Best methods for finishing MDF

[davepellegrene]

Re: Best methods for finishing MDF

BTW:

Looking over at another design, the designer put a cheap veneer over the MDF and then sprayed a very high gloss paint over his systems. The result was you-can-buy-this-in-a-store level of professional grade appearance.

Joe.

Would that be the post from mgrabow "Check Out This DIY Build". At the end of the pics I see were it looks like he used veneer then painted over it. It looks like he is covering three seams in the photo. That would probably be a good method. It also looks like he has a stack of what looks like resin. He really doesn't show any of his methods. If this is what you are referring to. If it is nice paint work.
From looking at my samples it looks to me that it is as simple as putting a trench in the seam around 1/16" deep, coating with what ever sealer you like, skim the seam with body filler, prime and paint.
Dave

[joekraska]

Re: Best methods for finishing MDF

BTW:

Looking over at another design, the designer put a cheap veneer over the MDF and then sprayed a very high gloss paint over his systems. The result was you-can-buy-this-in-a-store level of professional grade appearance.

Joe.

[joekraska]

Re: Best methods for finishing MDF

I made up 16 sample pieces a couple of weeks ago and,,,

I have two observations about this:

1. You are anally retentive.
2. It is highly appreciated.

:-)

[joekraska]

Re: Best methods for finishing MDF

And then peel the tried glue off your finger like you were six years old again. ;)

This is, perhaps, better than eating the paste off your fingers like you were four. :-)

Joe.

[davepellegrene]

Re: Best methods for finishing MDF

Just checked on the samples. All dried nicely.
I decided to weigh them to see if there was a difference from the amount that was soaked up. I will have to weigh my other unfinished samples to see if they are all the same.
Bin 123 280 Kg
Tite bond II 290 kG
Sanding sealer 300kg
Fib. glass resin 320 kg
left-Titebond, next fiberglass resin, then sanding sealer and Bin 123 on the right. They all came out very smooth with thinning them down. I can't wait til I am done testing them. I am going to cut them in half to see how much the sealer soaked in.

Its been a few days and seems the paint has dried. When I sealed these samples the fiberglass resin sample soaked up so much more then the rest of the products. I checked the trench after it was dry and the MDF expanded enough that the tench was only half as deep as it was originally.It ended up about 1/2" wide by maybe 1/32" deep. All the other samples seemed to have stayed the same, 3/4" wide by 1/16" deep. If you look at the pic you can see were the seam has shown through ever so slightly in the fiberglass resin sample. All the other sample are not showing any seam at all.
My conclusions at this point is all the sealers work as long as a trench of 1/16" deep is put in the seam and filled with either body putty or polyester finishing mud.

There is no change in any of the samples on my shower ledge. The ones without trenches show a seam the ones with the trench are not showing a seam.
Dave

[CokewithLime]

Re: Best methods for finishing MDF

Checking them out closely it appears the seam shows on 90 % of the joint. If I remember these were sprayed with a couple coats of satin black from a spray can back to back, with no primer. No sealer on the inside of any kind. Not sure if the one seam, on the first pic, opened up or was glued up this way. The seam, in the other pic same speaker other side, is tight and is almost unnoticeable on the surface. So there would be a chance you could use this joint and not have a seam show.

Looking at that pic I don't think that joint has budged from the time you assembled it.

This has happened to me a couple of times using that bit when I have eased off downward pressure towards the end of a pass and results in a less than perfect match with the other half.

[davepellegrene]

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

Just replaced my two year old surrounds that I made when I first happened along this site. Any way I realized I used the lock miter joint on them. When I glued these up I had no idea about the seams showing through paint on MDF. Checking them out closely it appears the seam shows on 90 % of the joint. If I remember these were sprayed with a couple coats of satin black from a spray can back to back, with no primer. No sealer on the inside of any kind. Not sure if the one seam, on the first pic, opened up or was glued up this way. The seam, in the other pic same speaker other side, is tight and is almost unnoticeable on the surface. So there would be a chance you could use this joint and not have a seam show.





The samples I set on my shower ledge have had no change after a few days. After showering the samples have enough moisture on them that when I run my finger across them water runs off. This really makes me think most of the seam show is from the moisture from applying the finish and not so much from relative humidity. One reason it could show up later is do to the primer and paint shrinking as it dries. I now in the body work I did years ago if you rush the auto filler and prime heavy it could show up months later in waves in the panels.
Tomorrow I am going to put the finishing putty on the four samples that I sealed a few days ago. Couple of notes. The fiberglass resin that I thinned with acetone did not dry, so I mixed some hardener in some acetone and coated them again and that seamed to work. I wonder since I cut the resin by 50% if that means I need to double the hardener. I will have to try it. I also noticed the trench I sanded into the seam seems to be only half as deep as it was before I sealed except the Titebond seams to be as deep. Probably because it didn't soak in like the other methods.
Dave

[davepellegrene]

Re: Best methods for finishing MDF

I just looked at the photos of that boat being constructed and I realized: I don't know s*** about building things out of wood! :eek:

That would be a fun job to go to every day. That,s pretty cool how they run the planking two directions. That would definitely make for a strong hull. Hopefully they built it close to the water.
Dave

[dwigle]

Re: Best methods for finishing MDF

I just looked at the photos of that boat being constructed and I realized: I don't know s*** about building things out of wood! :eek:

My wife's uncle had a 70's era Rybo. It was a work of art.

I did some enviro work at the Rybo shop in the mid 80's and the shop foreman gave me a tour. That experience got me started in woodworking.

The composite format of Okumi marine plywood as a core covered in glass and epoxy has many advantages over built up glass core. It's lighter, stronger and quieter. There is nothing like the ride of a wooden cored boat.

[Paul Carmody]

Re: Best methods for finishing MDF

Marine epoxy is good stuff.

http://www.rybovichandsons.com/the-process-03.html#gall-process/34.jpg

No seams, and this wooden boat is in the water 24/7.

http://www.rybovichandsons.com/last-...ll-125a/01.jpg

I just looked at the photos of that boat being constructed and I realized: I don't know s*** about building things out of wood! :eek:

[davepellegrene]

Re: Best methods for finishing MDF

Just checked on the samples. All dried nicely.
I decided to weigh them to see if there was a difference from the amount that was soaked up. I will have to weigh my other unfinished samples to see if they are all the same.
Bin 123 280 Kg
Tite bond II 290 kG
Sanding sealer 300kg
Fib. glass resin 320 kg
left-Titebond, next fiberglass resin, then sanding sealer and Bin 123 on the right. They all came out very smooth with thinning them down. I can't wait til I am done testing them. I am going to cut them in half to see how much the sealer soaked in.

[ckmoore]

Re: Best methods for finishing MDF

My Overnight Sensations build is anxiously awaiting the tabulated results from this study...

You are doing a great service Dave... many thanks.

[davepellegrene]

Re: Best methods for finishing MDF

Just finished sealing 4 more samples.
On these I hand sanded the seam with 60 grit paper on a 2" tube. The trench is just under a 1/16" deep.
I coated one with Bin 123 cut 50 % with alcohol. One with sanding sealer cut 50% with mineral spirits. One with Titebond II cut 60% with water. One with fiberglass resin cut 60% with acetone.
I got some really good results. I measured how much each sample soaked up. the bin soaked up 1.5 ounces, the sanding sealer soaked up 2 ounces, the titebond soaked up about a 1/4 of and ounce and the fiberglass resin soaked up almost 5 ounces and I finally just quite.
I can say by far the fiberglass resin is the best method for sealing the MDF of these four choices. The sanding sealer not far behind. What I like about the fiberglass resin is that it has a hardener in it so it will harden much faster. I assume the sanding sealer will take longer for the mineral spirits to dissipate. I think the Bin soaked up less because of it being alcohol based it started to dry then sealed up. As much as I would have liked to see the Titebond do well it seemed to kind of curtly up on the surface and not really soak in much.
Next I will fill the trench with the polyester finish mud. On the last tests the one thing I noticed with putting the putty directly on the wood I had some issues with were it feathered into the bare MDF when the sealer was applied. Especially with the Epoxy. I am trying this method with the sealer first because of the CPES I have used before is designed to soak in to wood and harden it so when the resin is applied it will stick to it well. The thinned fiberglass resin went on just like this stuff. Thinned down it is very easy to apply.
Dave

[hobbyhands]

Re: Best methods for finishing MDF

If you are near sighted then simply take off your glasses and poof! seems gone! At least from a few feet away

[MrkCrwly]

Re: Best methods for finishing MDF

There is a Composite Panel Association that might be able to help on this issue. http://www.pbmdf.com They even has a toll free number.
I had assumed that MDF was a monolithic uniform material throughout. But, in one of there publications "MDF Start to Finish" it states "Faces of MDF are generally more dense than the core,......." page 13 in:

http://www.pbmdf.com/CPA30/files/ccLibraryFiles/Filename/000000000729/MDF%20Start%20to%20Finish.pdf

This may be some of the problem since cracking is almost always caused by differing rates (or magnitude) of expansion and contraction. What does this mean? I have no idea. I posted so someone smart can find an answer (or tell me I'm full of it).