Description
Priming a whole facade before render is where a concentrate earns its keep. Atlas Uni-Grunt Ultra is a concentrate, never used neat, and this 4 kg container sits at the economy end of the Renders World render primer range. Every figure here comes from the Atlas technical data sheet for the 4 kg container, edition 31 January 2024.
Where Atlas Uni-Grunt Ultra Concentrate Suits UK Substrates
One tub diluted to the render ratio primes up to 280 m² of substrate, so one tub consolidates the masonry on a whole detached house. The polymer dispersion soaks into the pore structure and binds loose grains, so suction evens out and the next coat pulls water at the same rate across the elevation.
Atlas Uni-Grunt Ultra sorts walls and floors into three groups:
- Standard substrates: aerated concrete, silicate and clay brick or block, gypsum block, cement and cement-lime renders and skims, gypsum and polymer skims, cement and anhydrite screeds.
- Difficult but suitable: concrete, underfloor-heated screeds, sound old interior acrylic paintwork, walls already patched with filler and float coats.
- Not for this emulsion: tiling, terrazzo, OSB, stable linoleum or PVC, concrete varnish and oil paint, which go to Ultragrunt instead.
Matching Atlas Uni-Grunt Ultra to the wall in front of you is the part worth slowing down for, and the substrate matrix for brick, block and painted walls sets out how each behaves under a thin-coat system. For the dust, moisture and porosity checks that come first, the wall preparation method guide covers the order to work in.
Why Trade Specifiers Choose This Concentrate
- 280 m² from one tub at 1:6: that ratio uses 0.014 kg/m² of neat concentrate, so 4 kg covers the masonry prep on a full house.
- Three ratios from one product: 1:3 under floors, 1:6 under renders, waterproofing and adhesives, 1:8 under skims and paint.
- Control pigment tints the substrate wet and dry so missed strips show, and it does not reduce the covering power of later paint coats.
- Low VOC content: category A/h/FW at under 1.9 g/l against a 30 g/l limit, which answers specifications that set an emissions ceiling.
- Eighteen-month shelf life from the production date on the pack, so stock left after a programme keeps into the next season.
Technical Specifications, Edition in Force
| Property | Value |
|---|---|
| Product type | Deeply-penetrating priming emulsion, concentrate |
| Pack | 4 kg plastic container |
| Density | approx. 1.0 g/cm³ |
| Dilution 1:3 | Floors and screeds — 53 m² per 4 kg |
| Dilution 1:6 | Renders, waterproofing, adhesives — 280 m² per 4 kg |
| Dilution 1:8 | Skim finishes and paint — 360 m² per 4 kg |
| Concentrate used | 0.075 / 0.014 / 0.011 kg/m² at 1:3 / 1:6 / 1:8 |
| Diluted solution used | 0.1–0.2 kg/m²; approx. 0.3 kg/m² on screeds |
| Working temperature | +5 °C to +30 °C, substrate and air |
| Following work | 15 min on plasters and blockwork; 2 h on floors |
| Application | Roller, brush or spray unit |
| VOC content | Cat. A/h/FW, below 1.9 g/l against a 30 g/l limit |
| Product status | Not classified as a construction product |
| Hygiene approval | Hygienic Attest, issuing body not named |
| Shelf life | 18 months from the production date on the pack |
How to Apply the Concentrate
Dilution is set by the layer that follows, not by the substrate, and getting that right is what makes the yield figures hold on site.
- Prepare the substrate: dry and free of dust, dirt, oil, grease and wax, loose layers removed; on gypsum plaster and anhydrite screed, take off the sediment left by sanding.
- Measure water first, then add concentrate at 1:3, 1:6 or 1:8 and stir; Atlas Uni-Grunt Ultra must not be mixed with other materials or compacted.
- Apply thin and even by roller, brush or spray unit, in overlapping passes while the pigment shows what is done.
- On weak, highly absorbent walls prime twice, wet on wet — the second pass before the first has dried.
- On floors, pour and spread evenly without leaving puddles, then allow the full 2 hours before self-levelling compound.
Test it once dry: wet the surface and judge how quickly water is drawn in. A properly primed wall reads matt and takes water slowly.
What the 4 kg Edition Changed Against the Older 5 kg One
Two Atlas editions of this emulsion are in circulation and they do not agree. The current one is written for the 4 kg container. The earlier edition, dated 13 February 2020, covered 1 kg and 5 kg containers and prints a consumption figure more than three times higher at the same dilution.
| Ratio | Current, 4 kg | 2020 edition, 5 kg |
|---|---|---|
| 1:3, floors | 0.075 kg/m² — 53 m² | 0.100 kg/m² — 50 m² |
| 1:6, renders and adhesives | 0.014 kg/m² — 280 m² | 0.043 kg/m² — 115 m² |
| 1:8, skims and paint | 0.011 kg/m² — 360 m² | 0.033 kg/m² — 150 m² |
Quantities work off the 4 kg edition, and a yield quoted against a 5 kg container belongs to the older one and does not scale to this pack. Two further differences matter. The 2020 edition lists plasterboard among its standard substrates and the current one does not, so plasterboard sits outside what the edition in force covers. The working temperature did not move: both set +5 °C to +30 °C, substrate and air alike.
Weather Window and System Sequence
Shoulder-season planning is covered in the guide to render application temperatures through the UK year. In an insulated build-up Atlas Uni-Grunt Ultra consolidates bare masonry before boards are bonded, since the 1:6 row covers adhesives for thermal insulation. It is not the textured key coat that goes on the cured basecoat, a separate stage set out in the quartz primer application guide before thin coat silicone render finishes the wall.
- Protect glazing, woodwork and flashings before priming; the pigment is designed to mark the wall and will mark them too.
- Clean tools with clean water straight after use, while the polymer is still wet.
- Dried emulsion staining lifts with Atlas Szop 2000, named by the manufacturer for the job.
- Storage and transport conditions are carried on the pack label and the safety data sheet, not in the technical one.
Concentrate or Standard Emulsion
Atlas sells two formulations under names one word apart, and they are not pack sizes of the same thing.
- Atlas Uni-Grunt Ultra is a concentrate and is never applied neat: 1:3, 1:6 or 1:8, which is where 53, 280 and 360 m² from 4 kg come from.
- Atlas Uni-Grunt is the standard emulsion. It goes on undiluted on weak, highly absorbent walls, or at 1:1 and 1:3 elsewhere — up to 200, 400 and 800 m² from a 10 kg container.
Two smaller differences follow the same line: 18 months of shelf life here against 12 for the standard emulsion, and VOC below 1.9 g/l against 1.92 g/l. Each figure belongs to its own document and neither document covers the other product. Surfaces with no porosity go to Atlas Ultragrunt, a third formulation again.
Is This the Right Primer for Your Project?
- Yes, for large absorbent areas where material economy leads: full facades, multi-elevation programmes and floor prep, where one container at 1:6 handles 280 m².
- Yes, before bonding insulation: the 1:6 row covers adhesives used to fix thermal insulation, so the same pack serves masonry prep and board fixing.
- Weighing it against the other primers on the shelf? The primer comparison for thin-coat systems separates penetrating primers from quartz key coats, which sit in different consumption bands.
- Priming for decoration rather than render? The 1:8 ratio is the paint route, ahead of a silicone paint for masonry.
Ordering is by the tub: one Atlas Uni-Grunt Ultra 4 kg concentrate pack, supplied by Renders World with the rest of the primer shelf.
FAQ: Coverage, Compatibility and Application Limits
Does a second coat change how much I need to order?
On weak or very absorbent walls two passes wet on wet are called for, and the second pass halves the area one tub covers. The render coverage calculator works the same arithmetic through a full material list.
Can it be used before insulation boards are bonded?
Yes at 1:6, the ratio given for adhesives used to fix thermal insulation, and the 280 m² yield line names that use directly. It consolidates the bare wall only; the quartz key coat on the cured basecoat is a separate product at a later stage.
What temperature suits it, and how soon can the next coat go on?
Between +5 °C and +30 °C, measured on the substrate as well as in the air. Following work starts after 15 minutes on plasters, skims and blockwork, and after 2 hours on self-levelling floors.
Is Atlas Uni-Grunt Ultra the same thing as Atlas Ultragrunt?
No, and the two are kept apart deliberately. This emulsion penetrates porous substrates; Ultragrunt is directed at surfaces with no porosity to work with, such as existing tiling, terrazzo, OSB and varnished concrete, where a key has to be built on top instead.
Is it certified, and how does it perform on emissions?
Three separate things sit behind that question:
- Emissions: category A/h/FW, VOC content below 1.9 g/l against a 30 g/l limit.
- Hygiene: a Hygienic Attest is recorded, without the issuing body being named.
- Construction-product status: not classified as one, so there is no declaration of performance of its own.
It therefore sits inside a certified system on the strength of that system's documents, and Renders World supplies it alongside the render systems it goes under.
Technical Documentation