Ask five renderers which primer for silicone render they use and you get a consolidator, a quartz key coat and one shared assumption: that you are choosing between them. The manufacturer sheets take the question apart differently. The coats do different jobs at different moments, and the argument is really about order.
Primer for Silicone Render: Two Jobs, One Order
The primer for silicone render is not one product but a sequence, and six separate Ceresit documents describe it the same way. A consolidator works downwards: it soaks into bare absorbent masonry, binds the loose aggregate grains and lowers the wall's absorbency so the layer above does not overdry. A quartz key coat works upwards: it leaves a fine, gritty, scratch-resistant film on a cured basecoat that wet render physically grips.
Neither replaces the other, and both sheets point at each other. The CT 17 Profi sheet ends its scope section with a single instruction: "For substrate priming under thin-layer plasters, apply the Ceresit CT 16 or CT 15 priming paint." The CT 16 sheet turns the same corner from the other side: "The absorptive substrates, e.g. gypsum renders, chipboards, non-impregnated gypsum cardboards should be primed with the agent Ceresit CT 17 and then left for drying for approx. 2 hours." The render sheets for CT 74, CT 76 and both CT 174 grades repeat the same sequence in their own substrate sections.
So the order on a full external wall insulation build-up runs:
- Consolidator on the bare wall, where the masonry is absorbent or dusty.
- Adhesive, boards, reinforced basecoat — the insulation layers.
- Quartz key coat on the cured basecoat, tinted towards the finish.
- Silicone render onto the key coat.
Both families sit in the Renders World render primer range, and which product fits which wall is the choice that range is built to make.
How Many Coats Your Wall Takes
The number is not a preference. It follows from what the surface underneath is doing, and three cases cover almost every elevation:
- bare, absorbent masonry — consolidator, then key coat;
- a cured reinforced basecoat — key coat alone;
- a loose or very absorbent wall — a diluted pass first.
Bare, absorbent masonry — two coats
Brick, block, gypsum render, chipboard and non-impregnated plasterboard all pull water out of whatever goes on next. These take a consolidator first, then at least two hours of drying, then the key coat. The CT 16 sheet sets that interval itself, and the render sheets repeat it as a minimum rather than a target.
A cured reinforced basecoat — one coat
Where the wall is already a reinforced layer that has gone off, the consolidator has nothing left to do. One quartz key coat is the whole preparation. The CT 74 and CT 76 sheets put an age on that basecoat before the key coat goes anywhere near it: over three days for the standard reinforcing mortars they name, over two for the fastest of them.
Very absorbent or loose substrate — a diluted first pass
CT 17 Profi may be diluted 1:1 with clear water on very absorbent or loose substrates, with any further coats applied undiluted. That is the only dilution either sheet permits: the CT 16 sheet says "Do not dilute the paint!" in those words, because the quartz has to reach the wall at full concentration to leave a key at all.
The Figures, and the One That Travels Wrongly
Both Ceresit sheets are specific, and CT 17 Profi and CT 16 do not share a single number.
| Ceresit CT 17 Profi — consolidator | Ceresit CT 16 — quartz key coat | |
|---|---|---|
| Job in the build-up | Bare absorbent substrate, before the system | Cured reinforced layer, directly under the render |
| Consumption on the sheet | 0.1–0.5 l/m² | 0.3–0.5 kg/m², or 0.2–0.35 l/m² |
| Drying time | Approx. 2 hours | Approx. 3 hours |
| Density | Approx. 1.0 kg/dm³ | Approx. 1.5 kg/dm³ |
| Dilution | 1:1 with clear water on loose substrates | None permitted |
| Colour | Yellow, so work phases can be checked by eye | Tinted close to the render |
| Working range | +5 °C to +25 °C, air and substrate, humidity below 80% | |
The density line settles a pack question that trips people up. Ceresit CT 16 is sold here as a 10 l container and described on its sheet as a 15 kg bucket; at approximately 1.5 kg/dm³ those are the same thing. Coverage then agrees from either direction: 15 kg ÷ 0.3–0.5 kg/m² gives 30 to 50 m², and 10 l ÷ 0.2–0.35 l/m² gives 29 to 50 m².
One CT 17 figure travels much further than its scope allows. The fifteen-minute interval quoted across the trade belongs to gluing ceramic tiles onto cement and cement-lime substrates, and its scope is attached to it in the same sentence. For every other substrate and every other top coat the instruction is to wait until the primer has dried completely — approximately two hours. A facade programme built around fifteen minutes has taken a tiling figure outdoors. CT 17 Profi is a tiling, flooring and facade primer at once, and its data sheet is written for all three.
The Atlas Side, and What a Certificate Names
Atlas covers both jobs with its own products. Cerplast is the quartz key coat, in 25 kg and 15 kg buckets; Uni-Grunt, NKP and Ultragrunt are the consolidators, the last two formulated for critical and difficult substrates. Their consumption weights, drying times and shade counts belong on their own data sheets, so ask the Renders World technical desk for the sheet before specifying one. The numbers inside pack names and web addresses are packaging and routing; working from those is how a wall ends up under-primed.
Certificates work the same way, and they are stricter than most specifications assume. A certified system names its components individually — one adhesive, one mesh, one key coat, one finishing coat — rather than naming a product type. That is why a compliance job keeps the whole build-up inside one manufacturer's named set: the certificate covers the assembly, never the bucket on its own. On uncertified work the chemistry across the two brands is generally compatible, but the evidence trail is cleaner when the key coat, basecoat and finish come from one sheet set.
Key Takeaway: A consolidator and a quartz key coat are not alternatives — they are consecutive. Consolidator on the bare wall, two hours, quartz key coat on the cured basecoat, three hours, render. CT 17's own sheet sends the reader to CT 16 for the layer under a thin-layer render, and that is the clearest instruction either sheet gives.
Ordering the Two Coats Together
The key coat is tinted towards the finish, so the primer for silicone render and the render itself are really one decision made twice. Working from the CT 16 sheet, a 100 m² elevation comes out as:
- 100 m² × 0.3–0.5 kg/m² = 30–50 kg of key coat;
- ÷ 15 kg per pack = 2.0–3.3 packs, plus 10% for reveals and detailing;
- so three packs for a smooth basecoat, four for a coarse one.
The consolidator quantity is settled separately and later, because a porous wall can take five times what a dense one does and only the wall can say which it is.
Renders World holds the adhesive, mesh, key coat and finish of a thin coat render system in one place, so the layers arrive matched instead of assembled from three suppliers. Where the wall is unusual, the sequence for each substrate type is set out in the substrate preparation guide and the guide to rendering on brick, block and painted walls; the method for laying the key coat itself is covered in the quartz primer application guide for EWI systems. Which primer suits a given substrate and system is the question the primer range answers product by product.
Written by Mariusz Saja. Technically reviewed by Rafał Wyrzykowski. Last reviewed Sep 2026.
FAQ — Sequence, Coverage and Timing
Do I need one primer or two?
Two on bare absorbent masonry, one on a cured reinforced basecoat. The consolidator handles absorbency in the wall itself; the quartz key coat gives the render something to grip. Where the basecoat is already sound and cured, only the key coat is doing any work.
Is CT 17 an alternative to CT 16 under render?
No, and CT 17's own sheet settles it: for priming under thin-layer plasters it sends the reader to the quartz key coat instead. CT 17 strengthens and de-absorbs a bare substrate earlier in the build-up and leaves no gritty film behind. On a full build-up both appear, at different stages.
How much quartz key coat does 100 m² take?
Two to four 15 kg packs, from the sheet's 0.3 to 0.5 kg/m² plus 10% for reveals and detailing. The spread is wide because a smoothly finished basecoat sits at the bottom of the band and a coarse one at the top, so ordering to the upper figure avoids a part-primed elevation waiting on a delivery.
How long between the two coats?
At least two hours after the consolidator before the key coat goes on, and approximately three hours after the key coat before the render. Both figures are sheet values measured at +23 °C and 50% humidity; a cold or damp day extends them, and neither sheet publishes a cold-weather multiplier.
Can an Atlas primer go under a Ceresit render?
On uncertified work, generally yes. On work that has to demonstrate compliance, no: the certificate names the key coat and the finishing coat as a pair, so mixing brands steps outside the assessed system even where the chemistry is fine. The technical desk confirms a specific pairing before an order goes out.