Can You Directly Apply Cement-Based Self-Levelling Compounds Over Bitumen?
Many DIY enthusiasts and professionals wonder if it’s possible to lay traditional cement-based self-levelling compounds directly onto bituminous surfaces. The answer is generally no. Standard cement-based self-levelling products, which are mixed with water, require specific preparation of the subfloor to ensure proper adhesion and durability. Applying them directly over bitumen often results in poor bonding, leading to issues like cracking, delamination, or flaking off over time.
This is primarily because bitumen is a non-porous, flexible material that doesn’t provide the necessary grip for cement-based compounds. Without a proper primer or surface treatment, these compounds will struggle to adhere securely, compromising the integrity of your flooring project.
Why Can’t You Use Traditional Self-Levelling Compounds Directly Over Bitumen?
The core challenge lies in the non-porous nature of bitumen. Cement-based self-levelling compounds depend on the substrate’s porosity to seep in and form a mechanical bond. When applied directly, they often sit atop a slick, non-absorbent surface, which prevents proper adhesion. Consequently, the layer may remain loose, crack, or peel away over time. Visual evidence of this issue can be seen in older installations where the self-levelling layer has flaked off, revealing the slippery bitumen beneath.
Effective Solutions for Applying Self-Levelling Compounds Over Bitumen
Solution 1: Mechanical Surface Preparation
One highly effective method involves physically roughening the bitumen surface to create a mechanical key. This process, known as grinding or scarifying, involves using tools like a 4-inch angle grinder equipped with a diamond grinding disc. The goal is to etch the surface, increasing its surface roughness and porosity to improve adhesion.
However, this approach generates a significant amount of dust, so it’s essential to wear protective gear such as masks and goggles. Employing a vacuum attachment can help contain the dust, but thorough sweeping and vacuuming afterward are crucial for a clean, dust-free surface before applying your self-levelling compound. Remember, this method requires effort and patience, but it results in a robust bond suitable for subsequent flooring layers.
Solution 2: Applying a Primer (e.g., PVA)
Another reliable approach involves priming the bitumen surface with a suitable bonding agent. Using undiluted SikaBond® PVA or standard PVA glue, you can create a bonding bridge. Simply coat the entire surface with the primer using a brush or roller, ensuring an even application. Allow the primer to become tacky—this is when it’s ready for the next step.
This method is quick and cost-effective, but it requires patience to wait for the primer to reach the right tackiness. Once ready, walk across the primed surface to spread the self-levelling compound. Be aware that walking on the primed surface can cause uneven application, and excess primer on shoes may transfer to other areas.
Solution 3: Using Latex-Based, Pre-Mixed Self-Levelling Compounds
For a more straightforward and less labor-intensive approach, consider using a two-part latex-based self-levelling compound. These products are designed to adhere effectively to challenging substrates like bitumen without extensive surface preparation. They come pre-mixed, ensuring consistent ratios, and typically require no primer beforehand.
One recommended product is Ardex Arditex NA—a pre-mixed, latex-enhanced self-levelling compound that spreads easily and finds its own natural level, resulting in a smooth, durable surface. Its flexibility makes it suitable for various substrates, including old adhesive residues, concrete, quarry tile, ceramic, porcelain, terrazzo, and even polished concrete. It significantly reduces the risk of cracking and provides a stable base for your final flooring.
Summary of Recommended Approach
While traditional cement-based self-levelling compounds are not suitable for direct application over bitumen, you can achieve excellent results by either mechanically roughening the surface, applying a bonding primer, or opting for a latex-based pre-mixed product. Each method has its advantages and challenges, but using a latex-based, pre-mixed self-levelling compound like Ardex Arditex NA offers the most straightforward and reliable solution, especially for DIY enthusiasts or those looking to minimize preparation effort.