Ardex K40HB Rapid Drying, High Build, Fibre Reinforced Levelling and Smoothing Compound

• Product ID: 38990
• Suitable For: levelling and smoothing most new and existing internal subfloors
• Area of use: INT & EXT
• Application Method: trowel/float
• Time to full cure: 12 hours
• Volume: 22kg
• Container Type: bag
• Type: concrete compound
• Brand: Ardex
• Manufactuer: Ardex
• Box Size: 1

ARDEX K40HB is designed to level and smooth most new and existing internal subfloors in a single application. It is suitable for use on a variety of surfaces, including concrete, cement/sand screeds, anhydrite screeds, stone, terrazzo, ceramic tiles, and appropriate timber floors. Additionally, it can be used to address issues with uneven, damaged, or rain-damaged in-situ concrete subfloors, as well as to correct tolerances or camber problems between floors, slabs, or pre-cast concrete.

Substrate Preparation

Before applying ARDEX K40HB, ensure the subfloor is clean, sound, and free from dust, plaster, grease, polish, and any water-softenable or loosely adhered materials. Any adhesive residues must be hard, well-adhered, and unaffected by water. Use a suitable degreaser to remove contaminants like polish, wax, grease, and oil. Subfloors in direct contact with the earth must have an effective damp proof membrane (DPM). If the DPM is missing, damaged, or the substrate is damp, consult the ARDEX DPM 1 C, ARDEX DPM 1 C R, or ARDEX MVS 95 datasheet for guidance.

Priming

All surfaces must be primed to extend working time, maintain flow life, and prevent air bubbles in the levelling compound. For cement/sand or gypsum screeds, mix ARDEX P 51 Primer with water at a ratio of 1:3. For concrete subfloors, the ratio should be 1:2. For timber, use undiluted ARDEX P 51 Primer and allow it to dry. Note that ARDEX K 40 HB can be applied up to 6mm thick over gypsum or timber subfloors. For smooth, dense, or non-absorbent subfloors like ARDEX Damp Proof Membranes or power-floated concrete, ARDEX P 4 Primer is recommended. For ARDEX DPMs with smoothing applications between 3mm to 6mm or non-absorbent subfloors where ARDEX K 40 HB is applied up to 10mm, use ARDEX P 4 or ARDEX P 82 Primer. For thicker applications, use ARDEX R 3 E with ARDEX Fine Aggregate as the primer coat. When applying over flooring grade asphalt, the surface must be sound, cleaned with a neutral cleaner, primed with ARDEX P 82 Primer, and applied between 3-5mm thick.

Timber Floors

Plywood must be rigid, dry, and capable of supporting anticipated loads according to BS 8203 for resilient flooring and BS 5385-3 for ceramic tiling. Seal the backs and edges of plywood with polyurethane varnish when fixing ceramic tiles. Securely screw down loose boards before levelling. If the timber floor is uneven or worn, pre-level with ARDEX K 40 HB, then screw-fix a minimum of 6mm thick flooring-grade plywood or tile backing board before installing resilient flooring or ceramic tiles. Ensure subfloor ventilation is adequate to prevent deterioration. Allow 1 to 12 hours of drying time depending on timber porosity. For plywood free from adhesion barriers, ARDEX K 40 HB can be applied up to 6mm thick as a smoothing layer. For tongue and groove floorboards or timber floors in conservatories or non-domestic areas, overlay with plywood or consult the ARDEX FA 20 datasheet. Tongue and groove boards must be 22mm thick. Avoid using impregnated boards as they prevent primer penetration. In domestic and light-duty installations, chipboard must meet the latest BS EN 312 standard and be of suitable flooring grade. Sand and vacuum chipboard thoroughly to remove barriers to adhesion before priming with undiluted ARDEX P 51 Primer. If the primer does not soak into the board, adhesion may be compromised; consult the board supplier if in doubt.

Mixing

Use between 3½ and 3¾ litres of water per 22kg bag of ARDEX K 40 HB. Add the powder to the water in a clean container, stirring thoroughly until a lump-free consistency is achieved. Use an ARDEX mixing paddle with a 10mm chuck slow-speed (600-1000 rpm) electric drill for efficient mixing. For thicker applications or in cold conditions, use the minimum amount of water.

Application

Apply ARDEX K 40 HB at temperatures above 5°C. Pour the mixed compound onto the prepared subfloor and use a pin steel finishing trowel or float to spread and smooth it. The product’s extended workable wet edge time allows fresh material to be trowelled into pre-applied material up to 30 minutes after application. Protect the freshly applied compound from direct sunlight or drafts to avoid premature drying.

Applications Over Underfloor Heating

Underfloor heating systems must be installed per BS 8204 Part 1 and BS EN 1264 standards. The system should be commissioned according to the manufacturer’s instructions, and the temperature lowered to room level (not below 15°C) before applying ARDEX K 40 HB and floor coverings. After installation, gradually increase the temperature to avoid thermal shock. ARDEX K 40 HB can also encapsulate under-tile heating cables or mats on prepared subfloors before ceramic tile installation. For information on suitable underfloor heating systems, contact ARDEX Technical Support.

Encapsulating Low-Profile Waterfed Heating Systems

The floor should comply with Part L of the building regulations, be fully load-bearing with a deflection of no more than L/360 (L/720 for natural stone), and leveled to SR1 or better before installing underfloor heating. Ensure castellated systems are seated on a level, load-bearing surface. After securing and pressurizing pipes, install ARDEX K 40 HB to the height recommended by the heating manufacturer. Calcium sulfate boards should be securely installed and free from movement, with a perimeter movement joint in place. If bonding boards to the floor, prime both sides with ARDEX P 51 (1:3) before applying tile adhesive. Otherwise, only the surface receiving the levelling compound needs priming. Avoid installing onto metallic surfaces like aluminum plates. For tiling and flooring, cover the heating pipes with ARDEX K 40 HB to a height of 6 to 10mm. A bonded uncoupling system can be used for tiles where lateral movement is expected. Install movement joints according to industry standards. Ensure the heating system is commissioned correctly and the flooring chosen is suitable for both the environment and service duties. Contact the manufacturer for specific recommendations.