We purchased a new vanity top to replace our 12 year old builder grade piece, however, it does not appear to sit tight on the base. It doesn't really sit "in" the cabinet, and only the back sides seem to make contact. It's a standard vanity top size (49 x 22"), and my cabinets are standard also. What can I do about this? It appears to be fine from the top, but when she open the doors or look under the vanity top from inside the cabinet, you can see the issue. Any help would be greatly appreciated.

Some pictures

  • 2
    Opening the doors is a reasonable place to be concerned with how it looks. Anyone who is looking up at the underside from inside the cabinet needs to find something useful to do with their time and attention.
    – Ecnerwal
    Jul 26, 2016 at 15:04
  • FYI, "flush" in carpentry means two adjacent surfaces at the same level. For example, two boards of equal size laid next to one another would be flush on top. If your countertop was the same length and depth as your cabinet, it would be flush on the sides and front.
    – isherwood
    Jul 26, 2016 at 15:13
  • Thanks for that! All this is new to me. I'm more of a furniture makeover DIY slowly learning how to do minor home renos here and there.
    – hartes
    Jul 26, 2016 at 17:09

2 Answers 2


In my experience the normal, common way to attach such a top also fills any gaps, since it's good old silicone caulking - White or brown would seem like a good choice here. You can also attach by other means if you like and then caulk to seal and conceal. And you certainly should shim (or sand/grind the high spots on the base) to get it level. If the gap is larger than it seems in the pictures, use backer rod and caulking.

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    I'd use clear. It transmits the adjacent color and is almost always less conspicuous than solid colors (especially with toilet bases).
    – isherwood
    Jul 26, 2016 at 15:10
  • I'll try out some shims and see how that works for me. Sanding/grinding seems a bit intimidating for someone of my skill level when it comes to these things. Thanks for your help!
    – hartes
    Jul 26, 2016 at 17:15

Shims are your friend :-) . Since what you really want is for the countertop to be perfectly level, get some shims (and a good bubble level) and adjust the shim positions until the top is level. Then glue or clamp or whatever you're planning.
If you then have a cosmetic problem, i.e. the shims or some gaps visible, you'll need to get some luaun or other veneer material and cut (and paint) to match.

  • Thanks! I found some pine shims at Canadian Tire, so I'll pick a couple packs of those up. Since only the back two corners make full contact with the cabinet edge, and there is a huge gap in between the back centre...do you suggest I just shim the sides and the front for level?
    – hartes
    Jul 26, 2016 at 17:13
  • @hartes if the top were granite, I'd say you should shim all sides for support. You don't need that for your composite, but it might help stave off any sagging 10 years from now. Jul 27, 2016 at 11:33

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