Best methods for finishing MDF

[AMC]

Re: Best methods for finishing MDF

Has anyone tried using a 45 degree lock mitre bit


I have use these for years with great success in furniture construction - even works very well with most plywoods

I have used these, but on MDF the small spline tends to just pull off. Works great for hardwood though, hard to get much stronger a joint.

[speakerman19422]

Re: Best methods for finishing MDF

The putty hides the seams. Seems can be a problem on finish. Thanks for the tip. One tip I have shared is using wood clamps to pull in t nuts before getting the hammer out.

[davepellegrene]

Re: Best methods for finishing MDF

Dave nice finish. I did similiar using textured spray paint. Has any one found a brushed on paint that will give similiars results as the spray. I found the color fades over time unfortunately. I know some high end companies like Wilson are using automated paint finishing.

Dan N. used oil based floor and porch paint on his Blades speakers he is working on know. He wet sanded and buffed it. It looks pretty close to spray on as best I can tell.
Dave

[davepellegrene]

Re: Best methods for finishing MDF

Thanks for doing this, Dave. It took a of effort and experimentation on your part. A big thumbs-up to ya!

It's going to be a big help for future projects of mine.

Well your welcome. It is enjoyable to experiment. I like trying new things just to see what happens.
Here is another one I forgot to post. This sample is a 1/16" layer of auto putty over the bare MDF. It seems to be holding up as well.

I clamped a strip 1/16" above the surface of the sample piece wrapped with parchment paper so the putty has a straight edge to mud up against.



Here is a layer of finishing putty "Icing"



Sanded. If you look close at the front edge you can see the 1/16" thickness of the putty.



Here it is painted. Its been painted a few months.

[speakerman19422]

Re: Best methods for finishing MDF

Dave nice finish. I did similiar using textured spray paint. Has any one found a brushed on paint that will give similiars results as the spray. I found the color fades over time unfortunately. I know some high end companies like Wilson are using automated paint finishing.

[bmaupin]

Re: Best methods for finishing MDF

Thanks for doing this, Dave. It took a of effort and experimentation on your part. A big thumbs-up to ya!

It's going to be a big help for future projects of mine.

++++1

I have found Dave's experimentation invaluable as the seams showing was my biggest complaint about my first few speaker projects. I think I will stick with the thinned fiberglass, but thinned with styrene, until I find something that provides the same results but is easier to sand. Styrene is what fiberglass resin contains as a thinner, but not found at the local hardware store - I bought it from US Composites w/ my resin.

[williamrschneider]

Re: Best methods for finishing MDF

Thanks for doing this, Dave. It took a of effort and experimentation on your part. A big thumbs-up to ya!

It's going to be a big help for future projects of mine.

[davepellegrene]

Re: Best methods for finishing MDF

Thought I would throw some updates on my test seams.

Here is the piece with body putty in the trench. Still looks good



This is the one with the Finishing putty in the trench. It also still looks good.



This is the 1" relief cut I tried. This sample shows a very light wave were the seam is, but no line. It shows on the top couple of inches slightly. It showed up as soon as I was done with the sample and hasn't changed since.




This is the same 1" relief cut with poured on epoxy. I needed something to test the epoxy on so I used this sample. This one is not showing a seam at all.



Here is the test box I made up to try the trench method with.



With body putty



Primed



Three months since putty was put in with paint.



My link below has more picks of all the processes if you want to look. towards the bottom of the page.
Dave

[davepellegrene]

Re: Best methods for finishing MDF

Very inventive and great idea.
You're obviously really thinking about this.

I look forward to your (even more extensive) results.
Greg

Cabin fever has set in to its fullest point. No more football!
I was also thinking about sealing the 1/16 strip with thinned down resin. If I can apply it on the front side and the back side through the grove it may penetrate the full thickness then shouldn't expand at all. If this works it could be the simplest method yet.
Dave

[gregrueff]

Re: Best methods for finishing MDF

I glued together two layers of 1/2" MDF. I cut a groove with my table saw 1" deep back 1/16" from the face. I am going to fill this with latex caulking. Then glue a piece over the joint to make the but t joint. This should work similar to putting a 1/16 layer over a joint. Theoretically the only expansion/ contraction should be from the 1/16" thickness rather then the full 1" thickness.

Very inventive and great idea.
You're obviously really thinking about this.

I look forward to your (even more extensive) results.
Greg

[davepellegrene]

Re: Best methods for finishing MDF

Came up with another method to try out. I glued together two layers of 1/2" MDF. I cut a groove with my table saw 1" deep back 1/16" from the face. I am going to fill this with latex caulking. Then glue a piece over the joint to make the but t joint. This should work similar to putting a 1/16 layer over a joint. Theoretically the only expansion/ contraction should be from the 1/16" thickness rather then the full 1" thickness.



After the filler dries I will glue the piece over the end grain. Like the piece I have sitting on top. the little piece of plywood on top is just for weight.

[davepellegrene]

Re: Best methods for finishing MDF

I cut some pieces of MDF last night and sealed the ends with fiberglass resin thinned 30% with acetone. Not sure that was thin enough. It penetrated but I am not sure it went deep enough. If they show seams I will try thinning it some more. I am going to sand them with120 on my belt sander to rough them up, then glue them up with yellow wood glue, epoxy and polyurethane construction adhesive. I am also going to sand the flat smooth side of the MDF. I think it is a good idea anytime you glue it up. I am curious whether the yellow wood glue will make a strong joint.
Dave

I sanded the sample ends with 120 grite paper on a block so the glues would stick good. Glued the samples up last night. The wood looks a little strange from my flash.

Glued up with epoxy



Glued up with Polyurethane Construction Adhesive. Thanks Pete S. for telling me about this glue in another thread.



Last one glued up with Titebond. Not sure how this will bond with the resin. I will do a stress test on it.



Dave

[davepellegrene]

Re: Best methods for finishing MDF

I cut some pieces of MDF last night and sealed the ends with fiberglass resin thinned 30% with acetone. Not sure that was thin enough. It penetrated but I am not sure it went deep enough. If they show seams I will try thinning it some more. I am going to sand them with120 on my belt sander to rough them up, then glue them up with yellow wood glue, epoxy and polyurethane construction adhesive. I am also going to sand the flat smooth side of the MDF. I think it is a good idea anytime you glue it up. I am curious whether the yellow wood glue will make a strong joint.
Dave

[davepellegrene]

Re: Best methods for finishing MDF

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.



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 absorbtion ...



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.

Good observation. To bad you didn't seal the end joints before you put the box together. From my experiments so far any liquid will expand MDF. I assume the glue isn't "liquid" proof so when it is soften it allows the compressed MDF to decompress.
I had thought about the wood glue joint being weaker because it can't absorb into the wood as much. I suppose epoxy would cure that problem. I was in hopes of staying away from epoxy. I was also thinking about a method to rough up the surface after sealing with the thinned resin. Some kind of indents, deep scratch lines or small perforations along the end grain. Some kind of simple tool similar to how a wall paper tool puts the perforations in the paper for water to get behind.
Dave

[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.