CONSTRUCTING THE VAPOR BARRIER
The general contractor needed to complete the concrete pour phase of the construction in a timely manner to stay on schedule. In order to meet these specific requirements, the vapor barrier construction would need to be finished in a single day and the installation needed to wait until other construction tasks were completed. There would be very little notice as to when the installation could be scheduled and executed. Due to the nature of the construction schedule and tight window the job had to be completed within, a larger than average crew would be required. The workers would need to stay on the jobsite well past the close of day in order to see the project completed.
In order to address the various challenges, Vapor Mitigation Strategies coordinated and delivered an experienced certified vapor barrier installation contractor. Needing an individual with a quick response time, flexibility with rapidly developing changes in the construction schedule, and a fundamental understanding of the needs of contractors to stay on time and budget, Vapor Mitigation Strategies delivered the perfect solution.
Vapor Mitigation Strategies provided its general contractor customer a certified vapor mitigation system installation, passing both a thickness and smoke test.
First, careful measurements were made to ensure the installation was done according to the specifications of the design and that necessary penetration from wall mounts, plumbing, electrical conduit, etc. were not interfered with as the building project moved into the next phase.
Once the pattern for the trench had been outlined, the trench was dug out to accommodate the vapor venting channel. The venting channel material was rolled into the trench and the vapor venting channel was constructed. Once the venting structure was finished, it was covered up by the ground material (soil, gravel, sand, etc.), completing the venting portion of the vapor barrier system.
The second portion of the vapor barrier system project involved constructing the three-layer barrier. This began by applying a high density polyethylene (HDPE) tarp which was rolled out into open areas and tailored to fit around the vertical uprights. Each joint of tarp and upright cut were sealed with a Geo-Seal vapor barrier product applied either through spray or by hand. After the tarp was completely rolled out, and all uprights and edges were addressed and sealed, the main layer of Geo-Seal was sprayed over the entire tarped area.
Next, the Geo-Seal material was perforated in discrete areas near specific lines of the barrier construction for the purpose of conducting a smoke test to ensure that all the joints and uprights were properly sealed. The thickness of the layer was measured with calipers to ensure the Geo-Seal layer was applied at an appropriate thickness.
When all the perforations were sealed, and the smoke testing revealed no further leaks, a final layer of tarp was placed over the vapor barrier. Additionally, its joints and upright perforations were sealed with Geo-Seal as a final measure. This last tarp layer provides protection to the vapor barrier itself considering that in most cases, metal rebar and concrete will be layered on top as the construction moves forward.
The project required approximately 4,500 square feet of vapor barrier be installed, and that it be completed in a single day. Both of these requirements were met, ensuring the general contractor was able to pour concrete the next day and continue with their project scope with no delays. From start to finish, the process took approximately 12 hours to complete. The customer was satisfied by the craftsmanship, dedication, and ability to meet the tight time demands on this particular job.
After the building was constructed, the contractor involved with reworking the plumbing, electrical and sewage services needed to add penetrating uprights through the existing vapor mitigation barrier (vmb).
The contractor needed to adjust and add penetrating uprights to this space to fit the needs of a future tenant while restoring the vmb to full effectiveness in order to protect the occupants of this space from risk of vapor intrusion.
For this additional challenge, Vapor Mitigation Strategies coordinated the vmb demolition and repair utilizing an experienced vmb installation contractor’s vmb repair specialists.
Prior to the refit of the vmb, Vapor Mitigation Strategies consulted with the general contractor and the vmb installer in the proper dismantling of the vmb for the addition or adjustment of penetrating uprights. This is a key step in ensuring the success of a vmb refit.
Once the vmb was dismantled and the necessary additional uprights or adjustments to the uprights were installed, the vmb was rolled back over the area from which it was removed.
Experience in repair of these systems is essential as the vmb must be carefully handled in order to ensure it does not crack or form creases, greatly reducing its integrity as a barrier to vapor intrusion. Also, as this task involved the addition of penetrating uprights, the crew had to be well experienced in forming seals around the uprights.
Quick recognition of potential project hurdles was essential in these repairs as time was a factor. This well experienced crew realized this job would require concrete to fill the trench left after the uprights were installed. Without the addition of concrete, the new vmb installation would have had nothing on which to adhere. Immediate recognition and response to this issue and the application of quick drying concrete meant there was no extra time required for the installation.
When all the uprights are sealed and the larger sections of the original vmb are rolled out, Geo-Seal was applied to close the barrier’s new seams together and form a vapor tight seal. The integrity of the new vmb was tested in the same manner as the original with barrier thickness tests of newly added sealant and with a smoke test to confirm system integrity. Once the tests and thicknesses are inspected and determined to be within qualifications, the barrier and jobsite are left for work by following contractors to continue.
Published in Modern Contractor Solutions, November 2016