Reinforcing layer, a cementitious board, and method of forming the cementitious board

1. A reinforcing layer for a cementitious board comprising an alkali-resistant fabric, a non-porous membrane, and a first non-woven mat, wherein the alkali-resistant fabric comprises a glass fabric laid scrim, wherein the first non-woven mat is directly in contact with the non-porous membrane and the alkali-resistant fabric and wherein the non-porous membrane comprises a polymeric film having a filler content of less than 5 weight % based on the total weight of the polymeric film, the non-porous membrane having a thickness of less than 5 mils, wherein the non-porous membrane has a breaking strength of greater than 170 psi as measured by ASTM D751.

2. The reinforcing layer of claim 1 , wherein the polymeric film comprises at least one continuous polymeric film.

3. The reinforcing layer of claim 2 , wherein the at least one continuous polymeric film comprises a polyolefin.

4. The reinforcing layer of claim 1 , wherein the non-porous membrane has a water vapor permeance of less than about 0.5 perm as measured by ASTM E49 Method E.

5. The reinforcing layer of claim 1 , wherein the reinforcing layer further comprises a second nonwoven mat.

6. The reinforcing layer of claim 1 , wherein the first nonwoven mat, the second nonwoven mat, or combination thereof comprises a polymeric fiber.

7. The reinforcing layer of claim 5 , wherein the non-porous membrane is directly in contact with the second nonwoven mat.

8. The reinforcing layer of claim 1 , wherein the non-porous membrane has a thickness of at least about 3 mils.

9. The reinforcing layer of claim 1 , wherein the alkali-resistant fabric is directly in contact with the non-porous membrane.

10. The reinforcing layer of claim 1 , wherein the alkali-resistant fabric further comprises a polyester, a polyvinyl alcohol, a polypropylene, or combination thereof.

11. The reinforcing layer of claim 1 , wherein the alkali-resistant fabric further comprises a woven fabric, a braided fabric, a knitted fabric, or combination thereof.

12. The reinforcing layer of claim 1 , wherein the alkali-resistant fabric further comprises a binder.

13. The reinforcing layer of claim 1 , wherein the non-porous membrane has a waterproofness that holds for 48 hours with a 2 inch water column as measured by ASTM D4068.

14. The reinforcing layer of claim 1 , wherein the reinforcing layer is disposed on at least one face of the cementitious board.

15. The reinforcing layer of claim 14 , wherein the reinforcing layer provides an exterior surface of the cementitious board.

16. A cementitious board comprising:

(a) a cementitious core; and

(b) a reinforcing layer disposed on at least one face of the cementitious core; the reinforcing layer comprising an alkali-resistant fabric, a non-porous membrane, and a first non-woven mat, wherein the alkali-resistant fabric comprises a glass fabric laid scrim, wherein the first non-woven mat is directly in contact with the non-porous membrane and the alkali-resistant fabric and wherein the non-porous membrane comprises a polymeric film having a filler content of less than 5 weight % based on the total weight of the polymeric film, the non-porous membrane having a thickness of less than 5 mils, wherein the non-porous membrane has a breaking strength of greater than 170 psi as measured by ASTM D751.

17. The reinforcing layer of claim 16 , wherein the reinforcing layer further comprises a second nonwoven mat.

18. The reinforcing layer of claim 17 , wherein the non-porous membrane is directly in contact with the second nonwoven mat.

19. The reinforcing layer of claim 16 , wherein the first nonwoven mat, the second nonwoven mat, or combination thereof comprises a polymeric fiber.