"Mixing" finishes?

Hello finish gurus et al,

Title may be a little misleading, sorry. Our son and recently new DIL did a repair and refinish job on the dining set son had in his college apartment, but ran out of time (and aren't really woodworkers :-( so I volunteered to finish the project for them. I will shortly pick up two chairs that have one coat of Minwax Polyurethane Gloss on them. When I opened the can, the remaining finish had gone bad. I have leftover General Finish Arm-R-Seal from one of my recent projects. Rather than go and buy still more, I was thinking I would do a light fine sanding and put the Arm-R-Seal on top of the earlier (8 mos ago +/-) Minwax Poly.

The chairs are oak, and there is Minwax stain "under" the first coat of poly.

Will mixing these finishes cause any major problems? This doesn't need to be Trump Mansion-worthy in appearance, it's a starter set for them. I just don't want to find out that the new stuff "dissolves" the old or anything like that.

Thanks all!

With eight months of cure time you can put almost anything over almost anything. Two oil based polyurethane varnishes will work OK but be sure to cover the surface thoroughly with your light sanding. Since this is a dining set, you may want to do some cleaning first just to be safe. I'd be really gentle with any water given that they have only one coat of varnish. But mineral spirits or naphtha will remove any oily dirt without damaging the varnish at all. An non-poly oil based varnish would be even more of a sure thing as far as adhesion, but the sanding should provide enough tooth for polyurethane to adhere.

>>>> Will mixing these finishes cause any major problems?

None whatseever. In fact, the two are almost identical. Both are polyurethane varnishes and are totally compatable.