Wednesday, April 17, 2013

The difference a few mils can make

Now, I am a fan of the reusable grocery sack, and countless other items that are just plain better made with something besides plastic.  But in some cases, a sheet of plastic can't be beat. Below are two photos of concrete floors.


The photos were both taken within a few minutes of each other, within a few yards of each other.  Both are indoors, the left on in our shop, the right in the new apartment-in-progress.  What's the difference?  A six-mil sheet of plastic under the concrete on the right.  It rained a lot the past weekend, then turned quite warm and humid.  I can't explain the physics of it, but the damp in the soil under the slabs is sweating up through the concrete without a vapor barrier under it, while the other concrete stays dry.  Conclusion: use plastic wisely, in the right places.