Can you apply wipe-on poly over a varnished surface without stripping the varnish off? I have kitchen cabinets that were finished with varnish 3 years ago and would like to put a more durable finish like Minwax wipe-on poly.
Unfortunately "varnish" does not define a specific product. It is generally a drying oil combined with some sort of film coat, but there are hundreds of things it could be. Some of these would bond well to polyurethane (the varnish could actually be oil + poly) and some may not.
The only way to know for sure is to do a test in an inconspicuous area. Even then, problems might not show up for years.
You can increase your chances of getting a good bond by using a coat of shellac, which is known to bond well to almost all finishes, before you apply your poly.
That said, realistically if your cabinets were made in the last 30 years the varnish is probably poly-based. I'd say you have a better than 50/50 chance of success just applying poly (after a thorough de-greasing and scuff sanding - kitchen cabinets are notorious for getting cooking grease on them).
Short answer: yes, you can apply wipe-on over previous varnish.
Whether it'll work well in this specific case nobody can say, you'll have to try it and see. But following the basic prep guidelines it'll usually work fine.
It isn't as simple as just wiping on the Minwax product over the existing varnish. In addition to something that's probably obvious, cleaning the surface well beforehand, you must provide a texture for the new varnish to cling to. What this means in practice is washing down every surface you intend to recoat and then lightly sanding or scuffing them — be very thorough doing this and try not to miss any spots even in hard-to-reach areas. But also be careful you don't sand through along edges and particularly at corners.
- clean thoroughly;
- wait until dry;
- scuff or sand thoroughly but carefully;
- wipe away every trace of sanding dust;
- apply wiping varnish1;
- wait for the wiping varnish to get good and hard before the cabinets see much use, perhaps a full week if you can manage it2.
1 Note that it doesn't have to be applied by wiping, you can use a brush or roller if you want although you will probably still want to wipe away some or most of the excess.
2 Full hardness won't be achieved for approminately a month.