Clear finish on MDF?

[David Holmes]

I just built an assembly table based on the Wood Whisperer's outfeed table. Super easy and great to use. However, I wanted to make the top really smooth for outfeed purposes. I've added 1 coat of waterbased poly, and it feels like I didn't do anything. Do I need more coats, or should I be using something different. I have some oil based poly and some laquer in house. Trying to be cheap and only use what I have, but really want a smooth finish. Any suggestions?

Dave Holmes

[Jim Becker]

One coat of any finish is not going to give you smooth and slick...you'll need 2-4 coats, depending on the product and the method of application. And you'll also need to lightly sand anything containing poly between coats to insure proper adhesion. Use 320 paper for that and don't cut through the layers.

[Steve knight]

mdf is like a vacuum it will take many coats to seal it. water based product is not a good choice really.

[John Thompson]

I normally use 3 coat of oil poly on shop tops.. but I opted to try water based when I changed tops on my assembly table. Same scenario with a heavy coat and sand as Jim mentioned. Second coat and sand lightly (very lightly) and then the third coat with a buff out of synthetic equilavent of 0000.

I find MDF very tight grained as far as both types of poly (about the only time I use poly) with the exception of end grain. That will suck it up so just be patient with it if you are sealing it.

Very smooth top even though not quite as good as oil based for popping glue nibs off that were squeezed out as excess.

Good luck...

Sarge..

[David Holmes]

Thanks for the help. I knew 1 coat wouldn't do it, but I wanted to ask after 1 coat in case, I was really screwing up then I'd only have 1 coat to deal with. I have some oil poly in the shop too. Is it too late to switch to that after 1 coat of water based?

Thanks again

David Holmes