Epoxy-coated rebar needs longer laps than plain bar. Under CSA A23.3, the coating factor k2 multiplies the development length by 1.5 when clear cover is less than 3 bar diameters or clear spacing is less than 6 bar diameters, and by 1.2 for all other epoxy-coated bars, with the combined top-bar and coating factor capped at 1.7. Because a tension lap is a multiple of the development length, a standard Class B lap on coated bar ends up 20% to 50% longer than the same lap on uncoated bar.
This post explains where the factor comes from, gives a worked chart for 10M to 35M, and covers hooks, compression laps and couplers on coated bar.
Why the coating changes the lap
A lap splice works by passing force from one bar into the concrete and back into the next bar. That depends on the bar's ribs bearing against the concrete and on friction and adhesion along the bar surface.
Fusion-bonded epoxy is smooth and slippery compared with mill-finish steel. The ribs still bear, but adhesion and friction drop, so the bar needs more embedded length to develop the same force. The effect is worst where cover or spacing is tight, because a slippery bar is more likely to split the concrete around it. That is why CSA A23.3 has two values for the factor.
This is also the main reason swapping plain bar for coated bar, or the reverse, is a design change. Our guide on when epoxy-coated rebar is required covers why it gets specified in the first place.
The coating factor in CSA A23.3
CSA A23.3 Clause 12 builds tension development length (ld) from the bar size, steel and concrete strength, and four modification factors. Our lap splice chart for metric bars shows the full simplified equation. For coated bar, the relevant factors are:
| Factor | Condition | Value |
|---|---|---|
| k2 (coating) | Epoxy-coated, clear cover less than 3 db or clear spacing less than 6 db | 1.5 |
| k2 (coating) | All other epoxy-coated bars | 1.2 |
| k2 (coating) | Uncoated bars | 1.0 |
| k1 (bar location) | Top bars (more than 300 mm of fresh concrete cast below) | 1.3 |
| k1 × k2 | Combined limit | Need not exceed 1.7 |
"db" is the nominal bar diameter, so 3 db for a 15M bar (16.0 mm) is 48 mm and 6 db is 96 mm.
Which factor applies? In a parking deck with 60 mm cover and 15M bars at 300 mm, clear cover is more than 48 mm and clear spacing is far more than 96 mm, so the factor is 1.2. The same 15M bars with 40 mm of cover would take 1.5. Larger bars hit the 1.5 condition sooner: for 25M (25.2 mm), 3 db is about 76 mm, which is more than the 60 mm cover used for chloride exposure classes. The engineer sets the factor for each element; this example only shows how the rule works.
The 1.7 cap matters for top bars. A top bar with k2 = 1.5 would be 1.3 × 1.5 = 1.95 times the base length, but A23.3 caps the product at 1.7. Top mats in coated decks are common, so this cap shows up often.
Lap length chart for epoxy-coated bar
Assumptions for every number in this table:
- CSA A23.3 simplified method (Clause 12.2.3) with the 0.45 coefficient, which requires minimum cover, spacing and transverse reinforcement as explained in our uncoated lap chart.
- Grade 400 bar, normal-density concrete, f'c = 30 MPa.
- Class B tension splice = 1.3 × ld, with ld not less than 300 mm. Rounded up to the next 10 mm.
- Top bar values use k1 × k2 capped at 1.7.
| Bar | Uncoated, bottom | Epoxy k2 = 1.2, bottom | Epoxy k2 = 1.5, bottom | Epoxy k2 = 1.2, top | Epoxy k2 = 1.5, top |
|---|---|---|---|---|---|
| 10M | 390 mm | 470 mm | 580 mm | 610 mm | 660 mm |
| 15M | 550 mm | 660 mm | 830 mm | 860 mm | 930 mm |
| 20M | 670 mm | 800 mm | 1,000 mm | 1,040 mm | 1,140 mm |
| 25M | 1,080 mm | 1,300 mm | 1,620 mm | 1,680 mm | 1,840 mm |
| 30M | 1,280 mm | 1,540 mm | 1,920 mm | 2,000 mm | 2,180 mm |
| 35M | 1,530 mm | 1,840 mm | 2,290 mm | 2,380 mm | 2,600 mm |
For other concrete strengths, the lap scales with 1 ÷ √f'c. As a check at the worst case (k2 = 1.5, top bars), 15M comes to about 1,020 mm in 25 MPa concrete and 870 mm in 35 MPa concrete.
When this chart does not apply: the same limits as for uncoated bar. Where the simplified method's conditions are not met, A23.3 uses the 0.6 coefficient and laps get one third longer. Bundled bars, low-density concrete, 500W bar and the detailed method all change the result. Lap splices are not permitted for bars larger than 35M, apart from limited compression cases, just as for uncoated bar. The lengths on the structural drawings always govern.
Hooks and development length
Development length (ld) on its own matters wherever a coated bar has to be anchored without a lap: bars ending at a support, dowels into a footing, or top bars running past a column. The same k2 factor applies to straight development. For a fuller explanation of development length in general, see our guide to rebar development length.
Hooked bars. CSA A23.3 handles standard hooks with a separate basic hook development length, then applies modification factors. One of those is a factor of 1.2 for epoxy-coated bar. A hook in coated bar therefore needs 20% more embedment than the same hook in plain bar, which can affect footing depths and wall thicknesses where dowels hook into a footing.
Compression. The A23.3 expressions for compression development length and compression lap splices do not include a coating factor. Column bars that are only ever in compression can use the same compression laps as uncoated bar. If the engineer has detailed column laps as tension laps (because of load reversal or seismic design), the coating factor comes back in.
Couplers and other options on coated bar
Long laps on coated bar cost steel, take up space and add congestion. Designers often reduce them in one of these ways:
- Mechanical couplers. They remove the lap entirely and are not affected by bond. On epoxy jobs, the specification usually calls for coated couplers or for the coupler and any coating damage around it to be patched with the approved repair material. Our post on rebar couplers vs lap splices covers the types.
- Bigger cover or wider spacing. Pushing cover above 3 db and spacing above 6 db drops k2 from 1.5 to 1.2.
- The detailed method. The full equation in A23.3 Clause 12.2.2 accounts for actual cover and confinement and can shorten laps where conditions are generous.
- Staggered laps. These do not shorten the lap but keep long laps from all landing in one section.
Getting coated laps right on the bar list
Most lap errors on epoxy jobs are detailing errors, not design errors:
- Check the general notes. Many drawings give one lap table for uncoated bar and a separate one, or a multiplier, for coated bar. Make sure the bar list uses the right one for each element.
- Separate coated and uncoated marks. Coated bars are a different item on the bar list and are fabricated and bundled separately.
- Watch elements that mix both. Where coated deck bars lap with plain bars from below, the drawings should say how the lap is calculated. If they do not, ask.
- Add the extra weight. Longer laps mean more tonnage, which matters for ordering and for the cost comparison against other systems. See epoxy-coated rebar cost for what drives price.
We prepare bar lists and placing drawings with laps built in from your drawings, then cut, bend and tag the bar. We supply black steel and GFRP bar; we don't supply epoxy-coated bar. Send us your drawings for a take-off and quote, or see our services for detailing and fabrication.
Frequently asked questions
Do epoxy-coated bars need longer laps?
Yes. The coating reduces bond with the concrete, so CSA A23.3 applies a coating factor of 1.2 or 1.5 to the development length, and the lap grows with it. Laps can be up to 50% longer than for the same uncoated bar.
When is the epoxy coating factor 1.5 instead of 1.2?
CSA A23.3 uses 1.5 for epoxy-coated bars with clear cover less than 3 bar diameters or clear spacing less than 6 bar diameters, and 1.2 for all other epoxy-coated bars. The engineer decides which applies to each element.
What is the lap length for epoxy-coated 15M rebar?
Using the CSA A23.3 simplified method with Grade 400 bar in 30 MPa concrete, a Class B lap for 15M bottom bars works out to about 660 mm with the 1.2 factor and 830 mm with the 1.5 factor, against about 550 mm uncoated. Use the lengths on your drawings.
Does epoxy coating affect compression laps?
The CSA A23.3 expressions for compression development and compression lap splices do not include a coating factor, so compression laps are calculated the same way as for uncoated bar. Bars that see tension still need the tension lap with the coating factor.
Can you use couplers on epoxy-coated rebar?
Yes. Mechanical couplers avoid long laps and are common on coated bar. The coupler and any damaged coating around it need to be protected as the project specification requires, usually with coated couplers or epoxy patching.
