Ed in Tampa wrote:Something is wrong. Are you sure you are using MDF and not particle board. MDF should not absorb much.
In fact I have routed MDF to the point of having burnished edge that was shiney.
I do paint MDF and never have I had a problem of it drinking in the paint on the edges. That is why I say something is wrong.
I used MDF for a desk for my grandson and I knew I was painting it so I routed the edge so it was burnished to the point of being shiney and painted it. The finished top looks like a one piece sheet of polished plastic.
MDF edges will absorb oil but again no more than the surface.
The MDF product by definition is dense with glue binder that holds the wood particle together this product does not absorb paint.
Particle board will suck up paint, oil, water, you name it like it is going out of style.
I have a sheet of 1" MDF on my bench top. It has been sealed but it does react to moisture. It is definitely not impervious to being wet.
Set a piece on end in a small puddle of water on the shop floor overnight to see for yourself. I had a piece sitting near the garage door, leaning against the shop wall. It rained and water came in under the garage door - that is how I know.
"Making Sawdust Safely" Dusty
Sent from my Dell XPS using Firefox.
Please do not misunderstand what I said. I never said MDF was impervious to water. Nor did I mean to imply that MDF end grain will not take paint differently than the face will.
But MDF should not be so porous to suck up paint more than a coat or two depending on how thick you apply.
Also shellac is excellent advice and is one product I often use to seal wood, particle board, MDF, and other products.
I have found that I can actually burnish the edge of a MDF using various methods and when done properly the end grain surface is nearly identical to the face grain surface.
My wife wanted a bunch of false columns to go between some mirrors. She wanted them to be fluted. I cut the flutes with a round nose router bit. Then I painted the columns white. I found that the more I burnished the surface of the flutes the better they looked when painted.
I learned to cut the flute with a sharp router bit then take one of the bargain priced bits of the same size and shape and use it to burnish the surface.
It worked the paint went on and flowed in the flute like on the surface of the MDF, so the finished product looked as if it was cut from marble or plastic. I did in some places sand the surface with 220 or highter grit on a contour sander.
Thinking about it shellac would have probably made the surface even better and while I didn't think of it at the time, i would now.
Ed in Tampa wrote:Please do not misunderstand what I said. I never said MDF was impervious to water. Nor did I mean to imply that MDF end grain will not take paint differently than the face will.
But MDF should not be so porous to suck up paint more than a coat or two depending on how thick you apply.
Also shellac is excellent advice and is one product I often use to seal wood, particle board, MDF, and other products.
I have found that I can actually burnish the edge of a MDF using various methods and when done properly the end grain surface is nearly identical to the face grain surface.
My wife wanted a bunch of false columns to go between some mirrors. She wanted them to be fluted. I cut the flutes with a round nose router bit. Then I painted the columns white. I found that the more I burnished the surface of the flutes the better they looked when painted.
I learned to cut the flute with a sharp router bit then take one of the bargain priced bits of the same size and shape and use it to burnish the surface.
It worked the paint went on and flowed in the flute like on the surface of the MDF, so the finished product looked as if it was cut from marble or plastic. I did in some places sand the surface with 220 or highter grit on a contour sander.
Thinking about it shellac would have probably made the surface even better and while I didn't think of it at the time, i would now.
MDF should not absorb after the first paint coat, unless the MDF has been exposed to moisture before painting. Strictly speaking it should be sealed with a proprietary MDF sealer, but for most purposes, a couple of coats of PVA glue mixed with water in a 1:4 ratio works as a great sealer for paint.
I don't know if it's available in the USA, but Ronseal make a product called Paint 'n' Grain. It has a primer base color coat and a main coat. It also comes with 'tools' which allow you to fake a 'grain' in the paint and it's very convincing. Works great on unsealed MDF.
