Repair Systems
Moisture suppression primers
Two-part epoxy moisture-suppressing floor primer — technical reference for magnesite flooring deterioration in Australian remedial building practice. Covers system selection, product comparisons, and brand equivalents.
What is moisture suppression primers?
Moisture suppression primers are the critical first step in any magnesite flooring encapsulation or overlay system. Magnesite (magnesium oxychloride screed) is hygroscopic — it absorbs moisture from below and generates osmotic pressure that destroys adhesive bonds and blisters coatings and floor coverings. A moisture-tolerant epoxy primer forms a vapour-suppressing membrane directly over the prepared magnesite surface, dramatically reducing moisture vapour emission rate (MVER) to levels compatible with self-levelling underlayments and adhesive floor covering systems. Independent in-situ moisture testing to ASTM F2170 (relative humidity probe) or anhydrous calcium chloride testing to AS 1884 is mandatory before primer selection — different primers have different maximum RH tolerances. Two-part epoxy systems are preferred where moisture levels are elevated. Correct primer selection and application is the single most important factor in the long-term performance of a magnesite overlay system.
Product Reference
Scroll right to see all brands. Use each card's TDS link for verified specifications before specifying on any project.
System Description
Mandatory pre-application moisture testing — ASTM F2170 in-situ RH probe or anhydrous calcium chloride test. Substrate must achieve minimum CSP 2 profile. Remove all friable, delaminating, or actively corroding magnesite before priming. Allow primer to cure fully before applying self-levelling compound. Do not apply over active efflorescence or contaminated surface.
Technical Properties
- Creates a vapour-suppressing membrane that prevents moisture-driven failure of overlays and adhesives
- Two-part epoxy systems tolerant of high substrate RH — appropriate for moisture-affected magnesite
Limitations
- Application over friable, actively corroding, or heavily contaminated magnesite will fail — full assessment and spot repair mandatory first
- Each system has a maximum RH tolerance — independent testing required to select appropriate primer
PROCUREMENT SOURCES
Ardex MC Rapid
two-part epoxy moisture control primer for high-RH substrates, 10 L kit
System Description
Mandatory pre-application moisture testing — ASTM F2170 in-situ RH probe or anhydrous calcium chloride test. Substrate must achieve minimum CSP 2 profile. Remove all friable, delaminating, or actively corroding magnesite before priming. Allow primer to cure fully before applying self-levelling compound. Do not apply over active efflorescence or contaminated surface.
Technical Properties
- Creates a vapour-suppressing membrane that prevents moisture-driven failure of overlays and adhesives
- Two-part epoxy systems tolerant of high substrate RH — appropriate for moisture-affected magnesite
Limitations
- Application over friable, actively corroding, or heavily contaminated magnesite will fail — full assessment and spot repair mandatory first
- Each system has a maximum RH tolerance — independent testing required to select appropriate primer
PROCUREMENT SOURCES
Fosroc Nitoprime 28
two-part penetrating epoxy primer for damp and high-moisture substrates, 4 L kit
System Description
Mandatory pre-application moisture testing — ASTM F2170 in-situ RH probe or anhydrous calcium chloride test. Substrate must achieve minimum CSP 2 profile. Remove all friable, delaminating, or actively corroding magnesite before priming. Allow primer to cure fully before applying self-levelling compound. Do not apply over active efflorescence or contaminated surface.
Technical Properties
- Creates a vapour-suppressing membrane that prevents moisture-driven failure of overlays and adhesives
- Two-part epoxy systems tolerant of high substrate RH — appropriate for moisture-affected magnesite
Limitations
- Application over friable, actively corroding, or heavily contaminated magnesite will fail — full assessment and spot repair mandatory first
- Each system has a maximum RH tolerance — independent testing required to select appropriate primer
PROCUREMENT SOURCES
Mapei Primer G
solvent-free acrylic adhesion and moisture-barrier primer, 1 L
System Description
Mandatory pre-application moisture testing — ASTM F2170 in-situ RH probe or anhydrous calcium chloride test. Substrate must achieve minimum CSP 2 profile. Remove all friable, delaminating, or actively corroding magnesite before priming. Allow primer to cure fully before applying self-levelling compound. Do not apply over active efflorescence or contaminated surface.
Technical Properties
- Creates a vapour-suppressing membrane that prevents moisture-driven failure of overlays and adhesives
- Two-part epoxy systems tolerant of high substrate RH — appropriate for moisture-affected magnesite
Limitations
- Application over friable, actively corroding, or heavily contaminated magnesite will fail — full assessment and spot repair mandatory first
- Each system has a maximum RH tolerance — independent testing required to select appropriate primer
PROCUREMENT SOURCES
Parchem Epirez 510
two-part low-viscosity epoxy adhesion and moisture-control primer, 5 L kit
System Description
Mandatory pre-application moisture testing — ASTM F2170 in-situ RH probe or anhydrous calcium chloride test. Substrate must achieve minimum CSP 2 profile. Remove all friable, delaminating, or actively corroding magnesite before priming. Allow primer to cure fully before applying self-levelling compound. Do not apply over active efflorescence or contaminated surface.
Technical Properties
- Creates a vapour-suppressing membrane that prevents moisture-driven failure of overlays and adhesives
- Two-part epoxy systems tolerant of high substrate RH — appropriate for moisture-affected magnesite
Limitations
- Application over friable, actively corroding, or heavily contaminated magnesite will fail — full assessment and spot repair mandatory first
- Each system has a maximum RH tolerance — independent testing required to select appropriate primer
PROCUREMENT SOURCES
Sika Primer-3N
single-component adhesion primer for porous and semi-porous substrates, 1 L
System Description
Used over encapsulated magnesite where moisture levels are within acceptable limits (typically <75% RH). Apply to clean primed surface, allow to become tacky before applying self-levelling compound. Do not dilute. Coverage approx 8–12 m²/L depending on porosity.
Technical Properties
- Creates a vapour-suppressing membrane that prevents moisture-driven failure of overlays and adhesives
- Two-part epoxy systems tolerant of high substrate RH — appropriate for moisture-affected magnesite
Limitations
- Application over friable, actively corroding, or heavily contaminated magnesite will fail — full assessment and spot repair mandatory first
- Each system has a maximum RH tolerance — independent testing required to select appropriate primer
PROCUREMENT SOURCES
Ardex P 51
single-component acrylic adhesion primer for floor levelling systems, 5 L
System Description
Used over encapsulated magnesite where moisture levels are within acceptable limits (typically <75% RH). Apply to clean primed surface, allow to become tacky before applying self-levelling compound. Do not dilute. Coverage approx 8–12 m²/L depending on porosity.
Technical Properties
- Dual function: apply undiluted as a substrate bonding primer, or add to cementitious mortar mix as an SBR admixture
- Improves mortar flexibility, reduces shrinkage, and increases bond pull-off strength on existing concrete
- Specified component in the Ardex repair system — part of Ardex warranted application
- Water-based — easy clean-up, low VOC, suitable for enclosed spaces
Limitations
- Must be applied wet-on-wet as bond coat — if it dries before mortar placement it becomes a bond breaker
- Not a waterproofing coating — SBR improves bond strength only; it is not a substitute for membrane waterproofing
- Admixture dilution ratio must strictly follow the Ardex data sheet — do not over-dose
PROCUREMENT SOURCES
System Description
Used over encapsulated magnesite where moisture levels are within acceptable limits (typically <75% RH). Apply to clean primed surface, allow to become tacky before applying self-levelling compound. Do not dilute. Coverage approx 8–12 m²/L depending on porosity.
Technical Properties
- Standard bond coat for all Fosroc repair mortars — specified component in the complete Fosroc repair system
- SBR emulsion provides mechanical and chemical key for repair mortar on prepared concrete
- Adds flexibility to mortar mix when used as an admixture — reduces early shrinkage cracking
- Compatible with Nitobond EP for dual-coat priming on chloride-affected substrates
Limitations
- Wet-on-wet application required — if allowed to dry before mortar placement, bond improvement is lost and delamination risk increases
- Not an epoxy primer — for chloride-affected structural repairs, engineer may require Nitobond EP epoxy primer in addition
- Shelf life limited once opened — use within manufacturer-specified period
PROCUREMENT SOURCES
Mapei Eco Prim T
single-component acrylic primer for self-levelling underlayments, 1 L
System Description
Used over encapsulated magnesite where moisture levels are within acceptable limits (typically <75% RH). Apply to clean primed surface, allow to become tacky before applying self-levelling compound. Do not dilute. Coverage approx 8–12 m²/L depending on porosity.
Technical Properties
- Creates a vapour-suppressing membrane that prevents moisture-driven failure of overlays and adhesives
- Two-part epoxy systems tolerant of high substrate RH — appropriate for moisture-affected magnesite
Limitations
- Application over friable, actively corroding, or heavily contaminated magnesite will fail — full assessment and spot repair mandatory first
- Each system has a maximum RH tolerance — independent testing required to select appropriate primer
PROCUREMENT SOURCES
Parchem Concure SBR
SBR primer and curing admixture for floor applications, 5 L
System Description
Used over encapsulated magnesite where moisture levels are within acceptable limits (typically <75% RH). Apply to clean primed surface, allow to become tacky before applying self-levelling compound. Do not dilute. Coverage approx 8–12 m²/L depending on porosity.
Technical Properties
- Creates a vapour-suppressing membrane that prevents moisture-driven failure of overlays and adhesives
- Two-part epoxy systems tolerant of high substrate RH — appropriate for moisture-affected magnesite
Limitations
- Application over friable, actively corroding, or heavily contaminated magnesite will fail — full assessment and spot repair mandatory first
- Each system has a maximum RH tolerance — independent testing required to select appropriate primer
PROCUREMENT SOURCES
Brand Equivalents
Side-by-side view of equivalent products across all major brands.
| Material | Ardex | Sika | Fosroc | Tremco / Other | Parchem / Mapei |
|---|---|---|---|---|---|
| Two-part epoxy moisture control primer | Ardex MC Rapid | Sika Primer MB | Fosroc Nitoprime 28 | Parchem Epirez 510 | Mapei Primer G |
| Single-component acrylic adhesion primer | Ardex P 51 | Sika Primer-3N | Fosroc Nitobond SBR | Parchem Concure SBR | Mapei Eco Prim T |
Disclaimer
Information is general only. Product selection must be confirmed against project requirements, substrate condition, exposure class, manufacturer technical data sheets, NCC requirements, Australian Standards (including AS 3600), and consultant or structural engineer specifications. Do not rely on this reference as a substitute for professional engineering advice.
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