Prepare floor for vinyl tiles

F Ball Stopgap 300

Watch the videos on Youtube, use a spiked roller to move it around, dam the doorways (it will leak through the tiniest of gaps) and follow the manufacturer's instructs exactly - especially about priming the floor first.

However, as good as it is, I've observed it works best for a 5mm deep pour - you should get it to millpond flatness. 3mm is just about do-able. Much less and it won't self level that well. And this is the best product I know of (and have used).

I'd say get decent ply of a good thickness. That should be as level as it can be

how would you treat the edge gaps?

NT

I recently did a couple of Karndean vinyl plank floors... the usual recomendation is to give them a final coat of latex self levelling compound (I have used the Wickes one in the past, and its not too bad if you get it down fast - probably not as effective as Tim's F&B - although probably a fraction of the price!).

However on mine I just used 5.5mm WBP ply screwed down really well (6" grid), and then gave it a coat of feathering compound. That seemed to work fine as a base for the tiles. (although note mine do not have a high shine and so do not reveal every imperfection in the level)

Stopgap 300 was about £19 / 20kg bag 5 years ago - not too bad considering some of the sheds were charging similar for less good stuff :)

Not as much as I was expecting to be fair... ISTR the better of the two wickes ones were about £15 or £16 at the time. (they are listing the latex one at £18.69 at the mo, or 14.95 if you get 3 or more now)

but the OP will also need one bottle of:

for £34 and you cannot avoid using that (and expect SG300 to work!).

However, the end result is a flat surface that's virtually iron hard.