Flagstone floor advice

[luckyt1982]

We moved into our 1850 property three months ago. When we moved in we noticed some 'damp' patches on various spots on the flagstone flooring (which is in the lounge and follows into the kitchen, about 30m sq in total). The flagstones aren't in great condition, the 'grout' between them is worn away in places.

Part of the lounge is joists and floorboards with carpet on top, this meets the flagstones about a quarter way into the room.Today we have taken up the floorboards as my husband put his foot through one whilst looking for something behind the sofa! Several of the joists and floorboards have old woodworm and so we will replace these.

Having taken up the floorboards we have had our first chance to look at what the flagstones at laid on. There is 'earth', with a blue plastic sheeting dpc, then a layer of concrete about 1-2 inches deep followed by the flagstones, which are about an inch thick.

The concrete between the dpc and the flagstones is crumbly and damp. You can crumble a piece in your hand and it will leave you hand quite wet.

Im wondering whether moisture from day to day living has soaked into the flagstones and down into the concrete causing it to crumble or the dpc could be 'sweating'. Or I suppose there could be a leaky pipe buried in the concrete layer somewhere.

Does anybody have any useful advice? We are thinking that the flagstones need to be lifted, a new dpc, or not? New concrete bases and then flagstones relaid.

 

[FamilyWiggs]

Much of your answer will depend on the ground conditions under the DPC. If that is dry, then you should be fine without the DPC and just allowing the floor to breathe through the joints between the flags. If the ground is damp, then you need to investigate why, and check the DPC hasn't pushed the mositure out towards the walls too.

It is nigh on impossible I think to retro-proof against moisture in an old house. Far better to design breathability in - which means identifying and removing sources of damp where possible.

We had flags laid on earth, lifted them for a variety of reasons and relaid on a lime screed on the earth with lime pointing.

In your position I would probably be seeking to avoid a DPC and concrete if I could, but more expert opinions will be along shortly.

Any pics? We love PPUK Porn.... 8)

 

[MdB]

It is nigh on impossible I think to retro-proof against moisture in an old house. Far better to design breathability in - which means identifying and removing sources of damp where possible.

Though this is true, some old houses (like mine) were built on ground that is so damp that breathability isn't enough to make it suitable for modern living. Our house had (many years back) a sand floor which would have been damp when it had been raining hard outside. It would have dried out quickly though once the water table went down as sand is obviously highly breathable. Probably not an acceptable solution for you though.

In your case Lucky, the state under the DPM is of key. If it is damp, I would guess the DPM has failed or is bridged. If it is dry, then there is a source of moisture coming in from somewhere which needs to be investigated. It shouldn't normally get damp from daily living or everybody's house would suffer the same way which they don't.

To obvious solutions if your ground is as wet as mine is: First is to relay a modern floor with DPM but then expect higher levels of moisture in your walls. This is what we have done. However we only have a relatively small amount of old walls and can heat the place properly so the damp is at a level that it is minor.

The second solution is to fit a raised wooden floor with a highly ventilated cavity underneath.

As for the boards with woodworm, there is no need to remove them just because they have old woodworm holes in them. If you solve the damp issues, you will kill off the woodworm and if the damage is limited, there is no need to replace the boards. Most people here will have woodworm holes to show off but no woodworm to go with it.

 

[88v8]

Do the walls have a dpc? If so, is the dpm tied into it?
Come to that, what are the walls? Brick, stone, thickness....

Ivor

 

[MatthewC]

Lucky

Perhaps you'd tell us a bit more about the possible causes of the dampness? I'm assuming that there is no water pouring down the walls or chimney etc, but I'd still like to know if there is anything obvious like ground outside which goes up to floor level (or above?). Or are you in a flood plain? etc. I've taken the outside levels down by four to eight inches and there is now no dampness, even on the remaining quarry tile floor. (This house is 1840s, with 18" limestone walls.)

I've also laid a limecrete floor with (unsealed) flagstones, which is a solution not mentioned by MdB above.

Matthew

 

[luckyt1982]

Thanks for your replies!

I will try and get some photos posted but in the meantime, a bit of an update.

We have established that the ground below the dpc is dry. The wetness is between the dpc and the flagstones, in the cement. The kitchen is at a slightly higher level than the lounge and we think that a water pipe in the kitchen which is buried in the cement is leaking and the natural flow of gravity is causing the water to make its way down to the flagstones in the lounge.

There are central heating pipes and also a cold feed out to the utility room under the kitchen floor. I understand that burying copper pipes in cement is a no no! These have probably been under there since central heating was installed in the 80's.

There is a crack in one of the flagstones in the kitchen which seeps water if you stand on it. but no evidence that water is getting in from the outside wall in the kitchen.

There is also some 'rising damp' in a few spots down the side wall in the lounge. I suppose it's possible that this is also cause by the potential pipe leak.

Also, there are some white salt marks on a few of the flagstones near the edges.

At this stage we aren't sure how far the dpc continues into the kitchen or whether is is bridged somewhere.

So, we have a local builder (who has done some work for us already and we trust) coming over next week to take up a few of the flagstones in suspect places to see what's going on under there.

Hopefully a pipe leak in the kitchen will be found and the dpc in the front room and be isolated from the kitchen, then the cement in the lounge will dry out and we won't need the flagstones lifted.

Then we will have to take up the kitchen floor, sort the leak and then relay the floor. The kitchen is quite small (2 x 3 metres) so hopefully it won't be too bad!

With regards to the comment on the woodworm, the floorboards turned to dust if you blew on them, so couldn't save these ones! We do have some bare floorboards in the dining room with some woodworm tracks, it adds character we think!

Will post again once we have lifted some of the flagstones.

In the meantime, does anybody have any advice on the 'grout' to use when relaying flagstones and how to polish them up? The ones in the lounge are in quite good condition but the kitchen ones have seen better days.

 

[FamilyWiggs]

Well that's lucky, Lucky. Seems you have identified the cause and it is realatively easy to remedy.

In the meantime, does anybody have any advice on the 'grout' to use when relaying flagstones and how to polish them up? The ones in the lounge are in quite good condition but the kitchen ones have seen better days.

I used lime mortar, and the a few coats of linseed oil. Works a treat. I re-oil every couple of years. I'm told the domestic staff use Ecover floor detergent - it contains linseed oil too. You can either brush dry lime mortar mix into the joints and then water them, or mix up and apply wet. I tried both, but found the wet approach easier but slower.

There are many threads on here where we've discussed flags and mortar, sealing, oiling etc. A quick search should throw them up.

 

[chuckey]

The leak must be sorted!!! The other thing I am worried about is the lack of under floor insulation. As your flags are laid on concrete, on top of a DPC on top of soil, they must be at ground temperature. They will attract condensation which can't soak away because of the DPC hence the damp. My flags were laid on little chippings, so though they were cold, any moisture could drain away into the soil (under the chippings)
Frank

 

[luckyt1982]

Thanks for your reply Chuckey.

The dpc isn't actually laid on earth as in my first post. It looks like its laid on stone / bricks which are about a foot high. Does this make a difference to the advice in your post?

I'm assuming with chippings you do not have a dpc?

 

[luckyt1982]

UPDATE

We had our friendly builder around today, he lifted up a number of the flags.

Doesn't look like the pipes are leaking. They have been cased in foam sleeves and look to be in good condition.

I've taken a few pictures:

PHOTO 1 - this is where the flagstone area meets the joist and floorboard area. The DPC (blue) is wrapped around on the end and as mentioned in my earlier post, the ground beneath the DPC is dry, the concrete between the DPC and the flags is damp. You can see this from the different shades of concrete.

PHOTO 2 - the dpc appears to be bridged at the wall (you can see this on the top left corner of the gap). This wall has had dpc injections, however the holes (you can't see them in this picture) are about 2 - 3 inches above the skirting board. So there's an area about 10 - 12 inches up the wall that 'rising damp' can get it, which I'm assuming could get into the concrete in the floor via the bridge in the dpc.

PHOTO 3 - this is the same wall as photo 2, but further into the kitchen where there is no wall dpc injections.The dpc goes up the wall slightly in here. Not sure what the white patch in the concrete is, it's a bit gel crystal like.

TBC ....................

 

[luckyt1982]

PHOTO 4 - the wall by the skirting and slightly to the right of it is a bit damp, further to the right it's dry (concrete by the pipe is light).

PHOTO 5 - the pipes! Although the area around them is dry.

So our feeling is that there's damp coming up the walls around the kitchen / lounge (3 of the 4 walls in each of the rooms are outside walls) which is getting into the floor (between the dpc and the flags) due to the dpc being bridged at the bottom of the wall and the fact that there is no / poor positioned dpc injections.

There is a natural slope down through the kitchen and into the lounge down to where the flags meet the timber floor in the first photo, which could explain why there is damp at this spot.

If this is the case would an option be to inject dpc at ground level around the room and then continue the dpc from the floor up the wall slightly to meet / cover where the dpc injections are?

I've read plenty on here about dpc injections not being a good idea - but what other options are there?

Any advice / ideas would be gratefully received.

PS - sorry about the photo ordering!

 

[chuckey]

The standard reply for stone built cottages and damp is to lower the external water table (and to fix any obvious faults). My cottage's outside walls are an inner and outer skin of mainly limestone blocks which is then filled with the sweepings up from the stone masons floor and old lime mortar dust and rubbish blown in from the fields. This gives a wall thickness of 24". depending on the various levels (outside soil, rubbish in walls, water table), you could end up with the centre of the walls being wet and depositing their moisture into the floor at a level higher then the DPC. Hence lowering external water table. This is often the reason that "installing a DPC under the floor causes damp walls", this is because the excess moisture level in the walls can not now soak away into the floor.
What to do?, double check outside soil levels, better if you can dig a french drain around the house down to a level lower then the installed DPC. Leave the floor exposed with a fan on it to try and dry out your concrete sponge (foundation). This could take months. During this process the rate of drying might give a clue as where the dampness is coming from in case you really have got a ground water problem.
All in all not very useful, no magic bullet and you are right, silicone injection does not work on lime stone - its impervious already.
Frank

 

[MatthewC]

silicone injection does not work on lime stone - its impervious already.

Agreed that silicon injection of limestone is a generally bad idea, but surely the porosity of limestone depends on the exact type of limestone? I'm not a geologist but the Cotswold limestone in my house is most definitely porous, and I have some grey bits in the garden composed of visible fossil shells which seem pretty impervious.