Parquet floor and moisture level

[JHD]

I'm hoping to lay a parquet floor in my hallway, however the moisture level of the concrete subfloor has been measured today at between 8% and 10%. The recommended moisture level of the parque floor manufacturer is 2%, so my hallway is a fair way out. The solution being suggested is to use SikaBond Rapid DPM (http://gbr.sika.com/en/solutions_products/02/02a024/02a024sa010.html.

Firstly, can anyone advice whether or not 8-10% is high? I've not seen any evidence of damp.

Secondly, if the SikaBond DPM is used, is the moisture likely to be forced up the walls?

Thanks, James

 

[Toby Newell]

Hi

You do not state if your hallway slab is new, if so it will require one month per inch to dry out, if not then 10% is too high, 4 or 5% is ideal. 2% is very low, especially for an older house.

If the floor is existing (not new) and you have no known damp problems then there is little point heating and using a dehumidifier as the slab will soon return to equilibrium with it's surroundings.

Have you had recent building work done? Plastering? What is the ambient relative humidity of the air in the area? Ideally it should be 40 - 60% max. If you have had wet works carried out recently and the ambient reading is a little high then consider running a dehumidifier for a couple of weeks.

A liquid dpm should be used which is compatible with the adhesive you are using, do not mix brands and systems, liquid dpms and adhesives come in matched pairs e.g. Bona R580 and Bona R850, which I am using this week. Do not skimp on adhesive, cheap adhesives may not be the most economical long term option.

I am not qualified to comment on whether a liquid dpm would cause your walls to get damp, there are a few such qualified people on here so ask around, you are restricting the egress of moisture from the slab and it has to go somewhere but if you do not have an existing damp problem and the relative air humidity is not overly high then I would have thought you would be ok, but please check, I am a flooring expert, not a damp expert.

TIP:

Remember to take moisture readings over several areas and take the average, remember to take mositure readings every 24 hours, when the two readings from each test point remain the same over a 24hr period the air inside the meter can be said to be in equilibrium, this is the correct value.

 

[Matt Green]

You don't say how you are taking a moisture reading, but assuming you are using a resistance or capacitance meter be sure it is set to the correct material. These devices are designed for use on timber and there is often either a setting on the meter for masonry or a calibration guide that will allow you to compensate for the material.

 

[jackpoint]

We have some parquet down and it lifts at the meerest sniff of moisture!

 

[MatthewC]

Secondly, if the SikaBond DPM is used, is the moisture likely to be forced up the walls?

Like Toby, I'm not a qualified expert but, if you already have a concrete floor, I can't see how the use of any DPM on top could cause any more water up the walls than would otherwise be the case.

 

[Penners]

I'm no expert either, but I suggest that it's impossible to say whether a liquid DPM applied to the surface of the substrate would cause lateral migration of damp into the walls. It all depend son how much damp is actually percolating up to the surface of the concrete from below.

Has the concrete been laid recently, or is it old? If it's still drying out then I would try to give it quite a while longer before laying anything at all on top of it. Ideally, it would be good to let have a good spell of dry weather, too.

Bona R580

Mmmmm - nice!

 

[Zebra]

Did anyone else have to Google that?

 

[Keith Bowman]

Did anyone else have to Google that?

Yup. And I'm old enough to remember them. so Penners must be much, much older to have understood the innuendos

 

[JHD]

Thanks to all for their advice.

In answer to a common question: To the best of my knowledge the concrete was laid in mid 1980s, so it's had plenty of time to dry out.

Unfortunately I wasn't around when the moisture readings were taken. They were taken by the carpenter that is going to lay the floor, so it's possible that he didn't set it for the correct material.

In summary though, assuming that the readings were taken correctly, the advice seems to be that there is little reason to worry that any moisture will be forced up the walls, and that putting a liquid dpm down (or the same brand as the adhesive) is a good idea.

 

[MatthewC]

Did anyone else have to Google that?

Yup. And I'm old enough to remember them. so Penners must be much, much older to have understood the innuendos

Sadly no, I remember Kenneth Horne's radio shows in the 60s very well. However, I WAS too young to understand them, so Penners must be a lot older than me (or else he was a very well informed youngster).

 

[Penners]

OK, OK - that's enough of the "Penners must be VERY old" stuff. I've got a mirror, you know!

Anyway, I could easily claim to have heard all the Julian and Sandy stuff on 'Round The Horne' on BBC Radio 4 Extra (7.00pm on Monday nights - do listen if you've never heard it. It's one of the funniest shows that have ever been on radio).

However, truth to tell I clearly remember the original broadcasts in the 1960s. They included such illuminating news stories as:-

The two-man inter-rabbi bobsleigh championships - to be held on the down escalator at Leicester Square underground station, weather and platform tickets permitting.

Nark Fettering on ice.

Reports of the latest activities of the Over-Eighties Nudist Leapfrog Team.

 

[Toby Newell]

@JHD

The carpenter? I see. And the wood states 2% is required? Is the wood then kiln dried? I would presume so as normally dried wood can take 4 - 5%.

Does he have a British standard calibrated hygrometer? Or a cheap capacitance meter? A cheapo prod meter isn't going to cut the mustard really as the capacitance depends not only on moisture content but on the composition of the concrete and whether it was screeded or power floated.

:/

You need to hire a proper BS standard hygrometer kit to test. Readings need to be taken for several days to ensure the hygrometer is in equilibrium with it's surroundings, a quick prod with a cheap capacitance meter is only going to tell you what is occurring at the top 10mm or so of the slab anyway and even those results may not be accurate.

If your carpenter measures the moisture content properly and it is confirmed that it is 10% then a DPM is imperative as otherwise your kiln dried wood floor will fail.

Also, it is not good enough to choose a liquid dpm and adhesive from the same manufacturer as each manufacturer makes several different types of adhesive and these are not always compatible with each other, so, as I said before make sure you get the dpm and adhesive as a matched pair i.e. a system that is designed to work together. Failure to do this will again lead to the possible failure of the floor.

Check these manufacturers for matched systems, Bona, Pallmann, Sika, Ball.

 

[Keithj]

I have a cheap damp meter, but it's not a capacitance device. This one is a simple resistance meter. It's calibrated (0 - 10) but the calibrations are not in any known units: for what I do with it, they don't need to be. What it will do is tell me whether a specific area is drying out or not. The timbers in our dining room showed 8 - middle of the red - before we started. They now show 0 to 1 - at the lower end of the green. That tells me the problem has been (largely if not completely) cured.

Prodded into the wall of the south aisle of the church, they showed 5 (middle of the amber) last year, and 3 (top of the green) now. The fixes are working.

Would I use it to decide whether to lay parquet on top of concrete? No, because it will only tell me what moisture is there now, which may be the result of condensation and a cold floor - or could be something more tricky. Given that concrete is impermeable, if it's dry and there is no path for moisture to get in...

I'm not sure how even a sophisticated meter would provide any meaningful long-term information about a concrete floor. It may be useful to tell whether it's too wet at the moment to lay parquet. Once the concrete has set and dried out, I would not expect moisture to be rising through it. But having spent a small fortune removing ill-advised concrete from a Tudor house (the stuff isn't allowed through the gate now) I'm not researching concrete any more.

 

[Toby Newell]

@keithj

Hi Keith, you appear to be a little confused and have made a number of factual inaccuracies in your comment. The OP was asking whether he should use a dpm, to which the answer is yes and whether using a dpm would likely cause damp problems in his walls considering his measured subfloor reading, to which the answer was, probably not. I further added that if he was worried about damp problems he should first test the relative air humidity level and then that of the concrete slab with a calibrated hygrometer as is standard BS practice.

To elucidate upon some of your concerns, concrete is NOT impermeable which is the whole reason for the OP. Concrete if fully dried will come into equilibrium with its surroundings by absorbing or emitting water vapour. Air, concrete and wood have different water holding capacities for any fixed temperature and pressure in a closed system (like a well insulated house) The problem is if a kiln dried wood of very low moisture level is laid in direct contact with concrete with too high a moisture content then the wood will keep absorbing moisture from the concrete until they are in equilibrium. Wood expands across its width when it absorbs moisture, therefore if the difference between the relative moisture content of the concrete subfloor and the wood is too great the resulting expansion may be enough to cup, warp or cause partial or total failure of the applied wood floor.

It is important then to recognise this fact and avoid direct contact if necessary with an impermeable barrier called a damp proof membrane or dpm. Moisture content therefore is a crucial parameter to control in floor laying to ensure dimensional stability.

If a very high reading is obtained then it may be prudent to take air relative humidity readings and multiple subfloor readings with a calibrated equilibrium hygrometer over a 72hr period to try and ascertain whether or not there is an existing pervasive problem e.g. rising damp and/or leaking services/leaking or inefficient drainage. Readings accurately taken thusly with BS approved and calibrated devices may be passed on to a surveyor with the requisite experience or a damp prevention company who will then be better suited to confirm or deny the existence of any damp problem.

Hope this helps.

 

[Keithj]

Sorry, Toby, but I'm not sure which are the factual inaccuracies you accuse me of.

This house was close to falling down because a bodger builder had slapped concrete over the sole plates and other areas where there were rotten areas. As a result, according to the surveyor, the Conservation Officer, and the specialists who repaired it, the rot had been accelerated because (as they told me) the concrete was impermeable.

My damp meter (resistive, not capacitative like yours) gave very high readings on the internal sole plates before the repairs, and low ones after. So I am not at all confused. I have taken what I learned from the house and applied it in the discussions with architect and contractor in working on the church. Concrete is a no-no there.

I have an indoor and outdoor digital electronic hygrometer running all the time. The RH indoors is consistently lower than outdoors (because it's warmer inside) in winter, but follows the outside. Right now, it's 85% outside and 44% inside. Last week it was 98% outside and 65% inside. Last autumn we briefly had 45% outside and in. Equilibrium is a variable feast.

 

[Toby Newell]

@keithj

Please do not be offended and please do not hijack anothers post it is confusing for people searching for advice.

Your error was in stating that concrete is impermeable, meaning it cannot absorb or transmit water, which is patently wrong. I am just trying to help.

Equilibrium in the closed system that is the house of course! What the moisture content of the garden or patio decking is of little relevance here I do not understand your train of thought. The concrete, wood and air will all reach equilibrium in theclosed system that is the house. An air hygrometer is different to a solid substrate hygrometer which uses a covering or sheath to create a micro closed system close to the evaporating surface, they cost from 500 pounds.

And. FYI. I think you mean Botcher builders rather than Bodgers as Bodgers were highly skilled itinerant travelling wood craftsmen from the High Wycombe area and presumably you did not wish to infer that your builders were infact highly skilled.

This is my last post on this. All the facts I have divulged are learnable as the information is freely available.

Everyone makes mistakes either through lack of knowledge and/or miscommunication. The purpose of these forums is primarily for people to share help and advice, I try my best to give accurate qualified advice where I can and to point out glaring mistakes where I find them so it may help others in some way.

The OP was about flooring and dpms that is all. No need for your pride to be dented I am just trying to help.

 

[Penners]

@keithj

Please do not be offended and please do not hijack anothers post

I think the accusation of hijacking is a little harsh, Toby. There was a discussion about moisture meters and Keith added his contribution to that. I can't see that he was hijacking.

There are far worse offenders at dragging threads off at a tangent, on this forum. Mea culpa most of all! But we all enjoy a general chat about various aspects that may be vaguely related to the topic.

 

[malcolm]

Concrete floors with no impermeable membrane underneath will settle to equilibrium with their environment. Rubber carpet tiles on top will cause moisture levels to end up at 100% between the rubber and the concrete floor. (Wet! - we had that in a previous house.) Wood flooring is a bit breathable so better but I reckon you would still need to bed them on something impermeable and just accept there might be a bit more moisture going up the wall.

The way Parquet floor was laid in the 1920s (at least here) was sitting the wood blocks on a layer of hot bitumen. The bitumen would have been fairly impermeable. Mine was ruined by high external ground levels but I'm hoping to reinstate the floor on the same basis - sitting it on something impermeable.

 

[Keithj]

I still don't know what I said to attract Toby's wrath. I've never been attacked like that on a web forum before.
I'd better avoid giving answers from my experience, in case I get it wrong again or end up hijacking a thread. It's a pity, because I've enjoyed the friendly off-topic banter in here for the past three years.

 

[Toby Newell]

@keith see pm

@malcolm. 100% relative humidity you mean, that is quite common in these instances.

Yes. Bitumen was used widely until the 1960s. Whilst waterproof itself it would not form a complete barrier, ie therewouldbe 'holes'. Even 2% of holes can be a problem. In reality as you point out this is moot as the interface between the concrete and the bitumen is often at 100% RH, the concrete will then degrade chemically and the bond will fail.

Have just finished restoring a 40sqm 115yr old pitch pine floor in Marlow which was one of the most arduous parquet floors ever. Same problem. Massive shrinkage too. Make sure you scrape off all the bitumen off the blocks before you relay, it takes the same time again to dress the blocks as it does to lay but it should be done.