STP ShaliPrime PUM
Low-viscosity, moisture-curing aromatic polyurethane primer that soaks into porous concrete, binds down dust and gives PU membranes and coatings a substrate worth bonding to — 4–5 m² per litre per coat.
What is it?
A single-component aromatic polyurethane resin primer from STP Limited (formerly sold as ShaliPrime Penetration). Its very low viscosity lets it wick deep into porous substrates, where it cures with atmospheric moisture into a thin, tough bonding film.
Where is it used?
On cured concrete, masonry and clean metal ahead of polyurethane waterproofing membranes, PU protective coatings and PU floor systems — roofs, podiums, plant floors and structural steelwork.
Why use it?
Weak, dusty or manually prepared concrete is the most common reason PU systems debond. ShaliPrime PUM consolidates that surface layer and presents a chemically compatible PU-to-PU interface for the coat that follows.
How is it applied?
One thin coat by brush or airless spray on dry, prepared substrate (concrete cured 28 days, moisture under 5%). Surface dry in 35–45 minutes at 30°C; overcoat after about 2 hours.
About STP ShaliPrime PUM
ShaliPrime PUM is STP Limited’s penetrating primer for polyurethane systems — a single-pack aromatic PU resin thinned to a very low viscosity so it travels into the capillaries of porous concrete rather than sitting on top of it. Once in the pores it cures with ambient moisture, binding friable material into a sound, sealed surface. Site crews will remember it by its old name, ShaliPrime Penetration; the material’s role is unchanged. At 4–5 m² per litre per coat it builds a 40–50 micron film that dries to the touch in under an hour at 30°C.
Where a two-pack epoxy primer needs mixing discipline and has a ticking pot life, ShaliPrime PUM comes ready to use straight from the container, with a 6–7 hour working life at 30°C. That makes it forgiving on large roof and podium decks where priming runs ahead of the membrane crew. Space Arc Engineering supplies it in 1 L and 20 L packs across Delhi NCR and pan-India, with applicator support for full STP polyurethane build-ups.
The technical insight
The primer works on two fronts. Physically, its low viscosity and 0.92–0.97 g/cc density let capillary action pull the resin several millimetres into porous concrete, so the cured polymer anchors mechanically inside the substrate instead of relying on a surface skin. Chemically, the free isocyanate groups in the aromatic prepolymer react with ambient and substrate moisture, crosslinking into a polyurethane/polyurea network that consolidates dust and laitance in place. Because the cured film is itself polyurethane, the membrane or coating applied next bonds to like chemistry — a genuine intercoat weld rather than mere mechanical key. The same isocyanate reactivity is why the drum must be used completely once opened: humid air will start curing whatever is left behind.
Where it is used
- Priming porous concrete roofs and podium decks before liquid-applied PU waterproofing membranes
- Consolidating weak, dusty or manually prepared concrete before PU coatings
- Primer coat on clean, dry metal surfaces ahead of polyurethane topcoats
- Substrate preparation under STP polyurethane waterproofing systems in wet areas and sunken portions
- Sealing porous masonry before PU coating or sealant work
- Priming wood substrates prior to polyurethane finishes
- Re-priming floors and decks after old paint has been ground off, ahead of a new PU system
Key advantages
- Very low viscosity penetrates deep into porous substrates instead of filming over them
- Single component — no mixing ratios, no induction time, no pot-life waste
- Long 6–7 hour working life at 30°C suits large-area priming ahead of membrane crews
- Fast turnaround: surface dry in 35–45 minutes, recoatable in about 2 hours
- Consolidates friable surfaces, improving performance over manually prepared concrete
- Gives the follow-on PU layer better adhesion with retained flexibility
- Good chemical resistance in the cured film
- Works on concrete, masonry, metal and wood with one product
Limitations & considerations
- Aromatic chemistry is not UV-colour-stable — it must always be overcoated, never left as an exposed finish
- Concrete must be at least 28 days old with moisture below 5%; priming green or damp slabs invites blistering in the PU coat above
- Moisture-curing means an opened container should be used completely — part-used drums skin over and are wasted
- Shelf life is 6 months in sealed condition, shorter than most epoxy primers, so order against the job programme
- At 40–50 microns DFT it is a primer only — it bridges no cracks and is not a standalone waterproofing layer
- Solvent vapours demand ventilation and PPE, particularly in tanks, basements and other confined pours
Selection & best practice
Preparation decides the result. Grind the concrete mechanically and clear dust, flakes, oil and grease by sand blasting, wire brushing or compressed air; strip old paint with a surface grinder. Aim for a slightly textured, not polished, profile — that is where the primer keys best. Confirm 28 days of curing and substrate moisture below 5% with a moisture meter before opening a drum; on steel, the surface must be completely dry. Apply one thin, even coat by brush or airless spray at 4–5 m²/L — flooding the surface does not improve penetration and only extends drying. Let it reach tack-free (35–45 minutes at 30°C) and place the membrane or coating from about 2 hours onward, within the same shift where possible. Plan quantities so each opened container is finished the same day.
Specifications
| Composition | Single-component aromatic polyurethane resin, moisture-curing |
| Density @ 30°C | 0.92 – 0.97 g/cc |
| Surface dry @ 30°C | 35 – 45 minutes |
| Working life @ 30°C | 6 – 7 hours |
| Recoating time | 2 hours |
| Theoretical coverage | 4 – 5 m²/L per coat (surface-condition dependent) |
| DFT per coat | 40 – 50 microns |
| Packing | 1 L and 20 L containers |
| Shelf life | 6 months in original unopened sealed packing, stored cool and shaded |
Industry use cases
Roofing & Podium Waterproofing
Priming large concrete decks ahead of liquid PU membranes, where the long working life lets one crew prime hundreds of square metres before the membrane gang follows.
Industrial Plants
Dual-substrate priming — concrete plinths and adjacent steelwork — before chemical-resistant PU protective coatings in process areas.
Commercial Buildings
Wet areas, sunken slabs and utility decks where porous concrete needs consolidating before an STP polyurethane waterproofing build-up.
Flooring Contractors
Binding down dusty, manually prepared screeds so PU floor coatings do not peel off a weak laitance layer.
Maintenance & Refurbishment
Re-priming decks and floors after grinding off failed paint systems, restoring a sound base for the replacement PU coating.
Frequently asked questions
How much ShaliPrime PUM do I need?
Can I prime freshly cast concrete?
How soon can the membrane go on after priming?
Brush or spray — which is better?
Does it work on steel as well as concrete?
Why does STP say to use the whole drum once opened?
How we position STP ShaliPrime PUM
ShaliPrime PUM is the entry point to STP’s polyurethane family: pair it with STP’s liquid-applied PU waterproofing membranes on roofs and podiums, and with ShaliSeal PU sealants at joints so the whole assembly shares one chemistry. Where the specification calls for a two-pack polyurethane primer instead, STP’s ShaliPrime 2PU covers that slot. Outside the STP range, Space Arc also stocks Fosroc’s primer line — Nitoprime 30 low-viscosity epoxy for penetrating duty under Fosroc coating and flooring systems, and Nitoprime Zincrich where structural steel needs sacrificial corrosion protection rather than a simple adhesion coat.
Fosroc Nitoprime 30 — Specifiers running an all-Fosroc coating or flooring build-up typically prime with Nitoprime 30, a low-viscosity two-part epoxy that fills the same penetrating-primer role where epoxy chemistry is preferred over moisture-cured PU.
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