View Full Version : Preparing an MDF Carving for paint

07-12-2013, 11:15 AM
Any tips on preparing an MDF carving for painting? The carved area looks good but it's going to soak in the paint and it's a little "furry" fresh out of the machine. Sanding doesn't sound like a good idea. What I was thinking about is to brush on an Acrylic sealer or maybe even elmers White glue. Going to post 2 picts from my phone..

07-12-2013, 11:17 AM
Here in the close up you can see the fuzzy surface.

07-12-2013, 11:34 AM
Any water based primer or glue size will enhance the "fuzzies" - an oil based primer is necessary for MDF - Some MDF won't react with shellac based primer (BIN) but some will... you just have to try it, but Oil primer has always worked for me.


07-12-2013, 03:19 PM
Good point, Lawrence.. ;) I will carve another pattern to use as my tester piece to see what results I get from priming with the oil-based product.

07-12-2013, 07:17 PM
I've used full-strength Zinnser SealCoat on MDF with no issues. MDF is like a sponge (especially on the exposed, freshly carved areas and edges). I "slather" on the SealCoat, giving extra attention to the areas that drink it up. I put on three complete coats as a rule, but that's not really counting where I recoat the thirsty areas, as I go.

After reading Lawrence's recommendation, I'm thinking the oil-based primer might be the best solution. Please keep us posted on how it's working out.

07-12-2013, 11:26 PM
shellac (or shellac based primer) works for me really well as long as it is fresh. Once it gets even a little old it seems to get "gummy" on me and clogs up the sandpaper. When it is fresh it gets rock hard and sands easier.

Upon reflection, I suspect this may be the cause for my inconsistencies rather than the MDF.


07-13-2013, 06:24 AM
I've been using mod pudge glue to seal (very thin coat) the wood and it does a great job, painting or staining..... so might be good on MDF also.

07-13-2013, 09:01 AM
I have used the modge podge and it works well on wood... I have a few pieces of MDF I am going to run this weekend with a pattern carved so I can experiment before I attempt to finish the project I'm working on...

I need to look into the differences between the different grades of MDF also... I switched over to using the Lightweight stuff several years ago but I was looking at my large workbench top which is the type of MDF at the box stores... much heavier and darker in color. I have a dado routed down the center where I inserted a t-track for some clamps and I noticed it routed out very clean... not like the lightweight stuff does... maybe a denser grade of MDF would be better for carving work that will be painted..

I'll post some pictures once I have the samples done.

07-13-2013, 10:08 AM
gel stain works great for mdf.

07-13-2013, 11:08 AM
MDF "quality" varies a lot in my area. I never know what the two local big box stores are going to have in stock....sometimes it's the darker (denser) stuff...next week it might be the lighter (soft/fluffy) variety. I prefer the denser/harder MDF when I can get it.

07-19-2013, 09:41 PM
"Door Grade" MDF will probably be the best bet. We get ours from Georgia Hardwoods in Atlanta, but I'm sure you have a supplier somewhere nearby. It can be a bit more pricey than your box stores, but it's worth it. It machines much, much better.

It also pays to put the primer to it, especially the opened edges and carved areas.

07-19-2013, 11:23 PM
But how good does mdf carve compared to wood? Hardwoods are so detailed and do not need sanding. Would mdf not be fluffy after carving, loosing detail upon sanding?

07-20-2013, 09:09 AM
It takes large letters quite nicely and centerline texts VERY nicely... but yes, there are certainly limitations with MDF. To me, the main advantage is flatness and price.

When you are painting a project afterwards anyway, MDF can do quite nicely (especially when painting a project with textured paint)

http://i171.photobucket.com/albums/u313/ldr_klr/portfolio/DSCF02091024x768.jpg (http://s171.photobucket.com/user/ldr_klr/media/portfolio/DSCF02091024x768.jpg.html)
http://i171.photobucket.com/albums/u313/ldr_klr/portfolio/DSCF01691024x768.jpg (http://s171.photobucket.com/user/ldr_klr/media/portfolio/DSCF01691024x768.jpg.html)
http://i171.photobucket.com/albums/u313/ldr_klr/portfolio/DSCF01791024x768.jpg (http://s171.photobucket.com/user/ldr_klr/media/portfolio/DSCF01791024x768.jpg.html)


07-21-2013, 05:46 PM
I've carved some fairly detailed stuff in MDF. It sands easily though, so it pays to be careful. I'd prime before sanding, let it dry thoroughly, sand, then prime again.

07-21-2013, 09:34 PM
I read in one of my wood mags you should mix a 50/50 water/glue solution to seal the freshly cut areas. Brush it on just like paint. If I can re-find the article I will post more.

07-22-2013, 07:41 AM
The idea is to make the loose fibers stiff so as to be sanded off easily. You can do much the same thing with primer or sealer.

But if you start with a better grade of MDF, you won't have to do so much of that, because it already has more glue in it.

07-25-2013, 04:16 PM
Lawrence, what brand of oil primer have you been using?

I'm looking at our pre-cat varnish here at work, and it's about $30 gallon. I'm hoping to seal my MDF without so much cost.

And will Acrylic paint adhere to it?

07-27-2013, 09:22 AM
Zinnser SealCoat is really just a brand name for dewaxed shellac (note: dewaxed - important!) which is my favorite coating to seal all woods. For the best MDF results I flood the surface and let it soak in. Then after it dries I do it again until it will take no more, especially end grain. This will leave a semi-gloss sticky residue/coating that is hell to sand off. It will clog a sheet faster than uncured glue. But you don't have to sand! Shellac is nothing but bug spit dissolved in alcohol. Unlike most other coatings, it doesn't change the chemical linking when it dries so it will always dissolve in alcohol. So the easiest way to get rid of that excess shellac is to just wipe the surface with denatured alcohol and rags until it doesn't come off anymore. Be generous with the alcohol and rags and of course do it in a well ventilated area - the stuff's poison. Once you get to the flat look, let it dry for 24 hours and it will finish sand without clogging and prevent any further coatings, i.e. paint, varnish, polyurethane, etc. from soaking in.


07-29-2013, 09:54 AM
I'm going to try the Zinsser BIN shellac primer. It has a fast dry time and has been recommended by the finishing experts over on Sawmill Creek. We'll see how it goes. Since it also comes in aerosol spray, I'm going to try spraying it with my HVLP gun.

07-29-2013, 11:42 AM
If you plan to spray, make sure you have tons of ventilation! As I said before, the solvent for shellac is denatured (methyl) alcohol, not the nice friendly ethyl alcohol that you are familiar with in various consumable flavors, but the stuff that, during Prohibition, killed and blinded thousands of people drinking bathtub hooch that had been "stretched" with the still legal methyl alcohol. Since it is water soluble, it is very quickly absorbed through the lungs and into the bloodstream even faster than petroleum based solvents (i.e., glue sniffing) and instead instead of a pleasant drug high you get blindness, peripheral numbness, and permanent CNS damage. Baaaaaad stuff. It might even be prudent to use an organic filter air mask too.

When applying with a brush or rag, good ventilation is sufficient, just as fast, and you don't get overspray.

If I have a large flat area to saturate, I will just pour a significant amount into the middle of the piece and slosh it around with a brush or small rag until it is all absorbed or wiped off. Very quick.


07-29-2013, 01:07 PM
Thanks for the heads up.. I was planning to use a paint mask anyway, but this is good advice. I did a little more research on this, and apparently it is ethyl alcohol with the denaturing agent (toxin or bittering agent) added. In the case of a methanol denaturing agent, it can cause blindness and death. http://chemistry.about.com/od/chemicalcomposition/f/What-Is-Denatured-Alcohol.htm

I wonder if Zinsser provides this information?

07-29-2013, 01:32 PM
If they sell it, you can ask for a MSDS sheet. Its the law.


07-29-2013, 03:00 PM
Of course...

Thanks peep!

07-30-2013, 08:30 AM
Type of MDF carvings.
Is it a noticeable difference going from normal to best or optimal? It sure is in hardwood, but not much difference when going to Optimal from best in very soft wood.

Anyone with experience in trying different MDF carve types?

07-30-2013, 08:59 AM
I didn't notice an appreciable difference between best and normal on some recent carves in MDF. I created a sign and did one on "normal" with some v-carving around the edges of the lettering and border (took 3 hours) and then ran that same sign on "best" with only a raster carve (was still 3 hours). They look virtually the same as far as quality goes.