8-Inch 300GSM Unidirectional Carbon Fiber — The Standard Strap for Poured Concrete Foundation Walls
The Right Width for Most Residential Poured Concrete Walls. Balanced Bond Area, Reliable Reinforcement, Sold by the Foot.
8-inch width — the industry-standard strap dimension for poured concrete basement walls
300GSM unidirectional fiber — least elongation before full load, resists crack movement immediately
Ideal for moderately bowed poured concrete walls and corner reinforcement
800ml of Startech structural epoxy included per 10 ft ordered
Install at maximum 4 ft on center — vertical or horizontal
Unidirectional outperforms woven — woven fabric allows movement before engaging under load
Roller tray, roller, trowel, mixing bucket, gloves and instructions included
10 ft minimum order — upgrade to 150 ft for volume discount
Grinding equipment required to prepare wall surface before application
Free Technical Support — 1-866-445-3984
Ships USA & Canada
Why 8 Inches Is the Standard Width for Poured Concrete Walls
Poured concrete basement walls typically bow inward along their mid-height under lateral soil pressure — the point furthest from the floor slab at the base and the rim joist at the top. An 8-inch strap applied vertically at this zone provides sufficient bonding area to transfer tensile load into the strap and away from the crack or bowing point, without over-specifying a wider fabric that would be wasteful on a substrate where the concrete is still reasonably sound.
The 8-inch width has become the residential standard because it matches the realistic load-transfer capacity of typical poured concrete. The governing limit is almost never the carbon fiber — it is the tensile strength of the concrete behind it. An 8-inch strap on a sound poured wall concentrates load effectively. The same logic explains why the 12-inch version exists: when the substrate is weaker — cinder block, compromised mortar joints, or deteriorated concrete — the wider strap spreads load over more bonding area to avoid debonding before the fiber can work.
For most residential poured concrete basement walls with diagonal or vertical cracking and early to moderate inward bowing, 8-inch 300GSM is the appropriate specification. If you are unsure whether your wall qualifies, call 1-866-445-3984 — our team can advise based on wall thickness, crack pattern and degree of movement.
Why Unidirectional Fabric — Not Woven
Woven carbon fiber fabric is bidirectional — fibers run both lengthwise and crosswise. This gives it flexibility in both directions, which sounds advantageous but is a problem for concrete reinforcement. Before a woven strap can resist load in its primary direction, the weave must first straighten out and take up any slack in the interlocked fibers. This means the concrete crack can open slightly before the strap engages — potentially enough to propagate the crack or break the epoxy bond at the interface.
Unidirectional 300GSM fabric has all fibers running parallel in a single direction. There is no slack, no weave geometry to straighten. The moment the epoxy cures and bonds the strap to the wall, the fibers are already oriented directly against the direction of load. Resistance begins immediately under the first increment of movement — which is exactly what is needed to prevent re-cracking after epoxy injection.
What Is Included Per Order
8-Inch 300GSM Unidirectional Carbon Fiber (by the foot, minimum 10 ft):
Supplied uncut so you can cut to exact wall heights on site. Tensile Strength 4,100 MPa (ASTM 10618). Tensile Modulus 2.4×10⁵ MPa (ASTM D3039). Elongation at Break 1.6% (ASTM D3039).
Startech Hi-Modulus Fiber Matrix Structural Epoxy — 800ml per 10 ft ordered:
100% solids, solvent-free, two-component moisture-insensitive epoxy. 2:1 mix ratio by volume. Cures as low as 40°F (4°C). Long pot life with high early strength. Bonding strength to concrete ≥ 2.5 MPa pulling to cohesive concrete failure.
Consumables (scaled to order volume):
Roller tray, roller head, square trowel, mixing bucket, nitrile gloves and printed instructions. Disposable items increase proportionally with order length.
Surface grinding equipment is not included. A grinder with a diamond cup wheel and dust shroud is required to prepare the wall before application. If you do not have this equipment, contact us to discuss options.
300GSM Carbon Fiber Technical Specifications
| Property |
Value |
Standard |
| Weave |
Unidirectional |
— |
| Width |
8 in (20.3 cm) |
— |
| Basis Weight |
300 GSM |
— |
| Tensile Strength |
4,100 MPa |
ASTM 10618 |
| Tensile Modulus |
2.4 × 10⁵ MPa |
ASTM D3039 |
| Elongation at Break |
1.6% |
ASTM D3039 |
| Max Roll Length |
164 ft (50 m) |
— |
Installation — 8-Inch Carbon Fiber Straps on Poured Concrete
Watch the installation video →
Before starting: repair any active cracks in the wall using epoxy injection and allow full cure before applying carbon fiber straps. Carbon fiber stabilizes a repaired wall — it does not seal cracks in place of injection.
- Mark strap locations. Plan vertical straps at a maximum of 4 ft on center along the wall. For concentrated bowing at the wall mid-height, tighter spacing (2–3 ft) provides greater resistance. For corner cracks, install a strap on each wall face running away from the corner.
- Prepare the wall surface. Using a grinder with a diamond cup wheel and dust shroud, grind the entire strap contact area to bare concrete. Remove all paint, efflorescence, loose aggregate, and contamination. Vacuum the ground surface thoroughly — any dust remaining on the wall will prevent epoxy bonding.
- Cut straps to length. Lay the carbon fiber flat on a clean surface and cut each strap to the required wall height. Avoid touching the fiber side that will contact the wall — skin oils can affect epoxy adhesion.
- Mix the epoxy. Mix Startech Fiber Matrix Epoxy 2:1 by volume (Part A to Part B) in the mixing bucket until uniform. Mix only as much as you can use within the working time.
- Apply epoxy to the wall. Using the trowel and roller, apply a bed of mixed epoxy to the prepared wall surface over the strap footprint — approximately the full 8-inch width and strap length.
- Saturate the strap. Roll epoxy onto the side of the strap that will face the wall. Both the wall and the strap face should be epoxy-coated before contact.
- Place and press the strap. Position the epoxy-coated strap against the wall with the coated face down. Using the roller, roll firmly from the centre outward to eliminate air pockets and ensure full contact.
- Work epoxy through the fabric. Using the flat face of the square trowel, firmly work additional epoxy into the fabric from the surface inward. The goal is full saturation — the weave should be visibly wetted with no dry fiber visible. Add more epoxy as needed. Keep the strap held firmly against the wall while trowelling.
- Final roll and cure. Re-roll the surface to smooth the epoxy and eliminate any remaining air. Allow to cure fully before applying any coating or paint — typically 24 hours at temperatures above 40°F.
Tips & Notes
1. Repair cracks first. Apply carbon fiber straps after epoxy injection has fully cured, not before. Straps prevent re-cracking — they do not fill cracks.
2. Cold temperatures. Startech epoxy cures as low as 40°F (4°C) — lower than most competing products. In cold basements, allow epoxy to warm to room temperature before mixing.
3. Weak or compromised concrete. If the wall surface is spalling, chalking, or the concrete feels soft, consider the 12-inch 300GSM strap instead — the wider bond area distributes load more effectively on weak substrates.
4. High-load applications. For walls needing maximum stiffness in a narrow strap footprint, see the 6-inch 600GSM or 6-inch 450GSM options.
5. Volume orders. Order 150 ft or more for the maximum volume discount. See the bulk carbon fiber page for contractor pricing across all widths and GSM options.
Common Questions — 8-Inch 300GSM Carbon Fiber
How do I know if 8-inch 300GSM is the right product for my wall?
The 8-inch 300GSM is the correct choice for most residential poured concrete basement walls with moderate inward bowing, diagonal cracking, or vertical cracking where the concrete is still reasonably sound. If the wall surface is spalling, if you are working on CMU or cinder block, or if the concrete shows significant deterioration, use the 12-inch 300GSM instead — the wider strap spreads load over a larger bonding area on weaker substrates. Call 1-866-445-3984 if you are unsure.
Do I need to repair cracks before applying the carbon fiber?
Yes. For poured concrete walls, inject any active cracks with epoxy and allow full cure before applying straps. Carbon fiber prevents re-cracking and resists further wall movement — it does not seal or fill existing cracks. Applying straps over unsealed cracks leaves water pathways in the wall. The epoxy injection kit handles this step.
Why does unidirectional carbon fiber outperform woven fabric for concrete repair?
Woven fabric has fibers interlocked in two directions. Before those fibers can resist load in the primary direction, the weave pattern must first straighten under tension — allowing the wall crack to open slightly before the strap engages. Unidirectional fabric has all fibers parallel in one direction with no weave geometry to take up. Load resistance begins immediately when force is applied. For concrete reinforcement where preventing even minor movement is the goal, unidirectional is the correct specification.
What is the maximum spacing between straps?
Maximum spacing is 4 feet on center, applied vertically or horizontally. For walls with concentrated bowing at mid-height or significant lateral soil pressure, closer spacing of 2–3 feet provides greater resistance. Install straps on both sides of corners and on both wall faces adjacent to windows and door openings where soil pressure tends to concentrate.
Why is surface preparation so important?
The entire load-transfer mechanism depends on the epoxy bond between the carbon fiber and the concrete. Any paint, efflorescence, oil, dust, or loose material at the interface acts as a slip plane — the strap can debond before the fiber reaches its load capacity. Grinding to bare concrete and vacuuming all dust is non-negotiable for a repair that lasts the lifetime of the structure.
Can carbon fiber straps be used horizontally as well as vertically?
Yes. Horizontal straps are used to bridge wall openings such as windows and doors where vertical straps would be interrupted. Install horizontal straps above and below the opening to transfer load around it. Horizontal straps are also used in combination with vertical ones when wall movement is occurring in more than one direction.
How much epoxy is included and is it enough?
800ml of Startech Fiber Matrix epoxy is included per 10 feet ordered, scaled proportionally for larger orders. This is calibrated to the 8-inch width at standard application thickness. Very rough or heavily textured wall surfaces may require slightly more epoxy to fill surface irregularities before the strap seats. If you are working on a particularly rough surface, order a small amount of extra epoxy — call 1-866-445-3984 for guidance.
What other products work with the 8-inch straps?
Questions? Call our free technical support line at 1-866-445-3984.
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