I have a 1930's house and the wall ties have rusted away. I got my hand in the cavity and found one which broke easily. It is straight steel only about 5mm thick,and dosent seem to be of the fish tail variety. Can i replace the ties without isolating these old rusty ones? I was going to use the expanding mechanical stainless steel ties (pam ties) that grip to the inner and outer bricks as there is cavity insulation. A pro builder came round and said you need to drill from the outside starting in the middle of a brick - i thought you should drill the hole just to one side of the bricks centre?