Builders' waste?

We moved into our home just over 2 years ago, so coming into our 3rd summer. The soil is clay, though not really heavy, claggy stuff, but drainage seems to be poor in places. I am gradually developing the garden, including a veg plot which has 2 large raised beds and 2 smaller normal beds, incorporating organic matter as much as possible.
The smaller beds have been used so far for salad veg then tomatoes and beans. For the 3rd rotation I'd planned potatoes, so started double digging to prepare for planting. I hit problems with the last third of the bed, as at about 1 spade's depth there is a layer of what I thought was cement, but now think may be crushed lime. It's quite granular in texture, but also has stones mixed in, ranging in size from around 1" to a few as big as 4".
I'm wondering what's best to do about this - do I try to dig it all out (no idea how deep it goes, but even if only a few inches it'd be quite a job), try to dig it over and just mix it with the clay, removing the stones as much as I can (could this improve drainage?) or just leave it as it is and forget that end of the bed for potatoes? Also if it is lime how much would mixing it in or leaving it in situ affect the acidity of the soil?
Any advice much appreciated!

Re: Builders' waste?

Reply from Clockhouse Nursery

It might be sensible to do ph soil test kit on that area first to find out if it is lime. Potato plants prefer sandy loam with a ph of about 5.5. If the soil is strongly alkaline you may be better off growing the spuds in the raised beds.

Re: Builders' waste?

Reply from Ian McLintock

Digging out works. I use a mattock, but it's hard work and loads to dispose of. Try breaking it up a bit. If there's man made material in it, it's probably builders' waste - not alkaline. If it's waste break it up a bit and add organic matter. If it's sub soil, dig it out or leave it. Could try the My Soil app, which will tell you what type of soil you have. If you think it's limestone, pour some vinegar on a bit. If it fizzes, it's lime. You can use sulphur chips and/or acidic fertilisers to make more acidic, but limited impact and slow. Raised beds usual solution. More positively, I dug my borders out - painful, but it saved going to the gym and worked really well. Or philosophise your way out if it. Lots of vegetables don't need great soil depth and like alkaline conditions, and grow your potatoes in a planter!

Re: Builders' waste?

Reply from Jan Jones

Thanks both. I'd like to avoid digging it out if I possibly can! So think Ian's last suggestion might be the way to go - the lettuces, tomatoes and beans all did fine there so I'll live with it and skip the spuds, as they did well enough in the raised beds.