KTA Solutions

Damp CMU In-Fill Insulation


Problem:  Damp CMU In-Fill Insulation


Description:  A single-wythe CMU building was less than 1 year old when blocks on the back wall were damaged and the faces had to be replaced.  When the replacement work started, the contractor notified the owner that the spray polyurethane foam insulation (SPF) in the block cavities was damp.  The owner requested an examination of the insulation around the building to determine if the problem was widespread.  The specified SPF was low density open-cell, 0.8 lb/ft3.  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:


  1. Visual Observations – Small, isolated patches of efflorescence were visible on the exterior walls at random, but nothing stood out visually to suggest that the block and/or insulation were damp.
  2. Infrared Thermography – IR thermography was used to examine the building walls.  The images showed clear indications of thermal bridging in portions of all walls.  The results of the IR thermography were used to select test locations for in-depth moisture measurements.


  1. Moisture Content – Moisture readings were taken around the building.  Since the purpose of the assessment was to determine whether the in-fill insulation was damp, destructive testing was used.  Two ¼” diameter holes were drilled though the mortar joints or block faces.  Special probes designed in the KTA machine shop were inserted into the holes and connected to a conductivity moisture meter.  The probes allowed for a determination of the presence of moisture at the outer face of the blocks, the interior cavities of the blocks (the insulation), and the inside back faces of the blocks.

    Test sites were selected based on the thermal imaging results in order to obtain moisture readings in areas that did and didn’t exhibit thermal bridging.  In locations where the entire height of the wall appeared to be the same by IR imaging, testing was typically performed at 3 heights (ground level, 10 to 12 feet up from the ground, and below the upper bond beam).   The moisture testing showed mixed results: the in-fill insulation in some block cavities was damp, some was dry, and some of the block cavities were void of insulation altogether.  In some cases, the moisture content was so high that damp insulation was adhered to the probes when removed from the block.


  1. Optical Borescope – A borescope was used to view the inside of random wall cavities in areas where the moisture testing indicated that no insulation was present.  The borescope assessment confirmed that the cavities were empty.


  1. Samples – A few 1” diameter cores were drilled through the block face in both dry and damp locations and the insulation removed.  Each sample of insulation was double bagged and sealed to prevent the ingress or egress of moisture.


Laboratory Analysis:

  1. Samples of damp insulation were weighed upon receipt, dried in an oven, reweighed, and the percentage of moisture by weight of the insulation determined (the mass of moisture per unit mass of dry material).  Samples contained up to 226% of their weight in moisture.
  2. The insulation had open cell properties based upon the rate of absorption that was observed.  Open cell, low density foam had been specified.



While damp insulation was expected to be present to some extent based on the contractor’s initial observations, the investigation revealed a finding that the owner didn’t anticipate – many of the cavities, either in total or in part, were missing insulation.  The IR thermography indicated that thermal bridging was occurring.  Since thermal bridging can be caused by damp insulation or missing insulation, the destructive moisture tests and borescopes were used to investigate the walls further.  It was estimated that insulation was missing in the upper ½ to ¼ of approximately 25% of the wall cavities up to the bond beam.  In areas of thermal bridging where insulation was present, the insulation was damp.  In areas where thermal bridging was not visible, the insulation was dry.  Where the insulation was damp, the moisture content was extremely high as determined by laboratory testing, and because paint is present on both the interior and exterior sides of the walls, there is no opportunity for it to dry.


Determining the source of the moisture was not part of the scope of services, but it is not uncommon to find both missing and damp in-fill insulation in single-wythe CMU construction.  Common causes of damp insulation range from deficiencies in roofing, flashing, and sealants; poor wind-driven rain resistance of the exterior coating; cracks in the mortar and block; and air infiltration/exfiltration leading to condensation in un-insulated block that runs down the cavity to dampen the insulation beneath.


Pinpoint Rusting of a New Bridge Coating System

Problem: Pinpoint Rusting of a New Bridge Coating System


The existing paint system on a bridge over a fresh water lake was removed by abrasive blast cleaning to SSPC-SP10, Near White.  The existing paint contained lead, so surface preparation was performed in an SSPC-Guide 6 Class 1A containment.  Recycled steel grit abrasive was used. The new system was epoxy zinc/epoxy/urethane, applied within the same containment.  An inspection was made 11 months after completion of the work.  Corrosion of a few edges and crevices was present together with patches of deterioration ranging from a “ dusting of pinpoint rusting to discrete nodules of rust.   The crevices and edges were not part of the examination because all parties agreed that the rusting was due to insufficient coverage of the coating and the contractor agreed to make appropriate repairs.  The investigation was limited to the random patches of corrosion.  The Owner was concerned that the rusting might be the early stages of widespread failure.

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 corrosion:

  1. Appearance – When viewed from a distance, the coating on the majority of the bridge was performing well with the exception of very visible failures at some edges and crevices, and random discrete patches of pinpoint rusting.  The visible failures combined covered less than 0.5% of the surface.  However, closer examination revealed that a “dusting” of very light pinpoint rusting was also present on the surface.  There was no pattern to the rusting.
  2. Microscopic Examination – The rusting was examined microscopically up to 30X.  The discrete nodules were removed by careful knife probing.   The nodules appeared to have formed within the intermediate or finish coat.  When removed, the primer beneath the nodules appeared to be intact.  The dusting of rust appeared to be confined to the surface of the finish.
  3. Substrate Condition – Ribbons of coating were removed to the steel in both rusting and non-rusting areas by making very close (1/16” or less) parallel scribes to the substrate, dislodging the coating between them.   In all cases, the substrate had been blast cleaned with a dense surface profile.  There was no evidence of corrosion on the surface.
  4. Coating thickness – Total coating thickness was measured using a Type 2 magnetic dry film thickness gage.  The total thickness ranged from 8 to 15 mils, with no correlation between thickness and corrosion.     Tooke gage measurements showed 3 coats to be present, with the thicknesses in compliance with the specification requirements. There was no correlation between the thickness of individual coats and corrosion.
  5. Adhesion – Adhesion tests were conducted according to ASTM D3359 Method A (X-cut with tape) and ASTM D6677 (X-cut followed by knife probing).  The results were excellent in all cases, including areas that exhibited corrosion.
  6. Samples – Representative samples of coating and corrosion product were removed from the bridge for laboratory analysis.

Laboratory Analysis:

  1. The thickness of the coating on the samples was measured with a digital microscope at 200x magnification.  The laboratory measurements identified three coats of paint with a dry film thicknesses range consistent with that obtained in the field (compliant with the specification).
  2. Microscopic examination of the discrete particles of corrosion at 50-200X magnification showed them to be remnants of steel abrasive.
  3. Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy confirmed that the corrosion was structurally and elementally consistent with steel abrasive remnants.


The discrete particles of corrosion and dusting of corrosion are due to remnants of the steel abrasive used for blast cleaning, rather than corrosion of the steel.  The abrasive became embedded in the intermediate and finish coats before the coating had dried.  The source of the abrasive is not known conclusively, but it is likely due to inadequate cleaning of the containment prior to painting.  Movement of scaffolding or flapping of the containment (physically or by wind), likely dislodged pockets of abrasive and metallic dust which landed on the intermediate and finish coats before they had dried.

The coating can be repaired and overcoated in localized areas, rather than removed and replaced.

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.


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.