Can Self-Levelling Compound be Used on Bitumen Floors?

Bitumen is a black, petroleum-based product frequently used in the construction of roads and highways.

Additionally, its waterproofing and adhesive characteristics make it suitable for roofing, floors, and asphalt pavements in industrial buildings, warehouses, and outdoor sports surfaces like running tracks.

Many times, builders want to put a self-leveling compound over bitumen mastic flooring, thinking that it will make the floor smoother or even out its texture. But is it recommended?

Unfortunately, you cannot, and you shouldn’t directly apply the traditional cement-based product (mixed with water) on top of the Bitumen primarily because it results in a finish that will be far from ideal.

Self-Levelling Over Bitumen Flooring

A self-leveling compound, also known as self-leveling compound or self-leveling underlayment, is typically a polymer-modified cement used to smooth out uneven concrete or wooden floors indoors and outdoors.

When laying ceramic tiles or any other flooring, it’s critical to ensure the surface is leveled since uneven surfaces might cause tiles to fracture or crack.

A self-leveler is meant for that very purpose and is perfect for filling in dips in wooden floors or for smoothing out concrete ones. Also, if you are planning on placing ceramic tiles on uneven surfaces where it’s prone to cracking, you must use a self-leveling compound.

The reason you should not apply a self-leveling compound over bitumen floors is that to ensure proper adhesion of SLC, it needs a porous surface. But since Bitumen is oil-based and not porous, applying the self-leveler on it will not work as the compound has nothing to grip onto.

In addition, a self-leveling floor compound is applied in a thin layer. If you try to screed over Bitumen, there are chances that the compound will flake away or separate from the Bitumen, resulting in an uneven, cracked finish.

That said, self-leveling compound can be applied over bitumen floors if you choose the right type and prepare the surface carefully.

Since not all self-leveling compounds are compatible with bitumen, you must select one specifically formulated for this purpose, or a smoothing compound that can bond effectively to bitumen residue.

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Adhering Self-Leveling Compound to Bitumen

Bitumen is the binding component, which is used to make the finished construction material known as asphalt by combining it with aggregates such as sand, gravel, or crushed stone to create a strong, durable surface suitable for roads and other paved areas.

If you plan to use a self-level compound over the bitumen surface, it’s essential to know the steps that should be followed to ensure the compound sticks to the bitumen correctly.

1- Roughen the bitumen

The simplest way is to try a 4” angle grinder with a diamond grinding disc.

By roughening the bitumen using this mechanical grinder, you can provide a surface that allows the self-leveling compound to stick better. This will also help in scraping away all the loose or peeling bitumen.

Remember to wear a mask and goggles for safety before grinding. And after roughening the surface, be extra careful to sweep and vacuum all the dust.

2- Use the PVA primer

Priming is essential to promote strong adhesion between the bitumen surface and the self-leveling compound. To begin with, you should carefully check the surface. If there are any deep holes or gaps noticed in the bitumen surface, fill them with a suitable filler. 

Next, use a product like Regular or Undiluted PVA to coat the entire surface evenly using a paintbrush or 4’ roller. Then wait for the PVA to dry and become tacky.

The only downside with this method is that the PVA must be tacky before you can begin adding the compound, which requires precise timing. Also, applying the PVA to the surface correctly will require walking back and forth to apply downward pressure.

So, be prepared to have PVA stuck on your shoes and perhaps your knees, depending on how much pressing down is required.

3- Apply the self-leveling compound

For bitumen surfaces, a two-part, bitumen-friendly self-levelling compound such as Ardex NA or F Ball Stopgap 1200 Pro is a reliable choice, often used by commercial contractors.

These latex-based compounds are designed to overcome the adhesion challenges posed by bitumen’s oily nature and can be applied over a wide range of substrates, including concrete, floor screed, ceramic, porcelain, quarry tiles, plywood, terrazzo, and even old adhesive residues.

They’re economical, set in as little as four hours, and allow for quick application of the final floor covering. Their flexibility makes them suitable for timber floors that may experience slight movement, reducing the risk of cracking compared to traditional concrete-based compounds.

Another advantage is ease of use — the powder and latex are pre-measured for the correct ratio, so no mixing guesswork is required. Even for those with minimal experience, the compound spreads smoothly, thanks to its latex content, leaving a flawless, level surface ready for covering.

Important considerations:

When using self-leveling compound over bitumen, remember that each product has unique properties, so always consult the manufacturer’s datasheet or check the information provided on the packaging before starting work.

• Condition of Bitumen: Ensure the bitumen is old and well-established before application.
• Surface Preparation: Clean the surface thoroughly to remove dust, debris, and contaminants before priming.
• Primer Compatibility: Use a primer that is suitable for both the bitumen and the chosen self-levelling compound.
• Manufacturer’s Instructions: Follow all guidelines for mixing, application, and curing.
• Air Bubble Removal: Use a spiked roller to release trapped air and achieve an even finish.
• Application Depth: Check the product’s minimum and maximum depth requirements to ensure correct coverage.

What is the typical thickness for a self-leveling compound?

While self-leveling compounds can be applied in thicknesses ranging from 0.5 mm to 50 mm, they are generally intended for a thin layer of about 3 mm to 15 mm. Their primary purpose is to cover the entire surface, eliminating imperfections in the subfloor and creating a smooth, level finish.

Can You Paint Over Self-Leveler – What Paint to Use?

While traditional gypsum-based surface levelers are challenging to coat, cement-based self-leveling can be painted and polished to add a unique, stylish, and colorful touch.

When applied correctly, the paint over cement or concrete-based levelers (over bitumen floors) makes the surface stain-resistant and easy to clean, which can be left as it is for a long time.

There are, however, a few things you should remember when painting self-leveling concrete.

• Ensure that the surface is completely dry before painting.
• Self-leveling concrete can take up to 60-72 hours to fully cure, and it’s crucial to wait for the cure time before painting.
• Use a primer and paint product designed for concrete which will adhere better to the surface without chipping or peeling fast.

When it’s time to apply topcoat, consider using concrete dyes, acid stains, water-based stains, or a two-part epoxy paint over self-leveling cement.

These are usually thicker and more durable than regular paint and will help protect the self-leveling concrete from wear and tear over bitumen flooring.

What are the Problems with Using Self-Leveling Concrete?

Self-leveling concrete is a durable finished flooring option used in most residential and commercial properties. You can also modify its appearance with various coloring and finishing additives to match your design preferences.

The good thing is it’s easy to clean, and any damage can be fixed by simply patching it up with another batch of self-leveling concrete.

It is, however, essential to note that self-leveling concrete is not a complete solution, and it creates a superficial layer rather than fixing the underlying issues, such as cracks and gaps.

Self-leveling concrete can often also be problematic as it may crack or crumble due to inadequate bonding and slab movement.

Additionally, it is not advisable for DIY projects because precise measurements are required when mixing the compound for coating bitumen flooring. Too much water causes the mixture to be too runny and not set correctly, while too little water hinders effective self-leveling.

Self-leveling concrete must also be worked on quickly and accurately because it dries fast. If you’re not an experienced contractor, it’s better to let professionals do the job.

The Bottom Line

While putting a self-leveling compound on bitumen floors is not recommended, a few other tricks can help, like applying PVA primer or using Ardex 2-part self-leveling compound that combines latex with the concrete.

Professionals often prefer using the 2-part compound since it provides faster results and has a shorter application time compared to traditional self-leveling compounds.

Remember that if you use a self-leveling compound on Bitumen without proper preparation, you will simply waste time, effort, and money trying to get the product to stick. So, choose the method that results in a smooth process and application without much hassle.