KTA Solutions

Deficient Water Repellent D+D July 2014

Problem:  Deficient Water Repellent

Description:  In order to eliminate the need for painting, integrally colored masonry units were specified for the walls of a new building.   The specification also required the application of clear penetrating water repellent to the block. Within 5 years after construction, moisture was visible on the interior surfaces of the block after rain events.  The Owner wanted to know the source of the water and how to correct the problem.  Following is a summary of the types of testing and analysis undertaken by KTA to examine problems of this nature.

NOTE: The conclusions provided below cannot be interpreted as being relevant to other failures, even if they are similar in appearance. Likewise, the tests identified below may or may not be relevant or adequate for the investigation of other failures.

Field Sampling/Analysis:

  1. Visual Observations – The building walls were a mixture of split-face and smooth-face integrally colored CMU.  The walls appeared to be uniform in color.  Efflorescence was present on the interior surfaces of the block, indicating that water penetration had, or was, occurring.
  1. Rilem Tube – Rilem Tube tests were conducted throughout the building.  The test requires attaching a specially designed test tube to the surface with a clay putty.  The tube is approximately 6” in height.  It is filled with 5 milliliters of water and allowed to remain in place for 20 to 30 minutes.  At the end of the test period, the amount of water absorbed by the substrate is determined from a graduated scale on the side of the instrument.  In every case, the entire 5 millimeters of water was absorbed by the block within a few minutes.
  2. Water Racks – Water racks were used to spray water onto the surface.  Moisture meter readings are typically taken before and after testing for comparison, but this was done only for the first test.  Moisture was visibly present on the inside face of the block in the first test area after a few minutes of spraying (normal test duration is 30 minutes).  Subsequent tests were only evaluated visually, and in every case, water quickly penetrated the block.
  1. Samples – Core samples of representative blocks were removed for laboratory analysis to determine if the repellent was solvent-based or water-based.  In addition, liquid samples of the specified repellent were obtained from the manufacturer for comparison.

Laboratory Analysis:

  1. Microscopic analysis up to 200x was not conclusive in determining whether repellent was present in the surface of the core samples.
  2. Chemical analysis (infrared spectroscopy) of samples obtained collected from the surface of the cores showed that traces of the specified solvent-based repellent were present.

Conclusions:

Wind-driven rain is penetrating the block to dampen the interior surfaces.  This was proven by both the Rilem Tube and water rack testing.  The laboratory analysis showed that traces of the specified solvent-based repellent were present on the surface of the block, but either not enough had been applied originally or it had weathered away.  In any case, the remnants of repellent no longer constituted a functional water repellent.

Correction of the problem required cleaning the surface by pressure washing and after thorough drying, the application of one to two coats of water repellent.  Because a solvent-based repellent was applied initially, the new application was also solvent-based; water-based repellent typically will not adhere to solvent-based.

In order to confirm compatibility and suitability of water repellents before wholesale use, test applications in representative areas should always be performed followed by adhesion testing and Rilem Tube testing.  In some cases, a second application is required to pass the Rilem Tube test.

Chalking of Exterior Coating

 

Problem:  Chalking of Exterior Coating

 

Description:  The coating used to overcoat the exterior of a building exhibited a dull, faded appearance within 1 year of application.  The Owner had a 1-year warranty that indicated the coating would retain its gloss and color and would not chalk.  Following is a summary of the types of testing and analysis undertaken by KTA to examine problems of this nature.

NOTE: The conclusions provided below cannot be interpreted as being relevant to other failures, even if they are similar in appearance. Likewise, the tests identified below may or may not be relevant or adequate for the investigation of other failures.

 

Field Sampling/Analysis:

 

  1. Visual Observations – The building walls were a mixture of split-face and smooth-face CMU.  The colors applied to the block were three shades of gray.  All of the colors exhibited a dull, faded appearance except where protected from sunlight.

 

  1. Chalking – Chalk tests were conducted in accordance with Method A of ASTM D4214, Standard Test Methods for Evaluating the Degree of Chalking of Exterior Paint Films.  A black wool felt was wrapped around the finger and dragged across 2 to 3 inches of the surface.  The amount of chalk transferred to the cloth was compared to a photographic reference standard that depicts ratings of 2, 4, 6, and 8 (with 2 representing severe chalking).   Because of the texture of the split-face block, on those surfaces, the tests were conducted on the smooth mortar joints.  The ratings in sun-exposed areas were around 4.  In areas protected from the sun, the rating was 8 or better.
  2. Surface cleaning – A few square feet at random areas on all walls were cleaned with a bucket of water and a sponge.  At each location, washing revealed the original color.
  3. Adhesion – The adhesion of the coating was examined by knife cutting and probing.  The adhesion was good in all cases.
  4. Moisture Content – Moisture content of the face of the block and mortar joints was assessed using a radio frequency moisture meter.  All tests indicated that the walls were dry.

 

  1. Samples – Representative samples of coating were removed from each wall.  In addition few cans of paint in each of the 3 shades of gray had been retained by the owner for future touch up.  The owner stated that it was the same material that had been used for painting the previous year.  The labels were intact and the containers had not been opened.   One container of each color was returned to the laboratory for the controlled mixing and removal of the samples.

 

Laboratory Analysis:

 

  1. Chemical analysis (infrared spectroscopy) showed all of the samples from the walls to be consistent with the composition of the wet samples in the containers, indicating that the wet material in the containers and the dry paint on the walls were the same products.
  2. All 3 materials were PVA-modified acrylic.   Polyvinyl acetate latex coatings can be susceptible to water absorption resulting in swelling, leaching of additives, plasticizing and hydrolysis, which in turn causes discoloration, embrittlement, stress cracking, and reduced resistance to heat and weathering.

 

Conclusions:

 

The owner believed that the gray coatings had faded, but this was not the case.  The visual dulling and lightening of the film was due to chalking of the surface of the paint.  Chalking is a degradation of the binder that exposes the pigment.  The exposed pigment can be removed from the surface by wiping (which the chalk test assesses) and washing (as was evident when the original color was revealed in the test areas that were washed).  While washing and scrubbing will remove the chalk, when the paint is again subjected to sunlight and moisture, chalking of the surface will resume.

 

The chalking formed because the PVA modified acrylic is not as light stable as other acrylic coatings, such as styrenated acrylic or 100% acrylic.  Specifications had not been prepared to identify a specific coating type or brand to be used.  All the owner knew was that an elastomeric acrylic was going to be applied and a warranty was provided for chalking and color and gloss retention.  Note that “elastomeric” is not a generic type of coating.  It is an undefined term used by manufacturers to convey a given coating property.

 

The problem is solely the result of the coating that was used.   The building was found to be dry, eliminating any allegations that moisture in the building is related to the problem in some way.  The only solution to resolve the problem is to thoroughly pressure wash the walls to remove the chalk and repaint with a more UV-resistant acrylic coating.  When chalking is very heavy, it is also common to apply a prime coat designed to tie up any chalk that may remain after cleaning.

 

Peeling and Disbonding Coating on School Roofs April JPCL

Problem: Peeling and Disbonding Coating on School Roofs

Description:

Premature coating problems on the standing seam roofs of two school buildings were an issue for the school board that was in the midst of improving the school’s image. Embarrassed that the school roof, which had been installed only four years earlier, was so unsightly, the Board wanted an independent investigation to determine the cause of the peeling and disbonding roof coating. The following is a summary of the types of testing and analysis undertaken by KTA to examine problems of this nature.

NOTE: The conclusions provided below cannot be interpreted as being relevant to other failures, even if they are similar in appearance. Likewise, the tests identified below may or may not be relevant or adequate for the investigation of other failures.

Field Sampling/Analysis:

Following are the results of the observations and tests conducted in the field to begin determining the cause of the widespread corrosion:

  1. Appearance – Coating problems were observed to some degree in all areas; however, the vast majority of defects were concentrated on the horizontal, flat areas of both buildings’ standing seam roofs. The extent and severity of the peeling and disbonding of the coating from the underlying substrate over virtually all areas seemed to indicate that the problem was not a localized manufacturing or installation deficiency, but instead a much more fundamental problem.
  2. Coating Thickness – The thickness of the total coating system was measured using a calibrated non-destructive electronic dry film thickness gage. Initial readings were taken of the coating and substrate, and after removal of the coating system, readings were taken of the uncoated substrate to establish the thickness of the coating over the substrate.  Coating thickness measurements ranged from 1.2 to 1.9 mils.  The specified range for the coating system was 1.1 to 1.5 mils.
  3. Adhesion – Coating adhesion was assessed according to ASTM D3359, “Standard Test Methods for Measuring Adhesion by Tape Test,” Method B, Cross-cut, using 2 mm spacing between incisions. Then an assessment was made according to the 0 to 5 rating scale (5B being best, and 0B being worst, indicative of adhesion loss of greater than 65%).
    • The adhesion of the coating on the flat, horizontal areas of the panels was a 0B (very poor) in every case.  In fact, adhesion of the coating on the flat areas was so poor that 90-100% disbonding occurred on every roof panel when tape alone was applied to visually intact coating, without first making incisions.
    • Conversely, on the vertical portion of the standing seams of each roof panel, the coating exhibited much better adhesion.  These areas would not have been exposed to as much solar radiation from sunlight as the flat areas.
  1. Samples – Representative panels from the roof exhibiting both sound and delaminated coating, as well as an unexposed “control” sample were removed for laboratory analysis.

Laboratory Analysis:

  1. Visual Examination.  A visual examination revealed that spontaneous cohesive delamination was occurring within the prime coat.  When adjacent intact areas were probed with a knife blade, the prime coat exhibited poor cohesive strength. Yellow primer was present on both the back of the delaminating color coat, and on the substrate, with most of the primer remaining on the substrate.
  2. Coating Thickness.  Coating thickness measurements were taken on samples cut from each panel.  The samples were cross-sectioned with a diamond saw and mounted with epoxy, ground and polished.  The samples were examined using a digital microscope with 1000X magnification. Coating thickness was also determined using a destructive coating thickness gage conforming to ASTM D4138. The laboratory measurements identified two coats of paint with a dry film thicknesses range consistent with that obtained in the field.
  3. Adhesion testing.  Adhesion testing (similar to the field methods) was performed in the laboratory under controlled conditions of temperature and humidity. The loss of adhesion in all cases was within the underlying primer, with only slight traces of the yellow primer remaining on the underside of the topcoat layer. The majority of the primer remained on the steel.
  4. Solvent resistance.  Solvent resistance was determined according to ASTM D 5402, “Standard Practice for Assessing the Solvent Resistance of Organic Coatings Using Solvent Rubs.”  This test is often done to determine the adequacy of the cure of a coating. The cure was deemed sufficient as the coating on the unexposed control panel, and the coating on panels from the school roofs gave consistent results of 35-40 double rubs until slight transfer, and no additional transfer at 50 double rubs.
  5. Differential Scanning Calorimetry (DSC). DSC testing of the field samples of topcoat gave similar results, which were also consistent with the results obtained from the control.  Accordingly, there was no reason to believe the topcoat on the roof panels was inadequately cured.
  6. Infrared Spectroscopic Analysis (IR). IR was used to identify each of the coats generically:
    • yellow primer – epoxy
    • green finish – polyvinylidene fluoride (PVDF) coating copolymerized with acrylic

Additionally, the sample panels removed from each school exhibited significant oxidative deterioration of the epoxy primer, even when it was beneath what appeared to be intact (but poorly adhered) PVDF topcoat.

Conclusions:

The coating deterioration on both of the elementary school roofs occurred as result of ultraviolet light degradation of the epoxy resin used in the primer beneath the polyvinylidene fluoride (PVDF)-colored top coat.  As the epoxy primer degraded, it disbonded, lifted and ultimately peeled the topcoat from the surface.

A PVDF resin itself is transparent to UV light, even when copolymerized with an acrylic.  It will only resist solar radiation if UV absorbers and light stabilizers, as well as UV-resistant pigmentation are incorporated into its formulation.  Without these additives, deterioration of an underlying epoxy resin will occur, with heat and moisture aggravating the problem.