Messy subfloor...

[portuguesejohn]

Some context: 1930s house, groundfloor is all concrete with a thick layer of bitumen on top, most of the house is floorboards that were laid on top of the bitumen (probably once it was still hot...) and nailed down with flooring brads. Yes, apparently that was a thing back in the 1930s... whole street has houses like this.

Just had my front door pushed out into the storm porch to create space on the hall, as part of the job the floor was levelled with concrete.

Had the floor finish guys come in the other day to do the flooring on another section of the house, asked them about the prep work needed for this hall as well - they said the newest floorboard (seen in the pictures) was fairly loose and that just needed to be fixed before they would plywood/screed the area - FAIR ENOUGH. Pulled the floorboard up to find what looked like a thin layer roofing felt glued on the back of the floorboard, upon further inspection, also realised this layer of felt was under some of the concrete that had been laid before as well! Ended up pulling all of this old concrete out with my hands as it was all loose and crumbly.

What I found happens to be a mix of bitumen, concrete, a couple of holes that need to be filled - Please find all pictures attached.

I have a lot of questions regarding this subfloor, but the biggest one I have is: How do I go about making this good? A friend is saying we should just level with concrete and call it a day, but seeing as the DPM seems a bit compromised in a few areas, this is what I was thinking (pardon if full of nonsense, not very experienced!):

• Clean up the area.
• Fill bigger hole with some rubble and concrete.
• Layer of bitumen where required (or even the whole area for good measure?)
• Level whole area with concrete.
• Fix the horizontal floorboard with strong adhesive once area is levelled.

My concern is the concrete over the bitumen, will it adhere properly?

I suspect the felt was put in place as some sort of DPC, but it was never fixed properly so was easily pulled out. The last picture shows some of the concrete with the said felt.

The house has never shown signs of damp or rotten floorboards, location in the country and geography might have a say on that, so I am not too concerned over that.

Looking for suggestion on how to approach this!

 

[portuguesejohn]

One extra picture showing the horizontal floorboard.

 

[KenGMac]

portuguesejohn, good evening.

There is a 99.9% certainty that the bitumen and old felt is the DPM for the floor, all the way through the house.

Yes, back in the day that is what was used and [generally] if left alone ??? it works, OK it can break down as a DPM but only where the concrete topping fails.

As to what to do? clear away any loose apply overcoat the area with a liquid DPM, if it were me, I would apply "several" coats then lay a concrete screed using [say] 10.mm single sized aggregate, the latter to try to ensure that this concrete flows and permeates as easily as possible.

Ken.

 

[portuguesejohn]

portuguesejohn, good evening.

There is a 99.9% certainty that the bitumen and old felt is the DPM for the floor, all the way through the house.

Yes, back in the day that is what was used and [generally] if left alone ??? it works, OK it can break down as a DPM but only where the concrete topping fails.

As to what to do? clear away any loose apply overcoat the area with a liquid DPM, if it were me, I would apply "several" coats then lay a concrete screed using [say] 10.mm single sized aggregate, the latter to try to ensure that this concrete flows and permeates as easily as possible.

Ken.

Thanks Ken, only saw your post today. The felt is definitely not an "original" feature, it was only present in this area and just under a newer floorboard in the living room. I suppose the old owner was a bit worried about damp when doing these fixes. The felt under the cement wasn't ideal though and it was very easy to pull off.

We decided to tackle this over the weekend, here is what we did:
- 2 coats of thick bitumen paint, careful to cover the whole area and allow to dry overnight.
- Small coat of PVA as I was worried about the concrete adhering to the bitumen paint, probably not needed but didn't seem to hurt.
- Cement mix with some waterproofer thrown in (again, thought why not...), levelled as better as we could with a flat surface. Wasn't too worried about the texture at the top as the floor finish people will be using plywood on top of the floorboards and self leveller all across the area.

Attached picture was taken shortly after finishing. Seems to be drying alright!

First time ever laying concrete indoors and in such awkward conditions, the floor in this house gives me nightmares!! Now thinking of ways on how to conceal that earth cable you can see on the bottom left of the picture - it connects to my mains supply on the plastered collumn.