The parquet that I have is reclaimed, it was originally bonded to the floor using bitumen - this has left a residue on the blocks. There is much debate on the Internet about whether or not you can stick blocks down with old bitumen on them - the conclusion seems to be that you can if you use an adhesive formulated with old bitumen in mind, and that your blocks have "bitumen residue" on them.
So far so good - but what qualifies as "bitumen residue"?
I thought that it would be best to test this.
Here's a block that has had the minimum of cleanup - just enough to knock any protuberances off and make sure it's square:
This has had the bitumen knocked back a little, but there are still a couple of spots:
And this has been scraped for a couple of minutes:
I've stuck them all to a board using Sikabond 5500S:
In this order:
And will see how well they have all stuck tomorrow. If the almost untouched one bonds well then that has the potential to save days of work, so fingers crossed.