Appellee Gould brought this diversity suit against appellant, Trinity Universal Insurance Company, to enforce the penalty on its surety bond for the performance of a contract between Gould and Abney for the construction of Gould’s dwelling. Trinity asserted a material alteration of the construction contract which worked a breach and discharge of the bonded obligation. This appeal is from a judgment in favor of Gould on the surety bond in the approximate sum of $12 000. The cross-appeal challenges , n , only the amount of the award,
The construction contract obligated Abney to construct the dwelling for Gould according to specifications for the sum 0f $25,000 and to complete the same on or before May 1, 1951. The contract contained the conventional ten percent retainage, and also provided for changes an(j alterations without change in the contract price, unless the contractor, before making such changes and alterations, notified the owner in writing of added cost, in which event Gould had election whether to proceed with SUch changes. In conventional langUage, the bond guaranteed the performance of the construction contract in the principal amount thereof, provided among other things that the obligee should retain ten percent of the contract Price until complete performance; and that “no change shall be made in such plans and specifications which shall incrfse Seamount to be paid the princiPal“ore than ten Penalty of thls instrument without the written consent of the surety.
During the course of the construction of the dwelling, numerous changes were made m the plans and specifications, but 0nly tw0 items in the a^ate °f *- 425 were submitted m writing by the contractor for additional cost. Early in May, the contractor orally agreed with Gould’s father-in-law to construct a porch and certain other alterations in the kitchen and family room, in accordance w^h separate plans and specifications on a cost plus ten percent basis, estimated to be $5,000. On April 25, 1951, $12,888.23 had been paid on the $25,000 contract price. The house was not completed on May 1, 1951, and Abney and Gould agreed that Abney would continue performance of his contract. Abney failed to pay material and labor bills as they became due, and on or about May 10, 1951, Gould began to pay one hundred percent of the cost of work on *885the residence on certification of the labor and material bills. The bills were paid either through Abney’s controlled bank account, or directly through Gould’s account in the same bank. In August Abney had been paid the sum of §26,464 and the dwelling was not compíete. When Abney expressed a disposition to leave the job, the father-in-law offered to pay him not less than a §2,000 bonus in lieu of his prior separate cost plus agreement with him if Abney would “stay on the job and complete tte house”. Abney finally left the job unfinished on October 8, 1951, at which time a total of approximately §40,000 had been paid to him or for his account. Thereafter Gould completed the house at a total cost of §63,021.38. Gould first notified the surety in writing of the default on October 11, 1951.
The surety takes the position that the cost of the changes and alterations made by agreement between Gould and Abney and paid for by Gould, without the surety’s consent, exceeded ten percent of the penalty of the bond, and it is agreed that the changes authorized by the father-in-law exceeded tnis amount. Gould argues, however, that the changes authorized by the father-in-law were paid by him under a separate independent contract, which in no wise prejudiced the bonded obligation; that with respect to the other changes and modifications, only §l,42o was suomitted in writing for additional coso; that it must therefore be presumed that all other changes were within the contract price; that Abney simply undertook to build the house too cheaply, and that the bonding company should have known it.
The record does not show the cost of some sixty-seven changes or alterations; no attempt was made to segregate them; indeed, no attempt was made to segregate the cost of the father-in-law’s additions and alterations. All were paid from a common account, From the nature of the alterations, it seems fairly inferable, however, that the cost of those made without written noti-fieation greatly exceeded the allowable ten percent of the contract price. At the same time, it is arguable that inasmuch as the contract contemplated changes and alterations without change in the contract price unless submitted in writing and approved by the owner, all changes and alterations except those so approved carried no additional cost in excess of the contract price,
IS course alm°í af.1Qmatie that any change or modification the construction contract wine materially increases a compensated surety s risk discharges the obngation. See Restatement Security § 128. On the other hand> contracts of this kind conventionally contemplate changes and alterations in tke specifications; and any change or modification which does not materially affect the risk 18 inoperative. See Williston Contracts, Vol. 4, §§ 1239, 1240, 1241> The trial court made no specific finding on whether the changes and alterations agreed to between the parties witll0Ut the consent of the surety exceeded the allowable tolerance under the b(md> bence effected a discharge. Its judgment, however, presupposes a material alteration of the construction contract and a resuitant breach of the sure-^y bond, for it rests squarely upon the alternative grounds of equitable waiver, jn regard) the court specifically found that during the course of the congtruction, Gould informed Trinity’s local policy-writing Manager of all the developmenls in connection with the buildfng contract, including the failure of Abney complete the building on May 1; agreement of Gould and Abney that ^bney would continue the work; the change in the method of payment; the written statements of additional cost by reason of changes; and the cost plus agreement between the father-in-law and Abney. The court found that on July 3, 1951, the local representative advised the responsible agents of the company that there would be a definite shortage on the contract; that from time to time the local agent advised his superiors of all the information concerning the contract by telephone, letters and progress *886reports; that with this knowledge, the local agent was advised to “use his best judgment and go ahead and do the best you can”, and the surety took no other steps to protect itself after being informed of the facts by its local agent. The surety may of course waive a breach of its bond by consenting to the material alterations of the bonded contract. Our decisive question is whether the trial court’s findings to that effect are clearly erroneous.
While the surety may waive the breach, mere knowledge of the breaching alterations does not amount to requisite consent, nor does knowledgeable silence give consent. It was under no duty to declare a breach of the bond even with knowledge of material alterations of the construction contract. Citizens Building & Loan Ass’n of Emporia v. Jones, 149 Kan. 302, 87 P.2d 633, 636; Cure v. Midland Life Ins. Co., 109 Kan. 259, 198 P. 940; Musgrave v. Equitable Life Assur. Soc., 124 Kan. 804, 262 P. 571; Johnson v. Dumond, 130 Kan. 516, 287 P. 249. See also Annotation, 101 A.L.R. 1310. But, as a compensated surety, Trinity owed its patron the duty of good faith which ascends the morals of the market place — a duty not to deceive or mislead, Any course of action with knowledge of the breach which can be reasonably construed to indicate a disposition to continue the suretyship relation works a waiver of the breach. Jack v. Craighead Rice Milling Co., 8 Cir., 167 F.2d 96; Sormanti v. Deacutis, 79 R.I. 361, 89 A. 2d 191; Spring Garden Building & Loan Ass’n v. Rhodes, 126 Pa.Super. 102, 190 A. 530.
It is an established fact that the surety’s local bond-writing agent was present and familiar with all of the critical facts until September 1951. And, while it is agreed that he had no authority to alter or waive any provisions of the bond, it cannot be doubted that he was an effective conduit for the conveyance of information to his principal, And, it is undisputed on this record that he did advise with Gould from the time of the work lag under the contract in May 1951 until he left the employ of the company the following September, Gould discussed with him the various changes and variations in the construction. And, while they did not discuss dollar value, the local representative did in turn discuss generally such changes with his superiors either at the office in Dallas, Texas, or the General Agent in Topeka, Kansas. He knew of the father-in-law agreement and so did the surety, When Gould and Abney made changes, wben Abney’s checks to the materialmen and workmen were unpaid and Gould took °yer tbe responsibility for paying th® bdls’ when the completion date was ^tended and the ten percent retamage claus® waived the surety was informed and bad “° objections. And, Gould was. so advised. This course of conduct is taialy susc®ptlble °f the “ference that the appellant affirmatively acquiesced in the material alterations of the contract, _ and thereupon waived the nght t°insistt upon a breach. In these circumstances, we cannot say that the trial court s judgment based on waiver is c ear y erroneous.
The trial court did err in allowing the plaintiff interest from the time of original notice of Abney’s abandonment to the surety on the amount finally determined to be due the plaintiff as damages. Under Kansas law, interest is not allowed on unliquidated claims in the absence of unreasonable and vexatious delay of payment. Leader Clothing Co. v. Fidelity & Casualty Co., 10 Cir., 237 F.2d 7; Southern Painting Co. of Tenn. v. United States, 10 Cir., 222 F.2d 431; Winfield Mortgage & Trust Co. v. Robinson, 89 Kan. 842, 132 P. 979. In view of the perplexing questions of breaches of .the bond and waiver here, it cannot be said that the defendant’s re-fusal to pay under the bond was_ unreasonable or vexatious delay. Certainly the damages were unliquidated, as evidenced by the cross-appeal, which we now consider.
Cross-Appeal
The sole question involved in the cross-appeal is whether substantial evidence *887supports the trial court’s finding of the amount of damage suffered by the plaintiff as the result of the defendant’s refusal to perform under its bond.
The court based its findings of amount of damage on the testimony of a Wichita contractor as to his opinion of the cost of doing the work originally contracted for, less the contracted price. Gould says his testimony is unreliable and contends recovery should be based on the testimony of other experts as to the cost of the father-in-law's addition and other modifications for which he accepts responsibility subtracted from the total cost to Gould of completing the house. It is sufficient to say that since substantial evidence supports the finding of the trial court, credence will be given to such judgment. Kansas City Public Service Co. v. McMullin, 10 Cir., 142 F.2d 116; Smails v. O’Malley, 8 Cir., 127 F.2d 410.
The judgments on the appeal and cross-appeal are affirmed, except for the award of interest.