Ceresit CT85 - Adhesive for polystyrene foam and mesh - 25kg
What is Ceresit CT 85?
Ceresit CT 85 is a high-performance Adhesive and Basecoat Mortar specifically engineered for External Wall Insulation (EWI) systems using EPS (Expanded Polystyrene) boards. It is used for both fixing insulation boards to the substrate and creating the reinforced basecoat layer. It is highly resistant to mechanical damage, frost, and weathering, featuring specialized micro-fibers to prevent surface cracking.
| Technical Specification | Value / Detail |
|---|---|
| Material Base | Cement-based with synthetic resins and fibers |
| Primary Use | Fixing and Basecoating EPS insulation boards |
| Consumption (Fixing) | Approx. 5.0 kg/m² |
| Consumption (Basecoat) | Approx. 4.0 kg/m² |
| Key Benefit | High impact resistance and flexibility |
| Reinforcement | Micro-fiber reinforced |
| Application Temp | +5°C to +25°C |
- Can I use Ceresit CT 85 for Mineral Wool?
No. Ceresit CT 85 is specifically formulated for EPS (Polystyrene). For Mineral Wool (Rockwool) systems, you should use Ceresit CT 190 or the premium white Ceresit CT 87, which have the specific adhesion and breathability properties required for mineral fibers. - What is the difference between Ceresit ZU and CT 85?
While both are used for EPS, Ceresit CT 85 is a higher-specification mortar with increased resin content and better impact resistance. It is often preferred for high-quality residential and commercial projects where greater durability and crack resistance are required. - Is Ceresit CT 85 frost resistant?
Yes. Once fully cured, CT 85 is highly resistant to frost and extreme weather cycles, making it a reliable choice for the UK climate. However, it must be applied in temperatures above 5°C and protected from freezing during the initial drying phase.
- Mixing: Mix one 25kg bag of CT 85 with 6.5L to 7.0L of clean water using a low-speed drill.
- Board Fixing: Apply the "perimeter and dab" method to the back of the EPS boards, ensuring at least 40% of the surface is covered with adhesive.
- Basecoating: After the boards are mechanically fixed with Insulation Pins, apply a 3–4mm layer of CT 85.
- Mesh Embedding: Lay the alkali-resistant fiberglass mesh into the wet mortar and smooth over.
- Priming: Once dry, the CT 85 layer must be primed with Ceresit CT 16 before applying the final silicone render.
- Pro-Tip on Surface Prep: Before applying CT 85 as a basecoat, always ensure the EPS boards have been rasped (sanded) to a flat surface. This significantly reduces the amount of CT 85 needed and ensures a perfectly flat finish for the render.
- Pro-Tip on Mesh Overlaps: Always ensure a 10cm overlap at the joints of the reinforcement mesh. Failing to do this in the CT 85 basecoat layer is the most common cause of vertical cracks in finished render systems.
CERESIT® CT 85 mortar is designed to warm up external walls of the buildings with the application of a light-wet method and EPS-boards. It is an element of ETICS within CERESIT Ceretherm. CT 85 mortar is used for fixing EPS-boards as well as applying the armoured protection layer to insulate the newly erected objects and also the buildings to be thermo-renovated. CT 85 increases the resistance of insulation system on damage and resistance to the formation of cracks and hairlines. Available pack size: 25 kg