Is it necessary to put any finish on MDF shop jigs for protection?

[Alan Lightstone]

I'm finishing up replacing my router table fence with an add-on auxillary fence that is a little longer for my Incra LS sled.

I've made it out of MDF, and am wondering if, since I live in South Florida, I need to put some finish on them, like shooting a quick coat of shellac to prevent the MDF from warping / gaining moisture / getting out of square over time.

[Rich Engelhardt]

Necessary?
Maybe/maybe not.

Good idea?
Always!

IMHO - jigs need to stay true to be of any use. Anything that helps them stay true is a wise idea.

I keep a "slop bucket" of latex paint & waterborne clear around the shop that I use to paint jigs and fixtures.
Every time I have some leftover material, I dump it in the "slop bucket".
Eventually, all colors mixed together yield some sort of shade of gray.

To save money, instead of using expensive shellac, you can usually pick up mistints at the borg or a local paint store for cheap.

[Myk Rian]

Shellac works. I just slopped paste furniture wax on my router table.
Titebond watered down does good on the edges.

[Richard Wagner]

I believe that your MDF fixtures will remain stable as long as they do not collect moisture. The edges, in my opinion, "NEED" to be sealed. The surfaces probably do not need to be sealed until you spill something on them. Bottom line - seal all of the surfaces if you expect to maintain alignment and smooth surfaces.

[Jeff Duncan]

I'd guess my answer will be; it depends.....I'm in New England and never even heard of putting coatings on mdf jigs until this post:confused: I've got jigs that are a decade old and show no moisture problems. To be honest I don't want any coatings on my jigs as I prefer the hard slick surface of the mdf as is.

Of course if your in a climate that is really damp, or have a garage shop that maybe gets damp, maybe you would need to do something? However a couple things to keep in mind....first, moisture is not going to knock mdf out of square or ruin alignment. Second finishes slow the transfer of moisture, they don't prevent it. Different finishes do that to different degrees, shellac is on the lower end of the spectrum for moisture protection. Third, If your mdf gains or loses a little moisture seasonally it's not really going to warp it. What warps it, or ruins it in general is getting wet. So for instance, sitting in my shop in the middle of summer when the humidity is at it's worst, doesn't affect my jigs. Having a jig sit on the floor in a corner that gets wet when there's a lot of rain in the spring time......end of jig;)

hope this helps,
JeffD

[Bill White]

I shellac mdf fixtures all the time. Slap on a coat of wax too.
Bill

[Mac McQuinn]

I give them a coat or two of spray shellac as MDF really swells with moisture content.
Mac

[Alan Lightstone]

I have some pre-cat lacquer that I could easily spray on it too.

Any issues with using lacquer sanding sealer as a quick coat and calling it a day after using that? In other words, just the sealer, without subsequent coats of lacquer.

[glenn bradley]

I seal all around with shellac. No problems here.

[Rich Engelhardt]

Any issues with using lacquer sanding sealer as a quick coat and calling it a day after using that? In other words, just the sealer, without subsequent coats of lacquerNone I'm aware of.

Heck, I'm going to use some of the new floor wax that's out now on the next jig or fixture I make.
I've been reading up on them and it looks like they aren't a "wax" at all. All of them have gone over to a 100% acrylic product.
I've asked around at various places and nobody can tell me what the difference is between a $6.00 quart of 100% acrylic floor finish and a $20.00 quart of 100% acrylic varnish!

[Ken Fitzgerald]

I save my half-used cans of finish from projects and use them to seal jigs and cabinets in my shop. I just sealed the MDF fence pieces and the underside of the MDF table top on my new router table with some left-over polyurethane.

[John Coloccia]

Personally, I happen to use marine varnish because a lot of my fixtures get wet. Think bending forms :) I also happen to like the finish it leaves. That said, I have completely unfinished MDF fixtures that are as straight and accurate as the day I made them years ago. The only one that warped is the one I laminated to a piece of plywood because I needed the added thickness...so that's a bad idea, I guess :)

[Julie Moriarty]

Being that I am a minimalist, in that I find beauty in doing the minimal amount of work :rolleyes:, I never finish jigs regardless what they are made of. But I'm in Chicago, my shop is in the basement and I run a dehumidifier in the summer to keep moisture levels relatively constant year-round.

What I'd do, if you have any doubts about Florida humidity wrecking your MDF jigs, is take a piece of bare MDF and measure all the dimensions as accurately as you can. Then place it in the worst environment your jigs may see. Then check it in a week or so and measure it again. (A digital caliper would be great for this.) If you see a 3/4" piece of MDF swell to 7/8"...:eek: Then you can consider your time sealing MDF jigs as "practice". :D

[Frederick Skelly]

Rich: That slop buckets a heckofa good idea!

John: Isnt it pretty expensive to use marine varnish? I see that stuff at the marine store for $30/qt and then you still have to spend more for special thinner.

[John Coloccia]

Rich: That slop buckets a heckofa good idea!

John: Isnt it pretty expensive to use marine varnish? I see that stuff at the marine store for $30/qt and then you still have to spend more for special thinner.

It's pricey, but like I said a lot of my jigs worth protecting also happen to be the ones that get wet. Most of the rest just sit with no protection on them at all. They're either not worth doing anything to because they take a second to recreate (and frankly I wear them out/damage them before they ever have a chance to warp anyhow) or it's just not such a critical thing that it stays perfectly flat. About the only thing I can think of that you'd really like to have flat is a fence of some kind. Most everything else is really just not that critical.

But that's only my opinion and what works for me in my own shop.

I'm also of the opinion that finishes like shellac aren't particularly effective combating moisture problems, especially on MDF. I'm not sure that spar varnish is any better at combating moisture problems, but it does leave a nice surface that's easy to work with for what I'm doing.