Best methods for finishing MDF

[bobbarkto]

Re: Best methods for finishing MDF

That mirrors my experience.
For a sharp corner, miters are usually very effective. Light forms a natural reflected line of light or shadow right on the apex so any slight telegraphing is effectively hidden from view. Under ideal conditions and close observation you could probably detect the seam when it rears it's nasty little head.

Trouble really begins on flat surfaces, like when a chamfer or roudover is applied to that same edge. Now the light reflects differently and you can see the seam from practically every angle.

Actually, I have a pair of 3 ways, WATT/Puppy style that all seams are mitered....then did a simple edge sanding to take the sharp edges off....possibly a 1/8" roundover done with simple hand sanding. Then applied 3 coats of Urethane Enamel paint with a foam roller....letting 24 hours dry time go by between coats....then sanded smooth and did 5 coats of clear Minwax Urethane gloss....wet sanded to 1500 grit using minimal water with spray bottle.....followed by buffing out with Mequire's rubbing/polishing compound. Did that over two years ago....still no hint of a seam showing anywhere. I did not bother coating the inside of the cabinet walls with anything to seal it. So....I guess I was just LUCKY on that?
For those interested.....the Urethane paint I used was simple Home Depot Glidden Oil-based Urethane Enamel Porch and Patio paint. Tough stuff.

John

[johnnail]

Re: Best methods for finishing MDF

8 coats. Now that's dedication. Pictures?

Joe.

I have several pics of the progress on disc, but not easily at hand....would have to search several places and discs to come up with them....but I DO have one pic on my photobucket page.

Here it is. In this photo, the cabinets are at the 1.5 year mark....or close enough.

http://s254.photobucket.com/albums/hh84/JohnBNail/?action=view&current=Almostdone1.jpg

John

[johnnail]

Re: Best methods for finishing MDF

8 coats. Now that's dedication. Pictures?

Joe.

I have several pics of the progress on disc, but not easily at hand....would have to search several places and discs to come up with them....but I DO have one pic on my photobucket page.

Here it is. In this photo, the cabinets are at the 1.5 year mark....or close enough.

http://i254.photobucket.com/albums/hh84/JohnBNail/Almostdone1.jpg

John

[johnnail]

Re: Best methods for finishing MDF

I remember that the only surface that didn't get mitered was the bottom panel of the upper cabinet. It is just recessed in....like a **** joint would be. I did the same finishing on that surface as I did for all others.....I just took a look at it....both cabinet bottoms have yet to show any sign or even hint of telegraphing....still smooth and gossy from any angle....barring some scuffing here and there from being moved around from place to place.....that was before they got their rubber pads.
Also, the bass cabinet has a mitered in top panel and the sides have a 15 degree chamfer cut away...to sculpt the lower cabinet so that it matched the upper cabinet closely....and I estimate that the seam of the mitered glue joint is about 3/8" below the top edge of the cabinet...in the top 1/3 of the bevel edge....I took a good look at all those surfaces as well....I still do not detect any hint of telegraphing. Don't know for sure what I might have done righter than anyone else could have done to get that NOT to happen.
For what it's worth, on the bevel , which ended up being like an open endgrain, all I did to seal it was to wipe on some clear poly right out of the can with a rag.....just enough to wet it down....then rubbed it off.....let it dry overnight. When I did that, it didn't seem to take that much paint to cover that "end grain sucking up all that paint" effect that is usually the norm....so not sure if that makes any difference in how it turned out...but the fact remains that I can detect NO hints of telegraphing at all so far.

John

[bobbarkto]

Re: Best methods for finishing MDF

You must be living right, John!

I wonder if your climate might have some influence? Seems to me humidity levels are pretty consistent and somewhat high where you are?

I know on some of my own builds at times the effects aren't visible at all and other times those lines stare at me and mock me!

...

...I took a good look at all those surfaces as well....I still do not detect any hint of telegraphing. Don't know for sure what I might have done righter than anyone else could have done to get that NOT to happen.

......but the fact remains that I can detect NO hints of telegraphing at all so far.

John

[johnnail]

Re: Best methods for finishing MDF

You must be living right, John!

I wonder if your climate might have some influence? Seems to me humidity levels are pretty consistent and somewhat high where you are?

I know on some of my own builds at times the effects aren't visible at all and other times those lines stare at me and mock me!

I would have to say that I was very fortunate on that project's outcome. I live is Washington State, but not in the Seattle area along the coast....I live in the Southeastern corner of the state....in a valley that is classified as a partial desert basin....though we do get plenty of rain during the fall and spring. Then really hot and dry summers. What I attribute my good fortune to is simply LOTS of COATS of the stuff. That and the stuff I used was made for high-traffic/ lots of abuse....
I have had other projects not turn out that well in the past. One really sore memory was the MTM I did for someone...beautiful gloss black MTM, SEAS CA15RLY midbasses, Scanspeak 9500 tweeters.....and the black/clear combination I used was lacquer. Was a personal disaster for me. About a week after I got the finish all polished out......a telegraph arrived for me...and the message wasn't good! That was before I got the nice Incra Miter guage and fence system for my saw. At that time, I was still using b u t t joints on lots of projects.

John

[dlneubec]

Re: Best methods for finishing MDF

Very nice looking painted finish! How did you apply the Urethane? Did you sand between coats? Any other details you recall that would be helpful to know?

[williamrschneider]

Re: Best methods for finishing MDF

In this thread I had wondered if using two layers of veneer would prevent telegraphing of MDF joints. I'm now sadly reporting that telegraphing of joints is visible EVEN WITH two layers of veneer applied 14 days apart. :(:(

It's very faint, but in a backlit situation with glancing light, the joints are visible if you know where to look.

This shows the application of some scrap maple veneer just before applying glue over it for the cherry veneer on top. Veneer is 0.025" thick paper backed. It had been on there for 14 days when the picture was taken. The cherry veneer has the same physical specs, and was applied cross-ply to the maple. Glue was regular Titebond; the iron-on method was used.



I'll see if I can get some glancing light photos of the telegraphing cherry tomorrow, and edit this post to include the pictures.

Thought that you guys would want to know, and this is the best thread in which to put experimental data.

Edit: I've added a photo below of the cabinet in glancing back-light to best show the joint. It's very difficult to see in normal room light, and it certainly can't be felt by touch.



The humidity is going back up from the long cold snap of 10-25 degree weather we had experienced in the past weeks. I suspect the telegraphing joint will soon disappear again.

[davepellegrene]

Re: Best methods for finishing MDF

In this thread I had wondered if using two layers of veneer would prevent telegraphing of MDF joints. I'm now sadly reporting that telegraphing of joints is visible EVEN WITH two layers of veneer applied 14 days apart. :(:(

It's very faint, but in a backlit situation with glancing light, the joints are visible if you know where to look.

This shows the application of some scrap maple veneer just before applying glue over it for the cherry veneer on top. Veneer is 0.025" thick paper backed. It had been on there for 14 days when the picture was taken. The cherry veneer has the same physical specs, and was applied cross-ply to the maple. Glue was regular Titebond; the iron-on method was used.



I'll see if I can get some glancing light photos of the telegraphing cherry tomorrow, and edit this post to include the pictures.

Thought that you guys would want to know, and this is the best thread in which to put experimental data.

Edit: I've added a photo below of the cabinet in glancing back-light to best show the joint. It's very difficult to see in normal room light, and it certainly can't be felt by touch.



The humidity is going back up from the long cold snap of 10-25 degree weather we had experienced in the past weeks. I suspect the telegraphing joint will soon disappear again.

Bill,
Do you remember any of the details of the build? How much time did it take? Was there much time sitting after glue up before flushing the edges? After you applied the glue for laminating did you leave any time before you did the laminating?
Just currious.
On your last pic on the rear of the panels it looks like they are miter joints.

Dave

[lunchmoney]

Re: Best methods for finishing MDF

I've got a friend who is planning on baking his mdf cabinets in a big "shop oven" prior to sanding, in order to get all the moisture out of them.

I'll report back if/when he ever does this.

[williamrschneider]

Re: Best methods for finishing MDF

Bill,
Do you remember any of the details of the build? How much time did it take? Was there much time sitting after glue up before flushing the edges? After you applied the glue for laminating did you leave any time before you did the laminating?

On your last pic on the rear of the panels it looks like they are miter joints.

Dave

No miter joints yet, but I will strongly consider them for future builds. I bought another Incra miter gauge to be calibrated to the right side of the blade.

Timeline...dry fit was on October 19, first glue-up (left side, back, top and bottom) was on October 29...,



Final glue-up (right side) was on November 18, flush trim of joints was on November 25 and the first layer of veneer shortly after that.

I waited a while, sanded first veneer flat, and trimmed baffle to sides November 28 (and that included accounting for the thickness of the 1st layer of veneer)...



Assemble and listen for a while...



Final veneering lasted from December 10 through 12 and the top is the last piece I attached...



I'm a slow builder, so nothing was rushed. Veneer glue was ordinary Titebond applied with a foam roller. I always applied two coats, with probably 12 hours dry time after each application.

[davepellegrene]

Re: Best methods for finishing MDF

I've got a friend who is planning on baking his mdf cabinets in a big "shop oven" prior to sanding, in order to get all the moisture out of them.

I'll report back if/when he ever does this.

I wish, I think it is Aron Hero, would chime in. I have heard several times he has baked the MDF first and has a beautiful finish on his cabinets.

Bill, Are all of your seams showing? I don't see it on the left one in the pic.

I had another thought. Wonder how it would work if you cut all of your pieces for your build, then before you glue them up, soak all the edges with a thinned down sealer like fiberglass resin. It soaks in until you get tired of applying it. Then let them sit for several days. Then glue them up. I know when you get MDF wet it expands and stays that way. Buy soaking the ends with sealer it should make them expand. I wonder if this would stop the expansion/ contraction of the end grain. I think I will try a sample.
Any thoughts?
Dave

[djg]

Re: Best methods for finishing MDF

Bill Schneider, how do you like your Reference RBR compared to your Linkwitz? I built them and they are the best sounding speakers I have built. Also, mine are sitting on same Sanus stands as yours.

If you posted your RBR build before, I missed it.

[williamrschneider]

Re: Best methods for finishing MDF

Bill, Are all of your seams showing? I don't see it on the left one in the pic.

Yes, there's a seam on the other side. If the light/dark junction of the doorway reflected in the background doesn't "break" across the seam, you can't see it. The two-veneer techniques has helped, but not eliminated the telegraphing problem. I had thought that a ~1/16" thick sandwich of veneer and glue lines would help more, but I guess not.

I had another thought. Wonder how it would work if you cut all of your pieces for your build, then before you glue them up, soak all the edges with a thinned down sealer like fiberglass resin. It soaks in until you get tired of applying it. Then let them sit for several days. Then glue them up. I know when you get MDF wet it expands and stays that way. Buy soaking the ends with sealer it should make them expand. I wonder if this would stop the expansion/ contraction of the end grain. Any thoughts?
Dave

Anything's worth a try. All we can do is experiment and report the results. One issue with a coating like that is that a different adhesive would be better than wood glue. I once read an old US Forestry service bulletin about how an application of shellac greatly reduced the effectiveness of wood glue.

Before I knew that, I once applied a generous helping of shellac over some assembled cabinets before veneering. It also swells the MDF, and here's visible proof (showing the location of the biscuits beneath after some sanding) that it differentially swells areas of the MDF depending on whether glue in the biscuit slots is preventing deep absorption ...



Even with the heavy application of shellac soaked into the end grain, this pair of speakers, once veneered, also telegraphs seams through the veneer. These were built in dry weather, so the seams show in humid summer conditions and disappear in winter. My conclusion was that shellac after assembly (but before veneer) didn't work.

[williamrschneider]

Re: Best methods for finishing MDF

Bill Schneider, how do you like your Reference RBR compared to your Linkwitz? I built them and they are the best sounding speakers I have built. Also, mine are sitting on same Sanus stands as yours.

If you posted your RBR build before, I missed it.

I didn't post a build because I was a little sensitive about it not being a PE product.

However, they sound superb. Words can't describe how pleased I am with them. I still prefer the Plutos for their soundstage and imaging, plus they have a pair of 10" drivers (Pluto+) for a little deeper bottom end. Still, I've come under the spell of the ScanSpeak mystique with this build. The Scans are incredible drivers, and that special was a tremendous bargain for what you got. I'm glad I got in on that deal, and it makes me want to hear more of Jed's designs.