Restoring an Original Kitchen Sink Base Cabinet

In this first of a series of Restovation posts I'll describe a small project to preserve an original kitchen sink base cabinet. In this instance the original supply lines have been replaced by Pex pipe and a hole cut into the floor for access. Also, multiple leaks from the sink and garbage disposal have completely destroyed the cabinet "floor" to the point of bowing the floor in the middle and delaminating the plywood layers all about. Besides being unsightly, it's unsanitary, allows bugs to congregate and provides moisture for all manner of undesirable substances. The easy solution is to replace the unit - the issue is that the cabinets made back in the 50's/60's (when this particular home was built) were commonly built in-place, often at the whim of the particular carpenter who built or installed the cabinet (if by chance it was made off-site). It's not like today where you can buy each cabinet as a separate component and level them up on site - modern cabinets have interchangeable parts, something your very rarely see in cabinets from this earlier era (with the exception of some of the custom European cabinet makers).

To make the task more complicated, cabinets from this era also rely heavily on mortise-and-tenon joinery for the face frames (as does this particular example). This makes it difficult to replace the "floor" of a cabinet with a single sheet of plywood, as there may be a separator in the middle of the face-frame (the doors rest upon this separator and there is often a latch involved in these old cabinets).

I'll describe briefly the term for those not familiar with that mode of construction - the mortise-and-tenon allows sticks of wood to be joined at right angles to one another - this is accomplished by cutting a groove or slot in the flat side of one board (the slot is called the mortise and the stick in this case is the rail or cross-piece) and having an extension in the perpendicular board by extending a "tongue" at the end of the other stick (the tongue is called a tenon and the stick in this case is called a rail). This joint is very strong and still used today, however in production shops it's nearly been replaced by the use of pocket screws (screws that are inserted from the back so they are hidden, angled down into the cross piece from the end of the "stick". This comes into play as the face of the cabinet (basically the surface that all the doors rest on) is made up of a frame or multiple frames of wood - thus the "face-frame"...

So the task is to first remove the mortise-and-tenoned face-frame separator, cut out the existing rotted floor and replace with a single piece of plywood. In this example I noted that much of the problem was caused or at least exacerbated by the discharge pipe leading from the bottom of the garbage disposal through the floor into a trap in the basement. Modern dual sinks share a common trap, so I thought I would reconfigure the drains and remove (and cap) the extra below-floor trap. This did require a bit of head scratching to get the pipes all aligned and working correctly - as an additional benefit, there's now more room under the sink.

In this next shot you'll see the separator removed - to do so I developed a technique of jacking up the front of the cabinets to extend one tenon from the mortise - in this next photo you can see that the floor ahs been removed and the tenon removed - note that the other end has been carefully cut apart from the stile above. In some instances both ends of the rail's tenons can be successfully removed - however in this case only one end would come apart (don't worry I have a plan for reattaching it).

Also note that I've begun reworking the plumbing and that I've added some two-by-four supports for the floor to help prevent any future sagging.

The next step is to carefully measure and install the new floor. The trick is to get as custom a fit as is possible - so the same dimensional thickness of plywood is used and very little gap is allowed between the old and new floor. The floor back is drilled with holes just slightly larger than the Pex pipe to allow access for the supply lines. The floor is then installed using brad nails to minimize exposure of the fasteners.

After attaching the new floor comes the final step, which is preparing the removed rail for reinstallation in the cabinet face frame. I earlier mentioned the use of a pocket hole - well here is a photo of a Kreg pocket hole jig clamped and ready for drilling. The Kreg kit uses a flat-faced vice-grip style clamp to ensure that the two parts of the face frame are exactly on the same plane. The jig provides a guide for the special Kreg bit to drill the exact angle and depth needed for the thickness of the face frame. Once the screws are tightened it creates a very strong joint and since they're on the back of the rail the replacement is invisible.

For this particular example the last thing to do after face-frame reassembly is to complete the changes tot he drain plumbing. You can see in this final image how much neater everything looks - also there's a bit more room under the drains for cleaning products, sponges and whatnot.

Sheet 1/4" Luan plywood: $8

Scrap 2x4" material - Free

Misc PVC Drain bits: $16

Saving the original cabinets - priceless.

-- John