fter applying impregnation to the wall, I'm unsure about the shiny thin film that has appeared.

First of all, a glossy film on the wall after applying impregnation is usually a sign of over-application. If the substrate is solid and cohesive (such as concrete) and has been deeply penetrated, there is no risk of peeling from the surface. In this case, the surface should be lightly sanded to make it rough, and then a less diluted paint should be applied.

However, if the substrate is less cohesive, it is possible that large molecules of the impregnation remained on the surface. This means the substrate has not been fully reinforced and may be prone to cracking and peeling. In such cases, it is advisable to remove or scrape off the layer (assuming the impregnation hasn't penetrated deeply and there are still loose layers of old paint). Then, clean, repair, and treat the surface with Primalex Primer.