Stripping day. The last panel comes off a ground floor column, somebody photographs it, and ten minutes later a group chat has four opinions in it. Cosmetic. Render it before the consultant arrives. Break it out and recast.
None of those is an answer. The file needs a disposition: what the defect is, how deep it goes, whether it matters structurally, what the repair is, who accepts it. The engineering is in the classification, not the mortar.
Why this trips people up
Honeycombing usually looks worse than it is, and occasionally far better. Exposed aggregate stopping inside the cover is a durability problem. A tidy line of grout loss at a form joint can run through to the far face. A photograph cannot separate them.
The code will not settle it either. The Philippine structural code's concrete provisions, following ACI 318 in substance, require concrete to be consolidated so it fills the forms around the reinforcement without voids, and the specification will normally require the repair to restore code cover. What neither NSCP nor ACI 318 gives you is an acceptance criterion for honeycombing or a repair method. Those sit in ACI 301 and in the project specification, in its provisions for repair of defective areas, and that is what a stripped column is: nonconforming new work, not an existing structure being assessed. Acceptance rests with the designer of record under the project specification.
Classify before you repair
One caution before the list. Class 1, 2 and 3 below are this article's own shorthand for severity. They are not terms defined in ACI, ICRI or NSCP, so do not write "Class 2" on a non-conformance report or quote it to a consultant as though it were a standard designation. Use it to order your own thinking, then describe the defect in plain words on the record.
- Class 1, cover only. The void stops inside the cover and never reaches steel. A durability, fire protection and appearance matter, repaired against a pre-approved procedure.
- Class 2, reinforcement reached. A tie or main bar is exposed, or stripped of the concrete around it. That concrete was transferring force and keeping aggressive agents out, so this is a bond and corrosion problem needing the designer's written agreement.
- Class 3, structural. The void passes through the section, both faces sound drummy at one level, or it sits in a load path: a lap splice zone, a beam column joint, a bearing anchorage. Never a site decision.
Position decides, not size: a 100 mm patch inside a lap splice outranks a 900 mm patch of shallow honeycomb.
Find the extent instead of guessing it
- 1. Sound it before anybody touches it. Paint the drummy boundary and photograph it with a scale. It is almost always larger than the visible defect, which is only where paste failed to close at the face.
- 2. Chip at the worst point only. You want the depth to sound concrete, not a finished profile. Stop when the hammer rings.
- 3. Compare that depth with the cover geometry. Cover, tie and bar diameters give four planes: outside of tie, outside of bar, bar centre, back of bar. A cover meter finds the steel, not the soundness around it.
- 4. Check whether the void passes through. Sound the far face and both returns at that level. If a probe goes through, you have left patch repair territory.
- 5. Name the cause first. Segregation from a dropped pour puts aggregate low in the lift and repeats on every column poured that way. Vibration failure leaves pockets behind congested steel. Form leakage leaves a lean, clean-edged line, deeper than it looks.
Repairing without naming the cause guarantees a repeat on the next pour.
Repair families and their limits
- Cementitious patch repair. Chip to sound concrete, square the perimeter, prime, build up in the manufacturer's layers. Restores cover, not continuity.
- Flowable micro-concrete in formed pours. For larger or deeper voids; needs formwork and a saturated surface dry substrate.
- Pressure grouting. For narrow, deep voids chipping cannot reach economically. It fills, but does not compact.
- Full removal and recast. Section compromised, or bond lost over a length that matters. Designed temporary works, not a repair.
Worked example: a 400 mm column with one bad face
Column 400 mm by 400 mm, cover 40 mm, main bars 20 mm, ties 10 mm, eight bars with three on the affected face, lift 3.0 m. Honeycombing shows 600 mm by 350 mm, sounding 700 mm by 400 mm, the full face width, and chipping reaches sound concrete at 65 mm. Rates are illustrative.
What this disposition assumes
Every number below rests on inputs a real disposition would have to state. They are listed here because several of them change the answer.
- Concrete strength, bar grade and the column's axial utilisation are never given. This is the gap that matters most, and it is the reason the section loss below cannot be settled from the geometry alone. Whether losing 16 to 19 per cent of gross area matters at all depends on the demand to capacity ratio of that column, and that ratio is nowhere in the inputs. A lightly loaded column and one running at 0.7 Pn produce opposite dispositions from identical geometry.
- Where the 700 mm defect sits within the 3.0 m lift is not stated. Step 4 conditions the entire decision on whether it reaches the lap splice zone above the construction joint, so nobody can apply this example to their own column without that dimension.
- No propping or temporary support is priced in the repair option, while the recast option carries ₱28,000 for it. The repair opens the section to 90 mm behind three bars over 800 mm of a loaded column lift. If that condition needs any temporary support, the cost ratio below collapses, and that comparison is this article's main argument.
- Average removal depth 55 mm. Labelled illustrative, and the whole material take-off hangs on it. At 54 mm the total is 0.02583 m³ = 1.99 bags and you order 2, not 3: a 1 mm change in an assumed number moves ₱1,450 of cost.
- Bag yield 13 litres per 25 kg. Also illustrative, and it is the divisor that puts the order on a knife edge. At 12 litres per bag you need 2.17 and order 3 with margin; at 14 litres you need 1.86 and order 2.
- Undercut clearance 20 mm behind the bars, giving 70 + 20 = 90 mm, and a strip width of 20 + 20 + 20 = 60 mm. Both assumed, neither sourced, and together they drive the undercut volume and the opened section.
- Tie spacing 100 mm and tie length 1.4 m. Neither is an input. At 150 mm spacing you get 21 ties, steel drops to about 97 kg and the recast total to roughly ₱46,000. A 320 mm by 320 mm tie perimeter is 1.28 m, so 1.4 m implicitly assumes about 60 mm per hook.
- Lap length 1.0 m for the 20 mm main bars, used inside the 8 × (3.0 + 1.0) steel take-off. No basis is given, and a lap depends on concrete grade, bar grade, splice class and confinement. 1.0 m is at the short end for a Class B tension splice.
- Exposure condition is not stated. The Class 2 reasoning leans on keeping aggressive agents out, but for an interior ground floor column carbonation, not chloride, is usually the driver, and that changes the urgency of the disposition rather than its classification.
Step 1: where is 65 mm, relative to the steel?
- Outside of tie = 40 mm (the cover)
- Outside of main bar = 40 + 10 = 50 mm
- Centre of main bar = 40 + 10 + 10 = 60 mm
- Back of main bar = 40 + 10 + 20 = 70 mm
So 65 mm is 65 − 50 = 15 mm past the outer face of the bar and sits 65 − 60 = 5 mm beyond the bar centre. Read that 5 mm correctly: it is the height of the embedded circular segment still buried, the offset of the chipped plane past the centre, not a 5 mm skin of concrete behind the bar. The plane stops 70 − 65 = 5 mm short of the back of the bar, and the core deeper than 70 mm is untouched, so nothing here is 5 mm from being punched through. The half angle of the embedded arc has a cosine of 5 ÷ 10 = 0.5, or 60 degrees, so the embedded arc = 2 × 60 = 120 degrees and the exposed arc = 360 − 120 = 240 degrees. Since 240 ÷ 360 = 0.667, two thirds of that bar, at the point that was chipped, has no sound concrete on it: a bond question, not a cosmetic one.
Step 2: screening estimate of section loss
- Gross area = 400 × 400 = 160,000 mm²
- Loss at the chipped depth across the sounded width = 400 × 65 = 26,000 mm²
- 26,000 ÷ 160,000 = 0.1625, that is 16.25 per cent
- Remaining = 160,000 − 26,000 = 134,000 mm², or 83.75 per cent
Two fair objections. Cover outside the ties is not counted as confined core, so 16.25 per cent overstates the strength effect while ignoring the fire and corrosion protection it gave. Treat that as an engineering convention, borrowed from the way confinement provisions and ASCE 41 style assessments define the core, rather than as an established practice you can cite at somebody. And a tie is anchored by its hooks, not by bond along the leg.
Two more things about the 16.25 per cent. The 65 mm was measured at the worst point only, so applying it uniformly across the full 400 mm is an assumption presented as a measurement. And it is not the figure that governs the decision. Step 3 removes material to 90 mm behind three 60 mm strips, so the section actually open during the repair is about 400 × 65 + 3 × 60 × 25 = 30,500 mm², or 19.1 per cent of gross. That temporary condition, not the 16.25 per cent screening figure, is the number a reader should carry forward. Both remain screening figures rather than capacity checks: the real loss depends on void geometry, which only chipping confirms, and on the concrete strength, bar grade and utilisation this example never gives.
Step 3: how much repair material
Common practice is to cut back beyond the unsound boundary and leave a square shoulder rather than a feathered edge. The International Concrete Repair Institute's surface preparation guidance is the reference for the edge itself, a perimeter cut perpendicular to the surface with no feathering and a stated surface profile. It does not fix a lateral cut back distance beyond the unsound boundary, so the 50 mm used here is illustrative and has nothing behind it but convenience. Keep the perimeter saw cut shallow, of the order of 10 to 13 mm, or on this very column it saws through ties at 40 mm and main bars at 50 mm.
- Patch height = 700 + 50 + 50 = 800 mm; width = 400 mm, the full face, since the cut back cannot be squared sideways without turning the arris
- Patch face = 800 × 400 = 320,000 mm² = 0.32 m²
- Primed area = the face plus the shoulder standing around it: 0.32 + (2 × (0.800 + 0.400) × 0.055) = 0.32 + 0.132 = 0.452 m², say 0.45 m²
- Illustrative average removal depth 55 mm: 0.800 × 0.400 × 0.055 = 0.0176 m³
- Undercut behind each bar to 70 + 20 = 90 mm, so 90 − 55 = 35 mm extra over a 20 + 20 + 20 = 60 mm strip: 0.800 × 0.060 × 0.035 = 0.00168 m³, and 3 × 0.00168 = 0.00504 m³
- Subtotal = 0.0176 + 0.00504 = 0.02264 m³
- Add 15 per cent for mixing loss and overfill, a common method statement allowance and not a code figure: 0.02264 × 0.15 = 0.003396 m³
- Total = 0.02264 + 0.003396 = 0.026036 m³ = 26.0 litres
- At an illustrative 13 litres per 25 kg bag: 26.036 ÷ 13 = 2.003 bags. Bags are ordered whole and rounded up, so that is 3 on site. Be honest about what that does: 3 bags on top of an already applied 15 per cent allowance is close to a 50 per cent double margin, and those bags carry ₱4,350 of the ₱16,198 repair total below, and therefore the cost ratio.
- Treat this as a formed pour rather than hand application. The driver is not a general rule about layer thickness, since many hand applied mortars permit 40 to 50 mm per layer and expressly allow building up in layers, as recommended earlier. It is the undercut to 90 mm behind three bars, the 0.4 m face width and the vertical build up. The product data sheet settles it, not a generalisation about mortars.
Step 4: the threshold
The trigger is the load path, not a percentage.
This stops being a patch repair decision the moment the defect touches the load path or the bond, not at a percentage. Two thirds of a bar is exposed at the worst point, over a debonded length of at most 700 mm, which is the sounded extent rather than the 800 mm patch, since the patch includes 50 mm of cut back into sound concrete at each end. If that length reaches the lap splice zone above the construction joint, it goes to the designer of record automatically, and this example never says where in the 3.0 m lift it sits. Either way, a defect this size needs the designer's written acceptance of classification and method.
Step 5: illustrative cost of the two options
Repair, with designer acceptance:
- Material: 3 bags × ₱1,450 = ₱4,350
- Primer over 0.45 m² at ₱550 per m²: 0.45 × 550 = ₱248
- Formwork and hopper: ₱1,200
- Labour, two masons at ₱850 and one helper at ₱600: (2 × 850) + 600 = ₱2,300 per day × 3 days = ₱6,900
- Verification and record: ₱3,500
- Total = 4,350 + 248 + 1,200 + 6,900 + 3,500 = ₱16,198, with no temporary support in it
Demolish and recast the lift:
- Lift volume = 0.400 × 0.400 × 3.0 = 0.48 m³
- Designed propping of the floor above, lump sum: ₱28,000
- Demolition and disposal at ₱6,500 per m³: 0.48 × 6,500 = ₱3,120
- Main bars: 0.7854 × 20² = 314.2 mm², so 314.2 ÷ 1,000,000 × 7,850 = 2.47 kg per m; 8 × (3.0 + 1.0 lap) = 32.0 m; 32.0 × 2.47 = 79.04 kg
- Ties: 0.7854 × 10² = 78.5 mm², so 78.5 ÷ 1,000,000 × 7,850 = 0.616 kg per m; 3,000 ÷ 100 = 30 spaces, so 31 ties × 1.4 m = 43.4 m; 43.4 × 0.616 = 26.73 kg
- Steel = 79.04 + 26.73 = 105.77 kg, say 106 kg at ₱68 per kg fixed: 106 × 68 = ₱7,208
- Concrete: 0.48 m³ needed, 1.0 m³ minimum load billed at ₱5,200 = ₱5,200
- Formwork: 4 × 0.400 × 3.0 = 4.8 m² at ₱650 per m² = ₱3,120
- Total = 28,000 + 3,120 + 7,208 + 5,200 + 3,120 = ₱46,648
That is 46,648 ÷ 16,198 = 2.88 times the direct cost, and the schedule costs more again. The repair runs 3 days, the same 3 days its labour is priced at, plus 2 before the next lift is loaded, so 5. The recast runs 3 to prop, 2 to demolish, 2 to fix and form, 1 to pour and an illustrative 14 before props are struck: 3 + 2 + 2 + 1 + 14 = 22 days, so 22 − 5 = 17 days lost. At an illustrative ₱12,000 per day that is 17 × 12,000 = ₱204,000. This prices a repair the designer has accepted; it does not justify downgrading the classification.
The record that survives an audit
What the file needs, in this order.
Photograph with a scale and the element mark. Dimensioned sketch referenced to the construction joint. Sounding map, not just the visible boundary. Chipping depth and where it was taken. Classification and reasoning. Cause, with the corrective action for the next pour. Method and product. Designer acceptance, dated before work starts. Verification by re-sounding.
The same defect on an architectural fair faced column is a different decision from one that will be plastered, because the criteria then include colour, texture and edge line. And the procedure belongs in the file before stripping season, not at 5 pm with a subcontractor waiting.
Common pitfalls
- Plastering over honeycombing before it is recorded, turning a repairable defect into a concealed one.
- Feathering the edges of a patch instead of cutting a square perimeter. Thin edges shrink, curl and debond.
- Using a shrinkage prone site mortar for a structural repair. Restoring the shape is not restoring the section.
- Sizing the repair off the photograph rather than the sounded boundary, treating one face as the whole defect.
- Pricing labour for one duration and writing another into the programme, which is how a cost comparison quietly stops meaning anything.
- Letting the same pour method, poker and drop height continue on the next column.
Where the arithmetic gets fudged
Almost every number above is geometry or quantity: cover planes, section areas, patch volumes, bar masses, all guessed at while the pour card waits. The RHCES web tools page has calculators for them.
FAQ
Can we render it now and raise it later?
No. Rendering destroys the evidence needed to classify the defect, and any chance of proving the repair sound. A recorded defect with an accepted disposition is normal; a concealed one is a finding.
Who signs the acceptance?
Split it. The designer of record owns the classification and method for anything reaching steel. The contractor owns the workmanship, the QA/QC engineer the verification record. One signature carrying all three is how files fail an audit.