Dudley Primeaux
Primeaux Associates LLC
 

Background:

Since July, 2000, Polyurea Coating Systems, Inc. (PCSI) has been supplying the epoxy primer (PCS-30) and polyurea (PCS-355) to the applicator for the Remote Delivery Facility (RDF) waterproofing project. (please see “Pentagon Remote Delivery Facility “ case study). PCSI was asked in late June, 2000 to evaluate the RDF waterproofing project following the application of a coating system which was not performing as required. Numerous problems with the current system were evident; multiple pin hole formations, poor adhesion to the concrete, poor intercoat adhesion, and markedly lower performance characteristics than reported in the manufacturers product literature. After reviewing the project status, the applied coating, and the concrete surface, several suggestions were provided by PCSI technicians to the applicator and the general contractor on methods to provide a continuous waterproofing membrane on the deck of the RDF. 

PCSI is a manufacturer and supplier of polyurea and epoxy systems for coating concrete,  steel and other substates. Several products are offered, depending on application requirements, end use, and service conditions. PCSI has developed products based on a systems approach to an application. PCSI primers are matched with the PCSI polyurea to achieve optimum results of the finished coating. 

After reviewing the conditions presented at the RDF, PCSI offered a primer-polyurea system, which when properly applied, would meet the project requirements; waterproofing over 280,000 ft² of cast concrete.  PCS-30, a two component 100% solids penetrating primer was chosen due to the varying conditions of the concrete. PCS-355 polyurea was applied at 80 mils minimum thickness over the primed deck. PCS-355 is reported on PCSI data sheets as having a typical tensile strength of 2,500-3,000 psi, elongation of 500%, and a hardness of 90-96 shore A. These test results are based on testing that was performed at the PCSI laboratories by trained laboratory technicians. Results are reported as typical of the specific formulation and are meant as a guideline when choosing a product for a particular application. 

Over 15,000 gallons of PCSI product has been applied to the RDF deck. PCSI has supplied over 400 man hours of on-site technical assistance to the applicator and the general contractor during the application, provided recommendations on repair of inferior concrete surface, and consulted on additional surfaces requested to be coated. 

Discussion: 

As a requirement of this project, Quality Control reports were generated for each lot of PCS-355 manufactured and sent to the RDF, with the testing performed in the PCSI analytical laboratories. Each QC report was submitted to the applicator and general contractor prior to shipment of the lot. Each lot was analyzed for tensile, elongation and hardness. The individual QC reports provide the average value of a minimum of 3 tests for each specimen tested. 

All lots of PCS-355 supplied to the RDF have met and exceeded the specifications established by PCSI and reported on PCSI’s technical data sheets. 

However, a concern was raised that, after cutting a section of the applied coating from the deck and sending it to an independent testing lab for analysis, the elongation values reported by PCSI were not confirmed by the testing lab. Elongation values determined by the testing lab showed 50-70% lower values than those reported by the PCSI labs. 

As mentioned above, PCSI performs QC analysis on each lot of PCS-355 prepared for the RDF. Each lot tested exceeded specification. In the event a lot did not meet PCSI’s specification, the material would be removed from shipping status. No lots of PCS-355 were manufactured outside of PCSI’s specifications. 

In addition, sample coupons were prepared for each lot sent to the RDF and retained in PCSI’s files for future testing. These retained coupons were re-analyzed following the questions raised by the contractor. Each coupon again met specification. Full backup data for the QC summary reports were provided to the general contractor. 

Therefore, the question remained, repeated analysis of the PCS-355 by PCSI laboratories were not reproduced by samples taken from the RDF deck and analyzed by an independent lab. Specifically the elongation values were 10-50 points lower than that reported on the PCSI specification data sheet for the product. 

What conditions could affect these varying test results? PCSI technicians were convinced that the testing apparatus was properly calibrated and tests were performed following the ASTM D 412 and ASTM D 638 standards. Reproducibility of the various lots and retains were within ASTM standard deviations, as reported in the Precision and Bias sections. Yet the product sprayed on the RDF deck, removed and tested, did not match our results. PCSI began to look at how application, and atmospheric conditions could affect the results. 

ASTM D 638, Tensile Properties of Plastics, references note 2, describes the expected variations in test results between testing labs. “ This test method is not intended to cover precise physical conditions. It is recognized that the constant rate of cross-head-movement type of test leaves much to be desired from a theoretical standpoint, that wide differences may exist between rate of crosshead movement and rate of strain between gage marks on the specimen, and that the testing speeds specified disguise important effects characteristics of materials in the plastic state.” Note 2 goes on to say, “ special additional tests should be used where more precise physical data are needed.”  

Mr. Dudley Primeaux , consultant, recognized industry expert in polyurea chemistry and applications, and co-author of this study presented additional data demonstrating the non-precise nature of testing elongation of polyurea. In a documented test study, Mr. Primeaux provided the leading manufacturer of plural component spray equipment, Gusmer, with a master batch of polyurea. Gusmer sprayed this master batch with 8 different Gusmer gun models, holding all other application conditions constant. Panels were then sent for analysis. The results are remarkable, with elongations ranging from 96% to 248%, depending on the model and set up of Gusmer gun alone. The polyurea used was a 250% elongation polyurea per spec data sheet. All other conditions were held constant. Results from this study are shown in Table 1. 

Note the wide variation in %elongation in table 1. Results ranged from 96% elongation (i) to 248% (e). Similar gun set ups showed differences in elongation of 65 units by decreasing the passes of the spray, (e) and (f). Gun set up (g) is a repeat of (f), yet showed a 59 unit difference between the two. Choice of gun and set up of that gun will affect the results of elongation tests. 

Table 2 

This clearly demonstrates that as the mix temperatures at the gun are lowered, elongation is similarly affected. Temperature conditions at the RDF site have been dropping as fall and winter approached. The applicator employs 300’ of spray hose between the heater and the gun tip. Although the heating block at the proportioner is set to specified temperatures and the hose is traced, the loss of heat through the hose while laying on the cold concrete deck will decrease the tip temperature and affect elongation values. 

Mix temperature of 71°C. 
 

Table 4 

Sample thickness will change throughout the area being sprayed due to wind conditions, and applicator techniques. Lab evaluations are made at 60 mil sheets. Tests at the RDF showed film thickness varying from 70 mils to over 100 mils. Elongation values will reflect the differences in coating thickness. 

Graph 1

Polyurea formulations differ between products and manufacturer. In the case of PCS-355, ultimate elongation values of 500% are reached after one week of cure time. If samples were obtained and analyzed in less than a weeks time, differences in elongation will be observed. 

Summary: 

Typically, manufacturers of polyurea products report performance data of the supplied material in their technical data sheets. This data may consist of parameters such as tensile strength, hardness, and elongation. Additional tests may be supplied such as abrasion resistance, coefficient of thermal expansion, flexibility etc. These tests may be performed in house or by outside laboratories depending on the availability of expensive testing apparatus. Coupons prepared for analysis are made under laboratory conditions and controlled environments. The resulting data is designed to provide an indication of the performance values of the formulation. However, care must be taken in transferring these lab produced results to actual field applications. This reports demonstrates how application variables and conditions may result in a wide range of results performed on the same polyurea formulation. Simply utilizing a different brand or model spray gun, or using a different temperature or pressure at the gun tip may results in variations from reported values. Sample thickness and cure time also influence results for elongation. Atmospheric conditions at the application site will change day by day and will affect property development. Finally, it is recommended that the ASTM procedures be carefully read for expected deviations in data reported between laboratories.

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