Help with rustins plastic costing on veneered mdf

[Adam9453]

Hi,
I've made a windowsill out of walnut veneered mdf and I gave it one pretty thick coat of rustins plastic coating on Sunday afternoon.
I checked the finish today and it has sunk into the grain as I didn't fill the grain first.
My question to you finishing gurus is as follows;
Firstly, if I apply more layers of rustins plastic coating will I be able to sand it back to achieve a flat glass like finish or will the fact I didn't fill the grain first prohibit this from working?
Secondly, if I am to apply further coats should I wait a week for this first coat to fully harden, then sand back with wet and dry, then apply the next coat. Or do I not need to sand this first coat because it's already sunk into the grain?

As you can tell finishing is not my speciality and I could really use your help.

 

[ED65]

These previous threads I think answer all your questions:
avoiding-brush-marks-in-rustins-plastic-coating-how-t94088.html
rustins-plastic-coating-straight-from-the-horses-mouth-t61190.html

The first of these actually links on to the second, but has good info of its own.

 

[Adam9453]

Thanks I hadn't seen the first post you linked to but I had read the second numerous times to check the application method.
I spoke to a spray finishing guy today and he said it should flat back ok and more coats should make the grain disappear leaving the glass smooth mirrored finish I'm after.
If worst comes to worse and I wreck it then I'll put it down to experience and test on some scrap before trying again.
Thanks anyway