Wash. Rev. Code § 63.14.020
Every retail installment contract shall be contained in a single document which shall contain the entire agreement of the parties including any promissory notes or other evidences of indebtedness between the parties relating to the transaction, except as provided in RCW 63.14.050, 63.14.060 and 63.14.110: PROVIDED, That where the buyer's obligation to pay the time balance is represented by a promissory note secured by a chattel mortgage, the promissory note may be a separate instrument if the mortgage recites the amount and terms of payment of such note and the promissory note recites that it is secured by a mortgage: PROVIDED FURTHER, That any such promissory note or other evidence of indebtedness executed by the buyer shall not, when assigned or negotiated, cut off as to third parties any right of action or defense which the buyer may have against the seller, and each such promissory note or other evidence of indebtedness shall contain a statement to that effect: AND PROVIDED FURTHER, That in a transaction involving the repair, alteration or improvement upon or in connection with real property, the contract may be secured by a mortgage on the real property contained in a separate document. Home improvement retail sales transactions which are financed or insured by the Federal Housing Administration are not subject to this chapter.
The contract shall be dated, signed by the retail buyer and completed as to all essential provisions, except as otherwise provided in RCW 63.14.060 and 63.14.070. The printed or typed portion of the contract, other than instructions for completion, shall be in a size equal to at least eight point type.
RCW 63.14.020