Description
The smaller of the two Uni-Grunt containers stocked in the Renders World exterior render primers range, this pack carries the same emulsion as the trade container in a quantity sized to one wall. Every figure below comes from the Atlas Uni-Grunt product data sheet and the live product endpoint, both read this session; the area figure in the address does not appear in either.
Small-Pack Priming: Where 5 kg Fits on a UK Job
The Atlas Uni-Grunt 5kg wall primer covers 25 to 100 m² at the sheet's stated 0.05–0.2 kg/m², so a single gable, an interior room or a patched repair area is primed from one container. Which end of that span applies is decided by the wall, not the pack, and the sheet is explicit that consumption depends on substrate absorptiveness.
Three jobs suit this size, and the reasoning is arithmetic rather than performance:
- One elevation at a time — a gable, a single-storey extension flank or a garage wall, where a thirsty substrate at the 0.2 kg/m² end still finishes inside 25 m² of the container's range.
- Interior work on gypsum — the sheet's 1:3 dilution for newly made gypsum finish coats under indoor paints stretches a small container a long way, and the low emission figure below is what makes it workable in an occupied room.
- Repairs and patched areas — the sheet's own claim is that the next layer gets uniform setting conditions over the whole surface, including areas with local repairs, which is precisely the wall a small pack gets bought for.
What the container is not is a key coat. Atlas names this emulsion as substrate preparation ahead of paints, fillers, screeds and adhesives for thermal insulation, while BBA Agrément Certificate 13/5018 names Atlas Cerplast, Atlas Silkat ASX and Atlas Silkon ANX as the key coats of the certified Atlas systems. Two different layers, two different jobs.
What the 5 kg Container Gives an Applicator
- A shelf life you can actually use up: 12 months from the production date on the packaging, which is the argument for matching container to wall rather than buying long and storing the remainder.
- Fifteen minutes to an Atlas adhesive mortar: the sheet allows the next layer after approximately 15 minutes for Atlas adhesive mortars, and roughly 2 hours for painting coats, self-levelling floors and screeds.
- 1.92 g/l VOC against a 30 g/l permissible content under Cat. A/h/FW — described on the sheet as a fifteen-fold reduction against the legal requirement, and the product is solvent-free and water-soluble in the wet state.
- No discolouration under a pale finish: colourless after drying with a matt surface, and the sheet states the product does not cause substrate discolouration.
- Better per-square-metre value than it looks: £12.50 per 5 kg container, August 2026, works out at £0.13–£0.50 per m² across the documented consumption band.
Declared Values for the Uni-Grunt Emulsion
| Property | Value as documented |
|---|---|
| Composition | Impregnating sealer based on a water dispersion of polymer resins |
| Density of emulsion | Approx. 1.0 g/cm³ |
| Average consumption | 0.05–0.2 kg/m², depending on substrate absorptiveness |
| Substrate and ambient temperature during application | +5 °C to +30 °C |
| Further work — Atlas adhesive mortars | After approx. 15 minutes |
| Further work — painting coats, self-levelling floors, screeds | After approx. 2 hours |
| Appearance after drying | Colourless, matt |
| VOC | 1.92 g/l maximum content; permissible 30 g/l (Cat. A/h/FW) |
| Application | Roller, brush or sprayer; indoors and outdoors, horizontal and vertical |
| Packaging | Plastic containers of 1 kg, 4 kg, 5 kg and 10 kg |
| Shelf life | 12 months from the production date shown on the packaging |
| Classification | Not classified as a construction material |
| Other certification | Radiation Hygiene Certificate, named on the sheet without a number |
Two of those lines change how the product is specified rather than how it is applied. Because the emulsion is not classified as a construction material there is no declared performance and no DoP to quote for it — the data sheet is the document, and any certified performance belongs to the system built above the wall. And because Atlas also produces 1 kg and 4 kg containers, the 5 kg is the mid-size rather than the small one, which is worth knowing before ordering for a single reveal or a touch-up.
Diluting and Applying the Emulsion Indoors and Out
Substrate, then dilution
The wall wants to be dry and free from dust, dirt, oils, grease and wax, with loose or poorly bonded layers taken off first. The emulsion is ready to use and must not be mixed with other materials or thickened, so dilution is the only variable left:
- Sound mineral substrates: apply undiluted, once, with a roller or brush in a thin, uniform coat — the sheet's advised method.
- Very absorptive and weak substrates: double priming, the first coat diluted 1:1 with water and the second undiluted once the first has dried. The sheet labels this same operation the "wet on wet" method in the same cell, which contradicts its own sequence; take the sequence, since a dried first coat is the safer of the two readings.
- New gypsum finish coats under indoor paints: a single coat diluted 1:3 with water — and where the finish is paint, the sheet defers to the paint manufacturer's own priming guidance.
Some substrates are sent elsewhere entirely. Existing ceramic and stone cladding, terrazzo, OSB boards, stable linoleum and PVC, concrete varnishes and oil-colour paint coatings are routed by Atlas to Grunto-Plast or Ultragrunt, because a sealed surface needs a keyed film rather than penetration. Placing an unfamiliar wall before ordering is what the guide to rendering on brick, block and painted walls is for, with the cleaning and repair sequence ahead of it in the substrate preparation guide.
How far one container goes
The arithmetic is worth showing, because the figure in this page's address is not in the document: 5 kg ÷ 0.2 kg/m² = 25 m² on an absorbent wall, and 5 kg ÷ 0.05 kg/m² = 100 m² on a tight one. Order against 0.2 kg/m² and the wall is covered whichever way it behaves. On price, £12.50 ÷ 25 m² = £0.50/m² at worst and £12.50 ÷ 100 m² = £0.13/m² at best, material only and excluding labour.
Working Habits the Sheet Prescribes
- Thin and uniform is the instruction, not a preference — the emulsion's stated purpose is to penetrate and reinforce the substrate's top layer, which a flooded surface prevents.
- Clean tools with clean water directly after use, before the polymer resin cures into the pile; Atlas names a dedicated remover for dried emulsion stains on paints, primers and renders.
- Work inside +5 °C to +30 °C for both substrate and air, remembering the sheet ties drying time to temperature and humidity — so the stated intervals are a guide, not a clock.
- Follow with a key coat on render work. A thin-coat finish bonds to a quartz coat above the consolidated substrate, and the two products sit in very different consumption bands; the comparison is in the primer comparison for thin-coat render and the method in the quartz primer application guide.
5 kg Against 10 kg: What the Arithmetic Says
One emulsion, one data sheet, one consumption band — the decision is quantity against shelf life.
| Your Project | Best Pack | Standout Spec |
|---|---|---|
| Single wall, interior room, repair area, reserve stock | Uni-Grunt 5 kg | 25–100 m²; £0.13–£0.50/m² |
| Full or multiple elevations, EWI substrate priming | Uni-Grunt 10 kg container | 50–200 m²; £0.10–£0.42/m² |
Two of these cost £25.00 against £20.90 for the larger container, both fetched August 2026 — £4.10 for the same 10 kg of emulsion. That gap only pays if the surplus gets used inside twelve months, which is the whole case for one container of Atlas Uni-Grunt 5kg wall primer on a job that will not exceed one wall.
Choosing This Container for Your Substrate
- Take the 5 kg for absorbent mineral walls up to roughly one elevation — brick, silicate and cellular blockwork, cement and cement-lime plasters, and patched repairs needing their absorbency evened out.
- Take the 5 kg for interiors on gypsum at 1:3, where the 1.92 g/l VOC figure and the solvent-free, colourless chemistry suit occupied rooms.
- Step up where the programme covers several elevations: the 10 kg Uni-Grunt container is the cheaper order per square metre and keeps one batch across the wall.
- Choose a different primer for cladding, terrazzo, OSB, linoleum, varnished or oil-painted surfaces, which the sheet routes to Grunto-Plast or Ultragrunt; both alternatives and the quartz key coats sit in the same Renders World primer range.
- Then specify the finish — the silicone render range is where this preparation usually leads, with its own key coat requirement to check first.
Listed as available at the time of this fetch, August 2026, at £12.50 per 5 kg container as displayed on the product endpoint.
FAQ — Pack Size, Gypsum and Storage
How much wall does one container prime?
Between 25 and 100 m², following the sheet's 0.05–0.2 kg/m² band. Old brickwork and fresh sand-and-cement patching sit at the thirsty end, so plan on 25 m² and treat anything more as headroom rather than budget.
Is this the same material as the 10 kg container?
Yes — one formulation, one data sheet, one set of declared values covering density, consumption, drying intervals and VOC. Atlas lists 1 kg, 4 kg, 5 kg and 10 kg containers of it, so pack size is a quantity decision and nothing else.
What dilution does interior gypsum need?
Newly made gypsum finish coats under indoor paints take one coat diluted 1:3 with water. Where the topcoat is paint, the sheet asks you to follow the paint manufacturer's priming guidance, which is the one case where its own dilution table is not the last word.
Can render go directly onto the primed wall?
The sheet's two-hour group names painting coats, screeds and self-levelling floors rather than thin-coat renders, and BBA 13/5018 names Cerplast, Silkat ASX and Silkon ANX as the key coats of the certified Atlas systems. Treat this emulsion as substrate preparation and take the coat directly beneath the finish from the render manufacturer's instruction.
How long does an opened container keep?
Shelf life is 12 months from the production date printed on the packaging. Sizing the container to the wall is the practical way to stay inside that, which is the main reason this pack exists alongside the trade one.
Technical Documentation