How am I 'Sposed to Know when it's completely dry??

Hey Y'all,

I'd be ever so grateful if someone could clear this up:  In all of the blogs/books/forums/conversations/articles/etc. I've ever read about installing an earthen floor, it always says something to the effect of "wait until your floor has dried completely before you try to seal it."  So riddle me this- how am I 'sposed to know when my earthen floor is actually dry all the way through??  Cuz seriously, folks, working hard is something I don't begrudge, but it really chips my axe to put a gob of work into something then have it be messed up because of a detail.  This detail seems purty important though, so I'd REALLY love to hear how one might tell when hidden layers of earth beneath their feet are dry all the way through.

Thanks a bundle!!

Zee

Since there are no takers on this one, I'll give it a go. Perhaps somebody else will crack my suggestions and come up with something better.

I have no experience with packed? earth floors but i would try to devise a simple test. Take some simple property and test it when dry and wet. When processing earth samples i had to dry the earth in an oven for 24 hours at 180 °C. That supposedly removed all free water molecules from the sample. That is probably to much for your purpose.

1.- Colour - Wet earth has generally a different colour. Prepare a sample of packed earth - put it in the oven - dry it and check the colour. Modern camera's come with all kind of gimics that allow you to compare colours. Take a picture of your oven sample and compare it with your floor.
2.- Feeling - Wet earth feels different. Dry earth feels harsh an the skin and dries the skin. That's the way the builders of my house did my walls. It is still standing after 80 years.
3.- Electric conductivity/resistance is perhaps something you could test? You need a battery, 2 electrodes, 1 multimeter. It has been a while (almost 30 years) since i had to do this in the physics lab a Leuven University. I don't know a source for a good English text. Dry earth conducts electricity far less than wet earth. Perhaps people in the pottery business will have good suggestions.

Tests 1 and 2 are probably easiest to try out.

You probably want earth floors because of their 'breathing' properties? If so, the earth floor is always reaching for equilibrium with the moisture in the air and moisture in deeper earth layers. Perhaps you can devise a test along those lines?

Perhaps the temperature of a floor that is loosing water to evaporation would feel cold. Perhaps take a nap on it. Do you feel a chill?

Perhaps put something out of the refrigerator or freezer onto the floor. Does water leave the floor and condense onto the coldness?

You could drill holes in the floor (in places that you won't see the small patches later) and use a soil moisture meter.  You would watch the moisture levels decrease until they stay the same (and low) for a few days.  You could also put a hygrometer on the floor and outside.  If the humidity is consistently the same on the floor as outside - it is probably dry.  A drying floor will make the indoor air more humid especially immediately next to the floor.

There can still be a significant amount of moisture in the floor after the color lightens and appears to be dry - so the color change is probably not the best indicator.

However, I've never measured moisture in the floors I've done.  How quickly and how dry the floor gets depends on the relative humidity, temperature, ventilation, mix of the floor material, and how thick the layers were laid down. My advice would be to wait until humidity is the same inside as out, then wait a little longer for good measure.

Hi y'all!

Thanks so much for taking a gander at this!  
Ardilla,

There can still be a significant amount of moisture in the floor after the color lightens and appears to be dry - so the color change is probably not the best indicator.

That's what I kept thinking.  It makes sense that it would look dry on the surface before it's actually done- like a cake can look "done" but be all raw inside if you don't test it.  I think your meter solution is a good one.

Here's some background/fill-in information:

*I'm in Oklahoma, in the "cross timbers" where my particular part of the state is considered "sub tropical".  We have a good amount of humidity through the summer, which is why I'm extra concerned about my floor being all the way dry before I oil it.  Fortunately...

*my base is composed of decomposed granite which (from lots of experience) requires very little moisture to create a very solid rammed product, so I'm not too worried about that bit.  It dries completely in a fair amount of time, especially in the thickness I use.  The part I'm more worried about is the cob bit...  

*I plan to lay that fairly thin-about a 1/2" at a time and end up with an inch to an inch and a half of the stuff as my "finish".  So it won't be, say, 4 or 6 inches of cob.  In addition,

*my decomposed granite base will be completed before the walls are all the way up (we're building under a roof), giving it more air flow (plain-sweeping wind, we have!  The song is not a lie.)  In my experience, that means we will have that dry, topped with cob, drying WAY before the October wet season shows up.  Most of what I have to contend with is ambient humidity.

Honestly, we want need have to be in this house by this winter, and the floor is the part that gives me fits the most as far as the this-HAS-to-be-done-in-order-for-us-to-move-in factor.  So any suggestions are very welcome.  I know I can't slow time, but I'm gonna do everything I can think of to expedite drying without compromising quality.  As far as oil and all that, even if we have to wait until the house is all the way done to get that portion done, we will have a whole house attic fan, which should help with that drying, I would think.

So thanks!  I will look for some sort of moisture meter.  You suggested a soil moisture meter; pray tell, where might one find such a wonder?

Bless you all for your help!

Zee

I don't know if this kind will work, but soil moisture meters are available at many garden centers and most well stocked online gardening suppliers.  That is the only soil moisture meter I know of.

You may want to wait under construction is nearly completed before doing the last layer or two of floor and oiling it.  The floor will take some damage during construction - so the longer you can wait to do the final finishes the better.  Also, if you do the base and intermediate layers well before the final finish layer, you don't have to worry about drying so much.

Once the floor is finished (and oils/finishes cured) cover it with cardboard or drop cloths until the trim work, painting, etc. is done.

I tried using one of those moisture meters for my earthen floor and it worked okay, but I still didn't trust it and just let the floor dry for an extra long time--several months--before I oiled it. I've heard horror stories of people oiling too soon and wasn't risking it. Extra time is the best solution.

Thanks all!  Yes, the plan is to put in the capillary break and the rammed layers first and wait until the rest of construction is done to do the cob layer and finish layer.  That's the part I'm most worried about.  I've worked with the material we're tamping quite a bit on other projects and know that it dries pretty quickly.  I'm more worried about the cob portion being completely dry...horror stories and all.  
Thank you all for your help and suggestions!  They are very much appreciated.

Zee