I have an apartment that's a few years old and the corners where the walls meet the ceiling have started cracking. I want to fix it before I repaint. What product would you recommend and what's the correct process to make sure it comes out right?
For cracks in corners, the best option is acrylic caulk or a flexible sealant - it depends on how deep the cracks are: are they surface-level or pretty wide open? The process is you clean out the crack really well with a putty knife, apply the product (if it's really deep you might need two coats), let it dry according to what the package says, and then sand it lightly so it's smooth before you paint. If the cracks are new or there's still movement happening in your apartment's structure, use flexible caulk because it handles movement better than regular acrylic.
Corner cracks between walls and ceilings appear because there's natural structural movement happening there, so you need something flexible that won't break again in two months. The acrylic caulk mentioned above works for small, shallow cracks, but if yours look pretty wide open or have some depth to them, it's going to disappoint you because it gets rigid when it dries.
What really works is acrylic silicone sealant (also called white silicone or acrylic silicone caulk) that adapts to movement without cracking. The process: first clean the crack thoroughly with a putty knife or utility knife to remove dust and loose debris, run a dry brush over it, then apply the sealant with a caulking gun, pushing the tip deep into the entire crack. The key is to smooth it right away with a wet putty knife or your wet finger so it comes out even and without excess. Let it dry 24 hours before painting.
If the cracks are really deep or really wide, before sealing you can put painter's tape on each side of the crack so the sealant has something to grip onto and comes out more uniform. And even though it seems tedious, it's worth doing it right because afterward you really notice if it comes out bad or if it cracks again.
Log into answer.
