Glass fiber reinforced concrete is concrete reinforced with alkali-resistant glass fiber instead of steel rebar, cast in shells roughly ½ to ¾ inch thick. That thin wall is why a 70-inch Prism Hardscapes fire bowl weighs 650 lbs instead of thousands, and why nothing inside can rust and blow the face off.
On this page
- What is glass fiber reinforced concrete?
- Why does alkali resistance matter?
- How much lighter is GFRC, in real pounds?
- What do you gain by buying GFRC?
- What do you give up?
- Do concrete fire tables crack?
- Why do two of the same model look different?
- GFRC vs steel, aluminum and copper
- How do you seal and clean GFRC?
- What happens near a pool or the ocean?
What is glass fiber reinforced concrete?
Glass fiber reinforced concrete — GFRC, sometimes written GRC — is a composite of portland cement, fine aggregate, polymer and chopped alkali-resistant glass fiber. There is no steel rebar in it. The fiber carries the tensile load that rebar would carry in a poured slab.
That changes the geometry. Rebar needs an inch or more of concrete cover, so a reinforced casting has a minimum thickness set by the steel. Glass fiber is dispersed through the matrix — 2–3.5% by weight in premix, 4.5–5% in spray-up — so there is no cover requirement. American Fyre Designs puts it plainly: its GFRC parts are "typically ½ inch to ¾ of an inch thick," hollow rather than solid.
A GFRC fire table is not a block of concrete. It is a thin, hollow, fiber-reinforced shell with a burner inside. Everything below follows from that. See the range in our GFRC fire pits and fire tables collection.
Why does alkali resistance matter?
Because ordinary glass dissolves in concrete. Hydrating portland cement produces a pore solution with a pH around 12.5. Hydroxyl ions at that pH attack the silicon-oxygen bonds that form the backbone of silicate glass, corroding the fiber progressively. E-glass loses strength inside the material it is meant to reinforce, which is why E-glass is not used in GFRC at all.
Alkali-resistant glass fixes that with zirconium dioxide. Specifications call for a minimum 16% ZrO₂ by weight; commercial AR fiber runs 16–19%, the better grades higher. ASTM C1666/C1666M covers it, and long-term behavior is checked by the Strand-in-Cement test under EN 15422, where conditioned strands must still pull above 330 MPa. Prism Hardscapes, American Fyre Designs and Slick Rock Concrete all build on AR-glass. Generic "concrete" patio furniture often will not say.
How much lighter is GFRC, in real pounds?
Nobody publishes this, so here is our catalog data: shipping-verified weights for Prism Hardscapes pieces, with current prices.
| Model | Size | Weight | Price from |
|---|---|---|---|
| Moderno 2 | 29 in round | 90 lbs | $1,292 |
| Moderno 3 | 30 in round | 125 lbs | $1,338 |
| Moderno 5 | 36 in round | 250 lbs | $1,822 |
| Moderno 4 | 48 in round | 300 lbs | $3,102 |
| Moderno 70 | 70 in round | 650 lbs | $8,248 |
| Tavola 5 | 80 in rectangle | 650 lbs | $3,888 |
| Tavola 6 | 90 in rectangle | 418 lbs | $4,662 |
Weights and prices from the Outdoor Heat Direct catalog, September 2026.
Read the last two rows again. The 90-inch Tavola 6 weighs 418 lbs — less than the 80-inch Tavola 5 at 650 lbs, because Prism moved the larger table to a lighter mix. The bigger table became the easier one to place.
Then the 70-inch bowl. A solid concrete cylinder 70 in across and 16 in tall is about 35.6 cubic feet; at 145 lbs per cubic foot, roughly 5,100 lbs. Our own calculation, not a manufacturer spec. The real Moderno 70 is 650 lbs. The thin shell is what turns a 70-inch fire bowl from a crane job into a product.
The expensive mistake: ordering a 400–650 lb piece with no plan to get it off the truck. These ship freight, curbside. Two people cannot walk a Moderno 70 up a side yard. Line up four people and a dolly, or buy liftgate delivery. Dropping a corner is not a warranty claim.
What do you gain by buying GFRC?
Nothing inside it rusts. In steel-reinforced concrete, water and oxygen reach the rebar, the steel corrodes, and the corrosion products expand by up to six times the original bar volume. That cracks the piece from the inside and pushes the face off — the standard failure of reinforced concrete left outdoors. GFRC has no steel, so that mechanism does not exist.
The finish is the material. Texture, profiles and color are cast into the mold and pigmented through the body. American Fyre Designs states the color is "cast all the way through the product and won't scrape off like an applied, painted finish." A chip on powder-coated steel shows bare metal; a chip on GFRC shows more concrete.
Weight without immovability. A 90-lb bowl will not blow across a patio, but two people can still move it. See how the sizes ladder up across our 389 concrete fire features.
Not sure which size fits your space?
Send your patio dimensions, seating plan and fuel type. We will tell you which GFRC models clear your setback.
Ask our fire feature team Read the complete buying guideWhat do you give up?
GFRC is still concrete, and concrete is porous. Red wine, olive oil, coffee, citrus juice and pool chemicals mark an under-sealed surface; blotting fast matters more than any product you buy later. A planter left on the top leaves a ring.
Winter matters too. Concrete only suffers freeze damage once the capillaries in the paste are more than 91.7% full of water — Powers' critical saturation threshold — where water expanding about 9% as it freezes generates pressure the paste cannot relieve. A bowl that fills with rain and freezes is exactly that. Drain it, cover it, keep it off standing water. See winterizing a gas fire pit and fire pits on pavers and concrete, which covers spalling in the patio itself.
Do concrete fire tables crack?
Three unrelated things get called "cracking." Which one you have decides whether you do nothing, change habits, or file a claim.
| What you see | Mechanism | Severity | What to do |
|---|---|---|---|
| Crazing — hairline map, cells under 1½ in | Surface-layer shrinkage during cure; rarely over ⅛ in deep | Cosmetic. No structural effect | Nothing. Keep it sealed |
| Spalling — flakes lifting off the face | Trapped moisture freezing above 91.7% saturation; water expands ~9% | Preventable, progressive once started | Drain, cover, elevate, winterize |
| Through-crack — one line, edge to edge | Impact, point loading in transit, unsupported base | Structural. Defect or mishandling | Photograph before the driver leaves; claim same day |
| Rust stains, face lifting | Internal steel corroding, expanding up to 6× | Does not occur in GFRC | If you see it, it is not GFRC |
The honest version: fine crazing is normal on cast concrete and no manufacturer we sell treats it as a defect. Spalling is a drainage problem, not a material problem. A through-crack on arrival is a freight claim, and that window is short.
Why do two of the same model look different?
Because a person applied the finish. American Fyre Designs says so in its finish literature: products are "individually handcrafted and finishes shown are subject to slight texture and color variation." Its antique finishes — Dark Basalt, Light Basalt, Travertine — are hand-worked over the cast body, so patina depth moves piece to piece. Prism Hardscapes works the same way.
That variation is the product, not a flaw — but know it before you order, and order matching pieces together. The guides to Prism Hardscapes fire tables and fire bowls and American Fyre Designs fire tables, fire bowls and fire urns break the finishes down model by model; our concrete wood grain pieces show how far mold texture can go.
GFRC vs steel, aluminum and copper
No material wins outright. What changes is the failure you sign up for.
| Material | Weight | What fails first | Maintenance | Coastal / chlorine | Entry price at OHD |
|---|---|---|---|---|---|
| GFRC | 90–650 lbs | Staining; spalling if waterlogged | Reseal, cover, drain | Body fine; hardware is the weak point | $1,158 |
| Carbon steel, coated | Light–moderate | Coating chips, then rust spreads | Touch up chips early | Poor near surf | Model-dependent |
| 304 stainless | Moderate | Chloride pitting, tea staining | Fresh-water rinse | Fine inland, marginal coastal | Model-dependent |
| 316 stainless | Moderate | Very little, slowly | Rinse occasionally | Best: 2–3% molybdenum | 20–40% over 304 |
| Aluminum | Lightest | Dents; needs anchoring | Minimal | Good, does not rust | Accessories only |
| Copper | Moderate | Nothing structural; patina shifts | None, unless you fight the patina | Excellent | $2,746 |
Entry price = cheapest fire bowl in that material in our catalog today. Our aluminum listing is a single accessory, not a fire pit range.
How do you seal and clean GFRC?
Start with what is published. Prism Hardscapes and American Fyre Designs do not name a sealer for their fire features — their material pages describe composition, not a maintenance schedule. Better to say so than invent a spec; check your manual and our manuals and guides page.
Where the wider GFRC furniture industry does publish, guidance converges: a non-gloss penetrating concrete sealer, or carnauba paste wax every two to five months. Clean with mild soap or non-bleach dish detergent and a soft brush. Avoid bleach, ammonia, degreasers, abrasives and — this surprises people — citrus-based "natural" cleaners, acidic enough to etch the surface. Cover it when idle; we stock a short run of fire pit covers, and tenting the cover stops it freezing flat to the top.
What happens near a pool or the ocean?
The GFRC does well. No embedded steel means chlorides have nothing to corrode, removing the mechanism that destroys reinforced concrete in marine air. Salt spray and pool splash-out still leave deposits and can stain an under-sealed surface, so rinse with fresh water on a schedule.
The hardware is the real coastal question. Burners, pans, igniters and fasteners are metal, and 304 stainless tea-stains in chloride while 316 does not. Within sight of surf, or on the pool coping, ask which grade the burner assembly uses — doubly so for every fire and water bowl, where the hardware is wet by design. Prism Hardscapes specifies 4 ft of side clearance and 6 ft overhead, with a 2-year factory warranty.
419 GFRC pieces, one shortlist
Prism Hardscapes, American Fyre Designs, Slick Rock Concrete and The Outdoor Plus. Filter by size, fuel and finish.
Shop GFRC fire features Browse Prism HardscapesGFRC fire table FAQs
Is GFRC the same as regular concrete?
No. Structural concrete is reinforced with steel rebar and cast thick. Glass fiber reinforced concrete uses alkali-resistant glass fiber dispersed through the mix, which removes the concrete-cover requirement and allows shells roughly half an inch to three-quarters thick. Same cement, very different geometry and weight.
Do concrete fire tables crack over time?
Fine surface crazing is common and cosmetic — those hairlines are rarely more than an eighth of an inch deep and do not affect structural integrity. Spalling comes from trapped moisture freezing and is preventable with drainage and a cover. A through-crack edge to edge is handling damage, not aging.
How much does a GFRC fire bowl weigh?
From 90 lbs for the 29-inch Prism Hardscapes Moderno 2 to 650 lbs for the 70-inch Moderno 70; a 48-inch Moderno 4 is 300 lbs. The 90-inch Tavola 6 is 418 lbs, lighter than the 80-inch Tavola 5 at 650 lbs, because Prism switched it to a lighter mix.
Why does GFRC use alkali-resistant glass instead of normal fiberglass?
Hydrating cement produces a pore solution near pH 12.5. Hydroxyl ions at that pH attack the silicon-oxygen bonds in ordinary E-glass, corroding the fiber so it loses strength inside the concrete. Alkali-resistant glass carries at least 16% zirconium dioxide, commercially 16–19%, which stops the attack.
Can I leave a GFRC fire table outside all winter?
In a freeze-thaw climate, only if it stays drained and covered. Concrete is damaged once capillaries pass about 91.7% saturation, where the roughly 9% expansion of freezing water generates internal pressure. Keep it off standing water and use a cover tented so it cannot freeze flat.
Will my GFRC fire pit match the photo exactly?
Close, not identical. American Fyre Designs states its products are individually handcrafted and finishes are subject to slight texture and color variation; Prism Hardscapes varies the same way. Hand-worked antique and patina finishes vary most. Order matching pieces, such as a table and its tank enclosure, together.
What sealer should I use on a GFRC fire table?
Prism Hardscapes and American Fyre Designs do not publish a named sealer for their fire features, so check your manual first. The general GFRC standard is a non-gloss penetrating concrete sealer, or carnauba paste wax every two to five months. Avoid bleach, ammonia, abrasives and citrus cleaners.
Is GFRC good next to a swimming pool?
Yes, and better than steel-reinforced concrete, because there is no rebar for chlorides to corrode. Chlorinated splash-out can still stain an under-sealed surface, so rinse regularly. The real question is the burner hardware: 316 stainless resists chloride pitting far better than 304, thanks to 2–3% molybdenum.
Which brands at Outdoor Heat Direct actually build in GFRC?
Four, across 419 listings: Prism Hardscapes with 118, American Fyre Designs 87, The Outdoor Plus 82 and Slick Rock Concrete 43, with the balance in accessories. All four use alkali-resistant glass fiber rather than steel, and all four cast finish and texture into the mold.
Is GFRC cheaper than copper or stainless?
Usually, at the same size. Our least expensive GFRC fire bowl starts at $1,158; the least expensive copper fire bowl is $2,746. Large sizes flip it: the 70-inch Moderno 70 is $8,248, because a piece that size is hard in any material. Compare like sizes.
Sources and accuracy note. Fiber data: ASTM C1666/C1666M, published AR-glass zirconia specifications, Strand-in-Cement testing under EN 15422. Wall thickness, composition and finish variation: American Fyre Designs material and finish pages. Crazing depth and cell size: Portland Cement Association-derived ready-mix guidance. Freeze-thaw mechanism, the 91.7% saturation threshold and the ~9% expansion of freezing water: U.S. Federal Highway Administration research. Rebar corrosion expanding up to six times: forensic engineering literature on spalling. Stainless chemistry: published 304/316 composition data. Weights, models and prices are from the Outdoor Heat Direct catalog, September 2026.
The ~5,100 lb figure for a solid 70 in × 16 in cylinder is our own calculation at 145 lbs per cubic foot, given for scale only; no such product exists. Sealer schedules are cited only where a manufacturer publishes one. Gas fire features must be installed to the National Fuel Gas Code, ANSI Z223.1 / NFPA 54, by a licensed technician, and local code governs.