## 1 Introduction  
The assessment and verification of constancy of performance (AVCP) is a harmonized system defining how to assess products and control the assessment results' constancy. AVCP is a complex and multi-dimensional process. In the European Union, the Construction Products Regulation (CPR) lays down harmonized rules for the marketing of construction products [1]. The document sets out also methods and criteria for assessing and expressing the performance of construction products, and the conditions for the use of the CE marking. The CE marking indicates that the performance of the product has been assessed, and that remains constant. The CE marking enables a construction product to be placed legally on the market in any EU country and then be traded on the EU's single market. According to Regulation (EC) No 765/2008 [2], each member state must establish market surveillance authorities that will ensure compliance with this regulation's requirements in their countries. As a rule, if it is found that the product does not meet the criteria, i.e., the product does not meet the declared performance, actions must be taken immediately to adapt the product to the declared performance or to withdraw the product from the market. The type and manner of work should be related to the nature of the risk it creates. In Poland, the General Inspector of Building Control (GINB) is the central body of government administration in architectural and construction administration and construction supervision [3]. Construction supervision authorities (both GINB and voivodship inspectors of building control) perform tasks of market surveillance authorities, including inspections of construction products [4], in the field of CE-marked construction products. Construction product inspections are scheduled or ad hoc. They cover various tasks, including, among others, analysis of documentation and control tests of products performed at the request of construction supervision in notified laboratories. Due to the commonly performed tests of construction products commissioned by construction supervision authorities, the Polish market of construction products differs from other EU countries' construction product markets. The activities of construction supervisors are organized differently in the member states, and the role of construction supervision is understood differently [5]. Nowadays, dry-mix mortars prepared in specialized production plants (plaster, render, tile adhesive, grouts, waterproofing slurries, concrete protection and renovation, insulation and finishing systems, and others) are widely used in construction. Cemertitious adhesives for laying ceramic tiles are an essential assortment group among ready-made dry-mix mortars. In 2018, the production of ceramic tiles in the world amounted to 13.099 billion m\({}^{2}\), including 1.366 billion m\({}^{2}\) in the EU countries, and consumption reached 12.818 billion m\({}^{2}\) and 1.034 billion m\({}^{2}\), respectively [6]. Assuming the average use of cementitious adhesives for ceramic tiles of 4 kg/m\({}^{2}\), this means the world production of tile adhesives is over 52 million tons, including just over 4 million tons in the EU countries. Following the work carried out by CEN/TC 67/WG 3 in 2001, the European standard EN 12004: 2001 was established [7]. Since then, we can talk about the unification of requirements for CTAs at the European level. In Poland, the EN 12004 standard was introduced to the Polish standards set in 2002 as part of pre-accession activities aimed at the country's accession to the EU. However, only after Poland joined the EU on 1 May 2004 could Polish producers, on an equal footing with producers from other EU countries, take advantage of the opportunities provided by this standard. Previously, other requirements were in force in Poland, which additionally changed several times [8]. The EN 12004 standard with the requirements for CTAs had successive editions, i.e., EN 12004: 2001/A1:2002/AC:2002, EN 12004:2007, EN 12004:2007+A1:2012, and EN 12004-1:2017.