Denver Coleman discusses the challenges and methods behind removing bitumen from floors.
“We regularly come across bitumen on screeds when uplifting old floors. What is your recommendation with regard to laying over bitumen or removing it?” Benjamin Zietsman, Cape Town
In the past, many types of flooring including semi-flexible tiles, sheeting and wood floors were installed using bitumen-based adhesive. It is also a reasonable waterproofing agent and, as a result, quite successful as both an adhesive and a moisture barrier.
When removing an existing floor, bitumen is easily identified as a black substance that is firmly adhered to the screed, remaining behind after the floorcovering is removed. Due to the nature of bitumen, it seeps into the screed and is therefore very difficult to remove. Unfortunately, modern self-levelling and smoothing compounds as well as acrylic adhesives are unable to bind to bitumen. It is therefore essential to remove the bitumen before commencing with floor preparation for a new floorcovering.
Bitumen can be a challenge to remove and over the years many methods have been tried. Sanding it off, using a scraper or grinding can introduce several challenges; however, with modern technology, two possible methods are recommended.
The first method requires the screed topping to be hard so that a scabbling machine can be used to remove the top layer of the screed surface, which contains the bitumen. However, if the screed topping is soft, this method could destroy the entire topping.
The most common cause of failure when using screed bases is construction moisture or the lack of an effective moisture barrier on subfloors. Read more about installing quality vinyl flooring here.
The second method involves using an HTC grinding machine. These machines are available in different sizes for purchase or for hire and leave a very clean, smooth surface. If neither of these is available, the manufacturer of the screed preparation products should be contacted for further advice and assistance.
Prior to preparation
A moisture test has to be conducted prior to beginning a floor preparation. Bitumen is less affected by moisture than any other adhesive product and can therefore give a misleading impression that the original floor was dry, or give a misleading moisture reading if doing a surface moisture test. This is why a below-surface moisture test is needed. Failure to carry out proper moisture tests may cause adhesion problems after the new floor is installed, which could be difficult and expensive to rectify.
Once the moisture barrier has been applied, the surface should then have a blinding layer of screed/cement material applied over the damp-proof membrane to block any bitumen leaching into newly applied adhesive.
After removing all dust and surface contamination, apply a primer coat of bonding liquid from the same product range that will be used for the blinding/blocking coat. Once the blinding coat has been applied, screed preparation can be continued as per normal.
When planning a building renovation, it is advisable to check whether bitumen was used to adhere previous floorcoverings so that sufficient time, budget and preparation for its removal can be taken into consideration.
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