Subfloor prep. for solid wood floor- bitumen/asphalt

Hi, sorry if this has already been answered in another post, but I've been searching this to death and can not get a straight answer!

We had laminate flooring in our living room, dining room and hallway which we have taken up some time ago. Underneath the laminate was mostly parquet flooring, some areas had been cemented over due to work done on the radiator pipes in the past.

As we want to put solid wood flooring down in these areas, we decided to take up the parquet and prepare the subfloor with some self leveller and liquid DPM. As things are at the moment, the concrete subfloor is covered in bitumen with most of it covered in dust and small stones and even some small bits of parquet wood stuck to the bitumen in some areas.

Now in terms of what products to use on the concrete subfloor, I have spoken to someone from a certain company (not sure if I can mention company names in this post?) that has given me some suggestions as to what to use for damp and for levelling.

What I have had conflicting advice on is what to do with the bitumen?
On the one hand I am being told to get someone in to completely remove it - 'mechanically prep' or 'mechanically remove' it with a diamond tipped cutter. That if you don't remove 100% of the bitumen it will be a weakness in the subfloor and eventually we will have problems with the wood flooring.

On the other hand I have also been told it is not necessary to remove the bitumen, simply to clean off the dust and apply an adhesive before laying the levelling screed.

Can anyone advise me which is the correct answer?
I thought that to lay any screed down the subfloor must be completely clean and dust free, which as I have already mentioned, ours is not as all the dust has stuck to the bitumen and would be nearly impossible to remove.

Another question I have is with regards to laying the screed down. Our living and dining room is open plan but we were thinking to lay the screed individually in each room because of fears that the screed would dry out on us too quickly (never attempted to do this before, so maybe we won't be fast enough?). Does anyone think this is a good idea or would you say to just do it in one go?

In case anyone asks, we have already moved the radiator pipes above ground and the house was built early to mid 60's.

It completely depends on the screeding product that you plan to use.

Most reputable screeding companies will have an information line and will freely advise you on the best course of action with their product.

Both options mentioned above are possible depending on what companies product you are using, at the moment you make no mention of having moisture checked the subfloor. Have you done a moisture test? this will affect what may be required in the preparation process also.

Hi, thanks for the response.

I have spoken to Ardex, Bostik and F-Ball.

Bostik said they have no products that are suitable to go over the top of the bitumen and that they are not aware of anything on the market that makes anything suitable.

Ardex were very helpful in terms of advice to do with removing the bitumen, but again made it very clear that if we did not take up 100% of the bitumen (mechanically prep. or mechanically remove it) then that would be a weakness in the floor.

F-Ball recommended some of their products to use once the bitumen had been completely removed which are stop gap F77, P131 primer and then stop gap 300. Again, they used words such as 'installation failure' if the bitumen was not removed 100% and also made it clear that the floor has to be completely dust free.

We have not yet done a moisture test on the floor, although we plan to do this sooner rather than later.

If Ardex and F-Ball Both say to clean the bitumen, then I Guess you have your answer.

My gut instinct says that you might get away with a primer, DPM, Screed application but it's likely that as manufacturers of the product, they wouldn't want to leave any element of 'chance'.

I personally have never had an issue with primer and DPM/screed over the top and then fitting engineered or laminate flooring floating BUT fixing a Solid to a subfloor is a completely different spec, and far far more critical that the subfloor is perfect.

If you're planning to fully bond the solid wood to the sub floor (as it should be), then you have to remove the bitumen adhesive.
Take it back to the concrete, prime, use a smoothing compound with a high final strength like mapei trade plan, apply liquid dpm, prime again, another layer of the same compound then bond your flooring.
Products like Ardex NA and stopgap 1200 can be used over bitumen adhesive residues (most of it has to be removed still) but they have a low final strength. The seasonal movement of the solid wood can pull it off the floor.

You'd be better floating an engineered wood

Thank you both for your replies.

We are re-considering the solid wood flooring and may go for an engineered floor instead. Would this make a difference to whether or not we should remove the bitumen?

We have been looking to hire something to remove the bitumen, the only company that were sure their tool would do the job wanted near £500 for a days hire so we are now trying to find someone who can do it for us if it's any cheaper! This has proved more difficult than I imagined, most companies I have contacted won't do it or will only do it as part of an overall contract of laying the flooring afterwards, even though we were planning on laying the floor ourselves.

We tried heating the bitumen up and then scraping it off but it was just a hot sticky mess, although I haven't tried wiping it with some white spirit as someone suggested.

Solid and engineered floors fit in different ways. A Solid needs to be glued directly to a perfectly prepared subfloor, hence why you have found that all the bitumen needs to be removed prior to liquid DPM, Screed etc.

Engineered flooring will look the same, but is floated over the floor so you need a level surface to lay over, rather than fix to, so I would suggest on a Engineered installation, you may not need to lift the bitumen provided you use a recommended moisture tolerant range if products. The reason you can't just lay over the Bitumen is that a floating floors underlays and sheet DPM will creek and crackle under the flooring as it moves on the Bitumen.

In real terms, a fully stuck solid will feel a little more 'solid' under foot than a floated Engineered, but they will look the same, wear the same, and the Engineered is a far more stable product to live with.