How do you determine what the finish is?

Hey All, I am repairing a door to a bathroom vanity for a friend. Sadly, the cabinet maker passed away, but I must say that he did a beautiful job - cherry rails and stiles, cherry ply for the panel, great finishing job too! It is a clear finsih but I could not tell if it is lacquer or polyurethane. The crack is in the hinge stile of the door (someone walked into it the wrong way when it was open and stressed the stile) and I can make it disappear when I dry clamp it, but the finish shows evidence of the cracks. Would I encounter any problems if I ; a) use polyurethane over lacquer? b) use lacquer overpolurethane? Is there one best way to go about this? I want to add that I would make a test application on the unseen bottom edge first but I wanted some guidance from this esteemed group. Thanks in advance, Marc
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Lacquer and polyurethane don't get along well at all - the lacquer will get milky if you put poly over it - I had this happen on a guitar neck when I didn't get all of the lacquer off before I put on a coat of wipe-on poly. Had to let it dry, sand it all off, and start over. Not sure what would happen if you put lacquer over cured poly, but I'm thinkin' it won't adhere well. Any thoughts on putting a coat of shellac on first the keep the two apart?
Try dabbing a little lacquer thinner on a hidden spot - if it starts to dissolve the existing finish, then it's lacquer.
--Steve

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
marc rosen wrote:

Can but adhesion won't be great even if the lacquer is roughed up. Result of poor adhesion can be local separation if bumped/whacked. ____________

It will soften the poly which will then likely reticulate (wrinkle). I use lacquer thinner to remove poly.
--

dadiOH
____________________________
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.