Safe moisture reading for engineered wood floor

[Robbox]

I did a quick search here, but not what I wanted came up.
We have 1965 house built on concrete slab. It's unknown if they installed a DPM and even they did, it could be compromised after so many years.
Looking to install either engineered wood flooring or LVT (depends how far our budget goes..) but both require a dry subfloor.
At the moment it's finger parquet stuck with bitumen.
I would look to go belt and braces by stripping back the parquet, possibly grinding out the bitumen, levelling screed, liquid DPM and more levelling screed until desired thickness achieved.
Question: what is the maximum, safe moisture reading for non DPM concrete? I would hire a professional meter.

 

[dazlight]

65% RH if glueing the wood down
75%RH if floating or using LVT.

Go with system you said. Screed , dpm , screed

 

[Doggit]

Or you could go screed, DPM, and then SLC to keep the height down. Remember to throw some sharp sand on top of the DPM before it goes off, then brush the excess of before you do the top layer.

 

[Robbox]

Thanks guys. We just had a quote in for stick down LVT, 55 sqm......£4200 for cheaper tile, using screed, DPM, screed. I think that is using Ardetex products.

Anyone had experience with 'Tile Adhesive' from Screed Giant, seems a bit cheaper.

 

[Robbox]

Where to hire a proper meter?

 

[Doggit]

Just as cheap to buy one off eBay.

 

[Robbox]

I did some tests with a cheapo meter today. Testing the parquet with wood setting I get 13-14%. Pulled up a few pieces to exposed the bitumen, scraped off the bitumen to expose concrete and that gives 8-9% on brick setting. I'm curious why I get quite a high reading for the wood and much lower for concrete. Or is 13-14% classed as dry wood?

 

[Deleted member 174758]

I did some tests with a cheapo meter today. Testing the parquet with wood setting I get 13-14%. Pulled up a few pieces to exposed the bitumen, scraped off the bitumen to expose concrete and that gives 8-9% on brick setting. I'm curious why I get quite a high reading for the wood and much lower for concrete. Or is 13-14% classed as dry wood?

Timber and concrete read completely differently and the salts(?) near the surface of concrete will mean that a pin-type timber meter will give you wildly inaccurate measurements even if the manufacturer has given you a conversion table (because concrete reads very differently in any case - I have a Delmhorst J professional timber meter and even with the maker's conversion tables I wouldn't trust it on concrete). On the few occasions I've laid solid wood flooring onto concrete I've always got hold of a pinless floor inspection meter such as a Tramex CME4 which has three different scales and is specifically designed for the task. For solid wood the absolute maximum moisture level in concrete is 4%, ideally it should be nearer to 3% - your flooring manufacturer should have issued Tech Info sheets which cover their requirements in detail. If you are getting 8 to 9% MC on concrete then you really need a DPM (or maybe the right meter, brick isn't concrete). RH as quoted by Dazlight is just another way to arrive at an acceptably dry environment for the flooring. As it happens we put an £80k solid oak floor, cppings and staircase claddings onto concrete/screed last year (in a public building) and that 4% maximum figure was writ in stone by the manufacturer. To get the floor to where we needed it to be required two coats of Mapei ESM DPM before we installed timber or it would have puled itself off the floor over the winter.

13 to 14% is very far from dry wood, but possibly OK depending on the type of house, air flow, heating, location, etc. For example most kilned pine tarts out at about 10% MC and will reduce to between 6 and 8% MC (the equilibrium MC) in a central heated house over the first year. Air dried hardwoods are typically around 14 to 16% MC (rot and fungal attack can start at above 20% MC in many timbers, hence the need to dry it) but may be further kilned to 10 to 12% MC (or lower) if they are going into a centrally heated environment

 

[endecotp]

I suspect that 8-9% "brick" might be the same as 13-14% "wood". Try poking the meter into the concrete on wood setting and vice-versa and see if I'm right.

The point is that these moisture readings are the percentage BY WEIGHT of water relative to the material. For a constant amount of water, if the material is more dense the percentage of water by weight will be LOWER. I think that the different settings on the meter just scale the numbers based on the density of the material.

 

[Deleted member 174758]

Maybe worth pointing out that better quality timber moisture meters come with both a temperature sensor and a booklet containing correction factors for different species. So a 13% reading in softwood won't be a 13% reading in oak, even at the same temperature. There's also the issue of where you take the reading from - take it by surface contact alone and you'll potentially get a different reading to a reading taken using short pins (just below the surface) and yet again to a reading taken with longer pins (a hammer probe). Concrete and screeds really need to be measured at core, not surface, as water retained in the core will be the stuff that migrates to the surface and evaporates off. That's why a pinless unit such as the Tramex which takes a core measurement makes more sense than any pinned meter