I got your email, Louise - Sorry, I've been away at a bonsai show & visiting friends/family. This is a tough one. As I understand it, you have a concrete block planter constructed atop a concrete slab, with no way for the water to make its way into the sand below the slab. Drilling holes in the block walls won't improve drainage. The only 2 ways to effectively improve drainage would be to make sure there is a 'bridge' between the soil in the planter and the sand below the concrete so the water can percolate through the soil, or to make sure the soil you use is porous enough that it holds little or no perched water. This would mean that your soil particles would have to be large & stable, insofar as their structure is concerned. Even the soil you see me holding above would be inappropriate for your application because that soil depends on the wicking action of the earth (in RBs) to ensure it doesn't remain saturated after rain/watering. It looks great, but if you have high standards it would be a disaster in a container or in your app. I'm thinking that about an 80% fraction of a mix of all purpose sand and all purpose gravel and 10% each of pine bark fines and Michigan (reed/sedge) peat or good compost would probably be the direction I would head. In subsequent years, I think all you'll need to do is mulch with pine bark to keep the soil healthy. If expense isn't a major consideration, you could use Turface MVP as the base ingredient for your soil. Topsoil and fine sand just isn't going to drain w/o help. The alternative would be to remove the old soil and cut a hole in the slab so water can drain from the soil in the planter, but it would have to be a hole of considerable size - preferably at the lowest point on the planter's bottom. If you have pictures, it's possible that something else might be devised that will allow the water to move out of the soil via some sort of passive wicking mechanism that we/you could devise, but I'd have to see the application in order to envision the possibilities. There might be a way to employ a false bottom by placing FRP panel on top of cement blocks that are resting on the bottom & building it like a self-watering container in reverse - where you employ a wicking column of soil to REMOVE water instead of supplying it, but I don't know how far you want to chase the issue? ;-) AL

How large is a "fine crack"? A photo would be helpful. The saw cuts are control joints that do not go all the way through the slab and are intended to encourage the inevitable cracks to form there instead of elsewhere. An expansion joint is a separation between slabs to allow differential movement. Its impossible to know if the slab was poured properly but I suspect a high water content, poor curing efforts, insufficient reinforcement, or hot/dry/windy weather. If this is essentially a cosmetic issues, it should only matter if the slab is exposed.

Your photo looks like a surface stain rather than an integral color. Depends on the look you want. We did have some pigment added to ours, just so it would be less "sidewalk" colored. We are really happy with how it turned out. We do have hydronic heat, which is wonderful. That alone requires serious insulation since you don't want to be heating up the earth. Our contractor was extremely fussy with the subs regarding protection of the slab during construction. The whole thing was always covered with a layer of Ramboard and a layer of a felt-like geotextile. (Think of all the things that go on during construction with your finish floor already in place.) I think it was after the interior construction that the concrete guy came back and did the polishing and sealing steps. (We looked at tiling the slab instead, but it was going to be another 10K)

OK...so now we know the source of the issue = no relief cracks. Not all cement slabs have them. That means the concrete must create it's own stress cuts. And that's what yours has done. There is still plenty of work to be done before the engineered hardwood is put down. Slab concrete is rarely good enough to have flooring installed right over top. There is usually some sort of 'preparation' to be done. So long as these cracks remain stable and do not crumble too much on the edges then you should be fine.