How to finish first
Words and photos: Darren Oates
About two years ago while making one of my signature Parabolae hall tables, I had a thought. Instead of gluing all the pieces together and then applying the finish, why not apply the finish first and then assemble the parts once they had cured?
The reason I wanted to try this is that once assembled, my tables are not the easiest pieces to spray. They have a lot of curved angles and I was getting a lot of overspray onto other parts of the table which left a rough surface that was a real pain to remedy. Spraying the elements separately would take longer but might save time in the end, and without overspray, deliver a smoother feel.
When building cabinets it’s nearly impossible to apply a spray finish to the interior, as there is nowhere for the overspray to be evacuated by the action of the spray booth fan. In this instance I find that pre-finishing at least the inner carcase surfaces prior to assembly is the way to go.
The only downside is that it does add overall making time, but if, like me, you have other work to do while waiting for finishes to cure then this is not a problem. I save a lot of time sanding between coats on mostly flat surfaces rather than an assembled piece with lots of complex joinery and adjoining surfaces.
Finishing before assembly is really suited to spray finishing but can also work for hand applied finishes as well, depending on how many coats you apply and the curing time.
One great advantage of finishing before assembly is that glue squeeze-out is no longer a problem. For complex joins I use Techniglue, a two-part epoxy that has a very long open time. The latter means you have plenty of time to clean up any squeeze-out and this glue can be wiped off a cured finish and will not mar it in any way. It also allows you to ensure you use the correct amount of glue for a joint as you are not worrying about squeeze-out as much as you would with raw timber.
The above works for PVA as well but you have less time to clean up excess glue. In the photos I’m making one of my Pi side tables. The table shown is the fiftieth I have made to date. I started using the process described above about two years ago and have not looked back. I believe the end result is of a much higher quality.
How to make it work
Photo 1: Mortises and gluing surfaces must be masked so the glue adheres to the timber and not the finish. These are the legs for my Pi table using Festool domino joinery.
Photo 2: Once again this shows how gluing surfaces must be masked. I have yet to mask the mortises at the ends of the drawer carcase base.
Photo 3: This is how I mask drawer components before spray finishing. I only spray the insides of the drawers at this stage, as once assembled the drawers are finely tuned to their respective housings. The drawer slips have already been glued to the bases. Because I use veneered marine ply for bases, allowance for movement doesn’t need to be made as you would have to with solid drawer bases.
In summary the following have been masked: front and back dovetails on the drawer sides, pins on the drawer font and back, bottoms of drawer sides where the slips will be attached to sides, the front lip of the drawer base that is glued into the drawer front rebate, edges of the slips and the rebate on the inside of the drawer front where the base is fixed. The dowel holes on the inside of the drawer front have been plugged with spare dowel pieces.
Photo 4: This is how I spray the masked legs. I have a chain running from one side of my spray booth to the other, and then screw in hooks to the tops of the table legs to hang these off. This allows me to spray one side and then flip the leg around and immediately apply the finish to the other side to eliminate any chance of overspray drying to a rough feel on either side. I am spraying from top to bottom on this piece with a horizontal spray pattern. This method also allows me to spray the foot of the legs.
Photo 5: The drawer housing shown here was glued earlier. The mortises as well as dowel holes used to attach the tabletop have all been masked.
Photo 6: It is much easier to sand between coats while components are still separate. I use 400 grit paper and simply sand over the top of the masking tape so I don’t have to replace when applying successive coats.
Photo 7: These shop-made rubber backed cauls are used for pressing various components together in the glue-ups. I also have several sheets of soft paper towel that I tape to the cauls. In the last two years after letting the finish sit for 24 hours I have yet to have any paper towel stick to the furniture.
Photo 8: Several layers of soft paper towel are taped to 3mm MDF. This is fixed to my sash clamps with double sided tape for the final glue-ups. Once again, using this method and an appropriate curing time, I have never had any of these stick to the finished piece.
You can also see here how much more difficult it would be to apply a finish and sand between coats on a piece like this when assembled. There is no chance of overspray occurring on dried components using this method. I use domino joinery on most of my furniture and always glue the tenons into leg rails before applying the finish. Of course you have to mask the tenons (dominos) before applying your finish, so the glue adheres to raw timber.
Photo 9: This is the glue-up of the legs to the drawer housing using the rubber-backed cauls. I also use rectangular inserts in each drawer housing to ensure the front of the legs are glued square. The inserts are covered in packing tape so they don’t stick to, or mar the finish.
Photo 10: The final glue up. A 32mm sheet of MDF sits on the tabletop protected by a bath towel, and the rubber backed cauls are once again used on the underside of the drawer housing.
This technique has improved the overall finish of my furniture and made the process a little less tedious, particularly when sanding between coats. I believe that if you give this a go you may be surprised at the results you will achieve.
Darren Oates is a furniture designer maker in Windsor, NSW. Learn more at www.darrenoatesfinefurniture.net and Instagram @darrenoatesfinefurniture