moisture in crawl space

I have a 3 year old log home that I am having trouble with moisture in the dirt crawl space. I have a french drain around the perimeter below the foundation but I still get sweating from the duct work when the A/C runs and through the ground. Humidity measured 95% when he took it on Friday. I blocked all of the vents (this seems to be the new school of thought, make the foundation airtight) and this helped a great deal. I had a crawl space encapsulation comany come out and give me an estimate for $6000.00 for 1600SF. I think this is way to high and would like to do it myself if I can find the proper moisture barrier. Right now I have 6 mil blac plastic but that isn't doing the trick. The company uses 20 mil (similar to a pool liner). Any one have any idea where to purchase something similar? Other wise it's time to bite the bullet and spend the money. I know someone here has run into this problem before. I would hate to spend money on a project that doesn't fix the problem though. Thanks for any help.

Rich

Not an answer to your where to buy the barrier question, but I'll stick my nose in anyways. Your duct ac runs should be insulated or they will sweat no matter what you have for a barrier. Unless you get a dehumidifier and remove the moisture. Which is what I would do. $300 and a little electricity would solve the problem for now. Any chance of just pouring a concrete floor? Seems like $6000 would go a long ways towards that. Not my field of experience at all, but I have a hard time believing that more moisture will get through the barrier you have now than through a 20 mil one.

The ducts are insulated, they used to sweat the whole length but since I sealed up the vents they only sweat about 8 feet on each side of the A/C unit. The concrete might be the way to go, I hadn't really thought of going that route. I'll check into it. Thanks

wrangler6831

Does the floor have a vapor barrier (plastic) under concrete or if dirt on top of it?

I woulden't leave vents closes long you will be creating a good enviroment for mold and other nasties.
The ducts must have good insulation and have a vaspor barrier on them too.

If insulation on duct's get wet it wil not insulate properly.

tom

My last house had a crawl space under half of it (that was only dirt), and the other half was finished. I had a heck of a time with moisture accumulation in the crawel space, to the point where it would seep over the concrete slab and wick into the carpet padding in the finished room. It used to have the thick black plastic cover, but I eventually had to replace that with vapor barrier and a drain pump/line next to the slab. The vapor barrier really cut down on the humidity in the entire basement.

Try google-ing vapor barrier, you should be able to do the job yourself. Just be sure to seal the entire lenght - it won't work if it's not sealed properly. The duct work should also be insulated separately. Sadly, most builders take the cheap way out and use uninsulated ducts. That really irks me - we pay sooo much for a house and they save a couple hundred on cheap ducts...

I'll leave now while my blood pressure is still manageable!