STP ShaliPrime AC
Single-component silane-siloxane impregnation that lines concrete capillaries with an invisible, breathable water-repellent barrier — the first line of defence against chloride and sulphate ingress on facades, decks and masonry.
What is it?
A clear, single-component silane-siloxane penetrating primer from STP Limited (formerly ShaliGuard S-40). It soaks into concrete and masonry and reacts within the pores to form a hydrophobic polysiloxane lining — no surface film, no change in appearance.
Where is it used?
Bare concrete facades, bridge decks and piers, exposed RCC frames, brick and block masonry, natural stone, and as the primer coat beneath acrylic or liquid-applied waterproofing membranes.
Why use it?
It blocks waterborne chlorides and sulphates at the pore level while letting the substrate breathe, controls efflorescence in masonry, and gives film-forming topcoats a stable, water-repellent base.
How is it applied?
Flood-applied to saturation on clean, dry concrete with a low-pressure airless sprayer (brush or roller also acceptable) at 4-5 m²/L. Allow 4-5 hours drying before overcoating; apply only above 5°C.
About STP ShaliPrime AC
ShaliPrime AC is STP Limited’s silane-siloxane penetrative primer for concrete and masonry, supplied as a clear, colourless, low-viscosity liquid in 20 L packs. Unlike paints and membranes that sit on top of the substrate, it is absorbed into the capillary pore network, where it reacts with the moisture naturally present in concrete to form a permanent hydrophobic polysiloxane seal. The treated surface looks exactly as it did before — no gloss, no darkening, no film — yet water beads off instead of soaking in. Specifiers who worked with the earlier ShaliGuard S-40 will recognise this as the same product under STP’s current naming.
On Indian projects it earns its keep in two roles. As a standalone treatment, it protects exposed concrete and masonry from rain-driven water, waterborne chlorides and sulphates, and the efflorescence that follows. As a system primer, it conditions porous substrates before acrylic topcoats or liquid-applied membranes, so the finish coat is not fighting a damp, salt-charged base. Space Arc supplies ShaliPrime AC across Delhi NCR and Pan-India, with applicator support for spray-applied impregnation work.
The technical insight
The chemistry does the work below the surface. Silane molecules are small enough to travel deep into concrete capillaries, while the larger siloxane oligomers concentrate in the surface zone. Both react with pore moisture and the alkaline silicate substrate through hydrolysis and condensation, chemically bonding a water-repellent polysiloxane layer onto the pore walls themselves. This raises the contact angle inside the capillaries, so liquid water — and the chlorides and sulphates it carries — can no longer be drawn in by capillary suction. Crucially, the pores stay open to water vapour: internal moisture escapes rather than being trapped behind a film, which is why hydrophobic impregnations do not blister, peel or trap dampness the way sealed coatings on damp concrete can. Because the barrier is bonded within the substrate rather than resting on it, it is unaffected by UV and surface abrasion in the way a thin film would be, giving long service from a single flood coat.
Where it is used
- Water-repellent impregnation of exposed concrete facades, chajjas and architectural RCC before anti-carbonation or acrylic topcoats
- Chloride-ingress protection for bridge decks, piers, crash barriers and other highway structures
- Priming porous concrete before STP liquid-applied waterproofing membranes on parapets, podiums and terraces
- Efflorescence control on brick, block and rendered masonry structures
- Invisible protection of natural stone and cladding where the architect will not accept any change in appearance
- Weather protection of boundary walls, compound walls and exposed industrial structures in driving rain
- Supplementary protection of concrete surfaces prior to below-grade waterproofing build-ups
Key advantages
- Prevents ingress of waterborne chlorides and sulphates — the main drivers of rebar corrosion in exposed RCC
- Breathable: capillaries stay vapour-permeable, so trapped moisture escapes instead of blistering a coating
- Completely transparent with no change in surface appearance — safe on exposed concrete, stone and face brick
- Single-component, ready to use straight from the pack after stirring; no mixing ratios to get wrong
- Penetrates and chemically bonds within capillary pores, so protection is not lost to surface wear or UV
- Excellent water beading cuts absorption and the efflorescence cycle in masonry
- Economical at 4-5 m²/L per coat with fast, low-skill spray application
Limitations & considerations
- Works only on bare, absorbent substrates — existing paints, sealers, curing compounds and release agents must be removed first, or the primer cannot penetrate
- It is a hydrophobic impregnation, not a membrane: it will not bridge cracks, seal joints or resist standing or hydrostatic water
- Solvent-borne system — needs ventilation, PPE and xylene/toluene for tool cleaning; observe no-flame precautions during application
- Substrate must be dry at application and ambient temperature at least 5°C, which constrains monsoon-season programmes
- Because the treatment is invisible once dry, missed patches are hard to spot — coverage discipline and wet-on-wet saturation matter
- Supplied only in 20 L packs, which is inconvenient for small patch or trial areas
Selection & best practice
Start with the substrate, not the sprayer. The surface must be structurally sound, dry and free of grease, oil, dust and any curing compound or release agent — blow down with compressed air after preparation. Stir the pack well to disperse any sedimentation before use. Apply with a low-pressure airless sprayer for the most uniform result (brush or roller will do for small areas), working the material in a flood coat until the surface is visibly saturated, budgeting 4-5 m²/L and adjusting for how porous the concrete actually is — rough, absorbent surfaces drink more. Do not skimp: depth of penetration is what buys durability. Hold a minimum 5°C application temperature, keep rain off the fresh treatment, and allow at least 4-5 hours drying before any overcoating with membranes or topcoats. Wear a mask and gloves, ensure ventilation, and clean equipment with xylene or toluene immediately after use.
Specifications
| Chemistry / type | Silane-siloxane based penetrative primer, single component |
| Appearance | Clear, colourless, low-viscosity liquid |
| Specific gravity | 0.90 ± 0.02 |
| Theoretical coverage | 4-5 m²/L per coat (depends on surface porosity) |
| Minimum application temperature | 5°C |
| Drying time before overcoating | 4-5 hours minimum |
| Pack size | 20 L |
| Shelf life | 12 months in original unopened sealed pack, stored cool and dry under shed |
| Tool cleaning | Xylene or toluene |
Industry use cases
Bridges & Highways
Impregnation of decks, piers and crash barriers to slow chloride ingress and delay rebar corrosion on structures that cannot be easily recoated in service.
High-Rise & Real Estate
Invisible water repellency for exposed concrete facades and architectural features, applied standalone or as the primer under anti-carbonation coatings.
Waterproofing Contractors
System primer beneath acrylic and liquid-applied membranes on terraces, podiums and parapets, giving the membrane a dry, salt-blocked base to bond to.
Industrial Plants
Protection of exposed RCC frames, boundary walls and utility structures against driving rain and sulphate-laden atmospheres without repaint cycles.
Masonry & Restoration
Efflorescence control on brick, block and stone where the brief demands zero change to the original surface appearance.
Frequently asked questions
Is ShaliPrime AC a waterproofing coating on its own?
What coverage should I budget, and how many coats?
Can I apply it over painted or previously sealed concrete?
Will it darken or add sheen to exposed concrete or stone?
How long before I can overcoat with a membrane or paint?
Is this the same product as ShaliGuard S-40?
How we position STP ShaliPrime AC
Within the STP family, ShaliPrime AC is the front end of a system: on terraces and podiums it primes the substrate for STP’s liquid-applied membranes such as the ShaliCryl acrylic range, and on exposed structures it pairs naturally with STP’s protective and anti-carbonation coatings. Where a project needs joint sealing or crack repair before impregnation, those are separate scopes — talk to us about STP’s sealant and RestoFix repair lines rather than expecting the primer to cover them. Among our other brands, Fosroc Nitocote SN502 is the direct silane-siloxane equivalent and the usual choice where the consultant has standardised on Fosroc system warranties, while Dr. Fixit’s silicone-based water repellents suit smaller residential masonry jobs where pack size and availability matter more than deep silane penetration. Space Arc can supply and apply any of these; we will recommend the impregnation that matches your substrate, exposure and specification rather than defaulting to one brand.
Fosroc Nitocote SN502 — Specifiers standardised on Fosroc protection systems — or pairing the impregnation with Dekguard anti-carbonation coatings — often choose Nitocote SN502 for single-brand system accountability.
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