Overcoating reduces the overall cost of the application since it takes less time to prepare the surface and clean it afterward. Given that the cost per square foot is cheaper, more maintenance work may be completed.
Fremont, CA: The constantly changing environmental conditions cause many industrial coatings problems. The field environment varies depending on region and industry. For instance, the specifications for process piping in a refinery would be significantly different from those for a lead-coated water tower situated in a suburban neighborhood.
However, there is a solution that can lessen the overall expense for these project types while still guaranteeing the contractor's safety: overcoating. Overcoating, which involves adding a protective coating over an already-applied one, can save a lot of time and money but isn't always appropriate.
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The key benefits of overcoating:
Overcoating Requires Minimal Surface Preparation & Cleanup
Several high-performance coatings only need a small amount of surface preparation before being overcoated, which also saves a lot of time. This is especially true for coatings like Rustbond that have exceptional wetting properties. These cross-linked, penetrating coatings, bond, and adhere to the previously applied, weathered coating and the cleaned, corroded portions, finally forming a barrier that serves as a tie-coat over which a topcoat can be applied. If considerable surface preparation using power tools or abrasive blasting is necessary, surface preparation might also result in downtime for hot work permits. There is less downtime because overcoating simply needs a dry, clean substrate, which enables additional application time throughout the day.
Overcoating Generates Cost Savings for Application
Rather than removing that existing coating, it could be pressure cleaned and overcoated in place of removing the current covering. With this approach, significant savings on lead abatement expenses like mobile shower units, containment, cleanup, and disposal would be possible. Overcoating lowers the overall cost of the application since it takes less time to prepare the surface and clean it afterward. Given that the cost per square foot is cheaper, more maintenance work may be completed. Furthermore, because many of the high-performance coatings available today have high solids by volume, they can cover more square footage with less volatile organic compounds (VOC).
The Drawbacks of Overcoating:
Surface tension increased by overcoating
The overall surface tension rises when you add more coats to an already-applied coating. Given that the system is only as good as the original surface preparation, overcoating may not be a possibility if the pre-existing coating is thicker than 15 mils.
Overcoating could result in early failures
Assets have frequently undergone many coats of overcoating in the field, and as a result, the coating is now brittle, cracking, and checking due to stress. It's crucial to understand that these assets are not suitable for additional overcoating. In the wrong circumstances, overcoating can result in early failures like delamination.
Overcoating may result in adhesion problems
It's possible that a topcoat won't stick to an existing coating correctly. Applying a test patch of the overcoating system and performing adhesion testing in accordance with guidelines like ASTM D3359 - Rating Adhesion by Tape Test or ASTM D4541 - Pull-Off Strength of Coatings Using Portable Adhesion Testers should be done before providing the all-clear for overcoating. To decide whether the asset can be overcoated, this will act as a baseline.
Excessive Coating Lengthens Drying Time
Another drawback of an overcoated penetrating sealer is the length of time it takes to dry. The dry time is often substantially longer when using a penetrating sealer since the sealer needs to be in a wet stage for a longer period of time to adequately wet-out the surface of the current coating. This can thus result in unwelcome downtime during specific project phases.
As one can see, other considerations come into play when deciding if an asset is a viable candidate for overcoating. Although overcoating can yield quicker results at a lesser cost than more conventional techniques, it's crucial to first evaluate the benefits and drawbacks of overcoating as a potential remedy for the situation.
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