Insulation, above or below DPM or both - sharp sand blinding

[RedHerring2]

Opinions/advice appreciated.
Just relaying the concrete floor on a renovation project.
Here, in France soft sand, for blinding, is not available, well, as far as I can ascertain.
So, sharp sand it is.
I had a choice of yellow sharp sand at about 22 Euros a tonne from the local BM or grey sharp sand from the local quarry at 12 Euros a tonne. Both classed as 0/4 which I assume refers to the size of the particles.

The grey sharp sand that I used is more compressible and much dustier than the yellow sand.

I originally calculated for 100mm of Polystyrene insulation between the DPM and the concrete but 100mm is just not available here.
More over, 60mm is normally used which gives an R value of 2.1 (if that makes sense.) which I'm advised by the BM is the requirement here. (This is a renovation so regs don't particularly apply.)

Having originally calculated for 100mm I eventually decided on 2 X 40mm layers. This gives a R value of 2.3 (2 X 1.15)

As the sand blinding layer is sharp sand would the more experienced people on here use one layer of insulation below the DPM and one above, or both below the DPM, or take the chance and use both layers above the DPM?

I intended to tape the joints rather than use a second VPM on top of the insulation. I'm up against a deadline 'cos I hope to be able to order the concrete on Monday. My volunteer helper (the neighbour) goes on holiday next Friday for a month......well he is French.

Incidentally, I think the DPM is 300 microns from the UK.

Offers of volunteer helpers from the UK much appreciated but the only accommodation available is a 4 man tent.

 

[r896neo]

the grey sharp 'sand' sounds suspiciously like quarry dust to me. To be honest any sand or quarry dust will be fine its purely to stop the dpm getting torn by rough or sharp stones in the hardcore just make sure you compact it thouroughly.

Personally i use a second layer of dpm on top of the insulation which is then taped up with gaffer tape and its very quick to do.

 

[hotrod]

Ditto r890 re quarry dust - it sounds like granno. I'm surprised you can't get soft sand over there (what do they use for mortar?) but I suppose you use whatever comes out of the local quarries to a certain extent. As said above the idea of a blinding is just to protect the DPM from sharp stones/edges and getting torn.

Incidentally, I think the DPM is 300 microns from the UK.

Are you sure 300g? A standard rating for a DPM is 1200g here in the UK which is a hell of a lot tougher than 300 if you compare them side by side. I certainly wouldn't entertain pouring into a 300g DPM.

 

[RedHerring2]

Thanks for the replies, guys.
The DPM is definitely 300mu. It's Visqueen DPM Blue 25m X 4m X 300mu.
This is 1200 gauge : http://www.allplas.co.uk/acatalog/4mtr_x_25mtr_x_300mu__1200gauge___DPM_.html

I can only get 150mu DPM here which is why I brought it from the UK.

The yellow sharp sand is used for mortar round here. You can also get Multi bat which is 50% lime & 50% cement which is what I use for mortar, except when doing things like retaining walls or other totally exterior construction.

Incidentally, for anyone that's interested, the expanded polystyrene comes in two grades here. The normal grade that we use they consider to be too compressible under the concrete so a more dense, less compressible grade is used. And it comes in 1m X 1.2 m sheets.

 

[mointainwalker]

Hello RedHerring2

Hope you are still enjoying your idyll in your very attractive renovation.

I have the same experience re sand: just the one type available. Have to say though, your prices are very low. I pay E 22 for bulk sand I load myself at local quarry. I can however choose my colour

You are right about the 0/4 being the grain size, but the standard allows a certain percentage which is outside the size-range so you will still find 10 mm + pebbles turning up.

I'm puzzled about your inability to get 100 mm PS, it's a standard product at my BM down here in the South East, both in wall and floor-grade and in 2500 x 1200 sheets

i'm not sure i agree with your R values. I think 60 mm PSEXP ( polys. expanded) is going to be R 1.5 and 80 mm will be R 2. The difference could be down to some measuring methods . I was very surprised , for example to find out that all modern c/h boilers sold herel have efficiency ratings of more than 100% ( mine is 107% !) due to a certain way of interpreting the rules.

As far as I know, all regulations in French building only apply to professionals, so you can do as you like. When reading a Rockwool brochure recently I noted that they said "... minimum insulation standards have been mandatory since 2005...", but I believe this is a marketing attempt by them to push individuals to using more insulation prioducts by not adding " for registered building companies.." which would be the whole truth.

Logically i can see no difference in insulation value in positioning the poly above or below the DPM, so why not put it below and save yourself some taping.

 

[RedHerring2]

Thanks M'walker.
I appreciate your input , especially 'cos of your local experience.
Albeit, that there seems to be quite a few 'local' differences to be considered in the same country. Same as UK, I suppose.

The 40mm polystyrene is rated at 1.15 m2,K/W. Don't forget though that it is a different grade to the normal polystyrene. It's more compact than normal.

I can get the 2.4 X 1.2 sheets in 20mm, 30mm, 40mm thickness but in the softer version of polystyrene, which I'm using around the periphery as an upstand (30mm).

I'm going to put the insulation above the DPM. I've tested a bit of DPM, walked on it, jumped on it with no ill effects, to the DPM, that is, not to me. Under the insulation any load will be spread anyway.

Another reason is it'll be easier to deal with the upstands, 'cos the floor insulation will hold 'em in place.

And a third reason is I'll have no worries about the re-inforcing puncturing the DPM 'cos it'll be above the insulation.

Thanks to all for their input.

Too hot for work here today, but must press on. Fortunately, I'm inside.