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Production Quality


A consistentregular and high accuracy control programme is essential to the production of GRC products. From the raw materials to the finished products, proper examination and testing, either done in-house or by third-party, and certifications from suppliers, are regularly updated to ensure the products meet the designed properties and requirement. These test results are recorded systematically and kept safely to allow us to pinpoint manufacturing faults, be it materials or workmanship. Personnel with Civil Engineering, Structural or Architectural Engineering background performs the Quality Control and is not involved or responsible for production and procurement. He must maintain a good record of all materials used, test reports on materials and test pieces on everyday manufacturing and monitor the results to ensure consistent quality in production and products.


Ordinary Portland Cement (OPC) in grey or white and Rapid Hardening Portland Cement (RHPC) with mill certificates are needed from each cement shipment and must meet BS12 or BS12:1978 or BS146:1973: P12 and other relevant cement standard and or ASTM C 136 and or national or international standard. Cement will be kept in dry storage.

Sieve tests are done on each delivery to ensure the correct size and grade. Tests should conform to ASTM C 136 or BS 882, BS1199, BS1200 and BS812 or national standard. Wash honeycomb surface and soft building sand, and dry to get rid of contaminants. Silicon sand use conforms to the following specification:  


Silica                          >          96%

Moisture                    <          2%

Soluble Salts                        <          1%

Loss on Ignition       <          0.5%

Clay & Organic Matters      4000ppm maximum

Cl                                            600ppm maximum

Aggregates, fine or coarse, should be clean and compatible with the backing mix.

Use chemically analysed private well water if the government water supply is not available. The analytical will be updated annually.

All admixes must have Certificate of Compliance, Material Safety Data Sheet and Usage Instruction supplied by the admix supplier.

All curing agents must have Certificate of Compliance, MSDS and will not cause or affect the colour of the product or post-curing colour treatment.

Form release agents, Surface retardant and Sealers must have manufacturer specification, MSDS, and usage instruction.

Cold-Formed Steel, Brackets/Inserts, Hardware and Structural Shapes must accompany with manufacturer’s mill certificate.


All face mixes must comply with the proposed combination from the proposed supplier in the correct amount. Testing for volumetric changes due to moisture variation is crucial. 

Before design and production, a minimum of twenty unaged flexural strength tests (of six specimens each) produce on 20 days should be conducted.

For each design of Flex Anchor or Gravity Anchor Pull-off and Shear Before design and production, conduct a minimum of twenty unaged strength tests of each type and size of the anchor. The specimens and test procedures should accurately simulate various service conditions expected during the life of the project.


All moulds should be inspected after each use to ensure no defects will affect the thickness, surface finish, appearance and sizes of the product it replicates. Immediate repair is crucial to avoid defects or creating a new one ensures disrupted production schedule.

If the sand and aggregates are not bagged or stored under cover and protected from the elements, and moisture testing before production, the amount of water use needs to be adjusted accordingly.

Slump Test should be carried out at each shift unless incorporated with a high reduction admix in the mix. In such a case, the use of an ammeter indicates the relative resistance of the mixing motor.

Unit Weight Test daily and the variation should not be more than 48kg/m3(3 pcf) from the established unit weight for the particular mix design in use.

Temperature Test should be taken and recorded after making the specimens at the onset of each day operation. Thermometer within 10C accuracy should be inserted into the slurry until it becomes stable. The temperature recorded and filed accordingly.

Also known as “bucket test” for the slurry flow rate and “bag test” for the glass fibre dispensing rate should be carried out with each machine and at the beginning of each day or after prolonged machine stoppage. The dispensing rate should be adjusted accordingly to allow the correct designed mix spray to the specific pattern. Chopper gun cutting rotor should be inspected after each roving to eliminate the deposits accumulated at the cutter blades. Blades need an ocular examination to ensure that it is not broken or deformed. Glass fibre in the “Bag test” should be examined to ensure that the cut glass is of the same length. Should there be any glass exceeding the required specification, the gun needs to be adjusted, and the blade needs to be changed if necessary.

Test boards made at least once a week, every shift, machine, applicator, and mix. The test board should have no face mix and of the same way (distance, speed and trowel method). The lightly trowel test piece should be made according to BS EN1170-5 and will be stored the same way as the products.  For the Wash-Out Test, required are two extra pieces from the test board. The marked test board and test pieces should be immediately tested soon after the curing period of 28 days. Proper recording of the test result should be kept safely for evaluation and future reference.

Wash-Out Tests determines the amount of Glass Fibre content. It should be within –0.5 to +1% by weight of the mix. Initiate weekly tests similar to the Test Boards Test and whenever the Glass: Slurry ratio is adjusted.

The skin thickness designed for each product should be the minimum. The overall thickness must comply to the depth/thickness gauge at 0.5m maximum distance for each test point of at least 6 test points per product. Ocular check of bonding pad for thickness and compactness is essential. Bonding pad over gravity anchor should be with a penetration gauge at half of the anchor locations.

Additional thickness measurement checks are mandatory at places like reveals, corners, recesses, inside corners and breaks in plain surface to ensure there is no void, thin area and insufficient glass fibre reinforcement. It is particularly essential to spray-up this area with material from other parts of the mould.

Air content tests should be carried out daily on mixes containing air-entraining admixture.


BS EN1170-4 and –5 or PCI MNL130 Appendix F, ASTM C947 will be employed for the testing of properly cured GRC backing test pieces. Tests should be performed each day for each operator, each machine and each mix design. The test results will be evaluated on an ongoing basis to evaluate the consistency of the test results with a detailed graph.

The strength of the test piece will be considered acceptable if:

  1. The average of all sets of three consecutive yield strength test values (average of six specimens each) shall equal or exceed the f’ used in the design. The results of the average ultimate strength test values shall equal or exceed the f’u used in the design.
  2. All test result should reach at least 90% of the f’u and no individual ultimate strength results divided by 3 shall be less than 90% of the f’u used in the design.

If any strength test falls below these requirements, the GRC design engineer shall take steps to guarantee that the GRC panels represented by the test coupons are not compromised. The design engineer may request additional coupon testing from the same test board, have the panels load-tested, have coupons cut and tested from suspect GRC panels or take other appropriate action.

Compressive strength tests of the face mix should be conducted weekly following ASTM C3990.

These measurements should be used to establish the level of compactness of the GRC and should be performed weekly for each operator, each gun and backing mix design. Prepare a test sample (two specimens) from the test boards from portions of actual flexural specimens. Conducted tests follow ASTM C94897.

Anchor connections tests done on a 300 x 300mm (12” x 12”) specimens cut from the test boards. Two test specimens of one type and size to confirm production values should be made from the test boards produced during a week. The following week, test all types and sizes of anchors for evaluation. Of the specimens produced during one week, two test specimens of an anchor type and size should be randomly selected and tested approximately 28 days after spraying update. The anchor strength level is satisfactory if they meet both of the following requirements:


  1. The average of all sets of three consecutive anchor strength tests equals or exceeds one and two-third times the Pu used in the design.
  2. No individual anchor strength test is less than one and one-half times the Pu.

Bonding pad repair methods should be evaluated and documented by test data.

Daily Production Test Sheet:


For the Production of architectural use GRC Products, GRC (Thailand) will keep daily production record, mould inspection record, equipment maintenance record and product sample boards. The sample board will include information as follow:

Date, Application, Mix type, Add-Mix, Temperature, Humidity, 

Test Piece code, Test Date and Test Result and Wash-Out Test Result.

The above test conforms to BS1750 and PCL MNL 128 and meets all ASTM Standard.

Regular Test: Material and Anchor

Testing of the new batch of materials, add-mixes, and anchor is required to ensure that they meet the specific standard.