What kind of glue can I use to glue the ceramic knob back on to the cover of a ceramic casserole dish that can withstand go into a 400°F oven ?

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Direct answer to the question - Use a high-temperature, food-grade RTV silicone adhesivesealant rated ≥ 450 °F 230 °C, e.g. DowDowsil 732-FDA, Sil-Bond FG, or Rutland 500 °F RTV to bond the knob. - If you cannot source a product that is explicitly food-safe and 400 °F-rated, replace the knob with an oven-safe screw-on or bolted knob instead of gluing. Key points • Continuous-temperature rating ≥ 400 °F 204 °C with margin • FDA NSF-51 or equivalent food-contact compliance after full cure • Good adhesion to glazed or unglazed ceramic and tolerance to thermal shock • Flexible bond line – better survives repeated heat cycles than rigid epoxies --- Detailed problem analysis 1. Operating conditions • Lid sees 400 °F oven heat, rapid cool-down, steam, detergents, handling loads. • Ceramic CTE ≈ 6–8 ppm°C; the adhesive must cope with differential expansion. 2. Adhesive classes compared | Adhesive class | Typical rating | Food-safe versions? | Pros Cons for this job | Verdict | | --- | --- | --- | --- | --- | | Standard CA “super glue” | < 200 °F | Rare | Quick set but embrittles & outgasses | Reject | | Consumer 5-min epoxies | 200–250 °F | No | Strong but temperature limited | Reject | | High-temperature epoxies e.g. J-B Weld Original, ExtremeHeat | 450–500 °F | Generally not food-approved | Very strong but rigid; may spall glaze; food-safety uncertain | Only if food never contacts underside & datasheet allows | | Sodium-silicate furnace cements | 1 000 °F+ | No | Brittle, porous, not food-safe | Reject | | Food-grade high-temp RTV silicone | 450–600 °F | Yes NSF-51 FDA 21 CFR 175.105 | Flexible, steam-proof, dishwasher tolerant, easy to apply | Preferred | 3. Why flexible RTV beats rigid epoxy here ‑ Flexibility accommodates thermal cycling and different CTEs, reducing risk of the knob or glaze cracking. ‑ Cure shrinkage is low, so less stress on thin lid. ‑ Many industrial RTVs carry explicit “incidental food contact” approvals; few epoxies do at 400 °F. 4. Representative products always verify local availability & datasheet • Dowsil 732-FDA Dowsil 736 Red High-Temp NSF-51, –75 °F → 500 °F • Sil-Bond FoodGrade RTV NSF 51, –70 °F → 450 °F continuous • Rutland 500 °F RTV High-Heat Silicone marketed for stoves; check label variant—black version is NSF --- Current information and trends • NSF-51-listed silicones have become the de-facto standard for food-service oven door and steam-kettle seals; hobby cooks can now buy small tubes retail. • “Extreme heat” epoxies Cotronics Resbond™, Loctite EA 9628, etc. exist for industrial cookware tooling, but are usually sold in quart kits and lack consumer food-contact certification. • Manufacturers of premium casserole ware Le Creuset, Staub have moved from glued to bolted stainless knobs to avoid adhesive issues—one reason a mechanical replacement is often recommended if original knob breaks again. --- Supporting explanations and details Bond preparation 1. Degrease both ceramic surfaces with 90 % isopropanol or acetone; rinse and dry. 2. Lightly abrade glaze with 220-grit SiC paper to create micro-key. 3. Wipe away dust; avoid touching bonding area with fingers. 4. Apply a 0.5–1 mm bead of RTV, assemble, gently twist to wet surfaces. 5. Tape or fixture knob; do not over-clamp—RTV needs ~0.2 mm thickness to cure. 6. Room-temperature cure 24 h or per datasheet. Many RTVs reach handling strength in 2–4 h but need 72 h for full cross-linking and food-safe status. Post-cure proof test - Place the lid alone in a cold oven, heat to 250 °F for 30 min, cool naturally. - Inspect bond line; if intact, repeat at 400 °F. This staged cycle both post-cures the silicone and verifies adhesion before food use. --- Ethical and legal aspects • In the U.S. indirect-food-contact adhesives must comply with FDA 21 CFR 175.105 or NSF-51; EU equivalent is EC No 19352004. Using non-approved glues risks chemical migration into food condensate. • Many popular DIY “high-heat” epoxies state explicitly “not for food-contact surfaces; do not use on cookware” in their SDS. Ignoring this voids product liability and could create health risk. --- Practical guidelines Implementation best practice - Prefer a knob-with-bolt kit stainless screw + silicone washer if original has a through-hole: no chemical concerns, infinite temperature margin, repairable again. - When gluing, keep adhesive squeeze-out on lid exterior; wipe immediately with mineral spirits before cure. - Avoid shock cooling e.g. cold water on hot lid; even good adhesive cannot prevent ceramic fracture from thermal stress. Potential challenges - Some lids are fully glazed and non-porous → adhesion lower; roughening is essential. - Vinegar-cure acetoxy RTVs release acetic acid; sensitive glazes containing lead or tin oxides could suffer—use neutral-cure alkoxy or oxime RTV if concerned. Testing verification - After cure and thermal cycling, tap knob gently sideways; no movement should be felt. - Check annually; RTVs can dry-out after thousands of cycles—re-bond or re-bolt if necessary. --- Possible disclaimers or additional notes • No consumer adhesive will restore factory-original appearance; a faint joint line will always be visible. • Long-term dishwasher chemicals may dull silicone; hand-wash for best longevity. • Data presented is typical; always consult the current technical data sheet TDS and safety data sheet SDS for the exact lot you purchase. --- Suggestions for further research - Review NSF White Book™ listing for updated, certified high-temperature food-equipment adhesives. - Explore newly introduced sol-gel ceramic bonding films e.g., NGK’s Cerami-Bond that cure at kitchen-oven temperatures; these may reach consumer market soon. - For frequent high-heat repairs, consider small, screw-mountable Bakelite or phenolic knobs used on Dutch-oven lids to eliminate adhesive altogether. --- Brief summary A 400 °F oven demands an adhesive that is simultaneously heat-resistant, steamwash durable, and certified food-safe. Among readily available products, FDANSF-approved high-temperature RTV silicone sealants ≥ 450 °F best satisfy all requirements while accommodating thermal expansion stresses. Clean and roughen the ceramic, apply a thin bead, cure fully, and perform a staged heat test before returning the casserole to service. If a suitable food-grade high-heat adhesive cannot be sourced, switching to a mechanical screw-on knob is the safest, most durable alternative.

Best Food-Safe High-Temp Glue for Ceramic Casserole Knob Repair – Dow, Sil-Bond, Rutland RTV

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Adhesive class	Typical rating	Food-safe versions?	Pros / Cons for this job	Verdict
Standard CA “super glue”	< 200 °F	Rare	Quick set but embrittles & outgasses	Reject
Consumer 5-min epoxies	200–250 °F	No	Strong but temperature limited	Reject
High-temperature epoxies (e.g. J-B Weld Original, ExtremeHeat)	450–500 °F	Generally not food-approved	Very strong but rigid; may spall glaze; food-safety uncertain	Only if food never contacts underside & datasheet allows
Sodium-silicate/ furnace cements	1 000 °F+	No	Brittle, porous, not food-safe	Reject
Food-grade high-temp RTV silicone	450–600 °F	Yes (NSF-51 / FDA 21 CFR 175.105)	Flexible, steam-proof, dishwasher tolerant, easy to apply	Preferred