Home Depot MDF

[Phil Thien]

The latest sheet of MDF I got from Home Depot has so little binder in it that the surface sheds like crazy.

I used tape to glue some mitered boxes together and removed the tape by the next morning (I've done this a dozen times), and the tape was covered in MDF, and the surface of my MDF box is very rough.

Very frustrating as I'm going to be painting and will now need to do a coat of filler over the entire surface.

[Stwood_]

What filler are you planning on using.

[KC]

What filler are you planning on using.

The MDF at my HD is hit and miss.  I can usually tell by the shade of it... darker is denser and finishes (paint) much better.  Lighter is a crapshoot.

[Cooler]

What filler are you planning on using.

I use grain filler (meant for flooring).  It applies like shoe polish and sands easily.  I've tried almost everything else, and this is the easiest to use.  I get it at Home Depot in the floor finishing department.

After sanding you do have to seal the machined and sanded surfaces before applying any water borne finish or you will raise the "grain" which is particularly ugly with MDF.  I spot seal with SealCoat, but you can prime the entire thing with BIN primer, a shellac based primer.  The BIN can be tinted so it counts as one color coat.  Not too bad (but oh, the smell).

[Phil Thien]

I'm probably going to use Rock-Hard Water Putty, which is a plaster-based product.  Mix with water, smear it on, sand it smooth.

It works okay as long as whatever you're filling won't move (I wouldn't use it to fill voids in a joint), and provided the void isn't too large.

[rwe2156]

I would use some scrap & lay on a coat of primer first and see what you've got. I'll bet another couple coats would do the job.

If not, you can still go with the filler.

[Phil Thien]

I don't understand what you're doing.

You have to sand MDF before painting.

A couple coats of primer sanded with 320 leaves an extremely smooth surface.

I made a box with mitered corners, where you lay the pieces flat on the bench and tape the joints.  Then, you flip everything, apply glue, gold it up, apply one last piece of tape to hold it close, and wait for the glue to set.

When I went to remove the tape, it pulled a lot of the surface of the MDF off.

[rwe2156]

I made a box with mitered corners, where you lay the pieces flat on the bench and tape the joints.  Then, you flip everything, apply glue, gold it up, apply one last piece of tape to hold it close, and wait for the glue to set.

When I went to remove the tape, it pulled a lot of the surface of the MDF off.

10-4 see edited post above.

[Phil Thien]

I would use some scrap & lay on a coat of primer first and see what you've got.  I'll bet another couple coats would do the job.  

If not, you can still go with the filler.

I've already applied the filler I'm using to half the project.

The filler is pretty inexpensive compared to paint or even high solids primer.

Plus it is water based and applying and then sanding will keep the MDF from swelling from my water-based top coats.

I'm still frustrated though.

[Stwood_]

I used drywall mud one time to fill the end cuts. Sure helped with the sandin.