Sika Sikagard-551 S Elastic Primer
A one-part silane-siloxane primer that penetrates, strengthens and seals concrete so anti-carbonation and protective coating systems bond reliably, even on difficult substrates.
What is it?
A ready-to-use, one-part silane-siloxane modified penetrating primer on a solvent-based polymer binder, supplied as a colourless liquid for concrete surface preparation.
Where is it used?
On very dense or very porous exposed concrete, and over firmly adhering old solvent-based coatings, ahead of Sika anti-carbonation and protective coating systems.
Why use it?
It penetrates deep to consolidate weak, dusty or porous surfaces, stays water-vapour permeable so the structure can breathe, and gives topcoats a sound, uniform key.
How is it applied?
Stir well and apply neat by brush, roller or airless spray at 0.10-0.15 kg/m2; on very dense concrete add up to 10% Sika Thinner C to aid penetration.
About Sika Sikagard-551 S Elastic Primer
Concrete protection systems live or die on the primer. Sikagard-551 S Elastic Primer is the base layer Sika specifies when a substrate is either too tight to accept a coating or too weak and dusty to trust. Built on a silane-siloxane modified solvent-based binder, it soaks into the surface rather than sitting on top, chemically binding to the concrete and pulling loose, friable material together into a coherent, sound plane. On very porous or degraded concrete, where surface tensile strength has dropped below 1 N/mm2, that consolidation is what lets a protective or anti-carbonation coating develop the adhesion it needs. On very dense, low-absorbency concrete it does the opposite job, wetting out the surface and creating enough tooth for the following coat to grip.
For engineers and applicators across Delhi NCR and Pan-India, the appeal is practical. It arrives ready to use in a 16 kg container, needs only thorough stirring, and lays down easily by brush, roller or airless spray at roughly 0.10-0.15 kg/m2. It stays water-vapour permeable, so moisture in the slab can still escape and the coating system does not blister from trapped vapour. Because both water-dispersed and solvent-containing topcoats can go over it, it slots cleanly into Sika protective schemes built around products such as Sikagard-550 W IN and Sikagard-680 MY. As Space Arc, an authorised distributor and applicator, we supply it with the current data sheet and the site guidance to use it correctly.
The technical insight
The chemistry does two jobs at once. Silane and siloxane molecules are small enough to migrate into the capillary pores of concrete, then react with moisture and the alkaline substrate to form a hydrophobic, chemically bound network inside the surface zone rather than a film on it. That reaction is what strengthens weak concrete: the primer knits porous, low-cohesion material together and raises the effective pull-off strength of the surface a coating will later be tested against. At the same time the network is water-repellent but not vapour-tight, so liquid water and dissolved contaminants are held back while water vapour from within the slab can still diffuse out. This breathability is the reason the whole coating system resists blistering and osmotic failure. On dense concrete, where there are few pores to penetrate, the same binder simply improves surface wetting and inter-coat adhesion, which is why up to 10% Sika Thinner C is allowed to thin the primer and drive it further into a tight surface.
Where it is used
- Priming very dense concrete before anti-carbonation and protective coating systems
- Priming very porous or weathered concrete with surface tensile strength below 1 N/mm2
- Consolidating dusty, friable or weak concrete surfaces so a topcoat can bond
- Re-priming over firmly adhering existing solvent-based coatings before recoating
- Base coat under Sika protective schemes using Sikagard-550 W IN or Sikagard-680 MY solvent-based topcoats
- Surface preparation on facades, soffits, columns and exposed RCC in repair and protection works
- Priming difficult or absorbent substrates where a standard water-based primer struggles
- Preparing bridge, water-retaining and industrial structure concrete ahead of protective overcoats
Key advantages
- Deep penetration that consolidates weak, porous concrete rather than just coating it
- Chemically strengthens surfaces down to below 1 N/mm2 tensile so topcoats can develop adhesion
- Water-vapour permeable, letting the slab breathe and reducing blistering risk
- Ready to use, single component, so no mixing errors on site, just stir and apply
- Accepts both water-dispersed and solvent-containing Sika topcoats over it
- Works on the full range from very dense to very porous concrete
- Applies easily by brush, roller or airless spray for large-area productivity
- Colourless finish that does not affect the appearance of the following coating
Limitations & considerations
- Solvent-based, so it needs adequate ventilation and standard solvent handling precautions on site
- Not for use on concrete younger than 28 days, which delays priming on fresh pours
- Application window is restricted to +8 C to +40 C substrate and ambient, with relative humidity below 80%
- Over existing coatings the waiting time before overcoating doubles, extending the programme
- For water-based coating systems Sika specifies Sikagard-552 IN Primer W instead of this primer
- Cured primer can only be removed mechanically, so overspray and spills must be controlled
Selection & best practice
Prepare the substrate first: it can be dense or porous but must be free of loose, friable material, so use steam cleaning, high-pressure water jetting or blast cleaning, and make sure new concrete is at least 28 days old. On thin renderings, apply a levelling pore sealer such as Sikadur-31 IN and allow at least 4 days cure before priming. Check that ambient and substrate temperatures sit between +8 C and +40 C, relative humidity is under 80%, and the surface is at least 3 C above dew point. Never prime when rain is expected. Stir the container thoroughly and apply neat at 0.10-0.15 kg/m2; on very dense concrete add up to 10% Sika Thinner C to improve penetration. Respect the overcoating window, roughly 6 hours at +30 C and 24 hours at +10 C, and remember it doubles over existing coatings. Protect fresh primer from rain for at least 6 hours, and clean tools with Sika Thinner C immediately after use.
Specifications
| Product type | One-part silane-siloxane modified penetrating primer |
| Chemical base | Solvent-based polymer binder |
| Appearance / colour | Colourless liquid |
| Density | ~0.93 kg/L at +30 C (EN ISO 2811-1) |
| Consumption | 0.10-0.15 kg/m2, depending on substrate absorbency |
| Application temperature | +8 C min / +40 C max (ambient and substrate) |
| Overcoating time | 24 h at +10 C, 6 h at +30 C, 5 h at +40 C |
| Packaging | 16 kg container |
| Shelf life / storage | 12 months; store dry at +5 C to +35 C, out of sun and frost |
Industry use cases
Infrastructure and bridges
Consolidates weathered, low-strength RCC on piers, soffits and decks before solvent-based anti-carbonation coatings are applied to slow reinforcement corrosion.
Commercial and residential facades
Primes dense or dusty exposed concrete on columns, fins and elevations so decorative protective topcoats bond uniformly and resist peeling.
Water-retaining and industrial structures
Strengthens porous concrete surfaces and provides a vapour-permeable base for protective schemes on tanks, plants and process buildings.
Repair and rehabilitation projects
Re-primes firmly adhering old solvent-based coatings and binds friable repaired concrete ahead of recoating in structural refurbishment works.
Frequently asked questions
What exactly does Sikagard-551 S Elastic Primer do?
How much primer will I need per square metre?
Can I use it under any topcoat?
Does it work on very smooth, dense concrete?
How long before I can apply the next coat?
Are there conditions when I should not apply it?
How we position Sika Sikagard-551 S Elastic Primer
Sikagard-551 S Elastic Primer is the solvent-side primer within Sika’s concrete protection range and is designed to work under Sika topcoats such as Sikagard-550 W IN and Sikagard-680 MY. If your coating system is water-based, its natural counterpart is Sikagard-552 IN Primer W. Where thin renderings or pinholes must be levelled first, Sika epoxy fillers like Sikadur-31 IN are used ahead of priming. From our wider portfolio at Space Arc, this primer suits protective-coating and rehabilitation work; for pure water-repellent facade treatment without a full coating system, a penetrating silane cream is the better route, and for high-build elastomeric protection ask us to pair the correct topcoat.
Fosroc Dekguard Primer — Specifiers standardising on the Fosroc Dekguard protective system will pair this silane-siloxane primer with Dekguard topcoats instead of mixing brands, keeping the anti-carbonation system warranty and detailing under one manufacturer.
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Authorised distribution, technical advice & professional application across Delhi NCR and Pan-India.