Well, I don&#x27;t think that&#x27;s true.<p>Eventually, the plate will be higher density than the material available at the point of its construction, so it will need to take material from outside the plate&#x27;s current area to fill it.<p>As the plate extends further into lower-density regions, it will have to extend its materials gathering exercises further and further away from the actual construction site, so they&#x27;ll take longer and longer to get there.<p>Even if the plate is very low density indeed, eventually you&#x27;ll run out of planet and have to start dismantling the moon - which is quite a long way away - unless the plate has a lower density than the volume of space the moon encloses.