How to seal MDF seams for painting?

[Jim Holtz]

I have a project coming up that I want to paint gloss black which shows everything, especially seams as the cabinet ages and the MDF shrinks.

I remember reading that Jon used something that took care of the issue but I can't find the thread. I'd appreciate any feedback.
BTW, in the past, I've used bondo, glue, shellac etc. with limited long term success. I'd really like to hide the seams this time. Any other fool proof methods?

Thanks!

Jim

[Steve Manning]

Hey Jim ..... from what I recall a couple of coats of epoxy seems to work well. I know there are some sealers that cabinet companies use as well. I have that info somewhere, I'll take a look. I've also heard this works well though have not used it myself. http://www.rustoleum.com/product-cat...surface-sealer

[Steve Manning]

I also remember Wilson Audio using a gel coat to seal their cabinets as well. Here is a video on that http://www.wilsonaudio.com/videos/video=gel-coater

[BobEllis]

Good old Bondo has worked well for me. There's another brand/style of body filler that has less fiber and gives a smoother finish, but I can't recall the name. Check Ron's Ardent thread.

[TEK]

Hi Jim
Jon is sold on using West Cost System Epoxy to seal the case before painting:

http://www.westsystem.com/ss/105-epoxy-resin/

That is what you will find if you check his sub thread as well as the ardent thread. I have also used this method and so far there has been no problems (several months now, but not years yet...)

In addition to using Epoxy to seal everything I would recommend to first use a router and route a recess where the seem is and then fill that recess with filler to get a perfect seem. Wood-on-wood seems is hard to get perfect, by recessing over the seem and fill with filler/boundo it is much easier to get a perfect seem.
Ron might fill in with more details - but I'm pretty sure you will get a good result if you first recess, fill with bondo, sand even, cover it all with epoxy, sand the epoxy nice and flat, paint with filler/base/sealer, paint the top coat.

From my experience I usually have to add one or two layer of top coat, and then sand it down with 500 grid. Then add a new layer of top coat. The last layer then is usually much better then the two first layers. Not sure why (probably because I have not done a good enough work on the base coat).
Then (if needed) sand with 1200, 2000 and 3000 grid and finally polish it all up to a perfect finish.
I have found out that you can fix quite big mistakes in the paint by sanding and polishing the finial coat - and still get a quite perfect result. But of course, if you get it perfect straight out of the gun - that's a lot less work ;-)
NB: Be very careful on that last sanding - if you sand trough you will have to add a new top coat - and that's a drag. Especially the corners are easy to sand trough.

[Jim Holtz]

Thanks for the feedback everyone! I now have some new ideas and products to try. I hate seams showing though on paint or veneer and have used bondo, glue, shellac, high build primer plus everything else I could think of and have always been able to see seams after the cabinets aged a few years. Never bad but I'm trying to eliminate the seams showing through completely.

I vowed I'd not do another gloss black speaker cabinet but I've given in and am going to do one more. 8O I have a spray booth set up in my work room in the basement with air piped in from my 80 gallon air compressor in the garage. I recently bought a Warwick 904 HVLP automotive spray gun that allows even a complete amateur like me to turn out professional looking jobs. I'll use Crystalac which is water based and has almost no odor. Highly recommended! I'm going to do a base coat/clear coat application this time and see if I can lay the finish down smooth and glossy enough with the new gun to elimiate buffing it this time. We'll see! :W

Anyway, thanks again to everyone for the ideas!

Jim

[meb46]

Jim - Sounds like you are getting serious on the DIY Spray Booth!!! When I sprayed mine, I had my spare room masked off in plastic like a Dexter TV Episode! The HVLP Systems are genius, I had a huge amount of success with mine. Brings a sprayed finish into the realms of DIYers!

[kevinm]

Jim - highly recommend wrapping the cabinets in HDF or 1/8in MDF. With a round over, seams disappear and the finish is butter smooth.

[flamethrower1]

Jim, I did my Trtrix in gloss black and they look as good now as they did when I finished them.
I just used plain old high build automotive primer, not the stuff you buy in a can.
It is lacquer based and I block sanded it a couple of times

[Jim Holtz]

Jim - Sounds like you are getting serious on the DIY Spray Booth!!! When I sprayed mine, I had my spare room masked off in plastic like a Dexter TV Episode! The HVLP Systems are genius, I had a huge amount of success with mine. Brings a sprayed finish into the realms of DIYers!

I set this up several years ago and have done multiple projects both speaker and furniture refinishing. Crystalac rocks! The new paint gun replaced a knock off that no longer had parts available for it. The Warwick was a great investment!

The paint booth consists of PVC piping suspended to the floor (ceiling) of my basement work shop with shower curtains and then cheap tarps attached to the floor joist as extra protection from overspray since it's also a storage room. It's temporary so I can make it operational in less than an hour. Cheap plastic drop cloths cover the floor.

I wouldn't finish any other way!

Jim

[Jim Holtz]

Jim - highly recommend wrapping the cabinets in HDF or 1/8in MDF. With a round over, seams disappear and the finish is butter smooth.

Hi Kevin,

Actually, I've been using 1/8" MDF on the top and rear of the cabinet where all my seams end up. This is also why people wonder why I assemble cabinets the way I do. :lol: The main seam I want to completely eliminate is the one where the front baffle attaches to the rest of the cabinet. Round overs hide but I've still had that seam reappear after a few years. My goal is to hide it completely and provide a solid base for the Crystalac to adhere to. If I'm staining veneer, I usually use Bullseye dewaxed shellac sealer over the stain before applying the Crystalac. Since I'm shooting black Crystalac this time, I won't need the sealer.

Thanks for the suggestion!

Jim

[Jim Holtz]

Jim, I did my Trtrix in gloss black and they look as good now as they did when I finished them.
I just used plain old high build automotive primer, not the stuff you buy in a can.
It is lacquer based and I block sanded it a couple of times

I've used automotive high build primer in the past on MDF and it filler minor pits and imperfections well but it didn't hold up over seams. Thanks for the suggestion though.

Any progress on the Anthology build?

Jim

[flamethrower1]

I've used automotive high build primer in the past on MDF and it filler minor pits and imperfections well but it didn't hold up over seams. Thanks for the suggestion though.

Any progress on the Anthology build?

Jim

going to do the wiring harnesses tonight, still waiting for the veneer

[meb46]

I second the 1/8th skin... this is a great way to limit the visual impact of the seams. The only one issue I have had with this approach is getting large air pockets between the cabinet surface and the skin on very large panels. You need to apply pressure to the surface moving out from the center...

[PMazz]

Mitered joints work the best with MDF. Any butt joints will telegraph thru a finish after drying out. The 1/8" laminate would do it too.

[Rolex]

Mitered joints work the best with MDF. Any butt joints will telegraph thru a finish after drying out. The 1/8" laminate would do it too.

True. This the best way in my opinion. I always miter.

[Rony]

This sounds like a good sure way, not sure how difficult this would be though.

[TEK]

Mitered joints work the best with MDF. Any butt joints will telegraph thru a finish after drying out. The 1/8" laminate would do it too.

Hmm, if you recesses the joint, fill it with bondo, sand flat and seal it all with epoxy, base coat and then top coat - do you mean that you still will have the seams paragraphing trough?
I would expect that you would bot - but I have not recessed and filled with bondo, just used epoxy - and I have not enough years of experience to claim that I have proof of that working.

Have anyone tried this (recess, bondo, epoxy, paint), had the finished product for several years and could share their experience?

[BobEllis]

I had a skim coat of bondo over essentially the entire surface of a speaker I build in 2004. Still no signs of the seams. It's sealed, that could be part of the reason it stayed so well.

[blue934]

Has anyone ever cut open a PE painted cabinet? I'm curious what process they use. It seems like a very good finish for a well priced box.

David

[Alaric]

Has anyone ever cut open a PE painted cabinet? I'm curious what process they use. It seems like a very good finish for a well priced box.

David

That's a very good question. I don't know if it's worth buying one to sacrifice on my budget but I'm interested in an answer if it's available.

[Steve Manning]

One could use something like this stuff ......... http://targetcoatings.com/products/s...-filler-glaze/ ........ http://targetcoatings.com/wp-content...HSF5000_R2.pdf It's designed specifically for sealing porous materials like mdf, prior to paint. I would imagine the PE cabinets were sealed with something similar prior to paint.

[PMazz]

With MDF, it's not only sealing the edges but what happens long term when a butt joint is used. MDF changes in thickness as well as width (expands and contracts in all dimensions). What you usually see happen in a butt joint is the entire edge will change relative to the face it's joined to. It's subtle but with a gloss finish can be visible over time with humidity changes. This might only be a problem in areas like mine with wide seasonal swings in relative humidity.

Can't speak for painted PE enclosures but most commercial veneered products like these are v-grooved laying flat and folded and glued together using specialized machinery. I mitered these using pre-veneered MDF and used wide masking tape to fold them together.




Not sure what "recessing the joint and filling with Bondo" means.

[dar47]

All good ideas here, I would point out that MDF is a substrate material never design to be a top coat. It needs something harder and more stable for a true finish surface. I don't tend to prefer gloss black but if I did I would treat the final surface to something harder. Those folded miter production corners are convenient and allow the use of just 1, 3/4" layer of material. I did a Muodula MTM for a friend some 5 years ago that he want modeled after some Audio Tectnica's. and that had 1 1/2" front baffles and 1 piece wrap around veneer. Asked if he can see joints 5 years later and he said no they a great.



To give them a real hard substrate I used real hard board, the 1/8" peg board stuff not MDF (big difference). Now I only had a front rounded surface to deal with and a seam at the top and back. I call it a seam as the 1/8" hard board doesn't behave like a MDF joint.





Jim I know you said you have used 1/8" wrap before but I think if you cover bottom first, back, sides, front and then top you should only have a seam at top top that is visible. In this case if you seal that round over in an epoxy you should have a paint joint you never see.

[Steve Manning]

I believe the main reason for joint telegraphing, moving, what ever you want to call it, is moisture absorption. That's why using bondo, epoxy, a specialized sealer, whatever can work in preventing this. It's typically not an issue on a surface that has not been disturbed, edges are another story, there sponges for moisture. That's why a complete seal is needed ..... throwing on a coat or two of primer is not going to work (my Jensen's had multiple coats of primer applied and the joint still showed up). Fabrication options like mitered corners can help to minimize exposed material ...... though the bottom line is the stuff has got to be sealed, look at what Wilson Audio does to seal their stuff and there not even using mdf. http://www.wilsonaudio.com/videos/video=gel-coater What ever route one goes, it adds to the process that's for sure.

[blue934]

So how does Gel Coating compare to the West Coast Epoxy that Jon uses both in application difficulty and effectiveness?

[Steve Manning]

As I recall Jon applies the epoxy with a paint roller with sanding between coats, from the video, obviously the gel coat is applied with a sprayer, I'm not sure about being able to use a roller for it's application ...... I do know the gel coating is used in the boating industry to seal the hull prior to applying paint. That might point to it's ability to resist moisture rather well. I guess it would depend on if you have the ability to spray on finishes or not, as to what you could use. I like the idea of being able to use a water borne products myself ...... no nasty chemicals and very easy clean up. That's how I came across the stuff I listed earlier. It's used a lot for kitchen cabinets that have a lot of mdf used in the fabrication process and is used to seal the mdf prior to paint.

[PMazz]

Unless you also treat the interior of the enclosures with the same process as the exterior, you'll still have moisture related movement. Besides that, changes can occur fairly quickly due to the moisture content of fresh MDF and putting it in a home environment soon after construction.

[Jim Holtz]

Hey Jim ..... from what I recall a couple of coats of epoxy seems to work well. I know there are some sealers that cabinet companies use as well. I have that info somewhere, I'll take a look. I've also heard this works well though have not used it myself. http://www.rustoleum.com/product-cat...surface-sealer

Hi Steve,

I checked out West Systems epoxy today at Woodsmith. I'll bet it works well but at $65 for a quart of epoxy and a small quantity of hardner, it should. 8O

I also researched Zinsser GARDZ and based on all the reviews I read, it should also work extremely well. It's also affordable at $9 quart or $21 gallon at the local Menards. I think I'll give it a try.

Thanks for the suggestion and your help!

Jim

[Steve Manning]

Hi Steve,

I checked out West Systems epoxy today at Woodsmith. I'll bet it works well but at $65 for a quart of epoxy and a small quantity of hardner, it should. 8O

I also researched Zinsser GARDZ and based on all the reviews I read, it should also work extremely well. It's also affordable at $9 quart or $21 gallon at the local Menards. I think I'll give it a try.

Thanks for the suggestion and your help!

Jim

Your welcome Jim ..... yeah that West Systems is a bit on the painful side. Let me know how the Zinsser works out, I'm sure I'll be using mdf again (don' tell Jon) at some point and at the price the Zinsser would be a good option for sealing.

[Steve Manning]

Hey Jim .... wondering if you got a chance to try out the Zinsser GARDZ? Curious to see if it worked.

Steve

[Jim Holtz]

Hey Jim .... wondering if you got a chance to try out the Zinsser GARDZ? Curious to see if it worked.

Steve

Hi Steve,

I bought a gallon but haven't used it yet. My speaker cabinet planning is for in the future but thought that GUARDZ was something I could use around the house too. It sounds like very cool stuff.

Jim

[Steve Manning]

Hi Steve,

I bought a gallon but haven't used it yet. My speaker cabinet planning is for in the future but thought that GUARDZ was something I could use around the house too. It sounds like very cool stuff.

Jim

Thanks for the update Jim.

[wolf_teeth]

I recently won a gallon of Duratex 'Ultra Deep Tint Base' at a DIY event, and it's intended for tinting at a paint-store. I played around before I did that, and it's a natural/clear material on its own.

I coated the back panels of my recent Cecropia build to seal the MDF, and I used 2 light rolled on coats. Then I sanded it with the orbital sander when it was dry. Turns out it takes paint very well atop of it, and I could have sanded more to get all of the bumps out if I wanted to. I wanted a bit more durability on the rear side.

Point is- this was the easiest prep for paint I've ever done on MDF. No primer needed, and builds well.

Later,
Wolf

[TEK]

Thanks for the info wolf.

Anout Epoxy. Sure West coast systems is good stuff, however Epoxy is a surface treatment used A LOT in the boating industry and for glass fiber usage.
Our demands regarding were and there are wery limited, so I would imagine that almost any bramd of epoxy should work excellent for our usage.
Anyone tried out different, preferrable cheaper, brands of epoxy?

[BobEllis]

I'm using Total Boat, TEK. It's a house brand for Jamestown Distributors, a boat supply house and sells for about 2/3 of the equivalent WEST System product. It's been a while since I've used WEST System, but Total Boat seems to match in handling and finish. I've read elsewhere that it is compatible with WEST System additives and hardeners, in case you want something other than slow or fast, like water clear or very cold weather curing.

[JonMarsh]

West actually has several options on hardener, some not well known, like the 207 special clear hardener, and the 209 extra slow. Usually 205 works OK in moderately cold weather, but then, with TEK we're talking Norway, and GF wants to go to Norway to see Polar bears, so that speaks volumes... :W

I've been looking at gelcoat options, but as I've figured that out, turns out I'd need to do epoxy anyway, as gelcoat doesn't adhere well to wood. Well, who knows...

[Pknaz]

I recently won a gallon of Duratex 'Ultra Deep Tint Base' at a DIY event, and it's intended for tinting at a paint-store. I played around before I did that, and it's a natural/clear material on its own.
...
Point is- this was the easiest prep for paint I've ever done on MDF. No primer needed, and builds well.

Later,
Wolf

I wonder if you could use this as a prep for veneer?!??

[wolf_teeth]

I don't see why not, FNG, but you'd have to sand for a bit. I think why this worked so well is that the pigment was not in the paint to add the thickness you'd normally get from Duratex. I mean it too- it was a easy to do!

If you're using the glue-on veneer method, you might have more trouble bonding the veneer with the Duratex surface than the bare-MDF or wood surface. I've not tried gluing to Duratex, but painting it is just fine.

Later,
Wolf

[Steve Manning]

Just ran across something that I was not aware of that could be helpful in the sealing issues. Apparently there different grades of mdf. I picked up a sheet of what is considered cabinet grade mdf today. It has a higher amount of resins that help prevent absorption during the painting process. Price was only a few bucks more a sheet, though I did have to go to a real lumber yard to get it, forget the Lowes route.

[PMazz]

There is an exterior rated MDF called Extira that might be useful in speaker building. It is harder and heavier than standard MDF. There is also HDF (high density fiberboard) as well but it's much harder to find.

[shame302]

The method I used was pretty simple and worked well.

I hand rubbed two coats of poly over all surfaces and let cure for a couple days. I did this to help stabilize the surface. I then used a 50/50 mix or 60 (i think) minute epoxy and "micro balloons and skimmed any imperfections, screw holes (I used the screw and glue method for assembly). I didn't have proper micro balloons at hand so I used baby powder instead. Let it sit for another couple days and sanded everything down like bondo. I honestly think BONDO would have worked just as well. My home isn't really climate controlled and I've had no issues. I rattle canned the paint and did 5 coats or poly over that. They still need to be cut and buffed to be smoothed but its been a few years so I doubt that will ever get done. heh.