Tips for protecting mortises when prefinishing?

[Ken Platt]

Folks - I have a largish table nearing completion, and it'll make finishing a lot easier if I finish the trestle legs before attaching them to the stretchers. There are 4 through mortises. How do folks keep finish out of them?

Best idea I've had so far is to put painter's tape on the mortise sides, and to cut some wedges of foam insulation to shove in there to keep finish from seeping under the tape. The mortises are flared on the ends (for wedging), so the size is a bit irregular That's why I thought of the foam stuff rather than a piece of wood, easier to get a tight fit.

For those who've done this, how did you protect the mortises?

Thanks -

Ken

[glenn bradley]

I just use pieces of paper towel. Unless you are using a "flooding" technique in your finishing protocol, it should be fine.

[Cody Colston]

On the last episode of The Woodsmith Shop, they used foam insulation tucked into the mortise and wrapped the tenon with blue tape.

I don't finish before assembly so I can't offer any first-hand experience.

[Bruce Wrenn]

Backer rod for caulking. Lowes stocks it in several diameters.

[Doug Shepard]

I've only done it like that once and my fix for that problem was to leave the mortise walls rough and do the paring sidewall cleanup after I had the pieces finished. That way I was exposing bare wood again before doing the glueup. Haven't had any glue joint failure with it (knock on wood).

[Max Coller]

I too have used leftover styrofoam scraps, cut into strips the proper size on the table saw (the same size as my tenons, plus a smidge for a good snug fit) and wedged into the mortises. I don't pour or spray finish, so I can't tell you if it works with those techniques - but for me with oil, poly and spar varnish applied with a brush this has kept the stuff out of the parts with the Do Not Enter. The only caveat I would add from past experience is that some solvents used to keep spraycan finishes thin (spraypaint, specifically, in my experience) will eat styrofoam - and turn it into a really gunky mess. Test your finish of choice on one of your blocks before you get to experience the joy of those styro chunks decomposing into plastic goo while wedged in your mortises.

[John Coloccia]

Why not just mask over the mortise with masking tape? A standard "trick", or at least it was for me, was to lay down tape and then shoot a thin coat of clear. The clear seals the edges of the tape. Then I continue with the finish. In your case, I guess you'd seal the edges with a little shellac and move on.

[Russell Sansom]

This is a common operation. It's surprising, looking at a woodworker's show ( like the results of a class at Woodcrafter store ), how often people sand after assembly. It's pretty hard to disguise. So, good move on your part.
I'm with John. Mask it. I haven't used "Friskit" for ages, but it's the definitive stuff for keeping liquids off paper. It's pretty hard to make airbrush illustrations without it. Available at art stores. As I remember, some of the friskit backings ARE shellac, so there could be a problem there, but you should be able to find specs on line.

[glenn bradley]

Backer rod for caulking. Lowes stocks it in several diameters.

Ooooooh, that's a good one ;-)

[Bill Huber]

But wouldn't you have to tape the area around the mortise and around the tenon? If you just put something in the mortise would not the finish get on the part of the wood around it and then the glue would not stick?
I would think you would tape the whole area of the joint so the glue would stick to the mortise and the wood around it.

Just asking....

[John Coloccia]

But wouldn't you have to tape the area around the mortise and around the tenon? If you just put something in the mortise would not the finish get on the part of the wood around it and then the glue would not stick?
I would think you would tape the whole area of the joint so the glue would stick to the mortise and the wood around it.

Just asking....

I would just take a piece of tape smaller than the shoulder, put it down and trim it to length with a razor blade. It's not all that critical that you glue the shoulders. It's an end grain joint anyway so it's a lousy joint to begin with. You really just need to keep the finish out of the mortise and off the tenon. If you do tape the shoulders and the corresponding part of the mortise, no biggie, but it's probably just as well to finish them instead.

Draw bored mortise and tenons will hold together just fine with no glue at all. What's critical is for the tenon to not fall out of mortise. The shoulders are structural but adhesion isn't important, just like it's not important to glue the endgrain in a dovetail joint.

And that's all just my opinion. :)

[Larry Edgerton]

I prefinish everything before I put it together.

In your situation what I normally do is make a few extra mortises in scrap, and often I am using the same size mortise, so I keep them around for future use. I make them a little loose, slip them on the tenon and spray. I make them a little bigger than the rails so that I have a stand. About the time it is surface dry I pull them off. Don't wait too long, clearcoat can make a pretty good glue.;)

For the mortises I use green tape, and just cut it in a bit from where the shoulder will land with an Exacto knife, spray and remove tape.

When I do my cabinet doors I make a few extra copes on shorts left over from cutting parts and stick them in where the real ones will go and give the rabbit that receives the panel a coat before I glue up the doors. Helps with movement and the panels won't stick if you get a little to much glue in the joint. Prefinish my panels as well, and soak the end grain in West System on the larger panels.

I don't do production work, if i did I would come up with a different system. For what I do I feel it is best.

[Larry Edgerton]

But wouldn't you have to tape the area around the mortise and around the tenon? If you just put something in the mortise would not the finish get on the part of the wood around it and then the glue would not stick?
I would think you would tape the whole area of the joint so the glue would stick to the mortise and the wood around it.

Just asking....

Bill, I don't worry about that part of the joint. The end grain to cross grain is not going to make or break the joint, the mortise is doing all the work.

[Troy Turner]

On the last episode of The Woodsmith Shop, they used foam insulation tucked into the mortise and wrapped the tenon with blue tape.

Ah, come on Cody, I saw the same one and was going to say that...great, now I just have to +1...LOL