How Much Polyaspartic Do You Need
A polyaspartic floor is a stack of different products at different thicknesses, so there is no single coverage rate that describes it. Size it coat by coat and two things appear that a single number hides: the wet film you should actually be applying, and whether the system reaches the thickness it was specified at.
Size it one coat at a time. Solids by volume and the dry film thickness you want give a coverage rate, the area turns that into a volume, and the coats add up to the system. A 500 ft² garage with a 90% solids base at 6 mil and an 85% solids topcoat at 4 mil takes 2.31 gal and 1.63 gal, so 3.94 gal in total, and it builds a 10 mil system. Run your own products through the polyaspartic system calculator.
A system is not a coat
Almost every quantity tool for coatings answers the same question: how much liquid does it take to leave a given thickness on a given area. What changes between them is where the coverage rate comes from. Take it off the data sheet, or work it out from solids and a target thickness. Either way, one rate, applied as many times as there are coats.
That works perfectly for one product applied twice. It falls apart on a system, because the coats are different products bought for different reasons. A base coat is chosen for how it wets the slab and builds film. A topcoat is chosen for how it wears and how it holds its clarity. They rarely share a solids content and they are almost never applied at the same thickness, so a rate averaged across them describes nothing you can actually order.
It is also why a manufacturer’s own system calculator gives you a number you cannot check. It is built around their kits at their thicknesses, and the moment you substitute a product it is quietly wrong. Sizing per coat means the tool works for whatever you actually bought.
Solids by volume decides the order
Solids by volume is the fraction of what is in the tin that is still on the floor when it dries. The rest leaves. A gallon of a 100% solids product leaves a gallon of film behind; a gallon at 70% leaves seven tenths of one.
For a finished thickness, that means volume scales exactly inversely with solids. There is no curve in it and no threshold. Halve the solids and you buy exactly twice the liquid for an identical floor. Here is the same 500 ft² floor, finished at the same 10 mil, with a 10% loss allowance, built from one product at four different solids contents:
70% solids
- 4.95 gal
- 42.9% more than at 100%
- 8.57 mil wet for 6 mil dry
80% solids
- 4.33 gal
- 25.0% more than at 100%
- 7.50 mil wet for 6 mil dry
90% solids
- 3.85 gal
- 11.1% more than at 100%
- 6.67 mil wet for 6 mil dry
100% solids
- 3.46 gal
- The least this floor can take
- 6.00 mil wet for 6 mil dry
A full 1.48 gal separates the two ends of that, on one line of a data sheet. It is the single biggest lever on what a system costs in material, and it is invisible while you are looking at one product. Two products quoted per gallon are not comparable until you work out what each one costs per finished floor. The single coat version of this is worth reading first if the idea is new.
One caution on reading the sheet: check the figure is solids by volume and not solids by weight. Sheets print both, they are different numbers, and only the volume one has anything to do with how far the product goes.
The system thickness is a plain sum
When a specification asks for a 20 mil system, it means the total dry film thickness of the coats. So it is a sum, and it is worth being blunt about what does not enter that sum: the loss allowance.
A loss allowance covers what stays in the bucket, what stays on the roller, and what soaks into an open slab. It raises the amount of liquid you buy. It cannot raise the thickness of the finished floor, because the material it accounts for is precisely the material that never reached the floor.
A base at 6 mil and a topcoat at 4 mil build a 10 mil system whether your loss allowance is 5% or 40%. Against a spec asking for 20 mil, that stack is 10 mil short, and ordering more material does not close the gap. The only fixes are a thicker coat or another coat. The calculator says so directly rather than letting the volume figure imply otherwise.
Run your own system
Enter the area and the specified system thickness, then the solids and target dry film for each coat. Returns coverage and volume per coat, kits, the wet film to set your gauge to, and whether the coats add up to the spec.
Returns 2.31 gal for the base at 216.6 ft²/gal, and 6.67 mil wet to finish at 6 mil dry
Open the live calculator →Wet film is the only thickness you control
Dry film thickness is what the spec is written in and what a gauge measures once the floor has cured. It is also, on the day, entirely retrospective. The number you can act on while the coat is going down is the wet film, and at anything under 100% solids it is thicker than the dry target.
The conversion is the dry target divided by the solids fraction. A 90% solids product aimed at 6 mil dry needs 6.67 mil wet. The same 6 mil dry from a 70% solids product needs 8.57 mil wet. The difference is the part that evaporates.
Setting a wet film gauge to the dry number is one of the most reliable ways to finish a system under spec, and it is hard to catch, because a coat applied 20% thin looks exactly like a coat applied correctly. It is still wet, still even, still the right colour. Nothing looks wrong until somebody takes a reading on a cured floor and the system is 2 mil light.
The two coats, side by side
Here is that 500 ft² garage in full, with a 10% loss allowance on both coats, showing why the two coats behave so differently despite going over the same floor:
Base coat
- 90% solids, 6 mil dry
- 2.31 gal at 216.6 ft²/gal
- 6.67 mil wet on the gauge
Topcoat
- 85% solids, 4 mil dry
- 1.63 gal at 306.8 ft²/gal
- 4.71 mil wet on the gauge
The system
- 10 mil total dry film
- 3.94 gal of liquid
- Two products, so two kit counts
The topcoat covers 41.7% more area per gallon than the base, and it is the thinner coat that does it. Both facts come straight out of the same arithmetic, and neither is visible if you size the job from one averaged rate. Note also that the kits are not added together: they are two different products, so a combined kit count would be a number nobody can buy.
Flake is sized differently
Broadcast polyaspartic systems are common, and the flake in them is not sized by any of the arithmetic above. It has no solids content and no film thickness. It is sized by the area one pound covers at the broadcast density you are working to, which is a different calculation with different inputs.
Size the resin coats with the system calculator and the flake with the flake broadcast calculator. Two tools, because they are two genuinely different questions, and a single tool that tried to answer both would just be two calculators sharing a form.
Why this comes up on polyaspartics
None of the arithmetic here is specific to polyaspartic chemistry. Solids, thickness and area behave the same way for epoxy, polyurethane and polyurea, and for anything else sold by volume.
What makes polyaspartics the place this question bites is the schedule. The recoat windows are short enough that the whole stack often goes down in a single day, which means the entire system gets ordered at once, against a spec, before anybody has watched how the first coat actually behaves on that slab. There is no gap in which to notice you are a gallon short. The cure calculator gives you the recoat windows at your temperature, which is the other half of planning a one day system.
If you are sizing a single product across several identical coats, that is the simpler case and the film thickness and coverage calculator handles it directly, including an inverse mode that tells you what thickness a spread rate you already measured really achieved.
What not to take from this page
Any of the solids contents or thicknesses in the worked examples. Every figure above is an output of the calculator, computed from inputs chosen to show the arithmetic clearly. They are round numbers, not product specifications, and no real product is named or implied.
Solids by volume, the recommended dry film per coat, and the minimum and maximum thickness a product will tolerate all live on the data sheet for what you bought. This site does not print figures for them, because inventing a specification for somebody else’s product is exactly the sort of claim our methodology exists to rule out.
Frequently Asked Questions
Why can a polyaspartic system not be sized from one coverage rate?
Because the coats are different products bought for different reasons, and a coverage rate belongs to one product at one thickness.
A base coat is chosen for how it wets the slab and builds film. A topcoat is chosen for how it resists wear and UV. They rarely share a solids content and they are almost never applied at the same thickness. An average across them describes nothing you can put on a purchase order.
This is also why a manufacturer's own system calculator gives you a number you cannot check: it is sized around their kits, at their thicknesses, and it stops being right the moment you substitute a product.
What actually decides how much you need?
Solids by volume, and the thickness you want when it dries.
Solids by volume is the fraction of what is in the tin that stays on the floor. The rest evaporates. So a gallon of a 100% solids product leaves a gallon of film behind, and a gallon at 70% leaves seven tenths of one.
For a finished thickness, volume scales exactly inversely with solids. Not roughly, and not with a curve: halve the solids and you buy exactly twice the liquid for an identical floor. A 500 ft² garage finished at 10 mil takes 3.46 gal of a 100% solids product and 4.95 gal of a 70% one, which is 42.9% more material for the same result.
That is why comparing two products on price per gallon tells you very little until you work out what each costs per finished floor.
What is the system thickness, and why does the loss allowance not change it?
The system thickness is the sum of the dry film thicknesses of the coats, and it is the figure a specification is written against when it asks for a 20 mil system.
A loss allowance is a different thing entirely. It covers what stays in the bucket, on the roller, and in the pores of an open slab. It raises the amount of liquid you buy. It cannot raise the thickness of the finished floor, because the material it accounts for is the material that never reached the floor.
So a base at 6 mil and a topcoat at 4 mil build a 10 mil system whether your loss allowance is 5% or 40%. Against a spec asking for 20 mil, that stack is 10 mil short, and no amount of extra material closes the gap. The fix is a thicker coat or another coat.
What should the wet film gauge read?
The dry target divided by the solids fraction, which is always more than the dry target unless the product is 100% solids.
A 90% solids product aimed at 6 mil dry needs 6.67 mil wet. The same 6 mil dry from a 70% solids product needs 8.57 mil wet. The difference is the solvent or diluent that leaves.
This matters because wet film is the only thickness you can control while the coat is going down. A dry film gauge tells you what happened yesterday. Setting a wet gauge to the dry number is one of the most reliable ways to finish a system under spec, and it goes unnoticed because every coat looks right while it is wet.
How do the coats differ in a typical polyaspartic system?
The pattern is a base coat that does the building and a topcoat that does the wearing, sometimes with a primer under them.
Base coats tend to be applied thicker, because that is where the film comes from and, in a broadcast system, where the flake is locked in. Topcoats tend to be thinner and are chosen for clarity, wear and slip resistance. Neither of those preferences is a rule, and both are properties of the specific products you bought.
What is consistent is that they are not interchangeable and not equivalent, which is exactly why the sizing has to be per coat.
Does the flake get sized the same way?
No, and mixing the two up is a common way to get a broadcast order wrong.
Flake is not a liquid film. It is sized by the area one pound of it covers at the broadcast density you are working to, so it has no solids content and no film thickness, and none of the arithmetic on this page applies to it.
Size the resin coats with the system calculator and the flake with the flake broadcast calculator. Two tools, because they are two different calculations.
Does any of this only apply to polyaspartics?
No. The arithmetic is solids, thickness and area, and it holds for any coating sold by volume: epoxy, polyurethane, polyurea, or a polyaspartic.
The reason it is framed around polyaspartics is that a polyaspartic floor is where the coat by coat question actually bites. The recoat windows are short enough that the whole stack often goes down in a single day, so the entire system gets ordered at once, against a spec, before anybody has seen how the first coat behaves.
If you are sizing one product over several identical coats, that is the simpler case, and the Film Thickness and Coverage Calculator handles it directly.
What figures should I not take from this page?
Any of the solids contents or thicknesses used in the worked examples.
Every number on this page is an output of the calculator, computed from inputs chosen to show the arithmetic clearly. They are round numbers, not product specifications, and no real product is named or implied.
Solids by volume, the recommended dry film thickness per coat, and the minimum and maximum thickness a product will tolerate all live on the data sheet for what you actually bought. Check that the solids figure you read is solids by volume rather than solids by weight, because sheets print both and they are not the same number.