Replies

1. 
   datachanel | Sep 12, 2004 07:08pm | #1

   With my experience, most light weight spackle does shrink. That's the only thing that immediately comes to mind. Good luck.

   Datachanel

   Doing things the hard way

2. 
   bill_1010 | Sep 12, 2004 07:43pm | #2

   Bondo, or polyester autobody resin is a great patch, seam or gouge filler for MDF.   Full blown regular drywall compound also works, but beware of the water swelling the MDF.

   Small amounts of bondo with the cream hardener are available at auto parts stores or even wal-mart.  Bondo does shrink somewhat, but once dried it wont shrink and can be sanding smooth to the MDF.

   Get a small cup and mix some resin and squirt a bit of the hardener, and mix it to a consistant color, sometimes pink, sometimes grey. More hardener faster set time, less hardener slower set. Read the instructions. Apply to the area let dry and then sand it to your desired final application.   Prime and paint away.  

   Also you should glue all splices, 2p10 is what i use when i glue MDF joints, scarfed or Mitered.   Its basically a superglue thats been Ph treated to handle wood.   Its a 2 part glue, comes in thin, med, thick and gel consistency and the second part is an activator spray.   Its talked about and its given great reviews over at breaktime and over at Gary Katz's JLC forum, which is where i heard about this great stuff.  Its totally decreased up my trim carpenty time on the job and its well worth the cost.  Make sure you align the material up like you want it, because once its set, (10-20 seconds) its permanent.  Youll break the wood before you break the glue bond. 

   
   

   ---

   Edited 9/12/2004 12:48 pm ET by WmP

1. 
   Dave45 | Sep 13, 2004 01:17am | #5

   I've used Bondo on metal but would never have thought of it for MDF...........I'll stop by the local auto parts store tomorrow.

   What's this 2p10 glue?  I've never heard of it, but would like to try it on future trim work.  This crown problem is in my house so it isn't a big deal.  I would sure want to avoid a call back from a paying customer, however. - lol

   Thanks

1. 
   bill_1010 | Sep 14, 2004 06:24am | #10

   http://garymkatz.com/TrimTechniques/FastActGlue.htm

   2p10 is reviewed at the link above.  I buy mine from http://www.hghhardware.com/

   Its awesomestuff, its only drawback is the sprayed activator is acetone based, so on prefinished laq finishes it has to be carefully applied.

3. 
   sawdustmaker | Sep 12, 2004 11:59pm | #3

   As WmP mentioned, bondo works great. I repair furniture for a major retail sales company in Michigan, and we use bondo on a regular basis for a durable, fast drying repair.

1. 
   DustinT | Sep 13, 2004 01:02am | #4

   Most lightweight fillers that I have used say that they are not to be used on any joint with the potential for "movement."  So I guess that pretty much limits its use to nail holes and maybe gouges.  I'd be curious to hear which route you go to fix it, and let me know what works for you. 

   Dustin

1. 
   sawdustmaker | Sep 13, 2004 09:14pm | #9

   The bondo wouldn't work where there is a whole lot of movement. I use it to fill deep dents and gouges, sand it before it sets up, and add color and grain with blendal mixed with alcohol or graining liquid.

   Mohawk makes a two part epoxy filler that comes in a variety of colors. It looks like a tootsie roll with a cylinder shaped activator core in the middle. Cut a piece off, knead it to break the membrane separating the two parts. They claim it has similar properties to wood as far as density and movement, but I have never used it in a situation where there is a lot of movement. It does sand just like wood, and does not get rock hard like bondo would.

   One other option is to try a "planar stick" that you heat with an electric or butane knife. Not the old hard brittle sticks or the soft "crayon" sticks, but somewhere in between. You can dent them with your thumbnail in the stick form, so they would have a little "give". Mohawk carries these as well, but you might get them at a local Woodcraft or Rockler store if there is one close by.

   Mike

4. 
   Piffin | Sep 13, 2004 05:14am | #6

   The bondo type filler will help, but the MDF is one of the many man-made products that will grow and shrink lineally from heat as well as humidity.

   if you pin it realy tight at the ends, you can force the expansion into wrinkling along its length, where it might not be as noticeable.

   I never notice thermal expansion in casing length materials but in 16' long base or crown, it can show up.

    

    

   Welcome to the
   Taunton University of Knowledge FHB Campus at Breaktime.
    where ...
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5. 
   Clay | Sep 13, 2004 07:02am | #7

   Spackle doesn't work well at all for patching wood.  Even for nail holes it will often shrink back or the wood shrinks leaving the spackle standing proud.  Epoxies and Bondo work well but I like to use molding paste (by Golden Acrylics).  The molding paste does shrink but is so quick to apply that several coats may be done quicker than mixing up some other products.  It has the right blend of flex and strength to acheive great durability.  It can be carved or sanded but it is hard enough that I like to do extra coats rather than overfilling much.

6. 
   CRAIGCONEY_M | Sep 13, 2004 08:33am | #8

   You didn't mention if you glued the joint when you installed it.  Also, I am not sure of where you live, but here in So Cal, it is not advised to install MDF molding during certain weather conditions.   

   When  I do a seam like this, I glue the joint and shoot a couple of 23ga pins in the joint for added measure.    I haven't had any problems with my seams opening up.