Wis. Stat. § 766.63: Mixed property.

(1) Except as provided otherwise in ss. 766.61, 766.62, and 766.625 (2), mixing marital property with property other than marital property reclassifies the other property to marital property unless the component of the mixed property which is not marital property can be traced.

(2) Application by one spouse of substantial labor, effort, inventiveness, physical or intellectual skill, creativity or managerial activity to either spouse’s property other than marital property creates marital property attributable to that application if both of the following apply:

(a) Reasonable compensation is not received for the application.

(b) Substantial appreciation of the property results from the application.