As some of you know, I bring in Lantania from Italy. On the sealers I use, such as AVO, it says, "On highly absorbent surfaces, apply a second coat." Another sealer, TWINS.TW, it says "Apply using a cloth, performing circular movements, once completely dry, remove the eventual excess using a pad or cloth." This suggests to me that, the sealer...seals...enough for there to be an excess...in one application. Then again, it does go on to say "on highly absorbent surfaces, apply a second coat" a little misleading perhaps if the first coat leaves an excess???
On my other sealer of choice, HIDROSEBIN, again from Lantania, it says ..."on highly absorbent surfaces, apply a second coat". So, in my honest opinion, these sealers do their job in a maximum of 2 coats. Not the cheapest sealers in the world, but I am yet to find a better one.