What are some of the problems associated with older generation vapor retarders?
Four reasons to change your spec.1. Cross-laminations are layers of very thin plastic (less than 10-mils in thickness) that do not comply with the new thickness recommendations by the American Concrete Institute's Moisture Task Group Committee 302.
2. Laminations of thin layers of polyethylene and scrim offer varying degrees of permeance and puncture resistance. Testing for puncture resistance is conducted on top of scrim junctions (the strongest point). Architects should be interested in the puncture resistance between the scrim at the weakest point. Will a sharp piece of aggregate know the difference?
3. Fabric laminated vapor retarders total thickness exceeds ACI 302 recommendations. However, the vapor retarder material itself is less than 10 mils. Puncture resistance of the retarder plastic is dependent upon which side of the material is probed. Puncture resistance is tested through the fabric side not the retarder material.
In addition, there is confusion in the field on installation techniques. Does the fabric side install up or down? Up is recommended but seaming tape will not stick to the fabric. Therefore, in real world conditions the film surface gets installed up allowing for easier taping of the seams. This exposes the very thin polyethylene layer to construction traffic, tears and punctures.
4. Laminations of thin polyethylene, scrim and paper have been used extensively in the past mainly due to low cost. The problem is puncture resistance, or the lack thereof. Once punctured, the brown paper acts as a sponge drawing water in and throughout the paper. Delamination of the film structure occurs leaving the product in a degraded state. There have been many flooring failures associated with this style product, many of them schools.