I've done quite bit of reading, and just wanted to verify something before I try this. The Urethane in both cans I bought is like a good healthy thick maple syrup, and really needs to be reduced for better penetration, and lighter coating.

I bought a couple gallons of Varathane High Traffic oil based floor finish in semi-gloss, and from what I've found, the most common thinner is just plain old Mineral Spirits. Am I wrong on this one?

Will the mineral spirits ruin the semi-gloss finish on this stuff?

It is illegal to thin finishes with solvents in some areas of CA. Spread it at the rate that is specified on the can. Ask the person who sold it to you, or the manufacturer
the best way to applicate over your floor.

I purchased it throw HomeDepot online. I haven't been able to find it at any other store in the area. That's why I thought I would ask here if anyone knew more about using plain mineral spirits to thin Varathane oil based floor finish.
I did email Rustoleum, and they have not gotten back to me yet. Not sure if they even will. Also, I do not live in Californication, so I couldn't care less about what they think.

All that said, if anyone any suggestions as to the results they have receive while thinning this particular brand, I would greatly appreciate it.

If you warm the finish up in a bucket of hot water it will get runny.

Ok, I tried that, and it is still too thick to get a proper finish. It thinned a little, but as I brushed it onto a test piece, it immediately cooled and became thick again, and was no different. Don't get me wrong, it isn't like it's impossible to use, it's just too thick to get a really good finish like one would expect. Especially if I try to use a microfiber applicator. It should be very thin, more like the viscosity of Milk vs Mrs. Butterworths. It looks like garbage compared what it should be. I'm going to have to try and use some mineral spirits, and see what it does.

Rustoleum hasn't gotten back to me, and the only info I can find on the net digging through all the wood working forums, is that Penetrol and Mineral Spirits are the two best options. I would prefer trying mineral spirits because it is affordable and most available, unless someone has a really good reason this is not a good idea?

UPDATE:

Just got off the phone with Rustoleum, (finally) and this is good for anyone listening who wants to know the same. For the Varathane oil-based Premium Floor Finish, they recommend a few ounces of plain old Mineral Spirits to thin it just a bit to help work the product with an applicator or quality brush. He recommended no more than 8oz of spirits for 1 gallon of poly, or it will probably start to affect the quality of the gloss level in the finish.