Gap Filler

Agree with NE... there was no need to thin Mr Surfacer.  I have all sets... 500, 1000 & 1200 but the 500 works best for filling in the gaps.  You may need to do few coats to make it work. 

I use Mr Surfacer 500 all the time, but it's already thinned.  For anything but a hairline gap, it's too thin, and needs multiple applications to fill it.  For those Mr Dissolved Putty works better, as it doesn't sink and shrink as much as 500.

Gunze makes wonderful products, but usually have to mail order them if you live in the states.  They're not interested in the extensive labeling re-work they'd have to do to import them to the US for retail sale.