I need to make up some rock face block with my antique machine to use on two projects this summer and was wondering about using a light weight mix.

The first project requires just a single course of block to sit atop an existing retaining wall. The block will then have a concrete cap on top of it and will be parged on the inside along wit the retaining wall. So basically it is non-load bearing, non-structural and purely decorative.

The second project will be a low fence, three blocks high and about 40′ long with a concrete cap on top. Again, mostly decorative with the only weight being the cap and someone sitting on to.

Are there any downsides to using a light weight mix? The cores on this antique machine are small and the blocks weigh a lot when wet. I’m just trying to save my back on these.