Poor construction quality is a consequence of Spain’s insane property boom for 2 good reasons:
1) Even crap sold quickly in the boom. Developers noticed that everything sold fast at whatever price they asked, so many of them took the easy route, built crap, raised the price, and made a killing. Undiscerning foreigners buying off-plan investments on weekend inspection trips made this particularly easy to do. Fast deteriorating quality is one of the reasons why Germans stopped buying in Spain. Everyone who has worked in the business long enough will remember that Germans were quality conscious.
2) When a country like Spain builds 900,000+ properties per annum, you can rest assured that at least half of them will be built by low skilled immigrants in a hurry. You don’t have to be a genius to work out what impact that has on quality.
There are other reasons, but I won’t bang on about it.