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Best roof wetting process
06-18-2012, 12:41 PM
Post: #1
Best roof wetting process
What have you found to be the best method for wetting the roof prior to performing an infrared scan on a flat roof?
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06-18-2012, 12:47 PM (This post was last modified: 06-19-2012 12:29 PM by Gary Orlove.)
Post: #2
ITC RE: Best roof wetting process

However, when actually scanning the roof for moisture, you want the roof surface to be totally dry.

We are looking for subsurface moisture and do not want interference or artifacts from surface moisture.
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06-18-2012, 03:11 PM
Post: #3
RE: Best roof wetting process
I agree. However, I live in the high dessert and we get very little rain. we have to wet the roofs a couple of days prior to performing the inspection in order for the infrared camera to reveal the leaks.
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06-18-2012, 03:24 PM
Post: #4
RE: Best roof wetting process
We suggest wetting the roof surface using a standard water hose. Block all of the drains and allow the water to stand at least 4 hours or more. Then allow the roof to drain and sweep off all remaining water. Then allow the surfaces to dry 2-4 hours so that the entire surface is completely dry prior to conducting any thermography testing and/or moisture meter inspections.

Preforming roof inspections:
If there has been a dry spell, it may be necessary to flood the roof several hours before the inspection, but it must be drained/swept dry before the thermal survey
Conduct investigation with eyes, visual camera, moisture meters during full daylight
Infrared survey should start as the sun leaves the surface around dusk and continue until anomalies “appear”
Watch for thermal reflections from the sky and other buildings
Moisture meters are a must to verify the presence of moisture
Get permission to mark the damaged areas with spray marker paint
Need to consider access options in the planning stage
Health and Safety considerations are paramount:
Working at height
Do not work alone – have a “buddy”
Working at height AND in the dark…need torches, lamps etc
The moisture appears warmer at night after a sunny day due to its greater thermal capacitance
Roof surface must be dry and thermography works best with absorbent insulation
Heavily ballasted (large rocks or very thick pea stone present a huge thermal mass and generally cannot be inspected – they need to be removed from the suspected areas
Moss and other growth must be removed

Test Conditions: Moisture Detection in Roofing System:
Stringent conditions
Need to use the environment
Prior sun loading, clear sky's
Prior rain (or if not, flood the surface, and then dry the roof prior to the inspection)
Dynamic temperature change needed
Narrow timing window around dusk (in summer)
Consider standards and guidelines, if applicable
*Heat capacitance method

I hope this helps you..

Mike Eggman
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06-18-2012, 05:32 PM
Post: #5
RE: Best roof wetting process
Thanks. Do you have any experience using a spray rack? If yes, are the results any better than just flooding with a hose?
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06-19-2012, 02:16 AM
Post: #6
RE: Best roof wetting process
We have used spray racks many time, but normally not on a roof area, unless it is a known or suspected area of concern but even with this you will have a low chance of success. Normally spray racks are used on a building exterior in a controlled manner following ASTM standards.

With roofing you need to replicate the conditions of standing or pooling water over a period of time, so the best way to do it is with enough water applied (1-2 inches) and again a min of 4 hours to allow the weight of the water and the soaking of the roof deck so that if there are cracks/holes/damage it should be enough of both (water/time) to penetrate those areas, which then once dried and then with enough sun load to heat the trapped water you should be able to identify the areas where water was allowed to penetrate the roofing membrane. Just be clear the you have a limited window (sometimes 30 mins, sometimes 1 hour) under the proper conditions to be able to see this with a "Good" IR camera.
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07-09-2012, 10:55 AM
Post: #7
RE: Best roof wetting process
We have used spray racks pointed downward to cause local area flooding for 90-minute leak investigations directly below the suspect roof surface but, in agreement with meggman, to flood an entire roof for a significant amount of time (he recommends minimum of 4 hours), the issue is volume of water (given available dynamic water pressure), not surface area. You will achieve maximum flow rate from a hose with no nozzle; depending on the size of the roof it can take at least a half an hour to achieve a full flood. After the roof drains are plugged, be careful that the water level doesn't rise above the flashing. You may also want to bring some waterproof boots (possibly rare in a dry climate) and a mop or broom to break the water tension if some areas of the roof aren't being reached; you can also use the hose itself pointed to do that. Take care that the hose doesn't create its own dam and keep water from a section of the roof.

A spray rack has nozzles to form a mist pattern over a very small area (typically 2 foot x 2 foot per nozzle); it does not make sense to use mist to achieve the wetting you require.
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