Dear Mukund,
I think that your question relates to the casual employment directly done by the employer without any intermediary like a contractor. So, I prefer to leave out the case of permanency of contract labour in my answer.
In the first place it is important to analyse the definition of casual employment. Even the Model Standing Orders finding place in the Schedule I of the Industrial Employment (Standing Orders) Act,1946 simply defines a casual workman as a workman whose employment is of casual nature - that's all. Therefore, to the best of my knowledge and belief, the nature of the work for which a person is employed or engaged and the method of payment are the determinants in this regard. Here, nature of work is relative to the principal or main activity of the establishment or the employer. Every work which is incidental and required to be performed intermittantly alone can be a casual nature of work. Thus the absence of regularity of the work determines the method of payment for such workers on daily or hourly or piece-rate basis depending upon the convenience of monetary quantification of the work done by them. In other words, it is not the mode of payment i.e the periodicity in which wages are disbursed or simply put the wage period but in essence the method of payment.
Coming to the question of making the casual workmen as permanent workmen, I don't think that the Standing Orders of any establishment would be of much help for it would simply classify the workmen as permanent, probationer, badlis,temporary, casual and apprentices on the basis of the nature of their work or purpose of their engagement. Even, where some special enactment on the subject-matter of permanency of employment like the Tamilnadu Industrial Esatablishment ( Conferment of Permanent Status to Workmen ) Act,1981 is in force, if I were correct, the term "permanent status" has not been defined.
My conclusion is, therefore, the nature of a particular work being a question of fact, the questions of making the casual workmen as permanent workmen of the establishment and the time frame within which it should be done can not be precisely answered.But one should remember that item no.10 of Part 1 of the Fifth Schedule to the Industrial Disputes Act,1947 specifically states " to employ workmen as 'badlis', casuals or temporaries and continue them as such for years, with the object of depriving them of the status and privileges of permanent workmen " is an act of unfair labour practice on the part of employers.