Sika Ronacrete Unicell Primer

Unicell Primer — Rebar Primer & Bonding Aid

Unicell Primer is a liquid bonding and priming aid that requires mixing with ordinary Portland cement (OPC) to form a brushable slurry. Applied to exposed steel reinforcement, it forms a tough flexible passivating layer against damaging ions and oxidation. Applied to concrete substrates, it provides enhanced bonding and a barrier to water and ion ingress. Water-based formula with low VOC (<10g/L), economic and easy to use. Designed specifically for the Unicell range but also compatible with most cementitious mortars, renders, concretes, and screeds.

Key Features

• Steel passivation: Forms an anti-corrosion barrier on exposed reinforcement
• Enhanced bonding: Significantly improves bond between repair mortar and substrate
• Waterproofing barrier: Resists water and harmful ion penetration
• Water-based, low VOC (<10g/L)
• Simply mix with cement for easy application
• Economic
• Designed for the Unicell range, also compatible with other cementitious mortars

Unicell Concrete Repair System

Unicell Primer is the first step in the Sika Ronacrete concrete repair system:

1. Step 1: Unicell Primer — Rebar passivation + substrate bonding coat
2. Step 2: Unicell 25 or Unicell 40 — Repair mortar to fill spalled areas
3. Step 3: Finishing — Render or paint

Typical Applications

• Steel protection in reinforced concrete
• Bonding coat before concrete repair
• Thin/thick section bonding for mortars
• Primer for screeds and renders

Why Choose Unicell Primer?

• Dual function: Bonding primer and rebar passivation in one product
• High bond strength: With Unicell 40, achieves 2.7 MPa at 7 days, exceeding HKHA requirements
• Low VOC: Water-based formula with VOC below 10g/L
• Cost effective: Coverage rate of 4-8 m²/litre

Packaging & Consumption

Technical Specifications

Test Method: TM4

Important Notes

• Ambient temperature must be above 5°C
• Remove all defective concrete to a sound substrate; loose rust and scale must be removed
• Cut around repair perimeter to minimum 6 mm depth with angle grinder to avoid feather edges
• Mix with cement using a slow speed drill (approx. 500 rpm), adding cement slowly
• Allow the rebar passivation coat to dry, then apply a second coat of primer to reinforcement and concrete as the bonding coat
• Apply repair mortar (Unicell 25/40/WF) while the bonding coat is still wet/tacky
• If the primer dries completely, it must be reapplied

Unicell Primer vs Mapefer vs Fosroc Primer Comparison

FAQ

What is the difference between Unicell Primer and Mapefer?

Both serve similar functions but differ in formulation. Unicell Primer is a liquid polymer that must be mixed with cement (1:1.5 by volume or 1:2 by weight), providing both bonding and rebar passivation. Mapefer 1K is a single-component cementitious anti-corrosion mortar applied directly. Choose based on your repair mortar brand — Unicell Primer with Unicell mortars, Mapefer with Mapei mortars.

Is a primer necessary for concrete repair?

If exposed reinforcement is present, Unicell Primer is strongly recommended for steel passivation. For surface-only repairs without exposed rebar, the primer still significantly improves bond strength between repair mortar and substrate, reducing the risk of future delamination.

What is the coverage rate of Unicell Primer?

When mixed with OPC cement, coverage is approximately 4-8 m² per litre, depending on surface roughness and porosity of the substrate.