My husband and I are wanting to put rough-sawn western cedar trim on the outside of our garage. What can we use as a moisture barrier between the wood and the concrete wall? Would the waterproofing sealer paint work if it was between the wood and the wall? Or would it be best to use the 6 mil plastic sheeting? Thanks for any help!

Do you mean trim or siding? Water isn't going to be coming from the garage, it will be coming from the outside, into the garage. If you are talking trim, it is usually nailed into the roof structure. If you are going to put trim directly on concrete, that's a somewhat difficult proposition. I would use a good grade of landscape block adhesive and glue it on the concrete rather than trying to nail it on. If you are talking siding, how are you going to attach it, furring strips? Please explain a little more about your project.

Thank you for your response. It is trim and not siding as it will only cover parts on the wall. The garage will be stuccoed on the outside with the western cedar trim at the breaks in the stucco. The trim will be 1x8 pieces running horizontally and diagonally along the walls. Our framer (who also does trim) said we would need some kind of moisture barrier between the concrete blocks and the wood so that the wood would not rot and warp. He mentioned the 6 mil plastic, but I thought maybe the water sealer you normally use on the inside might work on the outside.

We're building a Japanese pagoda and want the garage to match. It will be similar to the pavilion in the Portland Japanese Garden : http://www.flickr.com/photos/itafroma/3298388469/ This one only has vertical trim; ours will have more trim running horizontally.

When you say "landscape block adhesive" do you mean Liquid Nails? Or something stronger? Where could I purchase something like this?

Yes, Liquid Nails or similar at HD or Lowe's. Landscape Block Adhesive has tremendous holding power. We use it to replace loose stone facing on houses. I don't think 6 mil plastic is going to hold the adhesive. Maybe a mobile home roofing plastic that is dry would work. Good luck

Brian is giving you some good advice but I'd like to know where you live. I'm in Illlinois and red cedar doesn't stay red for long. I have had much better luck with some Hardieboard siding that looks like cedar but does not rot, maybe something to consider.