Troubleshooting a Flaking Finish
The doors are made with a hard rock maple frame and an MDF panel. My question is, what is the best way to finish these doors and drawer fronts so that they don't chip and peel again? I need to match the existing color. The finisher I used said he applied 3 coats of sanding sealer, sanded between coats, then applied two coats of finish, which was a pre-cat lacquer.
Your goal is to create surfaces which have the proper tooth for the film-forming materials to establish a mechanical grip. Do not neglect to break the edges of your surfaces. No crisp edges is the goal. A coating does not like a crisp edge. Maybe wall paint can work itself around a sharp edged corner, but furniture coatings cannot. How many angels can stand on the head of a pin? Who cares, but how much dry mil thickness can be built up on the crisp edge of a door? Very little. And there is very little decent tooth to get your grip. Blunt edges, rounded edges, eased edges and broken edges are what coatings like. Give them their due respect and you have your best shot at adhesion.
As I understand it, your finisher used sanding sealer, and three coats of it. Then he used a pre-cat lac. Was this lac tinted to the color? There must have been a color for the guy to buy when he mixed it up. Do that again for the same color. The thing that I question is why there wasn't a primer used instead of sanding sealer. If you have a good primer and it has good adhesion, there shouldn't be any chipping or flaking of topcoat, if applied correctly.
Don't use sanding sealer and don't use precat lacquer. Get yourself a pigmented conversion varnish - better adhesion, better durability, better moisture resistance.
It seems like sanding sealer (clear stuff, used on stain-grade under clear lac, right?) wouldn't quite hold the colored lacquer the way a white primer basecoat would. I'm not the most experienced, but I've never heard of clear sanding sealer going under colored lac. If this is what he did, contact the maker of the brand he used and see if this is acceptable - if not, sounds to me like he's got some money to cough up.
For starters, three coats of sanding sealer on anything is bad. Lacquer on the cabinets is why the finish is failing - as was said before, it's much better to use the pigmented conversion varnish. SW makes a great one. It's a little pricey, but well worth it.
Sand the hard maple no finer than 180 grit - 150 is even better. Finer grits like 220 will burnish the surface and cause adhesion problems. If you don't do a lot of finishing, I don't think I would recommend CV. It's a great finish, but there are many pitfalls and potential for disaster. Go to a reputable supplier near you that has experience with industrial coatings (Sherwin Williams, Chemcraft, ILVA, etc.) and get their recommendations, stick to one brand of product and follow instructions exactly. Then, if there are problems, you have somewhere to go.
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