[Wind Chaser]

So I have a special project in the works... The wood (MDF) is all cut and routed to spec, what a filthy
job that was; and now it is time to think about painting...




What you see here is not yet bonded together; but when the project is finished it will consist of 5 x 1"
thick pieces of MDF stacked together. The top 4 layers are rounded over and the bottom 1" layer isn't.
There's actually more to it, but the end result will be a floating isolation riser that will lift my speakers
5.25" up off the ground and dampen vibrations.
 
So what is the best way to seal for MDF?  Are there any advantages/disadvantages to using an acrylic
or oil based sealer? I'm thinking the edges might require more than one coat?

After the pieces are sealed I may take it to an auto body shop to have it professionally painted, that is
assuming I can find one that will do it. Most shops are too busy painting cars, but there are two shops
that said they will consider it. If that falls through I am on my own, which would cost less, but the end
result might not be as nice as I had hoped for.

Anyhow, if you have any experience or tips with respect to painting MDF, I would greatly appreciate it.

John

[sts9fan]

I like to use shellac for that.

[Wind Chaser]

I like to use shellac for that.

Thanks, I just watched a Youtube video on using shellac to seal MDF. Looks like the solution. 

[FullRangeMan]

MDF exudes carcinogenic formaldehyde vapors for about 5 years, so it is guaranteed against termites and other insects for 5 years, best paint it inside and out.

[WGH]

WTF? Sure you are in a hurry but since you don't know what the top coat is you may be applying an incompatible primer/sealer. The primer has to be compatible with the top coat. There are all types of top coats, some are self priming.

A few years a client commissioned a very ornate coffee table and stools, not something I usually do but I like a challenge.
The coffee table top was made from combo-core plywood that has an MDF top and bottom for a super smooth, flat surface.
The legs are turned from hard maple.




The finish used was Sherwin Williams Sher-Wood Kemvar Conversion Varnish, a high solids catalyzed wood finishing system offering a superior quality for furniture, cabinets and interior wood product. Kemvar is a catalyzed colored varnish so you need a spray booth with an exhaust fan and a lot of time. Finishing will take as long or longer than construction.

Kemvar Sealer—catalyze and reduce Varnish as a sealer. Spray a full wet coat. Air dry 30 minutes, sand, repeat, sand, repeat.

The client wanted a distressed look so the parts were first sprayed a deep red then either black or cream depending on location and rubbed through. A clear coat of Kemvar Conversion Varnish added another layer of protection.

Prime coat


Finished stools and table in clients home


Wayne



 

[Wind Chaser]

WTF? Sure you are in a hurry but since you don't know what the top coat is you may be applying an incompatible primer/sealer. The primer has to be compatible with the top coat.

Yeah, I just got back from Home Hardware and they advised me to rethink shellac since it really puts a limit on what can be done afterwards. 

[Folsom]

I would be afraid to sit on MDF platform held by legs... I would have laminated some maple for that.

With speakers it seems like you basically have to bondo the MDF or you can never get a good result. It seems like you have to have something that can fill a tiny bit, and then sand it back to shape, at least anywhere the MDF has been cut/routered.

[WGH]

A good rule of thumb is the primer/sealer should always be from the same manufacturer as the top coat. The Sherwin Williams Kemvar is a high solid topcoat with a solid volume of 39 ± 1%. The MDF edges don't need to be filled with Bondo like particle board or plywood but there is always filling. A fast drying catalyzed sealer was also used.

The price may change your mind on how to finish. Kemvar is only available through a Sherman Williams Commercial Dealer, not the shop in the strip mall.
1 gallon Kemvar     $90.00
Catalyst                 $26.69
Lacquer thinner     $13.73
Sealer                    $37.01
Total                     $167.43

My first shop partner was always in a hurry so he blasted into projects without a complete cut list, knowing what hardware he was going to use, or the finish. All his jobs ended real close to a disaster and it took a lot more time for him to fix his screw ups than an extra hour at the beginning of a job to figure out all the details.

[Folsom]

So just a little primer is enough? That's nice.

The shop I use to work in, the plan was always there. But execution was another matter at times... imagine the overspray with 90psi at the regulator, which only dropped like 10psi over the hose . That got heavily readjusted by me.

Are there no easy water based recommendations? I didn't like the results we had spraying paint, but we did finish with an easy water based finish that worked on everything we did. It's still like $70-80 for a gallon, not including primer. And you have to sand and spray a few times.

[WGH]

I would be afraid to sit on MDF platform held by legs... I would have laminated some maple for that.

The stool tops are 3/4" plywood with a thin layer of MDF on both sides. You could hop up and down in the center of the stool, on one leg, all day long and nothing would break.
The table top is 1" thick, solid enough for a dance party. There is a support and leg in the center that is hidden by the books.

Stool parts


Caps are cut off and glued on top of plywood. Plywood edges have been filled, sealed and sanded before glueup to preserve the double line detail and 1/16" reveal around the top.

[WGH]

Are there no easy water based recommendations?

Option #1
Since the MDF speaker bases look round in the photo then I would drive a heavy screw in each end and turn them into a wheel, then set them on a couple of sawhorses.
Buy the most expensive latex paint, I like Dunn-Edwards, but whatever you buy get the best.
Then get a new Purdy 2-1/2" brush, the angled cut is nice. Purdy Pro Extra Glide is the best, no other brush is close and you need the best. About $22 at Ace.

After all is assembled - spin slowly and paint.
I could get close to a sprayed look but then I have over 40 years experience.

Option #2
Talk to someone who does this all the time. I own Salk speakers so I talked to Jim Salk when I had a veneer glue question and he was very gracious. Give him a call or post a paint question in the Salk circle, Jim is one of the good guys.

[Folsom]

Ah, I get your stools now. Call me over the top that I'd do maple

[richidoo]

Sherwin Williams Emerald latex paint is excellent, goes on like butter, very self leveling. No aldehyde stink.
First two coats spray it on thin, then wipe it off with paper towel so only a very small amount will soak into the MDF and you will minimize the wood swelling. Let dry, sand smooth, especially the cut edges that will absorb some paint and swell and get rough again. Repeat. After two light wiped coats and sanding, it will be sealed and smooth. Then apply 2 thicker coats with light sand between. If you want it to be harder wearing surface apply Polycrylic over the latex.

Modern electric sprayers do a fine job for spraying latex. like this.
Test spray to get the settings right, maybe add a little bit of water if needed to make it wet out, but that should not be needed with the newer sprayers.

Don't use a traditional latex primer like Kilz because they are high VOC (aldehyde) and the stink will never go away, even after covered in low VOC final coat. The only reason for a traditional primer is to stop the MDF from soaking up the paint and swelling. If you wipe off the first coat immediately you minimize how much soaks in, and you cause it to dry much faster, and it seals enough to prevent the full coats soaking in and swelling the wood. Do the first sealing coats out in the sun on warm day or use hair dryer after wiping off the wet.

[EdRo]

Amazing work, WGH!

[WGH]

Amazing work, WGH!

Thanks! There is more amazing work on my website:
http://www.wghwoodworking.com/

[alan.cassidy]

I may be too late but I read that you can seal the cut ends by painting glue on them. I made some amp stands and the cut edges looked terrible because I didn't seal them. As it happens they still look terrible because I never got round to fixing them.