31 Next, the plaintiff pleads that "as a result of the matters" pleaded in respect of the claim of estoppel, the first named defendant waived the operation of the condition precedent in cl 5.2(b). In argument, Mr Blow confined his submission to the proposition that the clause was waived by Miss Nguyen's communications by telephone on 21 February 1997, that is by her advising the vendor's solicitors that finance had been approved. He submitted that if finance had not been approved, the condition was not self-executing, but should be construed as making the contract voidable at the instance of the purchaser, provided that it had used reasonable endeavours to procure the finance. As to the last matter, I find that the defendants did use reasonable endeavours to procure finance and cannot be criticised for the failure of the condition being fulfilled. Mr Blow referred to Zieme v Gregory [1963] VicRp 34; [1963] VR 214, especially at 222 - 223. I note, however, that the "subject to finance" condition in that case was not expressed, as it is here, as a condition precedent. Mr Blow's submission continued to the effect that the purchaser, having a right to avoid the contract because of the non-fulfilment of the condition, could waive its right to do so, and in fact did so by Miss Nguyen's conduct on 21 February. If the condition was merely resolutive within the meaning of Zieme v Gregory (supra), by seeking and obtaining an extension of the date of settlement (in turn an extension of the time within which to obtain finance), the plaintiff no doubt would have waived its right to immediately avoid the contract by reason of the non-obtaining of finance at the time specified in the contract, but it would not have lost all its rights under the clause. As Jessell MR said in Barclay v Messenger (1874) 43 LJ (Ch) 449 at 456, "a mere extension of time, and nothing more, is only a waiver to the extent of substituting the extended time for the original time, and not an utter destruction of the essential character of the time". (See also Holland v Wiltshire [1954] HCA 42; (1954) 90 CLR 409 at 415 and Tropical Traders Ltd v Goonan (1963 - [1964] HCA 20; 1964) 111 CLR 41 at 52). Hence, had finance become available within the extended time, purported avoidance by the purchaser could have been resisted by the vendor on the basis of the purchaser's waiver, but once the extended time had elapsed without fulfilment of the condition, the right to avoid would have revived (cf, Charles Rickards Ltd v Oppenheim [1951] KB 616). However, it is not the extensions upon which Mr Blow relies, but the erroneous representation that finance had in fact become available. It has been said that "a right is waived only when the time comes for its exercise and the party for whose sole benefit it has been introduced knowingly abstains from exercising it" (per Brennan J (as he then was) in Commonwealth v Verwayen (1990) 170 CLR 394 at 427). The necessity for knowledge of the existence of the right is stressed in Craine v Colonial Mutual Fire Insurance Co Ltd [1920] HCA 64; (1920) 28 CLR 305 at 326, Grundt v The Great Boulder Proprietary Mines Limited [1937] HCA 58; (1937) 59 CLR 641 and Kammins Company Ltd v Zenith Investments Ltd [1971] AC 850 at 883. The purchaser and its agent, Miss Nguyen, were ignorant of the existence of the right to avoid the contract in the circumstances as they existed on 21 February because they believed the condition had been fulfilled. They were ignorant therefore of facts which could have given rise in law to a right to rely on the non-fulfilment of the condition. The representation that it had been fulfilled may have created an estoppel if the vendor had altered its position in reliance upon it, but it does not constitute a waiver of the purchasers' right to avoid the contract by reason of a fact the plaintiff did not then know. To constitute a waiver, the purchasers would have to have known that the condition was not fulfilled, thus making the contract voidable at its instance and to have intentionally acted to forego that right. That is not the case here. The purchasers did not intentionally abandon any right to rely on non-fulfilment of cl 5.2(b) by mistakenly indicating through its agent that that clause had been fulfilled.