My partner and I have just bought our first home.A 1950's bungalow which is need of refurbishment. So far it has thrown us a ton of surprises! The worst so far being the floor in one of the bedrooms. After pulling up the old floor boards we found a concrete poured floor underneath with broken bitumen on it. The concrete has gaps of about 4 inches between it. These concrete "slabs" are separated by very rotten wood. On closer inspection the concrete is only about 3-4 inches thick with soil directly under that. No damp-proof membrane (DPM)!The depth of the gaps is roughly 10 inches. The damp-proof course (DPC) in the walls seems to be intact.

I think the floor used to be a suspended timber floor but the previous owner decided to pour concrete under the floor boards and between the joists maybe using them to level the concrete and just left them there to eventually sponge up any moisture and rot away.

However, as it stands the concrete feels and seems dry. Possibly because the house is in an elevated position.

I know the best solution would be to dig up existing concrete, dig further down maybe 30 inches then put down insulation board , followed by a DPM and then pour concrete. Unfortunately we don't have the budget to do this.

As a cheaper alternative I have thought about filling the gaps with concrete, then applying an epoxy solution all over the floor, then floating a wooden floor on top of this. However i'm not to sure how to do the concrete mix for this, how much aggregate is required etc.

Here are some images of the floor. I have dug out the rotten timbers.


Gap Width

Gap & Slab Depth 1

Gap & Slab Depth 2

Any thoughts or recommendations besides the expensive approach would be appreciated

  • A late question: what's "DPM" and "DPC"? May 17, 2016 at 18:39
  • @DanielGriscom DPM = damp proof membrane; DPC = damp proof course May 20, 2016 at 20:03

2 Answers 2


(I'm assuming that you are in the UK).

Concrete floors without DPM are not unusual in houses of that age, so there is a possibility that it's not a cowboy job. The broken bitumen you mention was probably the remnants of an asphalt DPM over the slab. The wood has (as you suggest) likely been used to level the concrete. If they were previously joists for a suspended floor, some have certainly been removed, as the spacing is way to wide for floor joists.

Without ripping the floor up, I can see two basic options:

1: Fill the gaps with concrete and get an asphalt company to lay an asphalt screed over it to restore the DPM.

2: Fill the gaps with concrete, lay a DPM over it, insulation, then a concrete / fibre screed. Note though that this will raise the floor level by 75-100mm (depending on the insulation).

In terms of concrete, as it looks like it's not a structural element, you could just use a "basic" 4:2:1 concrete mix (4 parts stone, 2 parts concreting sand, 1 part OPC). Add enough water to make it workable, but not so that it gets sloppy.

  • Correct I am in the UK. I'm not to keen on option 2 as this would lead me to raising the floor throughout the house and adjusting all doorways etc. I'm pretty sure the same issue exists in every room. What does "OPC" stand for is that the one part cement? Also should i dig slightly under the existing slabs for a better concrete "bond"? Rather then asphalt I was thinking about using something like this: f-ball.co.uk/product_detail.asp?product=F75&catID=damp Thanks
    – davey
    Jan 6, 2015 at 8:59
  • Sorry, OPC is Ordinary Portland Cement - just the bags of cement you can get from DIY stores and builders merchants (some has plasticiser already in for mortar - you don't need that). I wouldn't bother digging under as it won't really help any with bonding. If you really wanted to bond, you could drill into the slabs and use a piece of reinforcement, but I'd not bother. That product sounds like it could do what you want it to do.
    – John
    Jan 6, 2015 at 14:01
  • Thanks i'm actually thinking i'm going to go for a tanking slurry. its product by these guys : kabuildingproducts.co.uk/page_2350337.html
    – davey
    Jan 7, 2015 at 9:33

I just purchased a house in the United States, Pennsylvania to be specific by a lake and I was considering pouring concrete over the floor which is identical to the floor pictured above. However I was told that this type of floor was designed this way for drainage should water enter the space...makes sense to me now. The wood floors that have since been pulled out were warped because a moisture barrier was not present. I plan on getting expert advice before doing something like pouring concrete that would block the egress of any water between the slabs of concrete.

  • This response is actually more commment than answer to davey's question. Recommending expert advice is close to being an answer, but it needs to be qualified. Why is expert advice important, or why would you suspect that the question could not be answered with merit here on the DIY stack exchange? May 20, 2016 at 20:07

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