Carteret Savings Bank's acquisition of Admiral-Builders Savings & Loan Assn. gave the thrift's 5,600 customers free access to their deposits for the first time in almost 13 months. A $1,000-per-customer monthly limit on withdrawal of nearly $40 million of deposits had been in effect since the beginning of Maryland's S&L crisis in May, 1985. Carteret also acquired First Federal Savings & Loan Assn. of Blacksburg, Va., and acquired the assets and some liabilities of Mountain Security Savings Bank of Wytheville, Va.