SA pedophile's sentence extended

South Australian serial pedophile Philip Cave will almost certainly die in jail, with a court extending his 50-year sentence following the abuse a 12-year-old boy.

Cave, 67, was found guilty of persistent sexual exploitation of the boy over a number of months between late 2005 and early 2006.

He has been in custody since 2006, serving a 50-year term for abusing more than 10 children over several years.

However South Australian District Court judge Geraldine Davison extended Cave's sentence to 55 years, with a non-parole period of 36 years, on Thursday.

Cave met the boy's mother though a newspaper dating column and brought the family over from Victoria to live in a shop that had an outside toilet and no bathroom facilities.

"You used the occasion to remove the complainant from his family and, under the guise of teaching him some skills including painting, you began to systematically abuse him in the most reprehensible manners," Judge Davison said.

"You did what you had done to numerous victims before him. You manipulated him and coerced him into sexual activities."

She said Cave normalised the behaviour and it took place on "many, many occasions".

Although Cave had pleaded not guilty, he admitted to the offending during sentencing submissions and offered an apology, which was rejected by the man.

"He thought it was too little, too late," Judge Davison said.

She said the boy was young and vulnerable with an "impoverished" home life when he was abused.

"He is deeply scarred by your offending," she said.

"He feels he can no longer trust anyone because of your behaviour."