Solvent Popping in Industrial Coatings: Signs and Repairs

Solvent popping appears as small holes or craters in a coating film, often during or after application. If you spot them on a tank, floor, or piece of equipment, the important next step is to determine the extent of the defect before covering it with another coat.

Similar-looking marks can have different explanations, so appearance alone isn't enough to establish what went wrong. A useful inspection starts with the film itself and the conditions recorded during the job.

Key Takeaways

• Solvent popping can leave small openings in an industrial coating, but pinholes and craters can also come from other defects.
• Inspection should cover the affected area, nearby coating, application records, and the service requirements for the surface.
• Film thickness, coating preparation, environmental readings, and cure time all belong in the application and inspection plan.
• Repairs should address the defective film and receive the same inspection attention as the original work.

How to Identify Solvent Popping

Small surface openings are easier to investigate when you know where they appeared and when they first became visible. A close inspection can also help establish whether the issue is isolated or widespread.

Look for Small Holes and Craters

Solvent popping may appear as tiny holes or crater-like marks in the finish. Depending on the coating and the surface beneath it, the marks can be difficult to see without good lighting.

Inspect the surface from more than one angle. Side lighting can make shallow texture easier to spot, while a magnifier can help show the shape of individual openings. Photograph the area before anyone sands or applies another coat.

Also note whether the marks cluster around welds, edges, overlaps, or other locations where coating thickness can vary. That information gives the contractor a starting point for reviewing the work.

Map the Affected Area

A few marks on one panel call for a different assessment than defects spread across an entire tank lining. Record the location, approximate size, and distribution of the affected areas.

Include adjoining surfaces that look sound. Comparing those areas with the damaged film can help an inspector identify differences in application conditions, coating build, or substrate preparation.

Separate Popping From Similar Coating Defects

A hole in a coating doesn't identify its origin by itself. The timing, shape, and condition of the surrounding film matter when deciding what to repair.

Pinholes, Craters, and Surface Contamination

Pinholes are small openings in a coating film. A crater is a depression in the finish, which may or may not extend through the coating. Both deserve attention when the coating must protect steel, concrete, or an existing lining.

Surface contamination can also interfere with how a coating wets and covers a surface. Inspectors look for residue, oil, dust, and other signs alongside the application record. A contractor should establish whether an opening reaches an underlying coat or substrate before choosing a repair.

Blisters and Moisture Damage

Blisters are raised areas in the film rather than open holes. They can form when moisture collects beneath a coating, and some eventually break or peel.

Damp concrete, condensation, and salt contamination require their own investigation. Our guide to humidity and salt-related paint failure covers visible signs that may point toward moisture or adhesion problems.

Avoid puncturing blisters casually. Photograph them first and have a qualified coating professional examine the film and substrate.

Inspect the Coating Before Deciding on a Repair

Start with a visual survey, then match the inspection methods to the coating system and its intended service. A decorative finish and a tank lining may have different acceptance criteria even if both show small surface marks.

An inspector can measure dry-film thickness, assess adhesion where appropriate, and examine prepared test areas. On suitable lining systems, holiday testing can locate discontinuities that visual inspection may miss. That test identifies openings; it doesn't establish why they formed.

Our guide to holiday testing for tank linings explains how that inspection fits alongside thickness and visual checks.

The work record matters, too. Useful details include the coating products and batch numbers, application dates, mixing information, environmental readings, and measured film thickness. Record the test location and result so the repair team can return to the same area.

If an inspection method damages the coating, include repair of the test location in the scope. Electrical testing also needs equipment and procedures suitable for the coating and substrate.

Control Film Thickness During Application

Film thickness is a measurable part of an industrial coating specification. Too little coating can leave inadequate protection, while excessive buildup can create product-specific curing or performance problems.

Measure the Wet Film

A wet-film gauge helps an applicator assess coating build while the material is still wet. Readings can guide adjustments before the entire area has dried.

The expected relationship between wet and dry thickness depends in part on the coating's volume solids. For example, a coating with 60% volume solids applied at 10 wet mils has a theoretical dry thickness of about 6 mils. One mil is one-thousandth of an inch.

Actual results depend on the product and application conditions, including any permitted thinning. Wet readings are useful during application, but they don't replace dry-film measurements.

Inspect the Dry Film

Dry-film readings show whether the finished coating meets the specified range. The inspection plan should identify where and how readings will be taken, including difficult geometry where coverage may vary.

Pay attention to welds, corners, edges, and spray overlaps. These areas need deliberate application and inspection rather than an assumption that the film matches a nearby flat surface.

Our guide to controlling thickness during tank recoating explains how wet and dry measurements fit into a project.

Follow the Coating System's Application Instructions

Industrial coating systems can include a primer, intermediate coat, and finish coat. Each layer may have its own mixing, application, and recoat requirements, so the schedule should address the complete system.

For a two-component product, the crew needs to use the stated mixing ratio and allow any required induction time. Pot life also matters: once mixed material passes its usable period, it shouldn't remain in application equipment for the job.

The specification should identify the required coat sequence and the recoat window for each layer. If a recoat window is missed, the surface may need additional preparation before the next coat. Simply adding material over a questionable layer can conceal a problem without resolving it.

Different systems can reach the same total thickness through different numbers of coats. When comparing proposals, look at the specified thickness of each layer as well as the total.

Plan for Temperature, Humidity, and Ventilation

Southwest Florida conditions can change over the course of a workday. The application plan needs to account for the surface and the surrounding air, not just the forecast.

Record Conditions at the Surface

Direct sun can heat steel above the surrounding air temperature. Morning dew can leave a surface damp even after the air begins to warm. For that reason, a useful record includes surface temperature, air temperature, relative humidity, and dew point at relevant stages of the work.

The product's technical data sheet and project specification establish the acceptable conditions. If readings fall outside those limits, the schedule needs room to pause rather than push ahead.

Allow for Drying and Cure

Ventilation and temperature are part of the application plan for many industrial coatings. Enclosed work areas also need ventilation and worker protection appropriate to the materials and space.

A finish that feels dry may still need more time before cleaning, handling, immersion, or other service. Our discussion of potable water tank lining controls covers the connection between coating schedules, inspection, and return-to-service requirements.

Prepare the Substrate and Existing Coating

Steel and concrete need different preparation, but both require a sound surface suited to the specified system. Before coating steel, address corrosion and prepare welds, sharp edges, and other irregularities as required by the project. Remove preparation debris before application.

Concrete may need repairs for cracks or damaged areas. Moisture within a slab also calls for separate consideration: a dew point reading identifies condensation risk at the surface, but it doesn't measure moisture moving through the concrete.

Existing coatings deserve attention as well. If the previous system is unknown, determine whether it can support the new coating and whether the materials are compatible. Failed or poorly bonded material may need removal rather than another layer over the top.

How to Correct Defective Coating

The right repair depends on the depth and extent of the defect, the coating system, and the service conditions. A small cosmetic defect on exposed equipment may have a different acceptance standard than an opening in an immersion lining.

Remove and Prepare the Affected Area

After documenting the defect, remove the affected coating as required by the repair specification. This may involve sanding a localized area or removing more of the system when the defect extends across a larger surface.

The prepared area needs a sound surface and a suitable transition to any coating that remains. Feathering the edges can help avoid an abrupt ridge, but the repair still needs to meet the coating manufacturer's requirements for surface preparation and compatibility.

Don't assume a thin finish coat will close every opening. If a defect extends through multiple layers, the repair may need to restore those layers.

Reapply and Inspect the Repair

Apply the specified repair materials at the required thickness, then allow the stated drying and cure period. Record the repair location, materials, application conditions, and inspection results.

Where the project calls for holiday testing, adhesion testing, or dry-film measurements, include the repaired area in the inspection plan. Deficiencies should be resolved before the coating enters service, especially where the film protects against immersion or chemical exposure.

What to Ask a Painting Contractor

A useful proposal should describe the coating system and how the contractor will inspect the work. Ask for the preparation method, individual coat thicknesses, environmental controls, and repair procedures in writing.

Also discuss access and shutdown time. A facility with a short maintenance window still needs enough time for the coating to cure under the conditions at the site.

We provide industrial coating services and free onsite estimates in Southwest Florida. Our industrial coating inspection checklist can help you prepare for that discussion.

Frequently Asked Questions

Can You Paint Over Small Pinholes?

An extra coat isn't always a sufficient repair. The contractor should assess the opening, the underlying film, and the coating system's repair requirements before recoating.

Does a Smooth Finish Mean the Coating Is Sound?

A smooth appearance alone doesn't establish film thickness, adhesion, or continuity. Depending on the project, inspection may include measurements and tests in addition to a visual survey.

Protect the Coating Before It Enters Service

Small holes deserve a closer look when a coating protects valuable equipment or contains liquids. Document the affected area and investigate the film before choosing a repair.

A measured repair gives you a better basis for acceptance than an undocumented extra coat. Once the work is complete, keep the inspection record with the rest of the project documentation.