Uneven concrete floor with bitumen under floorboards

As per the title, a friend has a bungalow with solid floors, and these appear to be uneven with an uneven layer of bitumen on top.
Floorboards laid on the bitumen (bitumen stuck to the underneath).
The nails holding the floorboards together have rusted away, and the boards are wobbly.
What is the recommended (economical) way to redo the floor? The old boards will come up, and new larger boards will be put down, but how should the floor be levelled before hand?
As far as I can see at the moment, trying to remove the old mastic is likely to be difficult and expensive, a screed over the old mastic will need to be quite thick and so raise the floor level well above original.
Possibly a bit more bitumen, but properly laid?
If I was doing it I might just Kango the floor out and then relay properly with under floor insulation, but this is likely to hit the 'expensive' barrier.
Advice welcome.
Cheers
Dave R
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On Saturday, 29 August 2015 18:25:47 UTC+1, David wrote:

An alternative is to screw down moisture resistant T&G chipboard with stainless steel screws.; I painted the underside of the chipboard with bitumous paint as a bit of belt and braces.
Best really is to take up the concrete & replace with insulation underneath. You won't get the bitumen off, I guarantee it.
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harry wrote:

You can normally soften bitumen either with a heat gun or white spirit. It is a pain to remove but can be done. There will always be a thin residue. You can always add some sand to the bitumen if you are trying to level it. Very messy.
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On Saturday, 29 August 2015 18:25:47 UTC+1, David wrote:

Cross batten the floor and level the battens, then lay chipboard over the battens. Inch thick battens should suffice if they are supported on packers every few inches.
Ensure there is ventilation to the void between the chipboard and the bitumen.
Alternative is a floor levelling compound which can be laid down to 1mm thickness but I don't know if that will be stable over bitumen - it would be direct over concrete.
Owain
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On Sat, 29 Aug 2015 11:25:08 -0700, spuorgelgoog wrote:

Problem is that cross battens plus chipboard would result in a step up into the room over the threshold.
Levelling compound is unlikely to stick to bitumen - which is why more bitumen is a suggestion.
No obviously easy solution.
Cheers
Dave R
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On 29/08/2015 18:25, David wrote:

Can you confirm that only a very thin layer of bitumen has been used to "glue" the floor to concrete below?
I have come across a bitumen floor (mixed with sand) that was around 10mm thick and used as a floor levelling screed. There were loads of embedded circles from creeping under the weight of various furniture.
It came up quite easily and I re-made the floor using "proper" floor levelling screed.
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On Sat, 29 Aug 2015 21:20:11 +0100, Fredxxx wrote:

10mm thick is still pretty thin - haven't measured it but where a floorboard was taken up there was bitumen stuck to the floorboard and cavities in the bitumen underneath which didn't seem to match the bits on the floorboards.
I don't think it was mixed with sand.
Still struggling to grasp how someone could lay a concrete floor/screed which wasn't flat and cover it with bitumen which also wasn't flat so I may well be missing something here.
Cheers
Dave R
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In my old ex-LA house 30 years ago I discovered that the bitumen ground floors were all laid on earth! Wycombe District Council, nota bene (anno 1947). Other councils may have built their council houses differently/better. By the time I came to installing wood floors the bitumen was lumpy and bumpy.
MM
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On Sunday, 30 August 2015 11:50:18 UTC+1, MM wrote:

In 1947 there would probably still have been building materials shortages and any housing was better than nothing.
By the Fifties building standards were improving (only to go downhill again from the Sixties IMHO)
Owain
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On Sun, 30 Aug 2015 04:37:53 -0700 (PDT), snipped-for-privacy@gowanhill.com wrote:

Yes, I reckon the people who were lucky enough to move into those new council houses on the edge of Wycombe would have been over the moon. The actual house was constructed very solidly. It had a grate in the front room and in the main bedroom above, plus a coal-fired stove area in the kitchen. Also, a large back garden which would have enabled a keen gardener to grow veg and soft fruit, and even perhaps keep a few laying hens.

I reckon my house, built in 2004, isn't bad. It's certainly better quality than Wimpy or Barratt. The local builder used to build council houses for the local council. However, that was when the father ran the business. Since the son took it over, I believe it went out of business during the recession.
MM
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On Saturday, 29 August 2015 18:25:47 UTC+1, David wrote:

If you're determined to avoid tearing the floor up & insulating, I'd just level it with bitumen/sand mix. The more sand, the less its going to move over the long term. And put down T&G flooring so each board/sheet is supported by its neighbours.
NT
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