Holiday (or as the Brits say Porosity) Testing Tips and Tricks:

NOTE: The following comments are the opinion of the author based on experience using the following equipment in both a laboratory and field environments. Any comments are welcome and can be forwarded to me at tswan@cci-inspection.com

Simply, holiday or porosity testing is looking for voids in the coating or coating system that go to the substrate. For holiday testing to work requires two conditions:

1. The coating system must be nonconductive.
2. The substrate must be conductive.

Holiday testing works best on conductive metallic substrates but will also work with concrete but is not as straight forward as metallic substrates due to variations in concrete that affect it’s conductivity.

NOTE: There is a new method to holiday test coatings that uses UV. I will discuss it at the end of the article.

Which Holiday Tester do I need?

A good rule of thumb is when testing nonconductive coatings on metal, coatings up to 20 mils should be tested using a low voltage (sponge) tester. Coatings over 20 mils should be tested using a high voltage tester. Lacking guidance from the specifications, coating manufacturer or product data sheets, the high voltage tester should be set at 100 volts per mil of coating. IMPORTANT: High Voltage testing can DAMAGE the coating being testing so make sure you know what you are doing.

Holiday testing on concrete must be done using a high voltage tester. Generally, a coating on concrete will require a higher voltage than the same coating on metal. Holiday testing concrete is as much an art as a science and if you are not experienced, seek help to avoid problems.

I have a coating on metal less than 20 mils, what do I do?

The standards that address low voltage holiday testing are

ASTM require 67.5 volts for testing these coatings.

ISO requires 9 volts for coatings to 12 mils and 90 volts for coatings to 20 mils.

These days, with the diversity of companies doing business in the US, it is possible to be working on specifications that reference ASTM or ISO. The only low voltage sponge tester that will handle all three voltages is the elcometer 270-4. It is easily adjustable among all three voltages; it is light and easy to use.

What is a wetting agent and do I need one?

Many people like to use a wetting agent to reduce the surface tension of the water. If you have a fairly thick coating near the upper end of the 20 mil range, due to the surface tension of water, the water may bridge the void and therefore not find the holiday.

If the surface is to be recoated, it is generally not advisable to use a soap as the wetting agent because it may leave a film. The most common wetting agent is Photo-flo.

Can I use a High Voltage testing on coatings less than 20 mils?

Yes, but the thinner the coating, the more likely the coating may be damaged by using the improper voltage. Suggested voltages in NACE RP0188 are:

How do I do high voltage testing on nonconductive coatings on metallic substrates?

High Voltage Holiday Testing is addressed in the following standards:

The first step is to make sure you know the dry film thickness of the coating. This is the first step in determining the voltage setting. Ideally, assuming the DFT is in spec, the specification should tell you what voltage setting to use. If it does not, some product data sheets or application bulletins will provide the information. Lastly, ask the coating manufacturer. If none of this works, use the above table or use 100 volts per 1 mil of coating thickness.

How do I do high voltage testing on nonconductive coatings on concrete substrates?

This can get complicated and there is no easy answer. I do not have any experience in very dry, desert like areas, but generally there is enough moisture and salts present in concrete to make it conductive. When testing pipelines, sometimes the ground cable is just drug along on the ground so soil and concrete both conduct electricity.

I generally recommend the following steps:

1. If available, ground the meter to rebar in the concrete.
2. If rebar is not available, often steel is bolted directly to the concrete. You can ground the meter to the BARE steel.
3. If testing a slab with no steel, drive a piece of rebar into the ground at least the depth of the slab and immediately next to the slab. Use this as your ground.
4. As with metal, first follow the specs, next go to product data and application bulletins and then go to the coating manufacturer.
5. If you still do not have a voltage setting, do not use the settings recommended for steel. The best way is to find several areas representative of the coating to be tested at varying distances from the ground. Create a holiday and determine the voltage necessary to create a spark. If the voltage increase as you move from the ground, you need to increase the test voltage or move the ground point.

Several coating manufacturers that make concrete coatings are now making conductive primers. By using one of these primers, you can follow the procedures for holiday testing metallic substrates.

Are Holiday Testers dangerous working with such high voltages?

All holiday tester output currents in the range of anywhere from 0 volts up to over 30,000 volts. The good news is the output is in DC volts which means you can not electrocute yourself if you get zapped, and if you do it often enough, you will get zapped. The danger is not from the current but that the current can make you jump. If your feet are planted firmly on the ground, this is generally the worse damage, but if you are on a ladder or scaffold, jumping can be dangerous. The voltage will not hurt you but the fall can.

Are all Holiday Testers Created Equally?

When discussing high voltage testing, the words that come to mind with most inspectors is heavy, cumbersome and difficult to adjust. Elcometer has addressed these concerns in the Elcometer 236 and 266 by making the meter light (less than 5 pound) which is lighter than the batteries on most units. The voltage is easily set using a digital display making testing with the wring setting difficult. There is little exposed metal to cause a shock except at the tip of the probe and the ground wire. If you can find a meter that is easier to use, lighter and less expensive, please let me know about it.

What is with all the probes?

There are four basic types of probes:

Wire Brush probes work best on textured surfaces where the brush can follow the contour of the surface. It comes in various sizes up to 40 inches and works well on large surfaces. For small surfaces, the band brush that come with the 236 works well

The Rubber Brush is a conductive rubber strip that works well on large, smooth flat surfaces.

Come in diameters from 1.5 inches to 12 inches for testing internal pipe coatings.

Comes in sizes from 2 inches to 36 inches for testing 360^o of external coating with one pass. Springs can be connected together for larger diameters.

I have an Elcometer 236 but do not understand the sensitivity knob.

In most cases leaving the sensitivity knob centered in it’s range will work for the setting. This knob only controls the audible alarm setting and has no effect on the meter sparking or the visual LED in the wand. On some coatings, as you run the holiday tests, the coating can become charged and discharge back to the wand causing a false holiday indication. The sensitivity knob is designed to tune down the audible alarm to avoid false alarms. If you are getting audible alarms when the meter is not producing a spark, turn the knob counterclockwise if you are getting sparks with no audible alarm, turn the know clockwise. Adjust knob as required to find the best setting so the alarm beeps only when there is a spark.

If the knob is set full clockwise the meter will beep almost continually even when no holiday are present.

If the know is set fully counterclockwise, you will still get a spark, but the alarm will not sound.

Elcometer 236 or 266?

On the Elcometer 266, the sensitivity know had been eliminated and a dead-man switch has been incorporated to minimize zapping yourself. The Elcometer 266 also has the standards built into it so if you know the Standard you are testing to and know the coating thickness, the meter will select the proper voltage.

The same attachments are available for both meters. At the current time you can use the 236 attachments on the 266 but not the 266 attachments on the 236.

How do I do a holiday test with a UV light?

A couple of coating Manufactures  have developed coatings that incorporates a UV pigment.  When you shine the UV light on the coaiting with the pigment, Holidays show up as a black spot.  When you coat over the primer hand shine the light on the coating, if you see bright spots, you have a holiday to the primer.  The Elcometer 260 ($450.00) was designed specifically for these coatings.

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