Concrete - Bitumen - Timber Floor - Advice Please

[1934norfolk]

Hello, I am new to the forum. I look forward to reading and getting involved, looks like a treasure trove of information.

We bought our first house about 18 months ago, its a 1930s detached house, not sure if this fits in the definition of period property? What we thought was going to be redecoration is now turning into a full refurbishment / restoration!

Anyway, onto my query. The original ground floor of the house seems to consist of a concrete floor with a bitumen layer and then timber floor boards on top. Currently some of the floor has an engineered timber flooring which has been laid on top of the original timber floor boards with a membrane in-between.

In the areas where I have exposed the original floor boards they are generally in good condition. There are some areas where the edge of the timber has touched an external wall and it has started to rot. There is also a small area of the floor which is close to where the front door was originally located, this also has some small rotten areas.

The ultimate goal is to tile the hall area and have a timber floor in the living areas. Unfortunately due to past wall removal and a 1970s extension the original timber floorboards are not continuous throughout the living area.

My question is - should the new flooring be installed on top of the old floor boards, like the current engineered floor seems to be? If so, presumably I should cut out the rotten bits and patch up the bituminous paint?

Or should the floor boards be removed? Is the bitumen likely to be the DPM? I suspect it is. If the floor boards are removed, how should the floor be built back up again? Should the bitumen also be removed?

I should point out that we plan to be in this house long term, 25+ years. Although I don't want to spend money for the sake of it I also want to do things right first time.

Hope someone can help. Cheers, Chris.

 

[Zebra]

Well, before one can answer the question of what to do next, I think the first thing to think about is why did those floorboard ends rot?
Is 30s too early for dpm? I don't know, perhaps someone will know. Is the floor damp in those areas? If you lay a piece of plastic sheet there and leave it a few days, does moisture accumulate underneath?
Aren't you tempted to restore the original boards? You could patch in new ones where they have rotted. Reclaimed floorboards aren't hard to find. Or new ones - there is an argument against using reclaimed, as then the age of any repairs is more readily apparent.
If you don't want to restore them, then I would think removing them would be a shame. They could just remain underneath.
I wonder whether the bitumen layer over the concrete is the only protection against damp. Might there be another damp proof layer under the concrete? In any case, I wonder whether repairing it, so that whatever you put there no longer rots, will be feasible. Forgive the ramble, it's hard to say without digging a corner up to see what's down there.

 

[paulc]

Is 30s too early for dpm?

My home is a semi built in 1929 (with an 1976 extension). The main floors are suspended timber over earth, and the sleeper walls have what looks like a bitumastic felt under the timbers.

Building standards were very variable between the war years and subject to local controls. It is quite possible that the concrete sub-floor & bitumen DPM is original, but as long as there is sufficient ventilation under there, it shouldn't be a problem. As for the membrane under the laminate flooring, this is quite normal.

I'm in the middle of a refurbishment myself (doing one room at a time) - The lounge is having a layer of aluminium foil put down, followed by a layer of wood-fibre boards, and then carpeted (with thick underlay). The foil and underlay will both act as a DPM to prevent moist are in the room condensing on the underside of the floorboards and causing them to rot (well, that's the theory). There is already a howling gale coming in through the air bricks which should take care of the ventilation down there.

Side note: The original boards are 22mm thick tongue & groove, modern floorboards are only 19mm thick - To get a decent match means either finding reclaim boards or a timber merchant that can plane fresh ones to size.

 

[88v8]

Hello and welcome.

1930s... I would be surprised if there is no dpc in the walls - felt or slate.
Perhaps however it's too high in relation to the floors or has been breached or bridged in places.

Given that the existing structure has largely worked, in terms of not having significant damp issues, as far as possible I would leave well enough alone.

The bitumen is the dpm. To what extent it is necessary, to what extent the underlying concrete is actually dry, cannot be known, but why bother to find out? Carefully maintain and extend the bitumen as necessary.
Pay attention to any penetrations such as pipework, and if any trades come to dig holes for heating or plumbing, ensure that you yourself carry out or carefully supervise the reinstatement of the bitumen.

I (slightly) wonder what has been done at the junctions of the old and extended floors.

Yes, it would be sensible to patch the rotted boards. Treat the surrounding area with Cuprinol Five Star <pong warning>
Do not butt the replacement boards against the wall, or if you must then interpose a layer of dpm.

As there is already an overlaid wood floor, I would lean towards retaining an overlaid floor, unless of course the original boards are meritorious - hardwood, that is.
Apart from anything else, retention avoids issues that might arise with door & threshold heights if you lowered the floor again, and avoids leaving a tidemark around the skirtings where the previous floor was higher.
If you wish to create a Period ambience - yes it can be considered a Period house - use reclaimed boards. It does not have to be that uniform modern blandness, 'Engineered'.
If using reclaimed, buy sufficient in one hit, their thickness is variable.

Consider however what you are going to do with the wood floors. Bare unstained softwood was not Period in the 1930s, except amongst the most poverty-stricken, and may not be considered very practical in the kitchen for example. There is little point in laying reclaimed boards, and then covering them up.

And other than the grandest houses, 1930s 'Period' does not embrace fitted carpet.
There are many threads on floor finishing, painting, and staining and with what to cover the floor in terms of rugs, carpet, lino, and to what extent.
Toby Newell is our resident expert on wood finishing.

Welcome to the forum.

Ivor

 

[malcolm]

I have a room with a 1910 parquet floor over a very thin concrete floor. For that the bitumen seems to have been used as a glue for the parquet. My floor has also rotten at the edges, mostly due to the ground levels outside the house being higher than the internal floor level providing a steady supply of water through the walls. Apart from that the system seemed to work.

Wood in an old house needs to be able to dry itself out by evaporation into the house. A vapour barrier between the old wood and new wood on top will probably cause the old wood to get damp and rot, so best avoided.

 

[paulc]

Wood in an old house needs to be able to dry itself out by evaporation into the house. A vapour barrier between the old wood and new wood on top will probably cause the old wood to get damp and rot, so best avoided.

Would a vapour barrier be a problem if it is a suspended floor over a well ventilated space ?

 

[1934norfolk]

Thanks for the great replies, it's good to have found some people to bounce ideas off.

So to clear a few things up:
1. It is not a suspended floor.
2. The external walls have a slate DPC.
3. The living area comprises 4 rooms which have been made open plan(ish) through wall removal (not by us). 3 of the rooms would have been part of the original house, 1 is a 1970s extension. I have pulled up a carpet in one quarter of the combined space, that is where I can see the floorboards. The rest of the floor is currently covered in an engineered wood flooring but on the edge that joined the carpet I can see that the engineered floor is on top of floorboards also (at least in that area).

Where the timber has rotted at the floor/external wall junction I have lifted a board. I can see that the lower edge of the timber has touched the wall just below the slate line, so that seems to have a logical explanation.

The small rotten areas in the middle of the floor near are in the hall, not the living area. This is where the original front door was located could be due to a damp door mat perhaps? Currently that area is a downstairs toilet and has been since the early 1980s.

I agree it seems a shame to remove them and I am also curious what happens at the junction between the original building and the 1970s extension. The reason I asked about removal is that I wondered whether it would be a bad idea should we choose to cover them up.

I think the next stage will be to lift up the engineered floor and see what total extent of original floor boards we have. Then we can start to formulate a plan. This may not happen for a while as I plan to finish the upstairs before tackling downstairs.

When Christmas is over I will take a few pics to help explain.

 

[malcolm]

I don't think it would be a problem if you have ventilation. It would only function as something to stop air getting between the floorboards above - the ventilation below would sort out the vapour.

 

[88v8]

I have a room with a 1910 parquet floor over a very thin concrete floor. For that the bitumen seems to have been used as a glue for the parquet.

Yes. That would probably have been hot bitumen, involving a tar burner. Very effective as an adhesive and a damp-proofer.

Ivor