Repair Systems — 06
Sealant adhesion primers — substrate preparation
Technical product reference for sealant adhesion primers used with silicone, polyurethane and polysulfide movement joint sealants in Australian Class 2 strata and commercial building remediation. Covers primer chemistry, substrate compatibility, pot-life after application, and brand comparisons by sealant system.
What are sealant adhesion primers?
Sealant adhesion primers are chemical surface treatments applied to joint substrates immediately before sealant installation to promote adhesion between the sealant and substrate. They are not optional on most substrates — without the correct primer, sealants that appear bonded at installation will fail adhesively under movement, thermal cycling or water exposure. Primer selection is sealant-system-specific: the primer must be matched to the exact sealant chemistry (silicone, PU, polysulfide), the sealant brand, and the substrate type. A primer that works for one sealant system on one substrate will not necessarily work — and may actively interfere — with a different sealant on the same substrate.
Different sealant chemistries fundamentally require different primer chemistries. Polyurethane sealants require isocyanate or reactive silane primers that penetrate porous substrates. Silicone sealants on non-porous or difficult substrates require organosilane primers. Cross-brand and cross-chemistry use of primers is not supported by manufacturers and is a known cause of accelerated sealant adhesion failure in Australian Class 2 and commercial building remediation.
Do not confuse with:
- Concrete bonding agents (e.g. SBR bonding agents, epoxy bonding agents) — used to bond concrete repair mortars to existing concrete — not for sealant substrate priming
- Waterproofing membrane primers — used under liquid-applied waterproofing membranes — different product for a different purpose — not sealant primers
- Paint primers — used under decorative coatings — not suitable for sealant substrates and may prevent sealant adhesion
- Sealant backing rod — polyethylene foam bond breaker — joint component, not a primer — used together with, not instead of, primer
- Sealant accelerators — products that speed sealant cure — different from adhesion primers — do not substitute one for the other
Product Reference
4 products — 3 brands — sealant adhesion primers — scroll to view all
System Description
Sika Primer-215 is a solvent-based polyurethane solution primer specifically formulated for the treatment of bond faces prior to application of Sikaflex adhesives and sealants on plastics and wood substrates including GRP, epoxy resins, PVC, ABS, timber, and concrete. It is not limited to masonry/concrete — it is primarily a plastics and timber primer for Sikaflex PU sealant systems. It reacts with moisture to form a thin bonding layer. Applied by brush to the cleaned substrate, allowed to flash off (≥ 30 minutes at ≥15°C; ≥ 60 minutes below 15°C), then the Sikaflex sealant is applied within the open time window. Preliminary tests on original substrates under production conditions are recommended as plastic compatibility varies. Confirm compatible sealant products and application window from the current Sika AU TDS.
Technical Properties
- Single-component solvent-based polyurethane solution primer — reacts with moisture to form bonding layer
- Suitable substrates: GRP, epoxy resins, PVC, ABS, timber and concrete
- Flash-off time ≥30 min at ≥15°C; ≥60 min below 15°C
Limitations
- Confirm this is the correct primer for the specific Sikaflex product and substrate — cross-check from current Sika AU TDS
- Do not apply sealant if primer is still wet — flash-off must be complete
- Do not apply sealant if dust has contaminated primed surface — re-prime before proceeding
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
System Description
Sika Primer-3 N is a 1-component solvent-based epoxy resin compound primer for porous substrates and metal, designed for use with Sikaflex, SikaHyflex, SikaBond, SikaSeal and Sikasil products. It is not limited to non-porous or silicone-only applications — it is used on porous substrates (concrete, masonry, aerated concrete, cement renders, mortar, bricks) and on metal substrates. Flash-off time is ≥30 minutes (< 8 hours) for porous and metal substrates before sealant application. Application must follow the TDS for the specific Sika sealant being used, as the primer must be matched to the sealant system.
Technical Properties
- 1-component solvent-based epoxy resin compound primer for porous substrates and metal
- Suitable substrates: concrete, aerated concrete, cement renders, mortar, bricks and metal
- Designed for use with Sikaflex, SikaHyflex, SikaBond, SikaSeal and Sikasil product ranges
Limitations
- Confirm this is the correct primer for the specific Sika sealant and substrate — always confirm from current Sika AU TDS
- Flash-off time must be followed precisely — sealant application window is critical
- Do not contaminate primed surface before sealant application — re-prime if contaminated
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
System Description
Dow Corning PR-1200 OS Primer is a one-component adhesion promoter for use with Dow Corning silicone sealants on glass, metal (anodised, powder-coated, stainless), painted surfaces, ceramic and concrete substrates. Widely used in structural glazing, curtain wall and facade remediation where Dow Corning 795 or other Dow structural silicone sealants are being used. Application must follow the Dow 795 or applicable sealant TDS — primer and sealant must be a matched system. Confirm current product name and formulation with Dow Australia.
Technical Properties
- Single-component organosilane primer — suitable for glass, anodised aluminium, stainless steel, ceramic, concrete and masonry
- Transparent and non-staining after cure
- Works as adhesion promoter for structural glazing applications
Limitations
- Must be used with matched Dow silicone sealant — cross-brand use without compatibility testing is not recommended
- Not suitable for use with PU or polysulfide sealants
- Confirm current product name — Dow product range may have been updated since this reference was written
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
Tremco Primer No. 12
TODO: owner confirm — Tremco sealant primer — confirm current AU product name
System Description
TODO: owner confirm — Tremco Primer No. 12 is not listed on the current Tremco Australia product page (tremco.com.au). The current Australian Tremco sealant primer product range includes TREMprime Non-Porous Primer (one-part primer for metal or plastic substrates for Tremco PU sealants), Vulkem 171 Primer and Vulkem 191 QD Primer (for Vulkem PU sealant systems), and TREMprime EP. Confirm the correct current AU Tremco primer for the specific sealant and substrate before specifying. The general description that follows is based on general product category knowledge and must be confirmed from the current Tremco Australia TDS.
Technical Properties
- TODO: owner confirm — Primer No. 12 not found on current Tremco AU product list — verify with Tremco Australia
- Solvent-based adhesion primer — suitable for Tremco silicone and modified sealant systems
- Suitable for concrete, masonry, metal and glass substrates
Limitations
- TODO: owner confirm — verify current AU product name before specifying
- Tremco system-specific — do not use with non-Tremco sealants without testing
- Solvent-based — PPE and adequate ventilation required
PROCUREMENT SOURCES
Confirm suitability with the current manufacturer TDS before specifying or applying.
Brand Equivalents — by Use Case
Primer selection by substrate and sealant type. Always confirm correct primer from current manufacturer TDS — primers are sealant-system-specific.
| Use case | Sika Primer-215 | Sika Primer-3 N | Dow PR-1200 | Tremco No. 12 |
|---|---|---|---|---|
| PU sealant on concrete/masonry | ✓ (confirm TDS) | ✓ (confirm TDS) | — | TODO: confirm |
| Sika sealant on plastics/GRP/PVC | ✓ | — | — | TODO: confirm |
| Structural glazing silicone | — | Confirm per TDS | ✓ | TODO: confirm |
| General concrete/masonry | ✓ (concrete) | ✓ | ✓ | TODO: confirm |
| Metal/anodised aluminium | — | ✓ | ✓ | TODO: confirm |
System Comparison
Technical comparison across the four listed primer products. Confirm all values from current manufacturer TDS before specifying.
| Property | Sika 215 | Sika 3N | Dow PR-1200 | Tremco No. 12 |
|---|---|---|---|---|
| Chemistry | Solvent-based PU solution | Solvent-based epoxy resin | Organosilane | TODO: confirm AU product |
| Target sealant | Sikaflex PU adhesives/sealants | Sikaflex, SikaHyflex, Sikasil, SikaBond | Dow silicone | TODO: confirm AU product |
| Porous substrates | Yes (concrete, timber, GRP) | Yes (concrete, masonry, mortar) | Yes | TODO: confirm |
| Non-porous substrates | Yes (PVC, ABS, GRP) | Yes (metal) | Yes | TODO: confirm |
| Structural glazing | No | Confirm per TDS | Yes | TODO: confirm |
| Flash-off time | ≥30 min (≥15°C); ≥60 min (<15°C) | ≥30 min (<8 hours) | 30–60 min | TODO: confirm AU TDS |
| Solvent/water | Solvent | Solvent | Solvent | TODO: confirm |
Critical — Primer is Sealant-System-Specific
- Always use the primer recommended by the sealant manufacturer for the exact sealant product and substrate combination — primer selection is not generic
- Using the wrong primer — or omitting primer — is the primary preventable cause of sealant adhesion failure on Australian Class 2 and commercial building remediation sites
- Cross-brand primer and sealant combinations are not supported — a Sika primer will not substitute for a Dow primer under a Dow sealant, and vice versa
- Flash-off and open time must be followed precisely — both too short and too long a wait before sealant application can result in adhesion failure
- Confirm all primer products from current manufacturer TDS — product names, formulations and recommendations are subject to change
Disclaimer
Information is general only. Sealant primer selection is sealant-system-specific — always use the primer specified by the sealant manufacturer for the exact sealant chemistry and substrate combination being used. Using the wrong primer can prevent adhesion or cause accelerated sealant failure. Confirm from current manufacturer TDS before application.