Building cracks, angle grinders ?

[rideforever]

Just a query. Down here in Brighton I see a lot of builders fixing cracks in the external render of houses by angle grinding them off and then re-rendering.

These leaves smooth "gulleys" with straight line edges to fill.

It seems to me however that it would be better to chisel the old cracks off, because then you get an uneven surface which the render can hold on to better.

If you render an evenly cut "gulley" surely that creates a weak line in the render where it could fail in the future ???

Or am I wrong about that ?

 

[vinn]

You are talking about undercutting which is a good practice on interior plaster but irrelevant on exterior render.
Using a cordless grinder and the thinnest blade/wheel you can source is adequate for cracks that are filled with polyurethane sealant.