness? That’s right... 1,604 square feet!

Of course that’s when the liquid is wet - now, let's move on to what happens when the liquid dries. If the coating is any bit less than 100% solids the thickness will decrease because any additive or extender that is not a solid must evaporate or “outgas.” Many floor coatings have water or solvents added to them, and neither water nor solvents are solids. Spread one gallon of either water or a solvent and it will initially cover 1,604 square feet to a depth of 1 mil when it’s wet, but in a short time how thick will that coating be? That’s right – zero mil thick; because both will completely evaporate and disappear.


So if you’re considering a coating that’s not 100% solids, how do you figure out how thick your floor’s final coat will be? Simple, you multiple the wet depth by the percentage of solids in the coating. For example, one of our competitors’ epoxy is only 40% solids and 60% solvents. They say that a 3 gallon kit will coat 600 square feet. We know that a gallon has 1,604 mils, so 3 x 1,604 = 4,812. Divide that by the number of square feet coated: 4,812 / 600 = 8.02. In other words, right after the 3 gallons is spread out on the 600 square foot area the wet coating will be 8.02 mils deep. Not bad, but then it dries…


To figure out the thickness after all the solvents have evaporated we need to multiple the wet depth by the percentage of solids; in this case 8.02 x 40% = 3.208. So even though you paid for and applied 8.02 mils worth of coating, when the job is done you’re left with only 3.208 mils of coating! In that case, even if a 100% solids epoxy cost twice as much, it would still have been the better deal.


Here’s another problem with most coatings that are less than 100% solids; the water or solvents must evaporate from the coating during drying. Each molecule of water or solvent leaves a trail as it travels from the substrate through the coating to the surface where it escapes. Most of the 'trails' are formed toward the end of the drying when the coating is beginning to go into the solid phase and can no longer refill itself. So these microscopic tunnels are permanent.


Therefore if you are going to compare apples to apples... you're going to need a higher mil thickness of a less than 100% solids coating to get the same performance as 100% solids. Think of it this way... If you take one 12"x12" board that is 1" thick and another board the same size and thickness and drill 100 holes in one of them, the one with 100 holes in it is just not going to be as strong as the one with no holes, right? So, to make the “holey” board as strong as the solid board, you'd have to add more board thickness... and it works the same with paint.

Now, think of the solid board and the 'holey' board on a floor. Which one is going to wear faster? Obviously, each hole is going to provide an opportunity for wear (abrasion) as well as a path for water, dirt, or chemicals (like oil or brake fluid) to attack the substrate. If the brake fluid is allowed to soak into the porous coating, it will begin to dissolve the coating from the underside after it travels along the surface of the concrete under the coating. And thanks to gravity, the brake fluid will be trapped under the porous coating and will have lots of time to attack! This is very common in garage floors.

Some products must have non-solids in order to perform well, nothing wrong with that. However most of the time non-solids are added just to boost profits at the consumers’ expense. Understandably those companies don’t advertise that they’ve added useless extenders, so it may take a bit of digging to find out that the products aren’t 100% solids. Be sure to carefully review product information and know what you’re buying.

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