The Dragons ran in 16 tries altogether in a record win for the Youth.
Treorchy's wing wizard Chris Clayton was the top scorer, touching down for five scores, while scrum-half Liam Davies bagged a try and four conversions.
Wales overcame Portugal 24-0 in their opening European Four Nations game last Sunday and this latest win has set up a
tournament decider against Italy at Dunvant on Saturday, kick-off 2.30pm.
Spain play their Iberian neighbours Portugal in the other match which kicks off at 12.30pm, also at Dunvant RFC.
Wales under 18 v Spain under 19
Tries: C Clayton (5), L Davies, B Lampitt, G Evans, D Robinson, H Gstafson, S Wahdan, A Hopkins, L Ryland, J Spratt, T Stephens, A Smith Cons: L Davies (4),
A Smith (2)