undercoat plaster cracking

[news.ntlworld.com]

we have been filling in where the electrics have been channeled out in the plaster work and other holds in the plaster work. Having applied hardwall to these areas some of them have developed hairline cracks and small like cracks between the new undercoat plaster and the old plasterwork. Will it be ok or will it need to be re-applied? and what could i do to stop it happening again. We pva's the brick work. Next month the plasterer will be coming in to re skim all the walls. help!!!!

[Andrew Gabriel]

It doesn't matter. It happens because plaster shrinks as it sets. Large volumes of plaster will always hairline crack. The finish coat is applied thin so that when it shrinks it does this mainly by getting thinner. (If hairline cracks appear as finish coat sets, that means it was put on too thick.)