[UtopiaNemo]

Hey all, I’ve read a various on various posts here about how using water-based finish products on routed/sanded/untreated sections of MDF can cause absorption and swelling. Does that apply to straight duratex? if so, should I primer these portions first, and if so, does it need to be a non-water based primer?

[Hobbsmeerkat]

Yes, Duratex is a water-based product, so MDF will absorb some of that water as well.
If you want to seal the MDF it's be best to coat the outside in shallac or a non-water based primer to seal it before coating it with Duratex.

[UtopiaNemo]

Another issue I’m having is that the wood putty isn’t adhering well to the MDF, and once it dries, it cracks at the joints. I’m using Elmer’s wood putty; is this a lesser quality product? Is there another brand or another product I can use that will close those joints and not crack?

[WGH]

Bondo auto body putty

[mlundy57]

I use Timbermate wood putty.

[jtwrace]

If you read the directions, wood putty is NOT what you want to use. Spackle or Bondo (auto body filler) is. 

[WC]

I used spackle and bondo. Bondo is more durable, but a little harder to sand down and spread than the spackle.

[UtopiaNemo]

I used spackle and bondo. Bondo is more durable, but a little harder to sand down and spread than the spackle.

If you read the directions, wood putty is NOT what you want to use. Spackle or Bondo (auto body filler) is. 

Spackle? As in drywall repair?

[UtopiaNemo]

I actually started with wood putty, but switched to drywall patching compound because I hated the wood putty. I was hesitant to mention it because I figured it’d draw some scorn. The patching compound is also cracking, but it’s not technically spackle.

[mlundy57]

When it comes to sealing MDF, I usually use West Systems epoxy.

[richidoo]

I just use a thin smear of titebond1 to seal MDF edges. It dries fast and there's not enough moisture to cause swell. After smearing it on wipe it dry and smooth with a paper towel. Doesn't have to be a filler, nor a non-waterbased sealant. 

[glynnw]

Does Duratex become a hard coating, very impervious to scratches, etc?

[Hobbsmeerkat]

Yes, it becomes fairly hard after an hour, and fully cures within a week. Its also very resistant to scratches and scuffs and wipes clean easily

[UtopiaNemo]

Does Duratex become a hard coating, very impervious to scratches, etc?

It does, but it also adheres to itself very well. There have been numerous accounts of people stacking speakers or gig boxes that have been finished with Duratex, to find that they’ve become stuck together. This is well after it should have cured.

My plan is to go over the duratex with a matte finish like Minwax polycrylic when I’m done, just as an added precaution.

[glynnw]

Good advice, thanks.

[Peter J]

It does, but it also adheres to itself very well. There have been numerous accounts of people stacking speakers or gig boxes that have been finished with Duratex, to find that they’ve become stuck together. This is well after it should have cured.

My plan is to go over the duratex with a matte finish like Minwax polycrylic when I’m done, just as an added precaution.

I would encourage you to let the Duratex thoroughly cure (not just dry) before top coating. The acrylic coating theoretically should be fine, but because bonding of most acrylics is primarily a mechanical function, you wouldn't want the Duratex to be curing after topcoating. I might even run your finishing schedule by the the manufacturer, whom I've spoken with and could shed light on any limitations.

I've attached a photo of something similar I did, but in all honesty I think I probably topcoated with something other than water base. It took some years to show up and the cabinets were in storage so I don't really have a timeline or even exact finishing schedule. I just don't remember, because it didn't concern me when I did it. Again, I think a conversation with the mfg. would be prudent.

[UtopiaNemo]

I would encourage you to let the Duratex thoroughly cure (not just dry) before top coating. The acrylic coating theoretically should be fine, but because bonding of most acrylics is primarily a mechanical function, you wouldn't want the Duratex to be curing after topcoating. I might even run your finishing schedule by the the manufacturer, whom I've spoken with and could shed light on any limitations.

I've attached a photo of something similar I did, but in all honesty I think I probably topcoated with something other than water base. It took some years to show up and the cabinets were in storage so I don't really have a timeline or even exact finishing schedule. I just don't remember, because it didn't concern me when I did it. Again, I think a conversation with the mfg. would be prudent.

Thanks, I'll do that!

[WC]

Seems to take quite a while for duratex to fully cure. It has been a month and a half and I am just comfortable putting the speaker on a surface without worrying that it was going to stick to it.

[Danny Richie]

Hmmm, typically I let Duratex cure for a day and then spray it with paint. I have never had drying issues.

And a second coat of Duratex can be applied within an hour or so. 

[Peter J]

Seems to take quite a while for duratex to fully cure. It has been a month and a half and I am just comfortable putting the speaker on a surface without worrying that it was going to stick to it.

I know exactly what you're talking about. In the paint world that's called blocking. Common with latex paints, maybe not so much with acrylics, but I honestly don't know. Google "latex paint blocking" for more than you probably want to read. I assume Duratex is similar.

Unfortunately that just makes me like water based stuff less, but I'm jaded.