Description
Priming a whole facade before render is where a concentrate earns its keep, and this 4 kg pack sits at the economy end of the Renders World exterior render primers range. Every figure below is copied from the manufacturer's current data sheet, edition 31 January 2024, which covers the 4 kg container sold here.
Where Atlas Uni-Grunt Ultra Works Best on UK Substrates
The Atlas Uni-Grunt Ultra concentrate primer 4kg pack dilutes 1:6 to prime up to 280 m² of render substrate, so consolidating a whole detached house takes one container rather than a pallet of ready-mixed emulsion. 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.
The data sheet treats these substrates as standard for the emulsion:
- Masonry: aerated concrete, silicate brick or block, clay brick or ceramic hollow block, and gypsum block.
- Renders and plasters: cement and cement-lime renders and skims, gypsum plasters and skims, polymer skims.
- Floors: cement screeds and anhydrite screeds, including underfloor-heated versions of both.
- Repair work: concrete, old interior acrylic paintwork, and walls already patched with filler.
Matching primer to wall 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 container at 1:6: that ratio uses 0.014 kg/m² of neat concentrate, which keeps material cost per square metre marginal on a full-house prime.
- Three ratios from one product: 1:3 for screeds, 1:6 for renders, waterproofing and tile or insulation adhesives, 1:8 for skims and paint.
- Control pigment: it tints the substrate wet and dry so missed strips show, and the sheet states the colour does not reduce the covering power of later paint coats.
- Fifteen-minute turnaround on blockwork: following work starts after 15 minutes on plasters, skims, silicate blocks and aerated concrete blocks, which keeps a scaffold lift moving.
- 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: 18 months from the production date printed on the pack, so stock left after a programme stays usable into the next season.
Technical Specifications From the Current Atlas Data Sheet
These values come from the 31 January 2024 edition, which is written against the 4 kg container. Figures published for other pack sizes are kept out.
| Property | Value |
|---|---|
| Product type | Deep-penetrating priming emulsion, supplied as concentrate |
| Pack | 4 kg plastic container |
| Density | approx. 1.0 g/cm³ |
| Dilution 1:3 | Screeds and floor substrates — 53 m² per pack |
| Dilution 1:6 | Renders, waterproofing, tile and insulation adhesives — 280 m² per pack |
| Dilution 1:8 | Skim finishes and paint — 360 m² per pack |
| 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 floor screeds |
| Substrate and ambient temperature | +5 °C to +30 °C |
| Following work | After 15 min on plasters, skims, silicate and aerated blocks; after 2 h on self-levelling floors |
| Application | Roller, brush or spray |
| VOC | Cat. A/h/FW, below 1.9 g/l (limit 30 g/l) |
| Construction-product status | Not classified as a construction product |
| Hygiene approval | PZH Atest Higieniczny (Poland) |
| Shelf life | 18 months from the production date on the pack |
How to Apply the Concentrate: Dilution, Mixing and Coverage Checks
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, with loose layers removed; on gypsum plaster and anhydrite screed, take off the laitance left by floating.
- Measure water first, then add concentrate at 1:3, 1:6 or 1:8 and stir; the sheet rules out mixing it with other materials or thickening it.
- Lay it on thin and even by roller, brush or spray, working in overlapping passes while the pigment shows what is done.
- Prime weak, highly absorbent walls twice, wet on wet — the second pass goes on before the first has dried, rather than after the 15-minute window.
- 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 watch how quickly water is drawn in; a properly primed wall reads matt and takes water slowly.
Working Out Packs and Cost Per Square Metre
A 250 m² facade at 1:6 gives 250 ÷ 280 = 0.9 containers, so one pack covers a single coat; specify two coats on soft aerated blockwork and it becomes 500 ÷ 280 = 1.8, rounded up to two. At £13.80 per 4 kg container, August 2026, that is 13.80 ÷ 280 = £0.05/m² at 1:6, against 13.80 ÷ 53 = £0.26/m² at the 1:3 floor ratio.
Installation Notes: Weather Window and System Sequence
Work between +5 °C and +30 °C substrate and air temperature, which the current edition tightened from the +35 °C upper limit still printed on older sheets for the discontinued 5 kg pack. Shoulder-season planning is covered in the guide to render application temperatures through the UK year.
In an insulated build-up the concentrate consolidates bare masonry before boards are bonded — the sheet lists insulation adhesives and the fixing of thermal insulation at 1:6. 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 Atlas thin-coat silicone render finishes the wall.
- Protect glazing and flashings before priming; the pigment is designed to mark the wall and will mark them too.
- Clean tools with clean water immediately after use, while the polymer is still wet.
- Dried emulsion staining lifts with ATLAS SZOP 2000, which the data sheet names for the job.
- Storage and transport conditions sit on the pack label and safety data sheet rather than in the technical sheet, so read the label before winter storage.
Which Atlas Primer the Data Sheet Points To
The same sheet that carries these yields also names the substrates this emulsion should not be asked to handle, and sends them to a different product. That table is the honest comparison, and Renders World lists both routes in the same range.
| Substrate | What the sheet directs | Why |
|---|---|---|
| Screeds, renders, skims, brick, silicate and aerated block | Uni-Grunt Ultra, diluted to the following layer | Porous surfaces the emulsion can penetrate |
| Concrete, heated screeds, sound old acrylic paint, patched walls | Uni-Grunt Ultra, listed as a difficult but suitable substrate | Absorbency is reduced but still present |
| Existing tiling, terrazzo, OSB, stable linoleum or PVC, concrete lacquer, oil paint | ATLAS ULTRAGRUNT instead, from the primer range | No porosity to exploit, so a mechanical key is needed |
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 insulation adhesives, so the same pack serves masonry prep and board fixing.
- Weighing it against the other primers on file? 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 masonry paint in white or grey.
Ordering is by the container: one Atlas Uni-Grunt Ultra concentrate primer 4kg pack, listed at £13.80 and shown in stock when this page was reviewed in August 2026, supplied by Renders World with the rest of the primer range.
FAQ: Coverage, Compatibility and Application Limits
Does a second coat change how much I need to order?
On weak or very absorbent walls the sheet calls for two coats wet on wet, which halves effective yield: 280 m² becomes roughly 140 m² of wall per container. 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 the sheet gives 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, silicate blocks and aerated concrete blocks, and after 2 hours on self-levelling floors.
Is it the same thing as Atlas Ultragrunt?
No, and the sheet keeps them 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 lacquered concrete, where a key has to be built on top instead.
Is it certified, and how does it perform on emissions?
VOC content is below 1.9 g/l in category A/h/FW against a 30 g/l limit, and the sheet records a Polish PZH hygiene certificate, a national approval with no UK regulatory standing. The same sheet states the primer is not classified as a construction product, so it carries no declaration of performance of its own and sits inside a certified system on the strength of that system's documents.
Technical Documentation