Seal, impregnate, or leave the shell limestone wall untreated?

Hello and good evening,

I had a natural stone wall made from shell limestone blocks built, see attached photos. The gaps between the blocks were filled with trass mortar, and the top surface, on which the fence will later be mounted, was unevenly smoothed with trass mortar. Now to the question: should the top surface primarily be sealed/impregnated, or can I leave it as it was built? There are various statements on the internet. One statement is that protection is not necessary, referring to castles and palaces that were also not impregnated/sealed. Others say that impregnation can even be harmful. What is your opinion? Which product (transparent) can you recommend if you think protection is necessary?

Best regards

What does the executing company say? Whoever constructs something like this and provides the warranty should know that, shouldn't they?

Good morning Schorsch_baut, this was not built by a company, the wall was constructed as a do-it-yourself project. My son and my son-in-law are trained bricklayers. They have built houses before and this time the wall. However, the question relates to whether protection is necessary or rather not. Neither my son nor my son-in-law could answer this question.

In our region, there are such walls made of greywacke, and they are not impregnated. But usually, these do not have a flat, but a slightly slanted or rounded top edge so that water can drain off better.