What Is a 100% Solids Epoxy Coating?
A 100% solids epoxy coating is a two-part resin-and-hardener system with no water or volatile solvent used as a carrier. Once it cures, nearly all of its applied volume remains as film, so wet-film thickness roughly matches dry-film thickness. It is often used on prepared concrete, but it is not automatically waterproof, moisture-proof, or a repair for weak concrete.
A common mistake is to treat “100% solids” as a complete performance rating. It describes a product’s formulation and expected film build, not whether it suits your slab, resists moisture vapor, or will last under your traffic. In product reviews, I often see people focus on the label before checking the technical data sheet and the concrete below it.
What “100% solids” means
“Solids” are the parts of a coating left behind after it cures. A product listed as 100% solids by volume is formulated so its cured film retains nearly all the volume applied, rather than losing a water or volatile-solvent carrier as it dries. Check the product data sheet (PDS) to confirm the stated volume-solids percentage.
Epoxy coatings usually come as two parts: resin and hardener. Mixing them starts a chemical reaction that turns the liquid into a solid film. “100% solids” does not mean the coating is harmless to breathe, odor-free, or free of every volatile compound. Check the PDS and safety data sheet for VOC content, ventilation needs, and protective equipment.
Wet-film and dry-film thickness
Wet-film thickness (WFT) is the coating depth just after application. Dry-film thickness (DFT) is the depth after cure. At 100% volume solids, the theoretical DFT is approximately equal to the WFT, before losses, surface texture, and absorption are considered.
For example, a 10-mil wet film theoretically leaves about a 10-mil dry film. A mil is one-thousandth of an inch, not a millimeter. This relationship helps with estimating material, but it does not replace the PDS spread rate or specified film thickness.
How 100% solids epoxy differs from other coatings
The main difference is how much of the applied volume remains after cure. Other coating types may lose some volume as water or solvent evaporates. That can affect film build, application, and ventilation needs, but it does not by itself prove which coating is best for a particular floor.
| Product description | What to check | Practical meaning |
|---|---|---|
| 100% solids epoxy | Volume-solids percentage, VOC, WFT, cure and use limits | Theoretical dry film is close to wet film |
| Waterborne coating | Volume solids, drying conditions, recoat limits | Water is part of the carrier; follow product instructions |
| Solvent-borne coating | Volume solids, VOC, ventilation and fire-safety guidance | Solvent carrier affects application and drying |
| Moisture-mitigation epoxy | Written moisture limits and system details | Intended to address specified slab moisture conditions, not all water problems |
Terms such as “high build” and “industrial strength” need context. Compare the stated film thickness, substrate limits, traffic type, and full system details. A 100% solids label alone does not tell you how well the coating will bond or how it will perform in your space.
Concrete substrate inspection, moisture testing, and surface preparation
Concrete must be sound, clean, and prepared to the coating maker’s written requirements. A dry-looking slab can still release water vapor, while oil, sealers, curing compounds, weak surface paste, or old coatings can prevent a reliable bond. Inspect and test before buying materials or starting surface work.
Check the slab’s age, cracks, joints, previous coatings, contamination, and signs of moisture. Follow the manufacturer’s instructions for moisture testing. Common methods include ASTM F2170, which measures relative humidity inside the slab, and ASTM F1869, which measures moisture vapor emission using calcium chloride.
There is no universal acceptable relative-humidity percentage or emission limit for every epoxy. Compare your test results with the specific system’s stated limit and any approved mitigation method. Vapor pressure can blister a coating or break its bond, even when the concrete looks dry. Do not coat a slab that fails the system’s written acceptance criteria.
Remove contaminants and weak concrete, then mechanically prepare the surface to the required ICRI concrete surface profile (CSP). Many thin coating systems call for about CSP 2–3, but thicker systems may need a rougher profile. The PDS sets the requirement. Use suitable dust extraction and compatible repair products; do not rely on a cosmetic patch to fix a structural problem.
Epoxy mixing, film-build control, and installation precision
The mix ratio, mixing time, pot life, recoat window, and temperature limits are product-specific. Measure the resin and hardener as directed, then mix thoroughly using the specified method. Guessing the ratio or applying material after its pot life can lead to poor cure or bonding problems.
Pot life is the usable time after the parts are mixed. It may shorten in warm conditions or when mixed material sits in a large mass. Plan the work so each batch can be spread within that time. Also check slab and air temperatures, humidity limits, and dew point instructions before application.
Calculate material from the PDS spread rate and required WFT. Use the recommended gauge or other stated method to check film build. Do not estimate epoxy coverage with tile mortar rules or trowel-notch charts. A 100% solids coating may still need extra material on a rough or absorbent surface, so theoretical coverage is not a promise of actual coverage.
| WFT example | Theoretical DFT at 100% volume solids | What to remember |
|---|---|---|
| 5 mils | About 5 mils | Before surface texture and application losses |
| 10 mils | About 10 mils | Use only if the PDS allows this film build |
| 20 mils | About 20 mils | A thicker film does not correct poor preparation |
The figures show the basic relationship, not recommended application thicknesses. Follow the PDS for primer, coat count, spread rate, and any aggregate broadcast.
Joints, movement, and slip safety
Epoxy cures into a rigid film, so it may not suit areas that move unless the system has a detail designed for that movement. Identify control, construction, and expansion joints before coating. Do not bridge active joints indiscriminately; follow the manufacturer’s instructions for leaving them open, filling them, or using a specified joint detail.
Concrete cracks also need assessment. A coating can cover some repaired surface defects if the system allows it, but it is not a structural repair. If movement is ongoing or the crack’s cause is uncertain, get the slab assessed before coating.
A smooth cured epoxy surface is not automatically slip-resistant. The system may call for a broadcast aggregate to add texture, but the right texture depends on the use and cleaning needs. Do not assume a surface meets a particular DCOF value or accessibility requirement without relevant test data and project criteria.
Two illustrative installation scenarios
These examples show how the same coating can call for different decisions. They are not test results or promises of performance. The PDS and site conditions control the actual design.
- Clean, sound garage slab: The owner confirms the coating’s moisture limits, tests the slab as required, removes old sealer by mechanical preparation, and meets the specified CSP. The owner then follows the stated primer and film-build steps. The label alone did not determine readiness.
- Slab with elevated moisture readings: The owner compares test results with the coating system’s written limit. If the slab exceeds that limit, the owner pauses rather than applying the standard coating. A manufacturer-approved moisture-mitigation system may be needed, or the coating may not be suitable.
Cure, cleaning, maintenance, and long-term protection
Cure is the chemical process that turns the mixed coating into a solid film. Recoat time and return-to-service time are not always the same. Follow the PDS for each, and protect the uncured surface from water, dust, traffic, and temperature changes. Do not assume it is ready for use just because it feels dry.
Before work, confirm final texture and the expected cleaning method. After cure, use cleaning products allowed by the coating maker. Avoid dragging heavy items across the film unless the system and use conditions permit it. Keep the PDS and application details so future repairs can use compatible materials.
Frequently asked questions
These answers clarify what the “100% solids” label does and does not tell you. For product-specific decisions, use the current PDS and the manufacturer’s written instructions. Slab conditions, installation details, and intended use all matter.
Does 100% solids mean zero VOC?
No. “100% solids” describes the portion expected to remain as film by volume; it does not guarantee zero VOC, zero odor, or zero emissions. Check the product’s PDS and safety data sheet for VOC information, ventilation guidance, and handling precautions.
Is 100% solids epoxy waterproof?
Not automatically. The label does not establish that the product is a waterproofing membrane or can withstand hydrostatic pressure. Confirm the system’s written water and moisture limits, and address water entry or pressure before coating the slab.
Does it stop moisture vapor from concrete?
Not necessarily. A standard epoxy coating may blister or lose adhesion if vapor transmission exceeds its limits. Test using the method required by the manufacturer, compare results with its stated criteria, and use only an approved mitigation system if needed.
Can I apply it over wood?
Only if the manufacturer approves the specific wood panel, framing, deflection, primer, and coating system. Wood can move with changes in moisture and temperature, while a rigid epoxy film may not accommodate that movement. Do not assume approval from concrete instructions applies to wood.
How thick should a 100% solids epoxy coat be?
Use the WFT and spread rate specified in the PDS. At 100% volume solids, theoretical dry thickness is approximately equal to wet thickness, before losses and surface effects. The product label alone does not set a suitable thickness for your floor.
How do I know whether my slab is ready?
Confirm the concrete is sound and free of contaminants, then prepare it to the required CSP. Perform the moisture tests and meet the system’s written limits. Check cracks, joints, temperature, and dew point requirements before applying primer or coating.
Can I coat over an active concrete joint?
Not unless the specified system detail allows it. Active joints can move and may crack or tear a rigid coating that bridges them. Identify joints before work and follow the manufacturer’s instructions for preserving, filling, or treating each one.
When can I walk or drive on the coating?
Use the product’s stated cure and return-to-service times for foot traffic and vehicles. These times can depend on temperature and other conditions. “Dry to touch” does not necessarily mean the coating has cured enough for full use.
(This article was written by one of our staff writers, Marcus Vance. Visit our Meet the Team page.)
