Concrete floors with DPM

[beris]

Hi all

a bit of advice please, we are renovating an old barn, with walls approx 500mm thick, no dpc .we have removed all the old concrete from the animal pens etc and dug down to place hard core and sand blind.

I have installed many concrete floors in England, always with a dpm that joins to the dpc.

I have read recently that incorporating a dpm may cause more proplems than it solves in this situation.

comments would be appreaciated.

Many thanks

Beris

[Chancer]

Just try buying DPM material in France!

[littlemouse]

[quote user="J.R."]Just try buying DPM material in France![/quote]

Like in the builders merchants for instance

[andyh4]

Our conversion was in a similar situation.  The builders laid 15-20cm river washed pebbles running out to a sump before the DPM and everything on top.  Any water flows through the gravel and drains out to the sump, so the walls stay dry above floor height.

 

[Nick Trollope]

[quote user="beris"]

Hi all

a bit of advice please, we are renovating an old barn, with walls approx 500mm thick, no dpc .we have removed all the old concrete from the animal pens etc and dug down to place hard core and sand blind.

I have installed many concrete floors in England, always with a dpm that joins to the dpc.

I have read recently that incorporating a dpm may cause more proplems than it solves in this situation.

comments would be appreaciated.

Many thanks

Beris

[/quote]

How can you install a DPC in a stone building, without taking it down? Stone ain't brick - it is not a half as porous - not old houses have DPC's. We always just lay a 200micron polythene sheet & pour the floor on that - the material is available everywhere (off the roll - 6M wide & in sheets (up to 10x15M IIRC)) - so I don't know where JR has been looking.

Or have I missed the point!?

 

[Dave&Olive]

hi

            ok I really cannot see the point if you are digging out the floor in first not fitting a d.p.c layer and at least a few inches of issolation both are here everywhere  and in more sizes than you can get in the uk

                      dave

[Chancer]

Nick

Builders round here don't seem to use DPM's and can't get there head around why I would want to - perhaps it's the chalk soil.

Granted my house is so old that she was built without foundations also but recent extensions just have a layer of "sable rivere" laid on the chalk and then carellage on top, not even any concrete.

When I have tried to buy DPM material as merchants  again they look confused at why I want something for this purpose and all I am offered are rolls of very thin plastic only suitable for paint masking or temporary protection, nowhere near thick enough to resist punctures by the poured concrete. One of the rolls was machine perforated (like shopping bags to stop children suffocating) when I pointed out that it would be like using chocolate for a teapot I was told "Ah but it will let the floor breathe"!

To be fair I have yet to see a damp building arouind here despite the solid brick walls and lack of DPM/DPC's.

[Nick Trollope]

Fascinating - I always thought that it was wet "up north"!

Here, no DPC, but every concrete floor has a membrane. New builds are built without a DPC onto a concrete (+ DPM) slab...

You pays yer money , etc etc  ....

 

[littlemouse]

new builds are built with "dpc" hydrofuge is added to the morter ,the last course before the

floor slab and the first two courses after the floor slab to form a waterproof joint that cuts the

capillary action.

[legs_akimbo]

The original floors of old propertys were stone on mud , beaten earth or lime ash and they could breathe naturally, however with the advent of concrete floors incorporating a damp proof membrane the damp can no longer evaporate through the floors but is forced towards the walls and can often then lead to problems with damp walls in stone built houses where no damp proof courses are present, as stated, crushed gravel and a simple means of alieviating any pressure of water bolow the concrete sub floor will prevent this. A dpm is nothing other than 1000 or 12000 gauge polythene but if a new concrete floor is being laid it would be folly not to also incorporate a 50mm layer of double foil backed floor insulation, the difference is excellent and well worth the extra expense.

[beris]

Thank you all for your comments, legs_akimbo got the point that i was afraid of, of the moisture being trapped and pushed out to the walls.I have decided not to use a dpm.

Thanks again

Beris

[powerdesal]

Legs_akimbo,

Am I right in assuming that the insulation is above the concrete or is it between the dpm and the concrete, or if no dpm between the blinding and the concrete.

Is it feasible to lay (say) a tiled floor directly on top of the insulation or should there be a lean mix screed then the tiles.

The reason I ask is that I would like to retile above an existing tile floor but incorporate an insulation layer. I am not inclined to rip up the existing tiles which are very good (I just dont like them!) and from the age of the house I would guess that there is no existing dpm, what lies below the existing tiles is anyones guess.

Any advice / comments will be most welcome.

[legs_akimbo]

If a new concrete floor is being poured personally I would always lay a dpm, you can get around most problems but not a damp finished floor. Generally the concrete floor is the sub floor and is laid fairly roughly and tamped to find its own levels but, unless it is well prepared with timber grounds to gain the perfect level and floated to perfection it is usually merely the base for the finished floor level of screed. Insulation batts can be laid on top of the dpm then concreted over or on to the concrete sub floor then screed onto them. Screeding onto insulation is classed as a non bonded screed so must be 75mmm thick whereas onto concrete is a bonded screed and should be 50mm.

Powerdesal unless you have some depth to play with then with insulation on the original tiles you would then require 75mm of screed, any less and it would curl (break up). There is a product which is only a couple of mm thick and comes on a roll that would be ok with a 50mm screed but of course this all depends on how much depth yo have to play with. 

[powerdesal]

I've actually got plenty of height to play with, it all depends on how much I take off the two affected doors. I figure it will mean 30mm of insulation, 75mm of screed and 10 /12mm of tile. Hence say 120mm max. I will have to check the internal doorway head clearance (no door) and see how it appears to work.

Thanks for the info.

ps. I intend to paint the existing floor tiles with a waterproofing agent first - would you recommend this?

[Btuckey]

Hi, 

Sorry to ‘high-jack’ this thread but I have a related question.  I have just ordered a 17m2 wooden garage from Carrefour.  The intended usage is for a workshop and not for cars but the building comes without a base.  I would like to lay a concrete plinth but how thick should it be?  I am also considering a DPM as when it rains here, it really rains...  How do you incorporate it into the base?  This is, as you can tell, the first time [blink] that I have tacked a job of this sort!

Brian

 

[legs_akimbo]

[quote user="powerdesal"]I've actually got plenty of height to play with, it all depends on how much I take off the two affected doors. I figure it will mean 30mm of insulation, 75mm of screed and 10 /12mm of tile. Hence say 120mm max. I will have to check the internal doorway head clearance (no door) and see how it appears to work.
Thanks for the info.
ps. I intend to paint the existing floor tiles with a waterproofing agent first - would you recommend this?
[/quote]

 

I would blackjack (bitumen) the tiles if there is any evidense of damp then lay a polythene sheet before the insulation was cut into place, if tiles are dry then a polythene dpm on the original tiles would surfise i.m.o.

[Alane]

We've put a DPM beneath the slab and have had no problem with damp in the adjacent brick and flint walls which were originally laid using some form of mud mortar. I was aware of this being a potential problem and comparing the walls adjacent to the slab and those where we haven't laid a floor there is no discernible difference. We are in Normand where it can get pretty wet! Not to say of course that someone elses experience won't be entirely different.

[powerdesal]

Many thanks legs_akimbo.

[HoneySuckleDreams]

just to add my 2c worth. 

I've got an old ferme, all downstairs rooms (that have not been carrelaged already) smell damp and musty so I am putting in a screed (think it's called chape in France) with a DPM and dry lining the walls. I also tried buying "polythene bleu" from various builders merchants.  After lots of odd looks the best I got was "polythene vert".  For additional information/discussion have a look at the screwfix.com forums.  I ended up going round in cicles about DPM or no DPM, or "what is rising damp anyway".  I'm also getting my fosse man to dig a ditch around the house and then fit a plastic sheet and field drains.  I think that the ditch will solve most of my damp problems.

Best of luck

 

 

[Chancer]

Jumping back into the discussion you may remember I said that my existing floors do not have a DPM and are just carrelage over sable riviere over the Somme chalk, and there is no damp.

However the cave (bare chalk soil) and the garage (thin concrete over chalk without DPM) both will rot out cardboard boxes stood on them as I have found to my cost. I am just fitting a lavabo unit that I bought on promo last year and some of the contiboard is also discoloured.

My conclusion is that the ancienne carrelage is doing a very good job of keeping out the damp, do others concur with this and are modern floor tiles, adhesives and grouts equally effective?

 

[BIG MAC]

I am fascinated by the various different approaches taken here.

We own a house in the Mayenne / Loire region and are about to convert what was our cave into our new kitchen.

The cave earth floor is approximately 1metre below ground level out side and we intend to lower it by another 100mm to allow for the make up of the new slab.

We are going to excavate some trial pits first to see where we are in relation to the footings of the walls but ideally we want to excavate  400mm to formation then place about 100mm of 20 mm sieve river wash pebbles to the entire floor surface (self compacting and free draining) we will then affix egg box type rigid material (Don't know the French word for it but its brilliant and cheap In England we would call it Delta membrane I think?) all around the internal walls so allowing moisture to transmit freely behind the membrane, we will place just 40mm of Jablite or similar material on top of the pebbles and include a 100mm upstand to the periphery, we will place a layer of 1200 gauge polythene with all joints and overlaps taped and the excess taped to the egg box, one layer of steel fabric reinforcement on 50 mm concrete stools then cast a 125mm thick slab in readymix c40 or equivalent. The egg box material shall extend to approximately 200mm above the outside Ground level we will ultimately cover it with thermalite block the top of which will be closed out using hyload dpc and hardwood capping scribed to the existing stonework. The blockwork will be rendered to receive ceramic tiles the natural stone above will be cleaned repointed as necessary then sealed with a breathable sealer to prevent it shedding dust / drying out.

The above may seem long and drawn out but we think its a good way to provide a dry and well insulated room without losing too much of the original character.

Mac