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Quality Inspection Standards for cast stone

On-site inspection and acceptance of Cast Stone should be performed at time of delivery and again after all material has been installed, pointed and cleaned. Final Inspection should be done prior to application of water repellents. The on-site inspector should be familiar with the project specification as well as the applicable reference standards. Test reports of compressive strength, absorption and other physical properties should be on file as well as the approved sample.

Before installation, check the color and texture of the approved sample against the delivered product. Cast Stone should approximate the color and texture of the approved sample when viewed under good typical lightling conditions at a 10' distance and should show no obvious imperfections other than minimal color and texture. The inspector (and stone setter) must be familiar with the dimensional requirements of the installation as they pertain to joint sizes and interfaces with other materials.

Stones should be appraised for color when dry as dampness will darken the surface color and make it appear blotchy. Curing time differentials may affect color since moisture will be retained within units for 6 months even in dry weather. Samples which have been stored indoors for long periods of time may look considerably different than product which was manufactured only a short time before delivery. Always compare color between units of comparable age subjected to similar weathering conditions.

Texture of Cast Stone should be approximately equal to the approved sample when viewed from a 10' distance in good typical lighting. Do not appraise texture under a sun wash when sunlight is skimming across the surface parallel to the plan of the stone face as this will unfairly accentuate minor irregularities.

Minor color variations
Minor variations in color and texture from stone to stone should be accepted within the limits of the accepted range, either established by several samples or mockups or by deviations from instrumentally measured color variation to be approximately equal to a good natural cut limestone project. More color variation should be expected than from building materials with painted or applied finishes.

Some projects will show more color variation than others. Units containing gray cement will show more light-dark variations than those containing white cement. Colors which require high amounts of intregal pigments such as reds and browns will vary more than moderately neutral shade such as buff. Special mixes containing contrasting and multi-colored aggregates may be subject to extreme color deviations when compared to homogeneous facing mixes.

Variations in color within the same stone may be caused by efflorescence or free lime migrating to the outer surface. This can usually be remedied by proper wash down. Staining, mortar smears or uneven washing can also cause color variations within stones and the manufacturer should be consulted for recommended treatment of these problems.

Patching is perhaps the greatest source for dissatisfaction with finished installations. When months have elapsed between the date of manufacture and the date of repairs, significant differences in color may exist between properly repaired areas and the remainder of the stone. These areas should be left alone and will blend in over time through curing, natural weathering and ultraviolet light. It is a mistake to require an instant color match at time of repair since this will usually cause dark patches later on.

Unacceptable deficiencies
Common deficiencies which are not normally acceptable in high quality Cast Stone installations include:
  1. Bug holes or air voids on the finished surfaces
  2. Ragged or chipped edges on formed edges.
  3. Stains on exposed faces from foreign substances.
  4. Twist, warp, out of square or bow exceeding tolerances.
  5. Out-of-plane or pie-shaped joints, or large or small joints out of tolerance.
  6. Areas of rough texture of smoothness not matching sample.
  7. Backup concrete bleeding through exposed faces.
  8. Visible cracks exceeding 0.005" (Not acceptable from any distance.)
  9. Reinforcing shadows or exposure on face.
  10. Rust on surface caused by staining, reinforcement or iron pyrites.
  11. Installations not matching joint layout on approved shop drawings.
  12. Form marks or local depressions in excess of 0.030".

The value of mockup panels
Building owners and their representatives will often apply some wishful thinking when viewing and touching a small 12" sample and then trying to imagine the way an entire facade will look. Wherever possible, an investment should be made in mockup panels and/or sample units. The sample units should demonstrate a variety of shapes and casting configurations, including vertically cast surfaces if they are to be encountered.

Careful quality control of Cast Stone units by competent personnel at the plant, combined with qualified ongoing inspection and acceptance at the job site, ensures that all parties are aware of each other's expectations. This eliminates disappointing results at the end of the job, since very little can be done to change the appearance of Cast Stone after it has been set into the structure.

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