Choosing the correct epoxy floor primer is essential for adhesion, coating durability and long-term flooring performance. The best primer depends on the condition of the concrete, surface porosity, moisture exposure and how quickly subsequent coats need to be applied.
FORTIS offers several options, including self-priming epoxy coatings, fast-curing primers, high-adhesion primers for soft or difficult concrete, and specialist moisture vapour barriers.
| Concrete Condition | Recommended Product | Main Advantage |
|---|---|---|
| Sound, properly prepared concrete | Coat 823 HS or AquaCoat™ | Self-priming options where permitted by the product specification. |
| Sound, dry concrete requiring rapid recoating | FORTIS 823 Prime | Fast-curing, solvent-based epoxy primer for quicker application of subsequent coats. |
| Soft, porous, weak-surfaced or difficult concrete | FORTIS 820 Prime | Excellent penetration, adhesion and consolidation of suitable soft concrete. |
| Properly prepared, slightly damp concrete | FORTIS 820 Prime | High-adhesion primer with suitability for certain slightly damp substrates, without standing water. |
| Significant moisture vapour transmission | HydroFort VB | Specialist moisture vapour control where specified following substrate assessment. |
Yes. Some epoxy floor coatings can act as their own primer on sound, correctly prepared concrete, avoiding the need for a separate primer product.
FORTIS Coat 823 HS can be diluted with FORTIS Sol-X for use as a primer before subsequent coats of 823 HS. Follow Fortis technical guidance for the appropriate dilution and application requirements.
FORTIS AquaCoat™ is a water-based epoxy coating that can also act as its own primer on properly prepared concrete. The first coat may be diluted 10–15% with water, as specified in the Technical Data Sheet.
Self-priming does not eliminate the need for mechanical surface preparation. A dedicated primer is often preferable where concrete is soft, porous, difficult or unevenly absorbent.
FORTIS 823 Prime is a two-component, solvent-based epoxy primer designed for excellent penetration, substrate wetting and rapid recoating.
It is particularly suitable for sound, dry concrete beneath high-build epoxy coatings and decorative flake flooring systems where installation speed is important.
Typical coverage is 8–14 m²/L, with a recoat time of approximately 3–4 hours, subject to temperature and application conditions.
Choose 823 Prime when: The concrete is sound and dry, a separate primer is required, and rapid recoating is a priority.
FORTIS 820 Prime is a two-component, high-solids, low-solvent epoxy primer developed for excellent adhesion and penetration into soft, porous and difficult concrete.
Its outstanding substrate wetting helps penetrate and consolidate suitable weak concrete surfaces, creating a reliable bonding layer for subsequent epoxy floor coatings.
820 Prime is particularly useful on older industrial concrete floors, porous substrates and difficult surfaces where improving surface integrity and adhesion is more important than rapid recoating.
It may also be used on properly prepared slightly damp concrete without standing water, subject to substrate assessment and the current Technical Data Sheet.
Typical coverage is approximately 6 m²/L, with an 8–48 hour recoat window.
Choose 820 Prime when: Concrete is soft, porous or difficult, and excellent penetration, surface consolidation and high adhesion are required.
Important: 820 Prime can help consolidate suitable soft concrete but cannot restore structurally unsound material. Loose or friable concrete must be removed or repaired before coating. It is not a moisture vapour barrier.
Moisture is a common cause of epoxy flooring failure. Where concrete is affected by significant moisture vapour transmission, rising damp or other elevated moisture conditions, a conventional epoxy primer may not provide adequate protection.
HydroFort VB is a specialist epoxy vapour barrier intended for moisture management beneath compatible flooring systems.
Moisture conditions must be assessed before coating. Select HydroFort VB where appropriate for the substrate and flooring specification, following its current Technical Data Sheet.
Correct surface preparation is essential regardless of the primer selected. Concrete must be clean and free from dust, laitance, oil, grease, curing compounds, loose material and other contaminants that can affect adhesion.
Diamond grinding is generally the preferred preparation method because it removes weak surface material and creates a suitable mechanical profile for epoxy adhesion.
Soft or porous concrete should be assessed for surface integrity. Primers can improve bonding and consolidate suitable surfaces, but structurally unsound concrete must be repaired.
Check concrete moisture, temperature and porosity before application. Follow the relevant Fortis Technical Data Sheet for mixing ratios, coverage, working time and recoat windows.
For more information, read How to Prepare Concrete for Floor Coatings and Polishing.
FORTIS 820 Prime is generally the preferred option for suitable soft or porous concrete because of its excellent penetration, substrate wetting and ability to help consolidate weak surface material. Structurally unsound concrete still requires repair.
820 Prime is a high-solids, low-solvent epoxy primer designed for excellent adhesion and penetration into soft, porous or difficult concrete. 823 Prime is a solvent-based, fast-curing primer designed for rapid recoating on sound, dry concrete.
No. 820 Prime is a high-solids, low-solvent epoxy primer. It should not be described as solvent-free or zero VOC.
Not always. On sound, properly prepared concrete, Coat 823 HS can be diluted with Sol-X to function as a primer. A dedicated primer may be preferable for rapid recoating, porous concrete or difficult substrate conditions.
FORTIS 820 Prime may be suitable for properly prepared slightly damp concrete without standing water. Significant moisture transmission requires separate assessment and may require a specialist vapour barrier.
No. Conventional epoxy primers improve adhesion and substrate wetting. A specialist product such as HydroFort VB is designed for moisture vapour control where specified.
Diamond grinding is generally recommended to remove laitance, contamination and weak surface material while creating a suitable profile for reliable adhesion.
Primer selection should be considered alongside the complete flooring system. For sound concrete, self-priming may be appropriate. Where rapid recoating is important, choose 823 Prime. For soft or difficult concrete, consider 820 Prime. Where significant moisture transmission is present, investigate whether HydroFort VB is required.
Explore FORTIS Epoxy Floor Coatings or contact the Fortis technical team for assistance with substrate assessment and system selection.