I just did a similar project and would like some advice on MDF. I noticed your first picture showed some “hairy” MDF in the pocket area. Your second post looked very clean. My project came out very hairy. I put a coat of Krylon on and did a light sanding but the second coat still had a hairy finish. Maybe I need several coats before I sand. Any Suggestions on finishing mdf? Some say the hairy finish comes from dull end mills. Mine have less than 10 hours most of that is on MDF. I did notice that my end mill got really clogged with the top coat paint. It had dried for a full 24 hours. Any help would be appreciated.
Mine always look fuzzy. The 2nd pic did not have clear coat yet so its just harder to see on flat black paint
Hmm, that’s disappointing. But the nature of the material I guess. Thanks for the reply.
My suggestion would be to paint with “no wax” shellac. The fuzzies will not go away, but they will stiffen up and be easier to sand. That’s what I did on the last MDF I cut (and hopefully it will be the last MDF I cut! 
)
2 Likes
So is there a particular wood you like to use for signs that will be painted? I’m thinking Birch or maybe Poplar. I don’t use Poplar generally but I made some end tables with Poplar this year and it seemed to mill ok with standard router bits but it is stringy and I’m not sure how it would hold up milling fine detail. Worried about chipping and tear out.
1 Like
I use a lot of white cedar, it cuts well and lasts a long time outside. It holds details but I wonder if you are wanting to cut something too small except for the hardest of woods with fine grain like maple.
1 Like
Now I had not thought about cedar. I happen to have some nice pieces. I will give that a try! I have been woodworking for 30+ years building furniture mainly so I am use to domestic hardwoods. I have had little use for MDF other than making jigs. CNC and Sign making is a new adventure. Barely a month old so I am testing and learning. This current project does have some fine detail. The test piece which is a 10 inch round sign in MDF came out quite good. There is some fine detail. So I have run the real one which is an 18 inch round sign. The detail appears to be there. It’s the finish that bothers me. This piece of MDF came from a different sheet and I think the quality of the MDF is part of the problem. MDF appears to be a rather inconsistent product. So for painted signs I may try Expanded PVC. It’s more expensive but yields superior results from what I read. I’ll post pics when I am done. I have done some inlay tests using maple and cherry and got good results. I am very excited about that!
1 Like
I’m no expert but you might try basswood, very close grain and cuts really clean. I’ve used it for indoor projects, not sure how it would hold up outside.
1 Like
I’m done! as promised here are some pics of my project. The small one was my test 10" and I was really happy with it. The larger one 18" had the “hairy MDF”. But with enough coats of paint, I was able to sand most of it out. My daughter, the technical director, will be hanging it in the Theater Department. It’s their theater Logo. She has already shared pics with them and they think it is great! In hindsight I think a down cut spiral on the roughing passes would have worked better cutting through the stencil mask.
6 Likes
That looks great, David. You pulled that rabbit out of the hat!
The only problem I’ve had with the Duck Brand “WalMart” shelf liner (not with the liner itself) is when I used it on some thin paneling with grain. I sealed with 3 coats of shellac and poly clear coated before I cut. Then after applying and cutting through the mask, I sprayed more clear coat to seal the cut area. That wasn’t a good enough seal to keep “whiskers” showing, at the edges of the cut, of the paint I used to color the carved area. The whiskers followed the grain under the mask in lots of areas. I had a lot of hand work cleaning up around the carved areas.
So, I don’t know how to seal any better than I sealed it on this last project. I’m guessing I need to choose less textured wood or use 3 coats of clear coat after carving. Perhaps brushing on a clear coat would get more on the edges.
1 Like
I don’t know that any mask would address the issues related to the paint or stain pigments following the “wiskers” of the wood as they travel below the mask. As you said, maybe some more or better sealant and/or some different wood species and or different types of paint or stain may be required to address this issue. Another thing to consider is the use of an aerosol from a can or spray gun vs using a brush to apply the paint/stain/sealant, maybe the smaller droplets sitting on top of the surface may reduce the wicking effect of the whiskers.
Wood finishing is certainly tricky, there is a lot of trial and error involved. I think that this could be the subject of a long thread with contribution of many members to better establish best practices.
1 Like
Absolutely! When it comes to staining, its the scariest part of the project. You spend hundreds building a table or whatever and it can all come crashing down if the stain job goes south. Sadly there is no fool proof method. I have read countless articles and videos and still looking for one!
Thanks Tex! I’m rarely totally happy with a project because, like many craftsmen, I tend to focus on the imperfections that most will never notice. That’s what people tell me anyway.
As we all know, it is so hard to unsee an imperfect part of a project! 
3 Likes
If you have a perceived imperfection, every time you look at the project your eye goes straight to it. When you give a gift with an imperfection do not point it out. Most people will not even see it. You may see it but the recipient will not notice.
4 Likes
I am working on a painted project and started with MDF - I figured its cheap, mills well, and its getting painted anyways. Got so frustrated with trying to get a finish that was not horrible that I just went and got a piece of poplar and started over. MDF is such a sponge and unless it is a big flat piece that you can keep layering and sanding its just not worth it.
1 Like
I use brushing lacquer to seal my cuts in 1/4" birch plywood, and have not had any bleeding problems. I’m not sure if that would help you, just a suggestion.
As you know, MDF is not all created equal and the different grades give different results. When I went to an industrial supplier recently, I was informed that they had MDF specially made for painting. The products sold at the big box store and building centers are what they can get at the best price and may be different from one shipment to another. I tried to get specs on sheet goods and got a blank stare from the staff who don’t even know who their suppliers are for the batch received.
2 Likes
MDF is very porous due to the nature of sawdust and glue. The faces are pressed more than the sides and ends and are still porous but not as much as the interior. I have found that two coats of dewaxed shellac (Zinnser Universal Sealer) on almost anything seals the wood and makes for less work with top coats whether paint or poly, lacquer or any penetrating oil. A light sanding of 320 or 400 between the first and second coat on MDF will make a solid smooth substrate in which you can apply any top coat you choose. I would avoid water based products due to MDF properties but you could try but dont say I did not tell you so. If you have carved into MDF be sure to get the shellac down into the carving. This seals the very porous inner surface of MDF. The shellac is alcohol based and when dried is compatible with any top coat you choose. Just remember that solvent based top coats could melt the shellac so test test test before applying to you work of art.
2 Likes
I tried the Walmart shelf liner for the first time yesterday and was quite happy with the results. My only complaint was all the fuzzies left on the paper from the V bit that I needed to clean up. I used downcut bits for other areas and they cut very cleanly. If only there was a downcut V bit!
5 Likes