Solid concrete floor problem in 1950s house

[houseonahill]

Hi everyone. I'm new to these forums and decided to sign up because my wife and I recently moved in to a 1950s property and it has a good deal more problems than we expected, causing us many headaches and a few sleepless nights.

I won't bore you with the whole list of problems but there are two things I was hoping for some advice on.

Problem 1: We found signs of damp throughout the ground floor and I've had a couple of specialists round to investigate it. One was extremely thorough and spent several hours trying to work out what was causing the timbers in the above photo (which are in the living and dining room) to read very high moisture content. (In the photo you can see where an old fireplace was. There's also damp issues with the chimneys and walls, but let's put those to one side for now - the problem I'm referring to here is that the timber floor, in all locations, registers moisture, which is coming from below.)

So, upon lifting a piece of the timber floor, he found it was laid over the concrete slab on what looks like a painted bitumen layer - the old DPM. I understand this is fairly common in properties of this age? (I should say at this point that there is parquet flooring in the hallway, same thing - also over a layer of bitumen on concrete. And yes, this timber too is moist.) Anyway, the issue is that now, 70-odd years later, the DPM has apparently begun to fail. In the living / dining rooms there are also wooden battons perpendicular to the flooring timbers at 500mm intervals, laid into the concrete. These were possibly dipped in bitumen before setting but are also, now, moist.

It seems as though the bitumen did its job for many years as the timbers haven't (quite) begun to rot yet, but they are very definitely damp throughout.

The damp guy's assessment is basically that all of this timber will have to come up and the floor cleaned, levelled, and then a new DPM applied (he suggested epoxy).

Firstly - would love any thoughts folks here have on this situation and the recommendation in general. (Should we lay a screed on top of the new DPM? Should we dig the concrete slab out slightly so as not to raise the new floor level too much?)

Secondly - one major issue this causes for us is that we were originally planning to track CH pipes through the concrete (they are currently exposed and hung on the walls, looking terrible.) But I'm guessing this is basically impossible now as you wouldn't want to bury pipes in moist concrete and then bring them up through holes in the DPM, right?. Tell me if there is a way to do this! OR, is there a means of hiding the pipes that doesn't require lots of boxing in / joinery?

Problem 2: (Apologies if I should have posted this in another sub-forum, just let me know...) My damp inspector also took the time to drill into our wall cavities in a few locations because damp is also associated with the walls. Now, part of this problem is that in the past someone has plastered right down to floor level, so the plaster is touching and clearly transferring moisture from the wet, poorly damp-proofed slab (see above). However, there also appears to be some rubble sporadically located at the bottom of the cavity, just above the DPC, which is likely bridging the cavity and bringing moisture across from outside. He didn't find huge amounts of rubble, and it's not consistently present along the walls, but there's enough there to warrant removal, he said.

By the way, we have polystyrene bead cavity wall insulation.

My question here - is it ever possible to get that rubble out without the insulation beads whooshing out everywhere or are we almost certainly looking at insulation extraction / re-insulation as part of this job??

Thanks in advance. We have been having such a stressful time with this lately and would really appreciate any help and advice.

 

[Deleted member 174758]

In the 1950s, prior to the introduction of plastic DPM, bitumen was indeed commonly used as a DPM (and was for decades the standard base for parquet). As you have discovered, though, it can crack and detach over time, allowing moisture through. The inset timber battens are ther to provide a fix for the floor boards (your floor pre-dates modern glued floating floors). I agree with your damp guy's assessment - take the timber up, strip the bitumen (horrible job), take the timber battens out and fill the holes, then put in a 2- or 3-coat epoxy resin DPM which will seal the surface properly. That won't raise your floor level (the epoxy I've used in the past was rollered on, so only microns thick, not inches). If your floor is acceptably level now surely it shouldn't be necessary to screed it at all? If the rooms are to be carpeted I think I'd replace the flooring with a floating floor of P5 T&G chipboard sheet leaving a 5 to 10mm gap all round for expansion.

In terms of the moisture bridging you need a brickie or similar to give you advice. We had it on this house (1881) but short of rebuilding the walls the only approach we could take was to strip the walls back to the masonry to waist height, tank the walls then "replaster" using a waterproof render up to about dado rail height (the joins are hidden by timber dado rails or beneath wainscotting). In our case, though, whilst the walls are cavity walls, we are on a hill, the damp never gets more than 12in above the floor, the previous owner's chemical DPM had prematurely failed and we have no cavity insulation because the cavities are too narrow. So a different situation.

As a chippy I'd just box the pipes, possible inside boxed out skirting, but I have used clip-on boxing solutions in the past such as Talon and Pendock (there are other systems out there) which may be a suitable solution

 

[houseonahill]

Thanks for your reply, JobAndKnock!

The inset timber battens are ther to provide a fix for the floor boards

Yes this is exactly what we found - the nails for the laid timbers go into the battens.

strip the bitumen (horrible job)

I can imagine... I'm considering taking the timber up myself and then handing over the rest of the job to a pro because I'm a bit out of my depth with all this!

If the rooms are to be carpeted I think I'd replace the flooring with a floating floor of P5 T&G chipboard sheet leaving a 5 to 10mm gap all round for expansion.

We were thinking foil-backed underlay and laminate actually - any issue with that, though?

As for the cavity walls, I'll be asking our builder who's doing a few other things for us, for sure. I think he or a colleague of his will be able to help.

As a chippy I'd just box the pipes, possible inside boxed out skirting, but I have used clip-on boxing solutions in the past such as Talon and Pendock (there are other systems out there) which may be a suitable solution

Not in love with the idea of boxing in but if it has to be, it has to be! One other option - I was wondering if the pipes could be set into the wall just behind the skirting, where there won't be much plaster once the replastering has been re-done, and then pipes cased vertically wherever needed to then come out of the wall at the point of connecting with rads? I don't like the idea of boxy skirting boards but if it can be done in a streamlined fashion that would potentially suit us.

 

[JohnD]

Not in love with the idea of boxing in but if it has to be, it has to be! One other option - I was wondering if the pipes could be set into the wall just behind the skirting, where there won't be much plaster once the replastering has been re-done, and then pipes cased vertically wherever needed to then come out of the wall at the point of connecting with rads? I don't like the idea of boxy skirting boards but if it can be done in a streamlined fashion that would potentially suit us.

if you like the idea, you can pencil along the wall at the proposed height of your new skirting, and remove all the plaster below that line. Use a wide bolster and club hammer. If you have an angle grinder or something you can zip a cut along the line first. It will be dusty.

Quite likely the plaster will be about 18mm thick. Old houses may have thicker.

If you screw 18mm square batten to the wall along the line (you can pack it out a bit if necessary) you can repair the plaster down to it.

Put another batten an inch or so from the floor

You can then fix the skirting to the battens (only small countersunk screws are needed) and put pipes, aerial, speaker, phone or LAN cables (but not electricity cables*) in the cavity.

Where you need to bring anything up, you can notch the batten with a multicutter.

Modern carpenters think this is needless effort, but IME it gives a really good job, and a useful cavity.

If the cavity is not deep enough, you can use a larger batten, but since this will project beyond the plaster, it is important to have it perfectly level so that the skirting will marry with it. When painted, there will not be a noticeable join. Allow for the extra depth of pipe clamps.

The skirting does not have to be tight to the floor, it is better if there is a slight gap to prevent squeaking or grabbing.

If you are having stained or varnished skirting, you can use small brass screws, which do not look unsightly. Some people use glue.

There are plastic or metal "skirting" trunking systems with partitions for pipes and cables, mostly used in offices. Example


*it is not permitted to run electricity cables along behind skirting because of the risk of putting a drill, screw or nail into them. You can come upwards to a visible socket which gives warning.

 

[Deleted member 174758]

We were thinking foil-backed underlay and laminate actually - any issue with that, though?

Only that, unlike modern houses which incorporate insulation in or above the slab, your floor will have none. So you might find it cold.

Also, if you are going this way you will probably may have to apply SLC above the DPM to level out any voids - check with a 6ft straight edge to see how good or bad the floor actually is

Not in love with the idea of boxing in but if it has to be, it has to be! One other option - I was wondering if the pipes could be set into the wall just behind the skirting, where there won't be much plaster once the replastering has been re-done, and then pipes cased vertically wherever needed to then come out of the wall at the point of connecting with rads? I don't like the idea of boxy skirting boards but if it can be done in a streamlined fashion that would potentially suit us.

Quite likely the plaster will be about 18mm thick. Old houses may have thicker.

In the late '40s and early '50s there was a major shortage of building materials and they were on strict rationing (until 1954), so the plaster might well be as thin as 6 or 8mm (browning coat plus finish) and not the 18mm referred to. In fact I've rarely come across plaster that thick on post-1930s buildings (when gypsum plaster came in), and although it is sometimes found at that thickness on lime plastered Victorian and Edwardian buildings, even there it isn't a given, especially on lower grade domestic buildings and at "back of house" in grander establishments

Modern carpenters think this is needless effort, but IME it gives a really good job, and a useful cavity.

It's more the case that most modern clients simply won't pay for it! I've done both fully boxed or partially boxed skirtings in a few listed building refurbs, but in terms of labour it doesn't come cheap, and you can't always guarantee a consistent thickness of plaster (at least not in stone buildings). I think the best approach is to install traditional timber grounds (in effect softwood ladder frames) direct to the masonry before plastering and have the plasterer work to the grounds. Once packed and fixed the ladder "rungs" can be removed if needs be. It is far easier to install straight and plumb-up a ladder frame than individual short battens. Pipework, etc can be installed after the plastering, but before the skirtings are fitted, giving the time for the skim to dry out first.

The OP could always go another way and opt to replace the plaster with resillient bars and foil backed plasterboard. The trapped air pocket between the back of the PB and the wall acts as added insulation and sound proofing as well as providing a useful void for services. This is much more like the solutions used on old building conversions where internal insulation (heat and sound) makes for a building which is quieter and cheaper to heat

BTW OP, if you are concerned about appearances, when you re-run the plumbing arrange for the radiator connections to be in the centre of each radiator on the wall - this avoids more than the minimum of visible pipework

 

[houseonahill]

Thanks for these thoughts, both. And sorry for the slow reply - was away for a week and just starting to get some works underway now. (Majority will be done next year.) My builder has actually recommended digging out the floors, new DPM, new concrete subfloor, insulation, screed (don't quiz me - can't remember the exact order). More expensive but a more complete job and will allow for tracking of CH pipes in the screed, no issues with skirting or boxes etc.

As for plaster, I think they'll be redoing it 1m up the walls, including interior walls. Wish I could do more of this myself but it's major stuff!

 

[Mr Chibs]

In my current house I replaced all the floors etc and found a hole host of issues that had to be dealt with very similar to your findings.

You will be able to do quite a lot of these jobs yourself, save some money and hopefully enjoy the process.

Listening to you talk about new concrete sub floor etc... have a think about wet ufh. You’ve got the ideal opportunity to install this, If you rip your floor up, and it’s great.