Coating system for cement composite articles
A substrate may be coated with a various combinations of a water-dispersible polyisocyanate, a water-soluble acid or salt thereof, and/or an isocyanate-reactive compound. The resulting coated article has improved coating adhesion, especially near coated burnished surfaces such as sawn edges or grooves.
1. A method for preparing a coated article, which method comprises:
(a) applying to at least a portion of an uncoated cementitious substrate a sealer composition comprising an aqueous mixture comprising water-dispersed polyisocyanate, about 1 to about 40 wt. % of a water-soluble inorganic or water-soluble monomeric or oligomeric organic acid or water-soluble salt thereof in an amount that affords improved coating adhesion on the cementitious substrate, and an optional isocyanate-reactive compound;
(b) at least partially drying the aqueous mixture; and
(c) overcoating at least part of such portion with one or more of a further sealer, primer or topcoat.
2. A method according to claim 1 wherein the substrate is a cement fiberboard.
3. A method according to claim 2 wherein the aqueous mixture contains an isocyanate-reactive compound comprising acetoacetoxy groups.
4. A method according to claim 1 wherein the aqueous mixture comprises an inorganic acid.
5. A method according to claim 1 wherein the aqueous mixture comprises a monomeric or oligomeric organic acid.
6. A method according to claim 1 wherein the acid or salt comprises a phosphorus acid or salt.
7. A method according to claim 1 wherein the aqueous mixture comprises a sodium, potassium or ammonium salt.
8. A method according to claim 1 wherein the aqueous mixture comprises a silicate salt.
9. A method according to claim 1 wherein the aqueous mixture contains about 60 to about 99 wt. % water-dispersed polyisocyanate.
10. A method according to claim 1 wherein the aqueous mixture contains the isocyanate-reactive compound.
11. A method according to claim 10 wherein the isocyanate-reactive compound is an emulsion polymer.
12. A method according to claim 11 wherein the isocyanate-reactive emulsion polymer comprises hydroxyl groups.
13. A method according to claim 11 wherein the isocyanate-reactive emulsion polymer is a latex.
14. A method according to claim 11 wherein the isocyanate-reactive emulsion polymer comprises acetoacetoxy groups.
15. A method according to claim 10 wherein the isocyanate-reactive compound comprises acetoacetoxy groups.
16. A method according to claim 1 wherein the aqueous mixture contains about 5 to about 40 wt. % water-dispersed polyisocyanate, and about 95 to about 20 wt. % isocyanate-reactive compound.
17. A method according to claim 1 further comprising pretreating at least a portion of such substrate with an aqueous solution of an acid or salt of such an acid, which acid or salt affords improved coating adhesion on a cementitious substrate, and at least partially drying the aqueous solution prior to applying such aqueous mixture.
18. A method according to claim 1 wherein the aqueous mixture contains an isocyanate-reactive compound comprising hydroxyl groups and acetoacetoxy groups.