Commercial and Industrial Floor Coatings for Professional Contractors
Article 03 of 24
Evaluating Existing Concrete and Previous Floor Systems
Determine What Is Under the Floor Before Building a New System Over It
Every successful flooring project begins with an honest evaluation
of the existing substrate. Concrete condition, contamination,
moisture, cracks, joints, repairs, previous coatings, and structural
movement must be understood before preparation methods or flooring
materials are selected.
The Existing Floor Is Part of the New System
A new floor coating can perform only as well as the surface to which
it is bonded. If the existing coating is weak, contaminated, or
poorly adhered, installing another system over it does not correct
the underlying problem.
The same principle applies to concrete. Weak surface paste,
delaminated concrete, oil contamination, excessive moisture, and
unstable repairs can all become failure points beneath a newly
installed floor.
The contractor must determine what can remain, what must be removed,
what requires repair, and what conditions require additional testing
or consultation.
Begin with the Floor's History
The owner, facility manager, and maintenance personnel may provide
information that cannot be learned from a brief visual inspection.
Ask about the building, slab, previous flooring, and operating
conditions.
- When was the concrete placed?
- Was the slab placed over a vapor retarder?
- Which curing compounds, sealers, or treatments were used?
- What flooring systems were previously installed?
- Why is the existing floor being replaced?
- Where have previous coatings blistered, peeled, cracked, or worn?
- What chemicals, oils, or process materials have contacted the floor?
- Have water leaks, flooding, or drainage problems occurred?
- Which repairs have been made, and what materials were used?
- Have building use or environmental conditions changed?
Historical information should be documented, but it should not
replace field inspection and testing. Records may be incomplete, and
current conditions may differ from past conditions.
Perform a Systematic Visual Survey
Walk the complete floor in a planned pattern rather than inspecting
only obvious damage. Use a marked floor plan to record locations and
photograph representative conditions.
Concrete Conditions
- Cracks and joints
- Spalls and pop-outs
- Scaling and dusting
- Laitance and weak surfaces
- Settlement or uneven areas
Moisture Indicators
- Dark or damp areas
- Efflorescence
- Blisters and peeling
- Rusting metal
- Recurring staining
Contamination Indicators
- Oil and grease staining
- Chemical discoloration
- Embedded dirt
- Adhesive residue
- Cleaning-compound residue
Existing-Coating Conditions
- Peeling and delamination
- Cracking and checking
- Wear-through
- Soft or sticky areas
- Multiple unknown layers
Map Cracks and Joints
Not every line in a floor has the same cause or requires the same
treatment. The contractor should distinguish among planned joints,
random cracks, construction joints, isolation joints, and repaired
areas.
| Condition |
What It May Indicate |
Contractor Concern |
| Saw-cut control joint |
Planned location for shrinkage movement |
Determine whether it remains active and how the system details it |
| Construction joint |
Boundary between separate concrete placements |
Possible movement, contamination, or edge deterioration |
| Isolation or expansion joint |
Designed movement between structural elements |
Usually must remain functional and should not be rigidly bridged |
| Random crack |
Shrinkage, settlement, load, thermal stress, or structural movement |
Determine whether the crack is dormant or active |
| Previously repaired crack |
Past damage or movement |
Identify the repair material, bond, and evidence of renewed movement |
A rigid coating or crack repair cannot stop structural movement.
Cracks that change width, show vertical displacement, or continue
through multiple building elements may require evaluation by a
qualified design professional.
Evaluate Surface Strength
Concrete may look solid while its surface layer is weak. Laitance,
dusting, scaling, poor finishing, improper curing, chemical attack,
or freeze-thaw damage can reduce the strength of the surface to which
the coating must bond.
Possible evaluation methods include:
- Visual examination under good lighting
- Scraping or probing questionable areas
- Sounding for delaminated or hollow concrete
- Trial mechanical preparation
- Pull-off adhesion testing
- Concrete testing by qualified personnel when required
Mechanical preparation should expose sound concrete. If preparation
continues revealing weak material, the contractor should stop and
determine whether deeper removal or structural repair is required.
Look for Laitance and Weak Surface Paste
Laitance is a weak layer containing fine particles, cement paste, and
water that may remain at the concrete surface. It can appear hard and
smooth but provide poor support for a durable flooring system.
Applying a high-strength coating to weak laitance does not strengthen
the bond to the underlying concrete. The coating may remain attached
to the laitance while the weak layer separates from the slab.
The specified preparation method should remove laitance and produce
the concrete surface profile required for the selected system.
Investigate Contamination
Industrial concrete can absorb oil, grease, coolants, fuels,
chemicals, cleaners, and process materials. Surface cleaning may
improve appearance without removing contamination from the concrete's
pores.
Warning Signs
- Persistent dark staining
- Oily residue returning after cleaning
- Strong odors during grinding or cutting
- Water beading instead of wetting the concrete
- Previous coating failure in a repeated pattern
- Softened concrete or chemically attacked surfaces
- Contamination around machinery, drains, and storage areas
Trial cleaning and preparation areas can help determine whether
contamination can be removed. Severely contaminated concrete may
require deeper removal, specialized treatment, or replacement.
Important: Grinding contaminated concrete can
spread contamination across the floor and into dust-collection
equipment. Identify suspected chemicals and establish an
appropriate safety and waste-management plan before disturbing
the surface.
Evaluate Existing Coatings
Installing a new flooring system over an existing coating makes the
old coating part of the new system's foundation. The existing layer
must be compatible, securely bonded, clean, properly prepared, and
capable of supporting the intended service.
Questions to Answer
- What type of coating is present?
- How many layers are installed?
- How strongly are the layers bonded to each other and to the concrete?
- Are there blisters, cracks, peeling, soft spots, or worn areas?
- Has the coating been exposed to oil, silicone, wax, or chemicals?
- Is the coating compatible with the proposed primer and flooring system?
- Will preparation remove too much of the remaining coating?
- Does the manufacturer permit installation over the existing material?
A few well-bonded test areas do not prove that the entire floor is
sound. Inspection and testing should include representative areas,
edges, traffic lanes, wet zones, repairs, and visibly distressed
locations.
When Existing Coatings Should Be Removed
Removal is generally appropriate when the existing system is
deteriorated, incompatible, contaminated, unknown, or unable to
support the new service requirements.
Conditions favoring removal include:
- Widespread delamination or blistering
- Weak adhesion between existing layers
- Soft, uncured, or chemically damaged material
- Unknown coatings that cannot be evaluated reliably
- Contamination that has penetrated through the flooring
- Excessive total thickness or incompatible movement properties
- A manufacturer requirement for direct application to prepared concrete
The removal process may reveal conditions not visible during the
original survey. The proposal should explain how concealed damage
and additional repair will be handled.
Use Trial Areas
Trial areas provide valuable information before the contractor commits
to a preparation method or complete system. They can help evaluate:
- How easily the existing coating can be removed
- The concrete condition beneath the existing floor
- The effectiveness of cleaning and degreasing
- The surface profile produced by preparation equipment
- The presence of concealed repairs or multiple coating layers
- Primer wetting and absorption
- Potential outgassing or pinholing
- Adhesion of the proposed system
Trial areas should be placed in representative and difficult
locations, not only in the cleanest and most accessible part of the
floor.
Moisture Evaluation
Visual inspection cannot determine the complete moisture condition
of a concrete slab. A floor may look dry while moisture remains
within the concrete or moves upward from below.
The evaluation plan should identify:
- The required test method
- The number and distribution of tests
- Building temperature and humidity requirements before testing
- The flooring manufacturer's moisture limits
- Who will perform and interpret the testing
- What action will be taken if results exceed the limits
Evidence of moisture-related failure should be mapped and compared
with slab edges, exterior walls, drains, cracks, below-grade areas,
plumbing, and changes in building use.
Sounding and Adhesion Testing
Sounding can help locate hollow or delaminated areas in concrete,
repairs, and some existing flooring systems. Changes in sound should
be marked for further investigation.
Pull-off adhesion testing can provide quantitative information about
tensile strength and the location of failure. The failure plane may
occur:
- Within the concrete
- At the concrete-to-coating interface
- Within an existing coating layer
- Between coating layers
- Within the adhesive used to attach the test fixture
Test values should be interpreted together with the failure location.
A high numerical result does not describe the full floor unless test
locations are representative.
Evaluate Repairs and Patches
Existing repairs may contain cementitious materials, epoxy mortar,
flexible sealants, asphaltic materials, gypsum-based products, or
unknown compounds. Their compatibility and bond must be evaluated.
- Is the repair sound and securely bonded?
- Is it flush with the surrounding concrete?
- Does it contain cracks or signs of renewed movement?
- Can it tolerate the planned preparation method?
- Is its porosity different from the surrounding concrete?
- Is it compatible with the proposed primer and flooring system?
- Does it contain flexible material that should remain exposed as a joint?
Unsuitable repairs should be removed and replaced using a material
appropriate for the flooring system and service conditions.
Document Existing Conditions
Documentation should establish the condition of the floor before the
contractor changes it. Useful records include:
- A marked floor plan showing cracks, joints, failures, and repairs
- Dated overview and close-up photographs
- Moisture, adhesion, and other test results
- Descriptions of contamination and damaged concrete
- Locations of trial preparation areas
- Samples or information identifying previous floor systems
- Written notice of unacceptable or concealed conditions
- Agreed procedures for additional work and change orders
Photographs should include enough surrounding area to identify the
location. Close-up images without context may be difficult to use
later.
Practical Contractor Checklist
- Ask the owner about the slab, previous flooring, spills, leaks, and failures.
- Walk and map the complete floor under adequate lighting.
- Identify cracks, joints, repairs, spalls, weak concrete, and drainage problems.
- Locate oil, grease, chemical, adhesive, and cleaning residues.
- Evaluate the identity, condition, adhesion, and compatibility of existing coatings.
- Use representative trial areas to investigate concealed conditions.
- Perform the required moisture and adhesion testing.
- Determine which materials can remain and which must be removed.
- Obtain professional evaluation for suspected structural movement or severe deterioration.
- Photograph and document conditions before preparation begins.
- Explain assumptions and exclusions in the proposal.
- Use written change procedures for concealed or changed conditions.
Safety and Professional Responsibility
Existing floors may contain hazardous substances, contaminated dust,
lead-containing coatings, asbestos-containing materials, reactive
chemicals, or residues from facility operations. Do not grind, cut,
blast, or remove unidentified materials without an appropriate
evaluation and safety plan.
Follow applicable regulations, site requirements, safety data sheets,
respiratory-protection procedures, dust-control requirements, and
waste-disposal rules. Testing and structural evaluation should be
performed by qualified personnel when required.
Key Takeaway
The condition beneath a new floor cannot be ignored. Contractors must
inspect, test, map, and document the concrete and any existing floor
system before deciding what can remain. A new flooring system should
be bonded only to a substrate that is sound, compatible, properly
prepared, and suitable for the intended service.
Knowledge Check
1. Why is a visual inspection alone insufficient?
Important conditions such as moisture, weak subsurface concrete,
contamination, hidden repairs, and poor adhesion may not be
visible. Testing and trial preparation may be required.
2. Why must an existing coating be evaluated before another system is installed over it?
The existing coating becomes part of the new system's foundation.
If it is weak, contaminated, incompatible, or poorly bonded, the
new floor can fail with it.
3. Why should cracks and joints be classified rather than treated alike?
Different cracks and joints have different purposes and movement
characteristics. A moving joint should not be treated like a
dormant surface crack.
4. Why are trial areas useful?
They reveal how the existing floor responds to removal, cleaning,
preparation, priming, and adhesion testing before full production
begins.
5. What should be done when preparation reveals concealed damage?
Document the condition, notify the responsible party, determine
the required corrective work, and obtain written authorization
before performing work outside the approved scope.
Technical References
-
ASTM D4258, Standard Practice for Surface Cleaning Concrete for
Coating.
-
ASTM D4259, Standard Practice for Abrading Concrete.
-
ASTM D4263, Standard Test Method for Indicating Moisture in
Concrete by the Plastic Sheet Method.
-
ASTM F2170, Standard Test Method for Determining Relative
Humidity in Concrete Floor Slabs Using In Situ Probes.
-
ASTM D7234, Standard Test Method for Pull-Off Adhesion Strength
of Coatings on Concrete Using Portable Pull-Off Adhesion Testers.
-
ICRI Technical Guideline No. 310.2R, Selecting and Specifying
Concrete Surface Preparation for Sealers, Coatings, Polymer
Overlays, and Concrete Repair.
-
ICRI Concrete Surface Profile comparator chips and related
concrete evaluation and repair guidance.
-
OSHA requirements applicable to respirable crystalline silica,
hazardous materials, respiratory protection, and workplace
safety.
-
Current technical data sheets, safety data sheets, preparation
requirements, and written recommendations supplied by the
flooring-system manufacturer.
Standards, regulations, and manufacturer documents may be revised.
Confirm that the current editions and the requirements applicable to
the specific project are being used.