Decorating new internal walls - patches

Currently painting a new build with a couple of coats of Dulux supermatt to kick off the decorating process. Have noticed that some walls have shiny patches in the plaster that is proving very hard to cover with paint even after 2-3 coats. The problem seems to be worse where block walls were scratched and skimmed as opposed to walls that were drylined and just skimmed afterwards. The plastering was finished months ago and the house is dry. Does anybody know what causes this or have any suggestions as to how to cover it?

i remember this hAPPENING TO ME BEFORE, AND WILL BE DOING A NEW HOUSE TOO MYSELF SOON, was it worse over the windows, where the lintels are

i think its just a case of keep painting,, its like there is an oily substance or some thing,, hope some one has a better idea of a cure,, heard to use milk, to neutrailise it?????

Paint the shiny areas where the paint is not covering with a flat oil based paint i.e. some undercoat. Then paint over the undercoat again as normal with your matt paint.

This is referred to as "mapping". It happens only on sand and cement based walls, something to do with paint reacting to the lime in it.

Got a tip from a guy when we were painting our new build. Simply , go over the areas using a good brush, and it definitely dissappears. Using a roller over theses areas only makes it worse.

Definitley works.

Secman

Thanks to all for your suggestions