I have not come across any mention of sealing MDF on this forum, especially on the inside of the cab. On some other forums people are adamant about sealing all exposed MDF surfaces to prevent moisture from being absorbed, swelling the MDF. I have read of painting all surfaces with a mixture of 80% yellow glue and 20% water, before gluing the cabinet.(seems paranoid) I found a few posts on DIYaudio concerning the use of Zinsser BIN spray primer to seal the inside. I just built a set of Tempests and sprayed them inside with Zinsser after the cabinets were fully assembled. All that was left to do was painting the outside with many coats of Duratex, spray gluing some egg crate foam in the bottom and stuffing the waveguide area with Dacron. My XO's are mounted up there also. Then of course mounting and wiring the speakers to the XO, Speakon and inserting ports My big question, am I the only one trying to seal the MDF? Is it a non-issue? I am out of town until Monday, 28th of July but look forward to any opinions. Foggy
If there's no danger of them getting wet, or being in high humidity for long periods, I wouldn't worry about it. If that is a possibility, then sealing would be a very good idea. MDF and water don't get along well.
I personally use Zissner Gardz to seal anything that is MDF. It's amazing stuff that has saved me tons of time and money. http://www.rustoleum.com/product-catalog/consumer-brands/zinsser/primer-sealers/gardz-problem-surface-sealer It's not very cheap these days at about $40 per gallon, but it goes a really long ways. I've always put a couple coats on my edges and exposed surfaces (interior also) and it actually paints beautifully. I started using this on all my mdf trim & crown molding as well as a final coat on pre-primed wood after an initial sanding. The top coat always benefits from a couple of initial coats of this. I use a large foam roller on all my large flat pieces of mdf or hdf and then use a cheap chip brush for the edges after the adhesive is applied. Even after final assembly I'll put some in an HVLP gun and lay out a few coats to seal it up nice. Since I'm in Louisiana and our humidity averages 88% annually I got tired of replacing pieces. A single gallon will usually last me through a full building season (winter). The drying is also super fast and you can easily lay down 3 coats within 90 minutes. This stuff was originally intended to apply over wallpaper damaged sheetrock. It literally turns the torn or exposed paper hard as rock and binds it to whatever you put on top. Most people make the mistake of skim coating directly over the exposed paper with mud and it ends up causing bubbles in the paint. Not with this stuff! I think now you can find it at Ace Hardware stores in the quart size...