I’m building my first custom stick (thanks to a lot of info from this forum!) and I’ve run into a problem with the paint. The primer specifically. I went with a roller to put the primer on which I’m thinking was the cause of the problem. I have little spots that are left even after sanding with 400 grit paper and was wondering a couple things.
Would switching to a spray primer fix it?
Is it even an issue? Will the color coats fill in the little dimples?
The box is all MDF and the primer used is Kilz oil based original.
Sand it right down. Usually mdf is sold pre-sealed. but if not then use wood putty to seal it. You will need to seal the edges where you cut the wood even if the mdf is sealed. And then just apply thin coats of paint. On the first coat you should still be able to see the mdf through the primer. Make sure it’s touch-dry before applying a second thin coat. On the third coat start sanding it down. 4 or 5 coats like that should do the job.
^Correct. Mdf is very porous and needs to be sealed before painting. Some use fiberglass resin to seal and add strength (especially useful for weak mdf edges). Me personally, I would have used bondo/glaze for sealing and filling the pores in the mdf. If you glazed the entire thing with bondo and then block sanded it, you would need a much smaller amount of priming and sanding to get it flat. Also, leave the Kilz for priming/painting your garage.
not exactly sure what the problem is, are you saying when your sanding your hitting wood?
if thats the problem thats sort of normal. you normally tend to hit corners alittle harder just because were human. generally i would prime heavy first time around then sand flat, use a guide coat one larger pieces but since this is just flat panels just sand flat. then light coat of primer. i dont sand this time around just scotch brite and tack cloth and go right into the base. after you get your base to what you want depending on how you want the base finished i normally just lighting scotch brite again tack cloth and clear. after that color sand buff polish and your done
The others pretty much covered it with sealing but just to let you know for future reference that if you’re going for a glossy finish then any small imperfection needs to be fixed before paint is applied. Anything that you can see or feel in primer stages will show once the surface is glossy (it will probably even show without a clearcoat applied), paint will not fill any imperfections and gloss will just amplify them.
And Shimmerman said to let it dry to the touch between coats but make you sure you don’t leave them to dry too long. It’s called flash time and it’s the time between coats which is usually 5-10 minutes (depending on the thickness). This is the time in which you can apply another coat without having to sand the old coat so the new coat adheres. You can leave them more than 5-10 minutes but don’t leave them like an hour otherwise you’ll have to wait for it to completely dry (a few hours) and then sand it again before applying the next coat. Dry to the touch doesn’t mean touch it btw, it will still be a little tacky and may get contaminated or get ridges from your finger. Just look at it and make sure there are no glossy parts on the surface (ie: no parts that look wet).
Finally, I guess you don’t need to worry about how thick you apply the coats since you’re on a roller. If you do get to spray it then thinner is usually better for sealing and is called applying it semi-wet. It’s just a mist and you can see the previous color through. Thicker is better for filling and is called applying it wet.