Granolithic finish over bitumen sheet membrane?

[GranolithicSG]

Hi All,

I have a job that requires me to cover up a pedestrian walkway in granolithic finish. However, the owner has already gotten his waterproofing contractor to install a bitumen sheet waterproofing membrane. I have read some disadvantages of tiling over bitumen, not sure if the same issues will be found if a granolithic finish is laid over it?

Walkway is external and will be under the hot sun all day, it is also on top of a shopping mall basement with shops below this location.

Not sure if anyone can advise.

 

[Ajax123]

Depends on the depth of the concrete under the grano toppng. It would need to be a minimum of 50mm as it would be classed as unbonded. that said most concrete would need to be laid mininum 75mm in this situation to get manufacturers approval. The use of concrete over bitumen is an age old method long since superceded but shoud not be an issue. Ive not come across a grano floor for probably 15 years.

 

[GranolithicSG]

Hmm seems like it would be dangerous in my case, screed thickness would likely be 25mm with another 20-25mm of granolithic finish on top.

There are also vertical upturns up to 300mm in height. These will not have any concrete sitting on them. I suspect the granolithic finish here will fall off if any cracks occur at the bends as they will be applied directly to the bitumen sheet. Perhaps I could layer it first with a slurry of Ardex NA. Not sure if that would work.