That is correct. 1% of damage received passes through the base's shield. In order to defeat a base, you have to make that 1% high enough to over come the repairs done by using just basic alloy; this will force it to consume the other repair materials and/or use more basic alloy.
If it runs out of repair materials it will begin to lose health, even with the shield up. Keeping the shield up forces the defenders to have to restock fuel also.
Take Smallwood for example. A very well stocked level 1 base. Took the Sairs a few days of high activity siege to drop it. Sieges aren't hit and and done. They are a war of attrition.