At issue in this case is whether the various parts of the *8manufacturing process are directly related to, or used in, the manufacture of appellant’s product. For the reasons which follow, we affirm in part and reverse in part the board’s decision.
Initially, appellant would have this court adopt the integrated plant theory. This theory views all the components of the manufacturing process as a single unit for tax purposes, and would allow no inquiry beyond whether the whole plant was purchased at the same time. It further implies that every component of the plant is directly used in manufacturing. However, “[t]his theory has never been accepted in Ohio * * Southwestern Portland Cement Co. v. Lindley (1981), 67 Ohio St. 2d 417, 419 [21 O.O. 3d 261], citing Youngstown Bldg. Material & Fuel Co. v. Bowers (1958), 167 Ohio St. 363 [5 O.O. 2d 3], and Ohio Ferro-Alloys Corp. v. Kosydar (1973), 34 Ohio St. 2d 113 [63 O.O. 2d 195]. While there is much to be said from a public policy standpoint for the integrated plant theory, its adoption would prevent a part-by-part analysis, which we think is essential. Likewise, we reject the commissioner’s rigid application of the “direct use” exemption contained within R.C. 5739.01(E)(2).
It is readily apparent that equipment used in the manufacturing of products is exempt from sales and use taxes. R.C. 5741.02(C)(2), 5739.01(E)(2), and 5739.02(B)(15) and (16). To qualify for such exemption, a particular component must be “used directly in manufacturing.” Southwestern Portland Cement Co., supra, at 419, citing Tri-State Asphalt Corp. v. Glander (1950), 152 Ohio St. 497 [41 O.O. 40]. To determine whether the component is used directly in manufacturing, we must ask, “ ‘when does the actual manufacturing activity begin and end * * *.’ ” Southwestern Portland Cement Co., supra, at 421. “Manufacturing” has been statutorily defined to mean, “transformation or conversion of material or things into a different state or form from that in which they originally existed and * * * the adjuncts used during and in, and necessary to carry on and continue, production * * *.” (Emphasis added.) R.C. 5739.01(R).
In the context of this case, it is readily apparent that the transformation or conversion of material or things into a different state or form occurs primarily in the drum mixer. There, the various ingredients are heated and mixed so that they become the product ultimately sold. However, the manufacture of the product is, in no sense, either initiated or ended in the drum mixer.
As a matter of factual determination, the materials utilized are prepared before they reach the drum mixer. A precise, computerized mixing system composed of various small conveyor belts regulates the flow of aggregates from the bins. The result is a uniform size and weight of aggregate, which is essential to the required standardization of product. Likewise, the feed belt conveyor and scale are utilized to regulate the amount of asphalt cement to be added to a particular weight/volume of aggregate. Without these pieces of equipment, there could be no mix *9specifications, nor constancy of finished product. Without doubt, they are “adjuncts used during and in, and necessary to carry on and continue, production.” R.C. 5739.01(R).
The heated main conveyor belt and surge bin are utilized to carefully remove the freshly mixed asphalt from the dryer drum and load it into the trucks. The product, although complete in the dryer drum, is nevertheless not capable of maintaining itself in the form required for delivery. The heated conveyor belt moves the material in small batches to maintain the aggregate consistency. Without this heated equipment, the material would harden after exiting from the dryer drum. Thus, far from merely transporting the product, these machines maintain the product in heated, usable form until delivery. As such, they are crucial for this manufacturing process. Further, in Hawthorn Mellody v. Lindley (1981), 65 Ohio St. 2d 47 [19 O.O. 3d 234], the tax-exempt equipment was for the refrigeration of raw milk and ice cream. Such refrigeration was said to be “essential to prevent spoilage during the processing * * *.” Id. at 48. The heated main conveyor belt and surge bin are utilized in the very same sense by appellant. Without the heat, and special handling, the asphalt will quickly become an unmarketable, solid mass. Consequently, the equipment utilized to preserve the required product state is an adjunct to property used or consumed directly in the production of tangible personal property. See R.C. 5739.01(E)(2), and Hawthorn Mellody, supra, at 49-50.
The unlicensed front-end loading vehicle as well as the holding bins are asserted to be tax-exempt under the holding of National Lime & Stone Co. v. Kosydar (1974), 38 Ohio St. 2d 206 [67 O.O. 2d 228]. In that case, the front-end loading vehicles were utilized to load and blend piles of stone aggregate as part of the processing of raw stone into special sizes of crushed stone. The holding bins were used to keep the materials categorized. Id. at 207. In the present case, the same equipment is put to the same use. Also, appellant’s finished product similarly requires special mixes of particular sizes of stone. We must therefore conclude that the bins and front-end loader herein were as directly involved in transforming materials into the finished product as was the equipment in National Lime & Stone Co., and thus subject to the exemption in R.C. 5739.01(R).
The control house, which functions to control all of the equipment and therefore regulate all variables, is exempted to the extent and in the direct proportion that it controls equipment subject to an exemption. Also, repair parts allocable to exempt equipment are also entitled to an exemption. However, we are unable to find any exception applicable to the truck scales, since they are used outside the manufacturing process.
Finally, we conclude that in view of the strong public policy considerations supporting the finality of judicial and quasi-judicial pronouncements, today’s decision shall, with the exception of the subject litigants, only receive prospective application. Accordingly, the validity of other decisions by the Board of Tax Appeals, rendered prior to the date of this deci*10sion, shall not be affected. Accord Schucker v. Metcalf (1986), 22 Ohio St. 3d 33, 39; Hoover v. Bd. of Franklin Cty. Commrs. (1985), 19 Ohio St. 3d 1, 7.
For all of the foregoing reasons, the decision of the Board of Tax Appeals is affirmed in part and reversed in part.
Decision affirmed in part and reversed in part.
Sweeney, Locher, Holmes, C. Brown, Douglas and Wright, JJ., concur. Celebrezze, C.J., concurs in part and dissents in part.