Chapter 14

Old Wall Inspection and On-Site Investigation: Diagnose First, Prescribe Later

Compiled by Guangdong Fortune Stone New Material Co., Ltd.

Key Points

• For facade retrofit projects, diagnose first, prescribe later. Eight out of ten problems with old walls lie in the substrate, not the facing. If the substrate is not clearly investigated, discussing material schemes is amateurish.
• Facade retrofit exterior walls have “seven common diseases”: substrate hollowing, substrate dusting, old facing not removed, water seepage and dampness, cracks, flatness exceeding standards, and contamination and efflorescence.
• On-site investigation follows the “five-step method”: look, tap, measure, ask, and record. The more detailed the investigation, the more accurate the scheme; the more accurate the scheme, the less rework.
• The investigation report must provide “four conclusions”: substrate condition conclusion, water seepage and waterproofing conclusion, flatness and leveling conclusion, and scheme recommendation conclusion.
• From investigation to scheme, the core is “translation capability”: translating investigation data into risk language that the client can understand, into scheme parameters that designers can use, and into operational instructions that construction teams can implement.

14.1 The “Seven Common Diseases” of Facade Retrofit Exterior Walls

Based on years of facade retrofit practice, common problems of facade retrofit exterior walls can be summarized as “seven common diseases.”

14.1.1 Substrate Hollowing

Symptoms: hollow sound when tapping the wall; local facing bulging and detachment.

Causes: inadequate substrate treatment during original construction, bonding agent aging and failure, debonding caused by temperature stress.

Impact: hollowing areas cannot be directly applied with flexible stone; they must be removed and re-leveled.

Diagnosis method: tap the wall with a small hammer and listen to the sound to determine the hollowing range; scan with a hollowing detector to determine the hollowing boundary.

Table 14-2 Diagnosis and Treatment of Substrate Hollowing

A failure case of “not investigating hollowing”:

In a facade retrofit project, the construction team did not check for hollowing and directly applied flexible stone on the old ceramic tile surface. As a result, less than half a year after application, local flexible stone detached along with the old ceramic tiles—the hollowing between the old ceramic tiles and the substrate “brought down” the flexible stone as well. Later, rework was done: first remove all hollowing old ceramic tiles, re-level, then apply flexible stone.

Industry saying: Hollowing in old walls is a “time bomb.” If you don’t defuse it, it will explode sooner or later.

14.1.2 Substrate Dusting and Chalking

Symptoms: sand particles fall off when rubbing the wall with fingers; a layer of floating dust on the surface.

Causes: insufficient original mortar grade, cement aging and carbonation, freeze-thaw damage.

Impact: dusting substrate cannot provide sufficient bonding strength; direct application of flexible stone will inevitably lead to detachment.

Diagnosis method: rub the wall with hands to see if sand particles fall off; test substrate strength with a pull-off tester.

Table 14-3 Diagnosis and Treatment of Substrate Dusting

A lesson of “directly applying on dusting substrate”:

In a facade retrofit project, the substrate had severe dusting. The construction team found it troublesome and applied a layer of primer before directly applying flexible stone. As a result, half a year later, the flexible stone began to detach locally. Pull-off test showed bonding strength was only 0.1 MPa. Later, everything was removed, the substrate was re-plastered and leveled, and then flexible stone was applied.

Industry saying: A dusting substrate is like a foundation made of sand. No matter how good the house you build on it, it will collapse when the wind blows.

14.1.3 Old Facing Not Removed

Symptoms: old ceramic tiles, old coatings, old mosaic, and other facing layers on the old wall.

Causes: multiple renovations of the original building, facing layers superimposed.

Impact: there may be hollowing and chalking between the old facing and the substrate; directly applying flexible stone on top has extremely high risk.

Diagnosis method: tap the old facing to check for hollowing; check the bonding state of the old facing.

Table 14-4 Diagnosis and Treatment of Old Facing

A controversy of “directly applying flexible stone on old ceramic tiles”:

There is a saying in the industry: “Flexible stone can be directly applied on old ceramic tiles without removal.” Our attitude is: it can, but with conditions. The conditions are: old ceramic tiles must be firmly bonded, no hollowing, no chalking, and the surface must be clean. But in actual projects, the bonding state of old ceramic tiles is difficult to guarantee. We have encountered too many cases of “old ceramic tiles look firm, but fall off as soon as flexible stone is applied.” Therefore, our recommendation is: for old ceramic tile surfaces, remove if possible; if not, conduct sufficient pull-off tests and reinforcement treatment.

Industry saying: Applying flexible stone on old ceramic tiles is not a question of “can it be done” but “whether the data supports it.” Only after the pull-off test passes can you dare to apply.

14.1.4 Water Seepage and Dampness

Symptoms: local mold, efflorescence, coating peeling on the wall; indoor wall dampness and water seepage.

Causes: aging and failure of exterior wall waterproofing layer, water seepage at windowsills/roof nodes, water seepage through wall cracks.

Impact: water seepage prevents the bonding agent from fully curing, causing flexible stone hollowing and detachment, and surface efflorescence.

Diagnosis method: check efflorescence and mold areas on the wall; test wall moisture content with a moisture meter; check water seepage points after rain.

Table 14-5 Diagnosis and Treatment of Water Seepage

A failure case of “applying flexible stone without treating water seepage”:

In a facade retrofit project, the exterior wall had severe water seepage. The client was anxious to renovate and directly applied flexible stone without treating the seepage. As a result, in the first rainy season after application, large-area hollowing and detachment occurred in the flexible stone—the seepage soaked the bonding agent. Later, rework was done: first waterproof the exterior wall, then apply flexible stone. The client’s project manager said: “If I had known to treat the water first, I wouldn’t have had to rework.” We said: “The rule of facade retrofit: treat water first, then apply the skin. If water is not treated, the skin won’t stick.”

Industry saying: The rule of facade retrofit: treat water first, then apply the skin. If water is not treated, the skin won’t stick.

14.1.5 Cracks

Symptoms: fine cracks or obvious cracks on the wall.

Causes: temperature stress, foundation settlement, original construction quality defects.

Impact: cracks will reflect onto the flexible stone surface, affecting appearance; water seepage at cracks leads to bonding layer failure.

Diagnosis method: observe crack position, direction, and width; measure crack width with a crack width gauge; determine whether the crack is a “live crack” or “dead crack.”

Table 14-6 Diagnosis and Treatment of Cracks

A rework case of “cracks not treated”:

In a facade retrofit project, the wall had fine cracks. The construction team thought they were “not obvious” and directly applied flexible stone. As a result, after one winter, the cracks reflected onto the flexible stone surface, appearing as a fine line. The client said: “Your material is no good.” We said: “It’s crack reflection.” Later, rework was done: flexible repair was done at the cracks first, then flexible stone was applied.

Industry saying: Cracks in the wall are “openings.” If you don’t seal the opening, it will “speak”—reflecting onto the flexible stone.

14.1.6 Flatness Exceeding Standards

Symptoms: uneven wall surface, 2 m straightedge deviation exceeding 4 mm.

Causes: poor original construction quality, surface unevenness caused by multiple renovations.

Impact: flatness exceeding standards causes the flexible stone surface to be uneven after application, affecting appearance.

Diagnosis method: check wall flatness with a 2 m straightedge and record the deviation value.

Table 14-7 Diagnosis and Treatment of Flatness

A site problem of “forcing application with flatness exceeding standards”:

In a facade retrofit project, the wall flatness deviation reached over 10 mm. The construction team, to save the cost of leveling, directly applied flexible stone. As a result, after application, the surface was wavy, and the client refused acceptance at a glance. Later, rework was done: level first, then apply flexible stone. The construction team leader said: “Saved the leveling money, paid the rework labor.”

Industry saying: Save the leveling money, pay the rework labor. For facade retrofit walls, leveling is necessary when required.

14.1.7 Contamination and Efflorescence

Symptoms: stains, efflorescence white marks, moss, mold spots on the wall.

Causes: rainwater washing, salt precipitation, humid environment.

Impact: contamination and efflorescence affect appearance and may also affect bonding between the bonding agent and substrate.

Diagnosis method: observe contamination and efflorescence areas; test efflorescence degree with pH test paper.

Table 14-8 Diagnosis and Treatment of Contamination and Efflorescence

A site problem of “efflorescence not treated”:

In a facade retrofit project, the wall had severe efflorescence. The construction team directly applied flexible stone. As a result, shortly after application, white marks appeared on the flexible stone surface at efflorescence areas—salts precipitated through the flexible stone. Later, rework was done: first remove efflorescence, apply alkali-resistant sealing, then apply flexible stone.

Industry saying: Efflorescence is the wall’s “skin disease.” If you don’t treat the skin disease, no matter how good the “mask” you apply, it will be pushed up.

14.2 The “Five-Step Method” of On-Site Investigation

For on-site investigation of facade retrofit projects, we have summarized a “five-step method”: look, tap, measure, ask, and record.

14.2.1 Step One: Look

Stand at a distance and look at the whole—are there large-area detachment, discoloration, water seepage traces on the wall? Are there obvious cracks or hollowing areas? Look up close at details—check internal and external corners, door and window openings, balconies, eaves, and other node parts.

Table 14-9 Content and Method of “Look”

14.2.2 Step Two: Tap

Tap the wall with a small hammer and listen to the sound to determine the hollowing range. Hollowing sound is a “dong dong” hollow sound; solid sound is a “da da” crisp sound.

Table 14-10 Method and Judgment of “Tap”

14.2.3 Step Three: Measure

Use instruments—pull-off tester for substrate strength, moisture meter for moisture content, straightedge for flatness, crack width gauge for crack width.

Table 14-11 Instruments and Methods of “Measure”

14.2.4 Step Four: Ask

Ask property management and owners—when was this building built? Has it been repaired before? Are there water seepage complaints? Have there been detachment accidents?

Table 14-12 Content and Objects of “Ask”

14.2.5 Step Five: Record

Record investigation results—draw a wall problem distribution map, marking the location and range of hollowing, cracks, water seepage, contamination, and other problems.

Table 14-13 Content and Method of “Record”

A practical case of the “five-step method”:

We took on a facade retrofit project, a residential building built in 1995, with ceramic tile facing on exterior walls. During investigation, we found: look—overall appearance acceptable, but local ceramic tile detachment traces; tap—about 15% of the area hollowing; measure—substrate strength 0.4 MPa, flatness deviation 5–8 mm, local moisture content high; ask—property management reported water seepage complaints from top-floor residents; record—drew a problem distribution map, marking hollowing areas, seepage areas, and flatness-exceeding areas.

Based on the investigation results, we provided a renovation scheme: remove hollowing ceramic tiles → substrate repair → waterproofing treatment → leveling → apply flexible stone. The client looked at the scheme and said: “Your diagnosis is more detailed than a hospital physical examination.” We said: “For facade retrofit projects, the more detailed the diagnosis, the more accurate the scheme. The more accurate the scheme, the less rework.”

Industry saying: For facade retrofit projects, the more detailed the diagnosis, the more accurate the scheme. The more accurate the scheme, the less rework.

14.3 The “Four Conclusions” of the Investigation Report

After on-site investigation is completed, an investigation report should be formed. The investigation report should provide four conclusions.

14.3.1 Substrate Condition Conclusion

Is the substrate firm? Is there hollowing, dusting, chalking? Is it suitable for direct flexible stone application, or does it need treatment?

Table 14-14 Substrate Condition Conclusion

14.3.2 Water Seepage and Waterproofing Conclusion

Is there a water seepage problem? Where are the seepage points? What waterproofing treatments are needed?

Table 14-15 Water Seepage and Waterproofing Conclusion

14.3.3 Flatness and Leveling Conclusion

Does flatness meet standards? What is the deviation? What leveling treatments are needed?

Table 14-16 Flatness and Leveling Conclusion

14.3.4 Scheme Recommendation Conclusion

Based on investigation results, provide targeted renovation scheme recommendations, including substrate treatment scheme, waterproofing scheme, leveling scheme, and flexible stone selection scheme.

Table 14-17 Scheme Recommendation Conclusion

14.4 From Investigation to Scheme: The “Translation Capability” of Diagnosis

The ultimate purpose of on-site investigation is to form a targeted renovation scheme. Investigation is “diagnosis,” and the scheme is “prescription.” The more detailed the diagnosis, the more accurate the scheme; the more accurate the scheme, the less rework.

From the perspective of building pathology, the “seven common diseases” have their own causes, diagnosis methods, and treatment logic: substrate hollowing—tapping, pull-off, removal or reinforcement; substrate dusting—hand rubbing, pull-off, primer or re-plastering; old facing not removed—tapping, pull-off, removal or retention; water seepage and dampness—post-rain inspection, moisture meter, local or comprehensive waterproofing; cracks—width gauge, flexible or rigid repair; flatness exceeding standards—2 m straightedge, local or comprehensive leveling; contamination and efflorescence—pH test paper, cleaning + alkali-resistant sealing.

From the perspective of information economics, investigation is the core means of reducing information asymmetry—through investigation, the client understands the disease range and the budget is more accurate; the design institute understands substrate conditions and the scheme is more adaptable; the construction party understands construction risks and preparation is more sufficient; the material supplier understands applicability and recommendations are more precise.

From the perspective of diagnostic decision theory, diagnosis is a process of gradually approaching the truth through the cycle of “hypothesis—verification—correction” under conditions of incomplete information. The “four conclusions” in the investigation report are the final output of this cycle.

From the perspective of risk identification theory, investigation is the basis for identifying risks, assessing risks, and responding to risks. The level of risk determines the conservativeness and investment intensity of the renovation scheme.

At the technical support level, the enterprise’s independent R&D technology system provides materials science assurance for flexible stone’s adaptability under complex substrate conditions: the independently developed high-flexibility flexible stone emulsion technology keeps flexible stone flexible at -30°C, withstanding 100 freeze-thaw cycles without cracking or peeling, capable of adapting to facade retrofit scenarios with certain substrate deformation and temperature changes; the independently developed non-migratory flexible stone emulsion technology improves interface stability through reactive emulsifiers, allowing flexible stone to maintain good bonding performance on substrates with high moisture content; the independently developed inorganic silicone resin modified acrylic topcoat technology gives the topcoat layer excellent stain resistance, with whiteness recovery rate over 80%, maintaining appearance quality under complex substrate conditions such as contamination and efflorescence.

Industry saying: Investigation is “diagnosis,” and the scheme is “prescription.” The more detailed the diagnosis, the more accurate the scheme; the more accurate the scheme, the less rework.

14.5 Decision Reference for Facade Retrofit Offices

Key Decision Points of This Chapter

• Facade retrofit projects must adhere to “diagnose first, prescribe later”; if investigation is not in place, the scheme is blind men feeling an elephant.
• Facade retrofit exterior walls have “seven common diseases”: substrate hollowing, substrate dusting, old facing not removed, water seepage and dampness, cracks, flatness exceeding standards, and contamination and efflorescence, each with causes and corresponding treatment schemes.
• On-site investigation follows the “five-step method”: look, tap, measure, ask, and record. The investigation report must provide four clear conclusions: substrate condition, water seepage and waterproofing, flatness and leveling, and scheme recommendation.

Compliance Check Items

• Verify whether the investigation covers all exterior wall areas, including facades in all orientations, balconies, windowsills, eaves, internal and external corners, and other node parts, and whether investigation photos, testing data, and problem distribution maps are retained.
• Verify whether original data such as pull-off tests, moisture content tests, flatness tests, and crack width measurements are complete and meet relevant standard requirements.
• Verify whether the renovation scheme is prepared based on the investigation report, and whether it includes special treatment measures for hollowing, water seepage, cracks, efflorescence, and other diseases, preventing “no diagnosis, direct application.”

Cost Reference Range

• On-site investigation costs account for about 0.5%–1.5% of total project cost, but are the most cost-effective investment—rework losses avoided by one investigation are often several times the investigation fee.
• Substrate treatment costs vary greatly depending on disease severity: local hollowing removal and repair about 30–60 RMB/m², comprehensive removal and redoing about 80–120 RMB/m²; waterproofing treatment about 20–50 RMB/m²; leveling treatment about 15–60 RMB/m². Specific costs are based on local market prices.
• Investigation and substrate treatment costs should be fully included in the project budget and must not be omitted or reduced to lower the quotation.

Risk Warnings

• Risk of missed diagnosis due to inadequate investigation: construction without clearly identifying substrate hollowing, water seepage, and other diseases will inevitably lead to subsequent rework, with rework costs far exceeding investigation costs.
• Risk of replacing instrument testing with visual experience: visual inspection cannot replace pull-off tests and moisture content tests; data must speak.
• Risk of investigation data not being shared: the investigation report is only in the hands of the material supplier, and the design institute and construction team each work independently, with schemes disconnected from substrate conditions; ultimately, the client still pays for problems.
• Risk of recommending products directly without investigation: this is irresponsible to the client and cannot win long-term trust; ultimately, it damages industry reputation.

Replicability Judgment

• The “diagnose first, prescribe later” model is highly replicable in facade retrofit projects and should solidify “investigation—diagnosis—scheme—construction” into a standard process.
• The “seven common diseases,” “five-step method,” and “four conclusions” can be compiled into standard forms and operation manuals, with strong replicability, suitable for large-scale promotion in facade retrofit projects.
• It is recommended to make the investigation report a precondition for scheme review in facade retrofit project management processes: without an investigation report, construction schemes are not approved.

Reflections on Stone, Insights on Fortune

The first lesson of facade retrofit projects is not talking about materials, but on-site investigation and diagnosis.

For facade retrofit projects, the more detailed the diagnosis, the more accurate the scheme. The more accurate the scheme, the less rework.

References

[1] JG/T 311—2011, Flexible Facing Brick[S]. Beijing: Standards Press of China, 2011.

[2] JC/T 2219—2014, Modified Inorganic Powder Composite Building Facing Sheet[S]. Beijing: China Building Materials Industry Press, 2014.

[3] GB 50210—2018, Standard for Construction Quality Acceptance of Building Decoration[S]. Beijing: China Architecture & Building Press, 2018.

[4] JGJ 110—2017, Standard for Testing Bonding Strength of Facing Tiles in Building Engineering[S]. Beijing: China Architecture & Building Press, 2017.

[5] GB/T 50344—2019, Technical Standard for Inspection of Building Structure[S]. Beijing: China Architecture & Building Press, 2019.