Concrete Countertops Guide
Concrete countertops are custom-cast surfaces made from Portland cement, aggregite, and reinforcement - either poured in place or precast in a shop. The material appeals to homeowners seeking a handcrafted, industrial, or rustic aesthetic that no factory-made product can replicate. This guide covers mix design, forming, finishing, sealing, and the business economics of adding concrete to your fabrication lineup.
TL;DR
- Concrete countertops are either traditional wet-cast (2"+ thick, 25-30 lbs/sq ft) or GFRC (3/4" thick, 10-12 lbs/sq ft)
- Material cost is $5-$15 per square foot; installed price is $65-$150 per square foot
- Fabrication time is 5-10x longer than natural stone - 3-5 days per project minimum
- Cracking and pinholes are the two most common callbacks, both preventable with proper technique
- Revenue per project is high ($3,000-$10,000+) but throughput is low
- Concrete work demands different skills, tooling, and scheduling than stone fabrication
- SlabWise helps shops managing both stone and concrete track jobs, schedule production, and quote accurately
Traditional Wet-Cast vs. GFRC
There are two primary methods for fabricating concrete countertops. Understanding the differences is essential before taking on your first project.
Traditional Wet-Cast
Traditional wet-cast concrete countertops use a standard concrete mix poured into a form, typically 1.5-2 inches thick. The mix includes Portland cement, sand, aggregate, water, and admixtures (plasticizers, fiber reinforcement).
Pros:
- Simpler technique - lower learning curve
- Dense, heavy feel that customers associate with quality
- Lower material cost per batch
Cons:
- Weight: 25-30 lbs per square foot at 2" thickness
- Requires steel or fiber reinforcement against cracking
- Longer cure time (7 days minimum, 28 days for full strength)
- Difficult to transport without cracking
GFRC (Glass Fiber Reinforced Concrete)
GFRC uses a thin (3/4") face coat backed with a glass-fiber-reinforced backer coat. This is the method most professional concrete countertop fabricators use today.
Pros:
- Weight: 10-12 lbs per square foot - comparable to stone
- Superior flexural strength (reduces cracking)
- Faster production cycle (demolding in 18-24 hours)
- Easier to transport and install
Cons:
- Requires spray equipment for backer coat
- Higher material cost (AR glass fibers, polymer admixtures)
- Steeper learning curve - technique matters more
| Factor | Wet-Cast | GFRC |
|---|---|---|
| Thickness | 1.5-2" | 0.75" |
| Weight per sq ft | 25-30 lbs | 10-12 lbs |
| Material cost/sq ft | $3-$8 | $8-$15 |
| Demold time | 3-7 days | 18-24 hours |
| Flexural strength | 400-600 psi | 2,000-3,000 psi |
| Cracking risk | Higher | Lower |
| Equipment needed | Basic forming | Spray equipment |
Mix Design Fundamentals
Getting the mix right is the single most important factor in concrete countertop quality. A bad mix causes cracking, excessive pinholes, poor color consistency, and weak surfaces.
Basic Wet-Cast Mix (Per Cubic Foot)
- Portland cement (Type I or III): 20-25 lbs
- Fine sand (mason's sand): 30-40 lbs
- 3/8" pea gravel (optional): 15-20 lbs
- Water: 8-10 lbs (water-to-cement ratio of 0.35-0.40)
- High-range water reducer (superplasticizer): per manufacturer spec
- Polypropylene fibers: 1-2 lbs per cubic yard
GFRC Face Coat Mix
- Portland cement (white or gray): 1 part
- Fine silica sand (30-50 mesh): 1 part
- Polymer (acrylic or PVA): 7-10% by weight of cement
- Water: to achieve pancake-batter consistency
- Pigment: 3-5% by weight of cement for integral color
GFRC Backer Mix
Same as face coat, plus:
- AR (alkali-resistant) glass fibers: 3-5% by weight of total mix
- Applied via spray-up technique in 3-4 layers, each 1/8-3/16" thick
Critical Rules
- Water-to-cement ratio determines everything. Too much water = weak, porous surface with efflorescence. Target 0.35-0.40 for wet-cast.
- Use superplasticizer instead of extra water to improve workability.
- Mix for a minimum of 5 minutes after all ingredients are combined.
- Integral color should be pre-blended with dry ingredients before adding water.
Forming and Casting
Concrete countertops are cast upside down (the bottom of the form becomes the finished surface). This produces a smooth, dense face with minimal air pockets.
Form Materials
- Melamine-coated particleboard: Most common. Smooth surface, releases well. $15-$25 per 4x8 sheet.
- High-density polyethylene (HDPE): Reusable, excellent release. $80-$120 per 4x8 sheet.
- Silicone caulk: Used for edge profiles and to seal all inside corners.
Forming Tips
- All inside corners get a bead of 100% silicone caulk to prevent sharp edges and air pockets
- Build forms on a dead-flat, level surface (check with a 48" level)
- Reinforce form sides with cleats every 12-16" - wet concrete exerts significant lateral pressure
- For sink knockouts, secure the knockout block with screws from below and seal all edges with silicone
Casting Process
- Apply mold release to all form surfaces
- For GFRC: Spray face coat to 1/8" thickness, allow to firm up (30-60 min)
- For GFRC: Apply backer coat in 3-4 spray passes
- For wet-cast: Pour mix into form, vibrate for 2-3 minutes to release air
- Screed top flat with a straight edge
- Cover with plastic sheeting to retain moisture
- GFRC: Demold at 18-24 hours. Wet-cast: Demold at 3-7 days.
Finishing and Sealing
Finishing transforms a raw casting into a polished countertop. Sealing protects the porous concrete from staining.
Finishing Steps
- Repair pinholes with a slurry of Portland cement, pigment, and polymer (same color as the countertop). Apply with a flexible putty knife, force into holes, wipe excess.
- Wet-sand progressively: 100 → 200 → 400 → 800 → 1500 grit diamond pads (wet process)
- Expose aggregate (if desired) by grinding the surface with 50-100 grit, then polishing through grits
- Apply sealer in 2-3 thin coats
Sealer Options
| Sealer Type | Protection Level | Appearance | Reapplication | Cost |
|---|---|---|---|---|
| Penetrating (silane/siloxane) | Good | Natural matte | Every 1-3 years | Low |
| Topical acrylic | Moderate | Slight sheen | Every 1-2 years | Low |
| Epoxy | Excellent | High gloss | 5-10 years | Moderate |
| Food-safe wax | Basic | Warm satin | Monthly | Low |
| Reactive (densifier) | Good | Natural | 3-5 years | Moderate |
For kitchen countertops, most fabricators use a penetrating sealer followed by a food-safe wax topcoat. This combination provides stain protection while maintaining the natural concrete appearance that customers want.
Pricing Concrete Countertop Work
Concrete countertops are labor-intensive. Your pricing needs to reflect the time investment.
Price Ranges
| Complexity | Installed Price/sq ft | Typical Project Total |
|---|---|---|
| Simple rectangle, one color | $65-$85 | $2,600-$3,400 |
| L-shape with sink cutout | $85-$110 | $3,400-$5,500 |
| Multi-piece with veining | $100-$135 | $5,000-$8,000 |
| Custom with embedded objects | $120-$150+ | $6,000-$10,000+ |
Time Investment Per Job
A typical L-shaped kitchen countertop with one sink cutout:
- Design and form building: 4-6 hours
- Mixing and casting: 2-3 hours
- Curing: 18 hours (GFRC) to 7 days (wet-cast)
- Finishing and sealing: 4-8 hours
- Installation: 2-4 hours
Total active labor: 12-21 hours. Compare that to granite fabrication for a similar kitchen at 4-6 hours total. Concrete commands higher per-square-foot pricing because it has to.
Margin Target
Target 45-55% gross margin on concrete countertop work. Below 40%, the time investment isn't justified when you could be running stone jobs through the shop.
Avoiding Costly Mistakes
Concrete remakes are expensive - you're losing 12-21 hours of labor plus materials. These are the errors that cause most callbacks.
Cracking
- Cause: Insufficient reinforcement, too-rapid drying, thin sections without support
- Prevention: Use GFRC for anything over 6 sq ft. For wet-cast, include fiber reinforcement and rebar/wire mesh. Keep countertops covered and misted for 3 days minimum.
Pinholes
- Cause: Trapped air bubbles against the form surface
- Prevention: Use a vibration table or palm sander on the outside of the form for 2-3 minutes after pouring. For GFRC face coats, back-roll with a paint roller to pop bubbles.
Color Inconsistency
- Cause: Inconsistent pigment measurement, varying water-to-cement ratios between batches
- Prevention: Weigh pigment to 0.1g accuracy. Use the same water-to-cement ratio for every batch. Mix all face coat material in a single batch when possible.
Warping
- Cause: Uneven drying, form not level, improper support during curing
- Prevention: Cure on a dead-flat surface. Store vertically during final cure with support every 24".
SlabWise's AI Template Verification catches dimensional and structural issues before casting begins, preventing remakes that can cost $2,000-$5,000 in wasted labor and materials.
Should You Add Concrete to Your Shop?
Adding concrete countertop fabrication makes sense if:
- You have space for a dedicated forming and curing area (minimum 200 sq ft)
- You can dedicate 1-2 employees to learn the craft (expect 6 months to proficiency)
- Your market has demand for custom, artisan-style countertops
- You're willing to price at $85-$150/sq ft installed (don't discount)
It doesn't make sense if:
- Your shop is at capacity with stone work
- You can't tolerate the slower production cycle
- Your local market is price-sensitive (concrete is hard to sell under $65/sq ft)
Frequently Asked Questions
How long do concrete countertops last?
Properly made and sealed concrete countertops last 20-30 years. They require periodic resealing (every 1-5 years depending on sealer type) and develop a patina over time that most owners find attractive.
Do concrete countertops crack?
All concrete develops hairline cracks over time - it's the nature of the material. GFRC significantly reduces cracking risk compared to traditional wet-cast. Most fabricators set customer expectations upfront: minor hairline cracks are character, not defects.
Are concrete countertops sanitary?
When properly sealed, concrete countertops are safe for food preparation. The sealer creates a non-porous barrier. Unsealed concrete is porous and should not contact food directly.
How heavy are concrete countertops?
GFRC: 10-12 lbs per square foot. Traditional wet-cast: 25-30 lbs per square foot. A 40 sq ft wet-cast kitchen weighs 1,000-1,200 lbs - standard cabinets can support this, but verify first.
Can you put hot pans on concrete countertops?
Concrete handles heat well - it won't scorch or melt. However, thermal shock can cause hairline cracks in thin sections. Recommend trivets as a precaution.
How much does a concrete countertop kitchen cost?
For a typical 40 sq ft kitchen, expect $2,600-$6,000 installed. Custom work with veining, multiple colors, or embedded features runs $5,000-$10,000+.
What's the difference between poured-in-place and precast?
Poured-in-place is cast directly on the cabinets in the customer's home. Precast is made in the shop and transported for installation. Precast gives you more control over quality and finishing.
Can concrete countertops be refinished?
Yes. The surface can be re-sanded and re-sealed to remove stains, scratches, or worn areas. This is a potential recurring revenue service for fabricators.
Do concrete countertops stain?
Unsealed concrete stains easily - wine, oil, and citrus will penetrate within minutes. Properly sealed concrete resists stains but requires maintenance. Set customer expectations during the sale.
What tools do you need for concrete countertops?
Essential equipment: concrete mixer, vibration table, GFRC spray system ($2,000-$5,000), variable-speed polisher with diamond pads ($500-$1,200), and forming supplies. Initial investment is $5,000-$12,000.
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Sources
- Concrete Countertop Institute - GFRC Training Curriculum
- Portland Cement Association - Decorative Concrete Manual
- Buddy Rhodes Concrete - Mix Design Guidelines
- ASTM C1364 - Standard Specification for Architectural Cast Stone
- Cheng Concrete - Fabricator's Handbook (3rd Edition)
- National Ready Mixed Concrete Association - Mix Design Standards