The Secretary shall adopt a uniform procedure for the acceptance of materials and products to be used in structures approved for mortgages or loans insured under this chapter. Under such procedure any material or product which the Secretary finds is technically suitable for the use proposed shall be accepted. Acceptance of a material or product as technically suitable shall not be deemed to restrict the discretion of the Secretary to determine that a structure, with respect to which a mortgage is executed, is economically sound or an acceptable risk