No, You can’t directly apply traditional cement-based self-levelling compounds that you mix with water, on top of Bitumen. Further preparation of the subfloor is required. See solutions 1 and 2 below if you are using the cement-based self-levelling compound.
You can, however, apply a 2-part Latex-based self-levelling compound, which does not require any extra preparation, this is detailed below in solution 3.
Why can’t you apply self-levelling compound directly onto bitumen floors?
The reason you cannot apply self-levelling compound directly over bitumen is that it is non-porous. The substrate must be rough and porous enough to allow the self-levelling compound to seep into its pores to achieve adequate adhesion.
Traditional cement-based self-levelling (Self-level) compound that you just add water to cannot be applied directly over a bituminous substrate without a primer, as it will not adhere properly.
Self-level is only applied in a thin layer, so it is important it is applied correctly otherwise it will start to dry, crack and then flake off. I know because I have seen it! The picture below shows some old self-levelling compound over Bitumen, that just flaked off in my hands when I disturbed it.
Solution 1: The Mechanical Approach
Mechanically roughen surfaces by grinding or scarifying to provide a mechanical key.
This can easily be done with a standard 4” angle grinder and a diamond grinding disc. It takes time and creates a serious amount of dust.
You can use a vacuum attachment which helps tremendously, but it still creates a fine layer of dust over every surface. You do have to get down and dirty, but it creates a really good rough surface for the self-level to adhere to. It is the same principle as sanding two surfaces with sandpaper to create a good key before sticking them together
I still rate this method, but only if you are working in an area where making some more dust doesn’t matter. It is important to wear a mask and goggles throughout the process to protect yourself. Just remember to sweep and hoover up thoroughly before applying your self-levelling compound!
Solution 2: The (PVA) Primer Approach
Treat the subfloor with Undiluted SikaBond® PVA or Regular PVA will work just fine
Fully coat the floor in PVA straight out the tub/tube and allow it to become tacky before applying the levelling compound.
PVA is cheap and readily available and all you need to apply it to the floor is an old 4” or 6” paintbrush or roller if you want maximum speed.
The only difficulties here are trying to wait the perfect amount of time for the PVA to become tacky, Also…
Once you have painted your floor in PVA you will need to walk back and forth across it to apply the self-levelling compound. It will end up sticking to your shoes and at some point and you will probably end up kneeling in it!
Solution 3: Take the easy way and/or the Ardway!
Ardex 2-part self-levelling compound
A lot of problems can be solved by getting the right stuff for the job. I have seen this being used by many commercial floor laying contractors. I have since used it myself and have had great success despite having no formal floor laying training.
Works on any subfloor – Ardex 2-part self-levelling compound can be applied directly to pretty much ANY floor substrate including, Bitumen, Old adhesive residues, Concrete floors, floor screed, Quarry Tile, Ceramic Tiles, Porcelain Tile, Terrazzo, Floor paint, Plywood, No more ply and even Smooth/polished concrete.
Suitable for 1st floors or suspended timber floors – where there may be some movement in the floor deck. The latex in the mixture gives a slightly flexible quality to the self-levelling compound, whereas traditional cement-based self-levelling compounds have more of a tendency to crack.
No need to measure anything out yourself – The bag of self-levelling compound and tub of latex are always sold together, in the perfect ratio.
Spreads easily and forms its own level (its magic!) – I found that the latex self-levelling compound finds its natural level and gives a much smoother covering. Cement-based – just add water self-levelling compound tends to form ridges if you are not careful and seems to require more skill to achieve a satisfactory finish.
Quick setting – you can start applying your floor covering in as little as 4 hours later.
A little goes a long way – Ardex NA will cover approximately 5sqm when applied at 3mm thick
The mix is always perfect – so it is easier to spread over the floor. This is kind to beginners who may not be used to spreading self-levelling compounds. Pro’s also like it, because they can get the job done more quickly and efficiently!
Want to learn more about self-levelling compound? Luckily for you, we have tonnes of info available, get stuck in.
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