Concrete fence posts widen

Hello, how many pillars are there?

If there are only a few (costs), maybe have a locksmith / metalworker build pillars that fit over the concrete pillars, but can be shifted left or right as needed because they are wider. Then prime / paint them in the desired color.

Other options, like pouring some kind of "sludge" into a form and hoping it holds, I consider (with affordable materials) out of the question. At least a reinforcement would have to be "stapled" to the old pillars for the "sludge" to hold onto. But the coverage will regularly be too small to withstand the weather permanently without crumbling away.

The "ivy plan" doesn’t make it any better. Ivy clings to the smallest cracks there and will break off your freshly installed "sludge" from the posts again. It certainly won’t look any better despite the ivy. Unless you like the "rotten look" or "shabby chic."

Hello, how many pillars are there? If there are only a few (costs), maybe have a locksmith / metalworker build pillars that fit over the concrete pillars, but because they are then wider, can be shifted left or right as needed. Then prime / paint them in the desired color. Other options like pouring some kind of "goo" into a formwork and hoping it holds I consider (with affordable materials) impossible. At least reinforcement would have to be "stapled" to the old pillars where the "goo" can hold on. But the coverage will regularly be too small to permanently withstand the weather without crumbling away. The "ivy plan" doesn't make it better. Ivy clings to the smallest cracks and will break off your freshly installed "goo" from the posts again. Surely doesn't look better despite the ivy. Unless you like the "decay look" or "shabby chic"

And what about the option with the construction boards ([doitBau Bauplatte XPS]) that could be glued together in width and then plastered together with the pillar? Or do you think that won't work? The locksmith option is definitely too expensive for us. There are 13 pillars in total.

Even cement-bonded XPS construction boards (XPS is "just" extruded plastic foam) are hardly stable enough to hold that and are apparently intended for wet areas (bathroom / kitchen), but I cannot imagine that these will last long if exposed to the weather permanently.

And what about the variant with the construction boards (doitBau Bauplatte XPS)? You could glue them together in width and then plaster them together with the pillar, right? Or do you think that won't work? The variant with the locksmith is definitely too expensive for us. There are a total of 13 pillars.

hits the nail on the head. It all sounds like half-baked methods that you won't enjoy because in the end it will be wobbly and also look crappy. Provided the concrete pillars are still stable, the locksmith can make brackets for you in the appropriate length. Also, it probably won't look good if you have a new railing with uniform shapes and in between 13 x Leaning Tower of Pisa-style little towers. My idea: remove the concrete pillars and set new suitable metal posts. Dig 13 holes for small foundations, put the posts in, and everything looks neat and color-coordinated. Everything else will be much more expensive with a lot of effort and... will look at best mediocre afterwards.

So of course you would have to check if that fits. But how about placing wall (form) stones on top and then concreting them in? It could only fail if these wall stones are again too large.

So of course one would have to see if that fits. But how about placing wall (form) stones on top there and then concreting them in? The only thing it might fail on is that these wall stones might then be too big.

Exactly, then the pillars would be too thick :-(