sapling111276 Posted March 25, 2018 Report Share Posted March 25, 2018 I have been making nick-nack type items out of mdf board. I am using spray paint to cover them. My question is, how do I get the paint to hold on the edge... grain?!? While spraying up these items, the face edge takes the paint on quite well. I have sanded down the edges with 120 and then 400, so to me, the edge looks as dense and smooth as the face edges. The paint seems to soak in and then the edge color (brown) starts to bleed back through. I have even tried primer spray as a substrate to the actual paint layer. Quote Link to comment Share on other sites More sharing options...
bleedinblue Posted March 25, 2018 Report Share Posted March 25, 2018 Seal it with something? CA glue maybe? Watered down PVA glue? Maybe spray it with lacquer first? Just spitballing ideas. 1 1 Quote Link to comment Share on other sites More sharing options...
Tpt life Posted March 25, 2018 Report Share Posted March 25, 2018 Glue sizing is the method referenced as watered down glue. That should help your research. 1 Quote Link to comment Share on other sites More sharing options...
Mark J Posted March 25, 2018 Report Share Posted March 25, 2018 Sorry, I have no particular experience with MDF, but I will comment that moving from 120 grit to 400 grit is a huge jump. Maybe that will work for MDF, but it won't do for wood. Quote Link to comment Share on other sites More sharing options...
sapling111276 Posted March 25, 2018 Author Report Share Posted March 25, 2018 Yeah, its definitely a huge jump but MDF sort of disintegrates as you sand it with most any grit paper. I used 120 to knock down the valleys created by my bandsaw and 400 to knock down any potential sand marks from the 120. The 400 is gritty enough to put a chamfered edge on the project pieces to remove sharp edges with little sanding as is. once I finished with the 400 I ran my hand over it and thought "hmm, feels just like the face edge now" Looks like the glue sizing could be the ticket. Thanks all Quote Link to comment Share on other sites More sharing options...
gee-dub Posted March 25, 2018 Report Share Posted March 25, 2018 Glue size, a mix of 4 or 5 parts water to 1 part wood glue applied with a brush for edges. The first coat will soak in quickly so go easy or the MDF will swell. 30 minutes after the first coat, do a second. 24 hours later, sand smooth with 220 or 320. 1 Quote Link to comment Share on other sites More sharing options...
Chestnut Posted March 25, 2018 Report Share Posted March 25, 2018 Primer also works well. I used MDF for trim so i had to seal and paint a lot of mdf edges. 1-2 coats of primer and then 1-2 coats of paint. I never got everything covered well in 1 coat. The above glue thing might work as well i was always hesitant to add so much water to something that swells from water. 1 Quote Link to comment Share on other sites More sharing options...
drzaius Posted March 25, 2018 Report Share Posted March 25, 2018 I've found that glue size works better than any primer I've tried. But I mix it closer to half & half with water, maybe 2 glue to 3 water. Brush it on the edge generously & then a quick wipe with paper towel a minute later, before it gets tacky. I've never had a problem with swelling using this method. 1 Quote Link to comment Share on other sites More sharing options...
sapling111276 Posted March 25, 2018 Author Report Share Posted March 25, 2018 You guys are awesome. I will try all and see where I stand. Quote Link to comment Share on other sites More sharing options...
Chestnut Posted March 25, 2018 Report Share Posted March 25, 2018 10 minutes ago, drzaius said: I've found that glue size works better than any primer I've tried. But I mix it closer to half & half with water, maybe 2 glue to 3 water. Brush it on the edge generously & then a quick wipe with paper towel a minute later, before it gets tacky. I've never had a problem with swelling using this method. I never tried it but that's mostly because i had 600 - 700 LF to get done and i wasn't about to experiment. Quote Link to comment Share on other sites More sharing options...
woodbutcher74 Posted March 25, 2018 Report Share Posted March 25, 2018 I have used drywall joint compound to seal he edges of MDF. Works great. 1 Quote Link to comment Share on other sites More sharing options...
bleedinblue Posted March 25, 2018 Report Share Posted March 25, 2018 Thanks C, I knew the watered down pva had a name, I just couldn't think of it. 1 Quote Link to comment Share on other sites More sharing options...
wdwerker Posted March 25, 2018 Report Share Posted March 25, 2018 Another use for glue size on MDF is hardening the edges of a template. I use very little water, maybe 70% glue 30% water and a disposable foam brush. Very thin coat to prevent swelling. Coat, sand repeat as needed. Keeps the edge from wearing/deforming from repeated use w pattern bit bearings. A client had me cut 20 sheets of 1/2" MDF for a rush job in his upholstery shop . I ended up with 20 - 22" x 97" x 1/2" scraps. Great stuff for jigs & mock ups. It's what I'm using for the arch templates. If your in the Atlanta area holler if you want a piece or 2. 1 Quote Link to comment Share on other sites More sharing options...
Llama Posted March 29, 2018 Report Share Posted March 29, 2018 Prime, then use wood filler on the edges. Sand everything with 180-220, prime again, then sand again... Your edge should be nice and pretty. If they aren't you didn't use enough filler. Fill again, prime, sand... Then you can paint. 2 Quote Link to comment Share on other sites More sharing options...
wdwerker Posted March 29, 2018 Report Share Posted March 29, 2018 Exactly ! Lather, rinse , repeat....... MDF finishes beautifully but it damages easily and loves to swell up if it gets wet so kitchens and bathrooms are poor places to use it. 1 Quote Link to comment Share on other sites More sharing options...
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