Purchased a house last year. built early 60's, cavity block, and some 4"x9"x18" block on flat around windows. Very cold over the winter.
Decided to insulate the house with 50mm drylining on all external walls.
Small bedroom, 2 external walls had non insulated drylining already, so builder advised removing the plasterboard...
the 20mm render came with it... in 2 and 3 foot sections...
exposing all the blockwork, which was dark grey and wet...
Not something you want to see happen to you house... when you have no idea of the building trade...
Engineer called to the house and discovered rows of 'patched' holes all around the gable end of the house. Someone tried to insulate cavity blocks, drilling each one, and pumping them. But the blocks were never sealed.
We now face having to strip and re-rended the whole house.
My advice... don't even think about. It will destroy you house.