How long should plaster last for?

If the walls where treated correctly before applying plaster to the walls the plaster should remain firmly to the wall for 15 years as this is the guarantee on Pva glue witch is used to treat the wall before plaster is applied. Although There are a few reasons why the plaster may have come off the wall even if the Pva was applied correctly. the most common is that the undercoat plaster has been applied to thick over 8mm and this may be the reason. Hope this helps Perfect plastering

There are many types of undercoat plasters, using the right one in the right place is important. Sand & Cement render is very hard wearing should last along time. HardWall is a powdered base undercoat not as hard wearing doesn't last as long never the less very good undercoat. If the walls were prepared properly and your landing and stairs was rendered Sand & Cement in my opinion should last 5 years up wards HardWall however 5 years max. I don't know what your consumer rights are but it wouldn't hurt to talk to your builder Hope this helps good luck.