Painting MDF, how?

[pochoboy]

my 1st coat of Kilz, there's a lot of sanding I'd have to do. I'll start that tomorrow and if it holds I'll not do a 2nd coat of it. here's a pic:



btw, I used a brush to apply the Kilz, it could be if a sponge roller was used it would have come out smoother. Live and Learn

[davepellegrene]

my 1st coat of Kilz, there's a lot of sanding I'd have to do. I'll start that tomorrow and if it holds I'll not do a 2nd coat of it. here's a pic:



btw, I used a brush to apply the Kilz, it could be if a sponge roller was used it would have come out smoother. Live and Learn

I usually spray it on. I have rolled it and you get a lot of orange peel.A sponge roller may work better. Every time I use a sponge roller with anything but water base it comes loose from the plastic piece inside the sponge and makes a mess.
When good and dry the kilz will sand really easy. If you got the alcohol base you have to move pretty fast with it.

[williamrschneider]

Heh... I've built speakers primed with Kilz alcohol-based primers...



I used a sponge roller to apply it, and got a light texture that was rather nice.

I didn't like sanding the stuff though. My sandpaper clogged easily with it.

The speakers above were eventually sanded down and veneered. Long story.

BTW, that was a removable front baffle shown above. I used a pin-registered mounting method to eliminate mismatches between cabinet and baffle. The seam was a mere hairline.

[pochoboy]

Heh... I've built speakers primed with Kilz alcohol-based primers...



I used a sponge roller to apply it, and got a light texture that was rather nice.

I didn't like sanding the stuff though. My sandpaper clogged easily with it.

The speakers above were eventually sanded down and veneered. Long story.

BTW, that was a removable front baffle shown above. I used a pin-registered mounting method to eliminate mismatches between cabinet and baffle. The seam was a mere hairline.

that looks Schweet!
I'm planning to veneer some of the panels, do I need to primer those panels too?

edit: oh btw, I couldn't wait so I started to sand the Kilz primer with 100 grit cause it had some mean brush streaks then I used the 150 grit before I primed with the red rustoleum primer. I was using a sand block and it kept on caking up with the Kilz so I figured I'd use my electric hand sander(1speed) and it sanded quickly but the cake on the paper built up quickly and pitted the primer here and there. Live and Learned not to use that sander as it caked quickly and messed up the primer coat. I filled up the pock marks with wood putty and resanded then primed with the red rustoleum. With the red primer I can see all the flaws so I'll try to fix it up or I may leave it as its only on the bottom and rears panels.

I'm using the semi-gloss black as the top coat and will probably sand it with the 320 grit. Now, do I need to use a clear coat on the last spray or should I just leave it after the 320grit sand? I'm not looking for a piano black finish but just a nice black finish.

[davepellegrene]

that looks Schweet!
I'm planning to veneer some of the panels, do I need to primer those panels too?

edit: oh btw, I couldn't wait so I started to sand the Kilz primer with 100 grit cause it had some mean brush streaks then I used the 150 grit before I primed with the red rustoleum primer. I was using a sand block and it kept on caking up with the Kilz so I figured I'd use my electric hand sander(1speed) and it sanded quickly but the cake on the paper built up quickly and pitted the primer here and there. Live and Learned not to use that sander as it caked quickly and messed up the primer coat. I filled up the pock marks with wood putty and resanded then primed with the red rustoleum. With the red primer I can see all the flaws so I'll try to fix it up or I may leave it as its only on the bottom and rears panels.

I'm using the semi-gloss black as the top coat and will probably sand it with the 320 grit. Now, do I need to use a clear coat on the last spray or should I just leave it after the 320grit sand? I'm not looking for a piano black finish but just a nice black finish.

Had you let it dry overnight you probably would not have had any problem sanding. If it doesn't powder right away its not dry. The sander should have been fine to use. The key is to let the thinners dissipate. If you rush the finish you trap the thinners in and they will eventually come up throught and sometimes create a mess. Sometimes it results in sanding the whole thing back down. As the primer dries it shrinks so all the imperfections you are filling will shrink over the next week or so and will start to show through. So satin finish will hide a lot of that, but the piano finish will make it stick out like a sore thumb.
I sand the bare MDF with 120-180. I sand the primer with 220.
When you spray the black on you should not have to sand it unless you are going to put another coat on it. In that case 220 is fine enough. If you want to work harder you can use 320.
I wouldn't prime under the veneer.
Oh and did i stress dry time between coats.

[davepellegrene]

Here is an example of rushing the finish. If you look in the right top corner of the front baffle you can see the seam of the 1/2" MDF. It also shows on the top right rear corner. This didn't show up until about two weeks after it was finished.

[Soupy]

Pochoboy-

I bypassed all so likely I'm too late.

Decision #1 ... did you purchase a paint? Latex/Latex?. Acylic/Acylic? Finish based on start. Mdf is unimportant beyond it's need to be sealed And acheive adherence to final media.

70/30 Elmers glue/water to seal. Sand 220. 70/30 Same, sand 400. 2 coats prime, either media sanding at 220 and 400. As many coats as you desire either media sanding at 440 and 600. Depth of finish dependent on steps taken.

All you need.

5 years spraying for General Electric FO1 finish as experience. Same stuff you see in Medical equipment ( yes-part wood!)

[pochoboy]

Soupy thank you for the low down but I've already done purchasing and started the paint job.

Dave,
Yeah, I read your responses and I got your main point on letting the paint dry before I started sanding. But I got anxious(like a kid pre Christmas) and went ahead with the sanding, now after seeing the imperfections using the red primer(it was hard to see the flaws when it was white) I'll fill in the flaws and prime. I have one **** joint thats exposed on the bottom rear panel, I'll sand down and reseal/prime with Kilz and let it dry a day before sanding.
After sanding the kilz, I was amazed how it sealed/primed the mdf and the smoothness of the sanded product that came to be. I'm beginning to see/understand the process of a black piano finish which would take some time and a lot of elbow grease to complete.

Thank you for all the tips and pointers as I'm learning a lot going thru this build!

[Paul Carmody]

BTW, that was a removable front baffle shown above. I used a pin-registered mounting method to eliminate mismatches between cabinet and baffle. The seam was a mere hairline.

"Pin-registered?"

I have no idea what that means, but it looks good. Care to explain?

[williamrschneider]

Hi Paul

On this build, I was following the North Creek plans for the cabinet. George Short specified a piece of plywood to serve as a brace for the front of the cabinet. It was positioned flush with the front cabinet surface and against the baffle.

When I was fabricating the panels for these cabinets, I decided to use two pins on each baffle to locate them precisely on the cabinet. With screws, there's a little slop in the clearance holes and the front baffle can shift around slightly. I used the pins to locate, and the screws to merely clamp the baffle against the cabinet.

Here are some pictures that may help explain:

The holes for the pins were drilled through the inner brace into the front baffle (but not through).



Note the pin holes in the baffle braces below. One is located beside the tweeter cutout at the 2 o'clock position, and the other pin hole is located in the lower left near the screw hole. The baffles carried the mating pins.


After assembly, the baffle is routed flush with the cabinet. The baffle will reassemble exactly this way (no offset, shifted position, etc.) each time it's attached.



It's certainly not necessary to assemble a baffle this way, but I wanted to try this out on this speaker to see what accuracy I could achieve.

[pochoboy]

william,
again thats some great work and from the looks of it you got a nice workshop and table to boot!!!

[davepellegrene]

Soupy thank you for the low down but I've already done purchasing and started the paint job.

Dave,
Yeah, I read your responses and I got your main point on letting the paint dry before I started sanding. But I got anxious(like a kid pre Christmas) and went ahead with the sanding, now after seeing the imperfections using the red primer(it was hard to see the flaws when it was white) I'll fill in the flaws and prime. I have one **** joint thats exposed on the bottom rear panel, I'll sand down and reseal/prime with Kilz and let it dry a day before sanding.
After sanding the kilz, I was amazed how it sealed/primed the mdf and the smoothness of the sanded product that came to be. I'm beginning to see/understand the process of a black piano finish which would take some time and a lot of elbow grease to complete.

Thank you for all the tips and pointers as I'm learning a lot going thru this build!

Sounds like you are getting it. Don't worry to much the Satin black will look great with the steps you are taking. As you can see with the pic I posted. I don't take my own advice sometimes and that's what you get. Its hard not to get excited when you get to the painting part of the project.
When I had said to sand with 220 before painting that is fine enough as long as you are not spraying lacquer. For that you would need to go to at leas 400. I assumed you were not using lacquer.
I see you are in Hawaii. If it is hot and sunny. You can set it out in the sun and speed up the process. That will really help getting the thinners out.
Another way you can tell if it is all the way dry is you don't smell it anymore. That may take a week or two.
Dave

[pochoboy]

As you can see with the pic I posted. I don't take my own advice sometimes and that's what you get.

hahaha, but it must be the pic cause I can't see anything wrong with your paint. I believe you though

I see you are in Hawaii. If it is hot and sunny. You can set it out in the sun and speed up the process.
Dave

I sure wish it was sunny, of all the years I've lived here I've just taken notice that April is one of the worst months for visitors to visit if they want sun and beaches. Most days skies are overcast during April/May

[pochoboy]

now I'm beginning to appreciate those who've gone before me and shown me the way to painting mdf. I have a better feel on what some have done to do a piano black finish which is a whole lot of work.

I went with the semi-gloss black and found it somewhat to glossy that brought out flaws on the mdf and sanding or lack there of. I've found the perfect color which is the Rustoleum Satin finish in black as it hides more of the imperfections as far as I can tell and it matches my plate amps finish. Also I've learned what it takes to get a smooth finish as far as sanding goes. What I got to learn is on the use of the spray paint as I got a couple of runs staying or going over a certain portion of the panel.