What type of sander is best -- skimcoating a luan plywood underlayment, prepping for vinyl sheet

I am re-using existing luan underlayment floor, in preparation for installing new vinyl sheet floor. This is on the advice of my installer, who has seen my floor underlayment and recommends its re- use.
Which type of sander should I buy, to touch-up the skimcoat after I have spread it?
Random orbital, belt, vibrating pad?
Please reply urgently. I am buying the sander tonight. I appreciate any input you have.
PS - I cannot stop the group from pontificating at length on my situation. But please: if you must type 1000 words on the wisdom of my project, at least throw in some advice about the sander. :)
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Dunno what you're calling skimcoat- assume some sort of patching/ leveling stuff for divots you'll pull out of the ply.
Given that, suggest you apply any such stuff sparingly, with wide knives. If advisable, in multiple thin coats.
My first guess as to sander would be a 6" PC ROS (with vac connection), and 60-grit. Combo I use for rough work.
J
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snipped-for-privacy@sme-online.com wrote:

...
For a floor prep my first choice would be to simply rent a floor sander if there's any sizable area at all.
Otherwise, if you're just touching up small patches here and there, the above choice is probably good as any. You have any other reason for buying a sander? Might as well try to make it serve some future purpose in life other than sit on a shelf forever.
If it's just the occasional nail hole and so on, and you don't do a lot of really heavy work, I'd suggest you might find the 5" ROS more handy in the long run and it will handle that kind of a job as well...
Really too little info to judge what you really need for the task...
--
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My first choice would be a belt, but if you've never used one, then can be dangerous. Well, in the hands of the inexperienced, they can take away a lot of material fast and leave you with divots and more work than you started with.
The vibrating pad sanders are not much good for anything but the lightest of work.
That leaves the ROS. Get a 5" or 6" and it will do a good job with no real learning curve. Just remember to let the machine do the work and don't use a lot of pressure. Ed
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Guys, thanks a lot.
More info: I will be spreading Dependable-brand gypsum skimcoat onto divots missing from the luan underlayment. When I pulled the perimieter-glued vinyl floor off, it tore sections of the top layer from the underlayment.
Since these sections were a small percentage of the overall area, this is why we decided to re-use the floor.
The random-orbital does seem like the best option. I will be sure to buy one with a vac port. I didn't think a belt sander would be necessary, and yes the vibrating ones don't seem to do much at all.
I am sure to buy plenty of knife sizes, too.
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wrote:

A random orbit sander will work fine, about $100 or less. If the floor is large consider renting a floor sander, but you will still need a smaller sander for the edges, corners. A belt sander is very aggressive.

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