(1) Where the contractor demands part payments in accordance with section 632a, the aggregate amount of the part payments may not exceed 90 per cent of the total remuneration agreed upon, including the remuneration for work done under change orders under section 650c.
(2) On effecting the first part payment, the consumer is to be provided with a security amounting to five per cent of the total remuneration agreed upon for the timely implementation of the work without major defects. If the claim to remuneration increases by more than 10 per cent as a result of an order by the consumer under sections 650b and 650c or as a consequence of changes or supplements made otherwise to the contract, the consumer is to be provided with a further security of five per cent of the additional claim to remuneration on effecting the next part payment. On demand by the contractor, the security is to be provided by retention such that the consumer retains the part payments up to the total amount of the security owed.
(3) Securities under subsection (2) also may be provided by way of a guarantee or any other payment undertaking by a financial institution or credit insurer authorised to operate its business in the territorial extent of this Code.
(4) Where the contractor demands part payments pursuant to section 632a, an agreement is ineffective that obligates the consumer to provide security for the remuneration agreed upon which is in excess of the next part payment, or in excess of 20 per cent of the total remuneration agreed upon. The same applies if the parties have agreed part payments.