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A process is provided for treating wood products including lumber, plywood and other engineered wood products comprising the steps of applying an aqueous fire-retardant impregnate and applying a coating to the surface of the wood product. In one embodiment, said process confers fire-retardant proper

A process is provided for treating wood products including lumber, plywood and other engineered wood products comprising the steps of applying an aqueous fire-retardant impregnate and applying a coating to the surface of the wood product. In one embodiment, said process confers fire-retardant properties to the wood products sufficient to pass the extended burn test of ASTM E-84. The present invention also provides fire retardant wood products.

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1. A method of treating plywood or oriented strand board (OSB) comprising the steps of: applying an aqueous fire-retardant impregnate to a wood product consisting of plywood or OSB with a thickness of up to approximately ¾ inch, such that the impregnate penetrates the wood product; andapplying a coa

1. A method of treating plywood or oriented strand board (OSB) comprising the steps of: applying an aqueous fire-retardant impregnate to a wood product consisting of plywood or OSB with a thickness of up to approximately ¾ inch, such that the impregnate penetrates the wood product; andapplying a coating to the wood product surface;wherein said treatment confers fire retardancy to the treated wood product such that the treated wood product exhibits a flame spread distance of not more than 6 feet in an ASTM E-84 30-minute burn test;wherein said fire retardant impregnate is applied by pressure or vacuum treatment, or both, or microwave treatment. 2. The method of claim 1, wherein said fire-retardant impregnate is substantially free of phosphates, ammonia, and salts thereof. 3. The method of claim 1, wherein said fire-retardant impregnate comprises a phosphate salt and a boron-containing compound. 4. The method of claim 1, wherein said fire retardant impregnate comprises a nitrogen-containing compound and a boron-containing compound. 5. The method of claim 3, wherein the boron-containing compound is selected from the group consisting of boric acid, ammonium borate, sodium octaborate, sodium pentaborate, and sodium tetraborate and hydrates thereof. 6. The method of claim 3, wherein the phosphate salt is selected from the group consisting of monoammonium phosphate, diammonium phosphate and triammonium phosphate, monosodium phosphate, disodium phosphate, trisodium phosphate, monopotassium phosphate, dipotassium phosphate, tripotassium phosphate, urea phosphate, ethylenediamine phosphate, guanylurea phosphate and melamine phosphate. 7. The method of claim 4, wherein the salt of a boron-containing compound is selected from the group consisting of boric acid, ammonium borate, sodium octaborate, sodium pentaborate, and sodium tetraborate and hydrates thereof. 8. The method of claim 4, wherein said fire-retardant impregnate comprises a nitrogen-containing compound selected from the group consisting of dicyandiamide, urea, guanylurea phosphate, melamine melamine phosphate, an ammonium phosphate, a cyanamide, a diammonium phosphate, ammonium polyphosphate, monoethanolamine, diethanolamine, triethanolamine and hexamethylenetetramine, and a boron-containing compound selected from the group consisting of boric acid, tetraboric acid, metaboric acid and salts of a boron-containing compound. 9. The method of claim 3, wherein the phosphate salt comprises monoammonium phosphate and the boron-containing compound comprises boric acid. 10. The method of claim 9, wherein the fire-retardant impregnate further comprises ethylenediamine. 11. The method of claim 4, wherein the nitrogen-containing compound comprises one or more of urea and dicyandiamide and the boron-containing compound comprises boric acid, sodium tetraborate pentahydrate or both. 12. The method of claim 1, wherein said fire-retardant impregnate is retained within said wood product in an amount of about 1 to about 6.0 pcf. 13. The method of claim 1, wherein said fire-retardant impregnate is retained within said wood product in an amount of about 1 to about 4.5 pcf. 14. The method of claim 1, wherein said fire-retardant impregnate is retained within said wood product in an amount of about 2.0 to about 3.0 pcf. 15. The method of claim 1, wherein said fire-retardant impregnate is retained within said wood product in an amount of about 1.5 to about 3.0 pcf. 16. The method of claim 3, wherein said fire-retardant impregnate is retained within said wood product in an amount of about 1 to about 6.0 pcf. 17. The method of claim 3, wherein said fire-retardant impregnate is retained within said wood product in an amount of about 1 to about 4.5 pcf. 18. The method of claim 3, wherein said fire-retardant impregnate is retained within said wood product in an amount of about 2.0 to about 3.0 pcf. 19. The method of claim 3, wherein said fire-retardant impregnate is retained within said wood product in an amount of about 1.5 to about 3.0 pcf. 20. The method of claim 4, wherein said fire-retardant impregnate is retained within said wood product in an amount of about 1 to about 6.0 pcf. 21. The method of claim 4, wherein said fire-retardant impregnate is retained within said wood product in an amount of about 1 to about 4.5 pcf. 22. The method of claim 4, wherein said fire-retardant impregnate is retained within said wood product in an amount of about 2.0 to about 3.0 pcf. 23. The method of claim 4, wherein said fire-retardant impregnate is retained within said wood product in an amount of about 1.5 to about 3.0 pcf. 24. The method of claim 1, wherein said coating is applied to said wood product an application rate of about 0.04 to about 0.11 lbs/ft2. 25. The method of claim 1, wherein said coating is an intumescent coating. 26. The method of claim 24, wherein said coating comprises a polymer binder, a source of mineral acid catalyst, a source of carbon, and a source of non-flammable gas. 27. The method of claim 26, wherein the weight concentration of the polymer is from about 20.0% to about 50.0%, the weight concentration of the acid source is from about 20.0% to about 50.0%, the weight concentration of the carbon source is from about 10.0% to about 30.0%, and the weight concentration of the gas source is from about 10.0% to about 30.0%. 28. The method of claim 1, wherein the wood product is plywood with a thickness of approximately ½ inch. 29. The method of claim 1, wherein the wood product is plywood with a thickness of approximately % inch. 30. Wood produced by the method of claim 1. 31. A fire retardant wood product comprising: a fire-retardant impregnate in an amount of about 2.00 to about 3.00 pcf; anda coating in an amount of about 0.04 to about 0.10 pcf;wherein the wood product has a thickness of approximately ½ inch, and wherein said wood product exhibits a flame spread distance of not more than 6 feet in an ASTM E-84 30-minute burn test. 32. The wood product of claim 31, wherein said wood is plywood or oriented strand board (OSB). 33. The wood product of claim 31, wherein said wood product is Southern yellow pine plywood. 34. The wood product of claim 31, wherein said fire-retardant impregnate is substantially free of phosphates, ammonia, and salts thereof. 35. The wood product of claim 31, wherein said fire-retardant impregnate comprises a nitrogen compound and a boron compound. 36. The wood product of claim 31, wherein said fire-retardant impregnate comprises a phosphate salt and a boron-containing compound. 37. The wood product of claim 36, wherein the phosphate salt comprises monoammonium phosphate and the boron-containing compound comprises boric acid. 38. The wood product of claim 37, wherein the fire-retardant impregnate further comprises ethylenediamine. 39. The wood product of claim 35, wherein the nitrogen-containing compound comprises one or more of urea and dicyandiamide and the boron-containing compound comprises boric acid, sodium tetraborate pentahydrate or both. 40. The wood product of claim 35, wherein the boron-containing compound is selected from the group consisting of boric acid, ammonium borate, sodium octaborate, sodium pentaborate, and sodium tetraborate and hydrates thereof. 41. The wood product of claim 36, wherein the phosphate salt is selected from the group consisting of monoammonium phosphate, diammonium phosphate and triammonium phosphate, monosodium phosphate, disodium phosphate, trisodium phosphate, monopotassium phosphate, dipotassium phosphate, tripotassium phosphate, urea phosphate, ethylenediamine phosphate, guanylurea phosphate and melamine phosphate. 42. The wood product of claim 35, wherein said fire-retardant impregnate comprises a nitrogen-containing compound selected from the group consisting of dicyandiamide, urea, guanylurea phosphate, melamine melamine phosphate, an ammonium phosphate, a cyanamide, a diammonium phosphate, ammonium polyphosphate, monoethanolamine, diethanolamine, triethanolamine and hexamethylenetetramine, and a boron-containing compound selected from the group consisting of boric acid, tetraboric acid, metaboric acid and salts of a boron-containing compound. 43. The wood product of claim 31, wherein said coating comprises a polymer binder. 44. A method of treating plywood or oriented strand board (OSB) comprising the steps of: applying an aqueous fire-retardant impregnate by pressure or vacuum treatment to plywood with a thickness of approximately ½ inch in an amount of about 1 to about 4.5 pcf, such that the impregnate penetrates the plywood; andapplying a coating to the plywood surface in an amount of about 0.04 to about 0.11 lbs/ft2. 45. The method of claim 44, wherein said fire-retardant impregnate is substantially free of phosphates, ammonia, and salts thereof. 46. The method of claim 44, wherein said fire-retardant impregnate comprises a nitrogen compound and a boron compound. 47. The method of claim 44, wherein said fire-retardant impregnate comprises a phosphate salt and a boron compound. 48. The method of claim 47, wherein the phosphate salt comprises monoammonium phosphate and the boron-containing compound comprises boric acid. 49. The method of claim 48, wherein the fire-retardant impregnate further comprises ethylenediamine. 50. The method of claim 46, wherein the nitrogen-containing compound comprises one or more of urea and dicyandiamide and the boron-containing compound comprises boric acid, sodium tetraborate pentahydrate or both. 51. The method of claim 46, wherein the boron-containing compound is selected from the group consisting of boric acid, ammonium borate, sodium octaborate, sodium pentaborate, and sodium tetraborate and hydrates thereof. 52. The method of claim 47, wherein the phosphate salt is selected from the group consisting of monoammonium phosphate, diammonium phosphate and triammonium phosphate, monosodium phosphate, disodium phosphate, trisodium phosphate, monopotassium phosphate, dipotassium phosphate, tripotassium phosphate, urea phosphate, ethylenediamine phosphate, guanylurea phosphate and melamine phosphate. 53. The method of claim 46, wherein said fire-retardant impregnate comprises a nitrogen-containing compound selected from the group consisting of dicyandiamide, urea, guanylurea phosphate, melamine melamine phosphate, an ammonium phosphate, a cyanamide, a diammonium phosphate, ammonium polyphosphate, monoethanolamine, diethanolamine, triethanolamine and hexamethylenetetramine, and a boron-containing compound selected from the group consisting of boric acid, tetraboric acid, metaboric acid and salts of a boron-containing compound. 54. The method of claim 44, wherein said wood product exhibits a flame spread distance of not more than 6 feet in an ASTM E-84 30-minute burn test. 55. The method of claim 44, wherein said fire-retardant impregnate is applied by pressure treatment, vacuum treatment, or both. 56. The method of claim 44, wherein said coating is an intumescent coating comprising a polymer binder, a source of mineral acid catalyst, a source of carbon, and a source of non-flammable gas.