What is the best way to paint mdf?

[Æ]

Re: What is the best way to paint mdf?

And by the way, the wood glue/water sanded much better than the shellac.

Well, I'll agree with you on this one.
Sanding shellac is a total pain, it was hard work. Maybe next time I'll try thinning the shellac first before applying it.

[Æ]

Re: What is the best way to paint mdf?

I think the best way to paint MDF is to pay a professional. Now all I have to do is save up.

[bobbarkto]

Re: What is the best way to paint mdf?

You guys should be using fresh shellac.
When it's old the film won't fully harden.
If it's fresh the film sands pretty readily and without gumming up the paper.

Well, I'll agree with you on this one.
Sanding shellac is a total pain, it was hard work. Maybe next time I'll try thinning the shellac first before applying it.

[Wolf]

My methods....

http://techtalk.parts-express.com/blog.php?b=22

And- it does work!
Wolf

[lunchmoney]

Re: What is the best way to paint mdf?

You guys should be using fresh shellac.
When it's old the film won't fully harden.
If it's fresh the film sands pretty readily and without gumming up the paper.

Mine was 10 minutes old. Fresh enough? :p

Perhaps it had been sitting on the shelf too long in home depot. Gummed up like crazy.

[r-carpenter]

Re: What is the best way to paint mdf?

Home Depot shellac is like speakers from Boss.

[Starkiller4299]

Re: What is the best way to paint mdf?

Home Depot shellac is like speakers from Boss.

Ouch.

It is truly unfortunate that the only hardware stores in my area are the big chains-- HD, Lowes, Ace, and True Value. Pick your poison.

[Paul Carmody]

Re: What is the best way to paint mdf?

You guys should be using fresh shellac.
When it's old the film won't fully harden.
If it's fresh the film sands pretty readily and without gumming up the paper.

I know shellac dries pretty fast, but I believe the general rule when sanding down a finish (shellac, lacquer, poly, whatever) is that it needs at least a week to cure.

Regardless, I still stand by the thinned wood glue method over shellac.

[danklugherz]

Re: What is the best way to paint mdf?

Yes, seams do tend to emerge. But it's very slight, and not really noticeable unless you're up close.

I question spending crazy amounts of time to achieve what's only a very slight visual difference, but that's just me.

I agree, The side panels on a sub I built are 2-ply 3/4" and after 4 coats of black I couldn't see any seams, after sanding w/ 400 sure enough there was a seam down the middle. You would think with semi-gloss it would show more before sanding but I couldn't see it.

[highfigh]

Re: What is the best way to paint mdf?

Mine was 10 minutes old. Fresh enough? :p

Perhaps it had been sitting on the shelf too long in home depot. Gummed up like crazy.

It was definitely old. If it's really fresh, it dries incredibly fast and will be hard in an hour. Sanding shouldn't be a problem unless the humidity is high or something in hte wood is keeping it from curing. Wipe some on a piece of glass and see how long it takes to dry- a thin coat shouldn't take long at all. It can definitely be thinned, too. I have used shellac to seal edges on MDF and it worked well, followed by 150 grit on my random orbital sander hooked up to my shop vac.

I have also used Krylon to seal the edges and when I did hte last sub cabinet, the customer asked is the box was made of plastic because the joints were invisible. As the paint continues to shrink, I expect them to show but as long as the sanding is done right, they shouldn't be very obvious. Another way to eliminate the edge's tendency to absorb so much is to clamp the joint and not use fasteners and when it's dry, route a very shallow recess and use maple veneer tape to fill it in. Once that's sanded, it will be invisible. If it's being rounded over, adding a beveled cleat at the inside corners along the edges being routed will add strength for the next step- rout a rabbet that's equal to the thickness of the edge x the radius of the round-over. Then, the rounded over edge will only be long grain wood. I use maple or very dry poplar and it works well. The only end grain will be at the top of the filler piece but it's easy to fill real wood.

BTW- for anyone who has a Porter Cable sander with the 1" round port for the black plastic dust catcher, if you're sick of emptying it all the time and you want to just be as dust-free as possible, go to the aisle at Home Depot where they have hoses for washing machines. It's light gray and has a plastic piece to create a hook so it will hang on a stationary tub or sink and it has a rubber fitting on the other end. The rubber end fits on the end of thel plastic tube on the small diameter hose and the other fits right onto the Porter Cable sander. I used wire ties to keep the hose and cord together and it also helps to keep the hose on the sander.

[highfigh]

Re: What is the best way to paint mdf?

Ouch.

It is truly unfortunate that the only hardware stores in my area are the big chains-- HD, Lowes, Ace, and True Value. Pick your poison.

There's nothing wrong with Zinsser shellac. Use the blond- it has less solids and will dry faster, harder. I used it to French Polish a case for a customer's McIntosh tuner and it turned out great. It will soak in and while it will take a week to completely off-gas the alcohol, it will sand smooth before that, without gunning up the paper. You didn't use anything finer than 220 grit at first, did you?

[stevev]

Re: What is the best way to paint mdf?

Lot's of good info here, but at the beginning of all of this i asked about using 'fiberglass Body fill". Apparently different from Bondo. As I remember it is a can of gooey pudding like stuff and you mix in the hardener from a tube which turns the final mix to a pale pink color. Sorry, the best way I can describe it. So, is this different from bondo? someone said that sanding Bondo was difficult, but I remember the fiberglass body fill was not that hard to sand down and feather out. Maybe I am confused, is Bondo the same as the fiberglass mix used in auto body repair, and fiberglass boat repair?

[bobbarkto]

Re: What is the best way to paint mdf?

Could be the same thing.

The basic formula for all these products is an acid catalyzed styrene/polyester resin with various fillers and additives to make a workable putty that sands readily. The type of filler will greatly effect the end properties and workability. Almost all use the same cream (or liquid) hardener.

The "fiberglass body fill" probably contains long strand, chopped or shredded fiberglass for added strength. Bondo makes a few of these products, as do other companies.

Regular and lightweight "Bondo" and similar products are relatively easy to sand when dry. About like a medium hard wood.
Adding fiberglass fibers makes it a little to much more difficult to sand depending on type/how much fiberglass is added.
Wear a good respirator when working any of this stuff.

Lot's of good info here, but at the beginning of all of this i asked about using 'fiberglass Body fill". Apparently different from Bondo. As I remember it is a can of gooey pudding like stuff and you mix in the hardener from a tube which turns the final mix to a pale pink color. Sorry, the best way I can describe it. So, is this different from bondo? someone said that sanding Bondo was difficult, but I remember the fiberglass body fill was not that hard to sand down and feather out. Maybe I am confused, is Bondo the same as the fiberglass mix used in auto body repair, and fiberglass boat repair?

[bobbarkto]

Re: What is the best way to paint mdf?

They put a date code on the cans now.
You get 1 year. Yours was DOA. :D

In fact, Zinsser expects the retailer to pull old stock from the shelves. I think it says that on the can now too, don't have one handy to check...

There isn't anything bad about it really. It's just not the prettiest shellac and is less suitable for some of the more refined finishing techniques.
But as a sealer it's fine; cheap, easy and readily available. Can't ask for much more than that. As long as it's fresh!

Mine was 10 minutes old. Fresh enough? :p

Perhaps it had been sitting on the shelf too long in home depot. Gummed up like crazy.

[gowa]

Re: What is the best way to paint mdf?

A cabinet maker with 20 years experience told me that he uses auto products for MDF.