Announcement

Collapse
No announcement yet.

a MUST if using MDF

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • a MUST if using MDF

    I used 4 inch mdf baseboards which came primed on one side bought from Windsor Plywood. Having never used MDF before I just painted the side that came primed from the factory and put it up in the house. I put it up in summer. Now in winter, every inside mitred corner has open up (some as much as 1/4 inch on long runs).

    In my head I'm thinking MDF is supposed to be more stable than wood (so I always heard)...so...causes...

    1) I painted and primed the BB in my garage/shop and once cut brought them into the house for direct install...you MUST acclimatize it to the space. Keep it in the room to be installed for a couple of days before you cut and install it. OK, so that was my first mistake.

    2) I didn't seal the cut ends of the BB after i cut them, again, I'm thinking this stuff is stable...ha! Seal all cut edges of MDF with Titebond III...or any waterproof glue. It dries very fast...I mean 30 seconds or less because it gets soaked in the the cut end. Also, glue the inside mitres and glue and pin nail outside mitres. Coping was not an option with this BB design and it wouldn't have helped me anyway.

    3) I'd never heard of "back priming" and since the BB came primed on one side, didn't even think about it. Back prime/prime every edge. (Except the cut edges you seal with Titebond III) Yes, prime the side that faces the wall. Using a non water based primer on MDF is best (doesn't raise the grain) and I would think it'll be more moisture resistant in use.

    I routed my own casings and made corner blocks from MDF for all the doors and windows (saved big $ and they look great!)...guess what...what started as a tight block to a casing...is now maybe 1/16 gap space there. All caused by what I'm certain is moisture affecting the MDF.

    If you do what i suggest above, I hope it'll save you the troubles I now find myself in.

    Fix for this??? I'm seriously looking at redoing all the long BB runs (i'll leave the closets and caulk the joints there) and popping off and backpriming, gluing cut edges of all window and door casings. We're selling this house (already moved actually, wife's medical condition forced move), but I don't want to screw over the next buyer and want to do it right. Why not just caulk the space at the window casings and doors to the corner blocks? I popped off the clorner blocks and reset them "tight" when the spaces appeared. I'm guessing in summer, if I don't control this now, the casings will absorb moisture and POP those corner blocks.

    I made my own solid wood casings and corner blocks for the bathrooms to match the MDF ones in the house. The bathrooms ones I did prime all sides etc...due to it being in a "wet" area. Everything has stayed put so far.

    One more tip for the corner blocks, Titebond's Moulding glue works great... Don't go crazy with it, but put a couple dabs behind those corner blocks and you'll never have to nail them. All the above advice applies to MDF corner blocks as well. Acclimatize, prime all sides etc...

    Hope this helps someone out there.

    Mitch in Saskatoon...back to the house now, cause time is money on this one, I'm so pissed I could throw up. This is/was a BIG reno for me, wall taken out, Kitchen island biuld, solid wood drawer fronts, Stile and rail cabinet doors to match existing, Melamine cabinet construction, 100LBS drawer slides install, pantry drawers, install Cabinet crown moulding, move stove hood exhaust in attic, paint whole house, BB and corner blocks/casings, overhead drywall on ceiling drop, pot lights, island column for light switches, bathroom sinks, lino, etc..
  • Thread Continues Below...

  • #2

    Re: a MUST if using MDF

    Re: a MUST if using MDF

    How about a humidifier?

    Comment


    • #3

      Re: a MUST if using MDF

      Re: a MUST if using MDF

      You can also use a hot glue gun to glue pieces together or what I learned from my chiropractor is to use PL Premium construction adhesive. Used PL on my bathroom reno on all the joints and they are still perfect.
      Don't trust everything you see on Holmes on Homes;
      http://forum.canadianwoodworking.com...lems-with-them

      Comment


      • #4

        Re: a MUST if using MDF

        Re: a MUST if using MDF

        Adding a humidifier would help to tighten things up, BUT, I still say follow the steps and try avoid issues to begin with. MDF/wood will still be affected my moisture no matter what you do, but I'm convinced it will greatly help to control it/slow it. A 1/4 gap at a mitre looks like an amateur did it without thought and I had those mitres perfect. Thanks for the reply.

        Comment


        • #5

          Re: a MUST if using MDF

          Re: a MUST if using MDF

          I guess a chiropractor has to be an expert on joints . I don't have a problem with mdf (backprimed) upstairs, but I learned the hard way not to use it in a finished basement, The darned stuff sucks up every drop of moisture even with a dehumidifier running. No problem with wood. Good post, Mitch
          Jim

          Comment


          • #6

            Re: a MUST if using MDF

            Re: a MUST if using MDF

            Did you back prime your BB in the bathroom as well? I'm asking because I had "fixed" the 1/4 " corner gap in some of my baseboards, by literally hammering the opposite end until the whole thing moved along the wall, it closed the gap but I had to back the BB away from the wall to meet the matching corner. I glued the cut edges and the inside mitres once moved, but wonder if it'll still swell in summer without that back priming. Good idea about the PL adhesive. Thnx.

            Comment

            • Thread Continues Below...

            • #7

              Re: a MUST if using MDF

              Re: a MUST if using MDF

              The 1/4" gaps appeared in 3rd level of my 4 level split. It's below grade and yep, without backpriming, I think i'm screwed without redoing it all. Solid wood, is tough to beat, this MDF is killing me labour wise. Thanks for info Jim.

              Comment


              • #8

                Re: a MUST if using MDF

                Re: a MUST if using MDF

                One thing to consider is that not all MDF is the same. It is like particle board, it is available in a variety of density's. For a paint grade moulding it is hard to beat poplar. When buying MDF mouldings I would try and find a place that caters to contractors as They may have a better quality, In this area we have 3 or 4 places that only sell doors and mouldings. I would stay away from Big box stores.

                Brian
                If your dreams don't scare you, you are not dreaming big enough

                Comment


                • #9

                  Re: a MUST if using MDF

                  Re: a MUST if using MDF

                  I pre prime all 4 surfaces of all the Victorian paint grade trim I make whether in wood or MDF,exterior or interior .On wood I shellac the knots first . Yes it costs more for the product, but no call backs and the customer pays .Same with windows and doors. I found that home owners bought stuff fully intending to paint it and it was left for ages un protected, then they complained about warping etc. So now I prime and put a disclaimer on the invoice.

                  Comment


                  • #10

                    Re: a MUST if using MDF

                    Re: a MUST if using MDF

                    Originally posted by Jayked View Post
                    I guess a chiropractor has to be an expert on joints . Jim
                    lol

                    Originally posted by mitch hrycan View Post
                    Did you back prime your BB in the bathroom as well? I'm asking because I had "fixed" the 1/4 " corner gap in some of my baseboards, by literally hammering the opposite end until the whole thing moved along the wall, it closed the gap but I had to back the BB away from the wall to meet the matching corner. I glued the cut edges and the inside mitres once moved, but wonder if it'll still swell in summer without that back priming. Good idea about the PL adhesive. Thnx.
                    Did not back prime any of it. I did caulk it to the wall and tile floor though.
                    Don't trust everything you see on Holmes on Homes;
                    http://forum.canadianwoodworking.com...lems-with-them

                    Comment


                    • #11

                      Re: a MUST if using MDF

                      Re: a MUST if using MDF

                      Must have really been humid in the summer when you did it as well as the density of the MDF you got possibly being really low. Which brand caulking did you use? I've always heard that DAP Alex-Plus was the best one and is what I've always reached for in the past, but I'm just a DIY guy.
                      Kevin

                      Comment

                      • Thread Continues Below...

                      • #12

                        Re: a MUST if using MDF

                        Re: a MUST if using MDF

                        Originally posted by Lost in the Woods View Post
                        Which brand caulking did you use? I've always heard that DAP Alex-Plus was the best one and is what I've always reached for in the past, but I'm just a DIY guy.
                        Yes I used Dap Alex-Plus, but wasn't happy with how much it shrank. I can't remember the brand I used to use but it didn't shrink nearly as much.
                        Don't trust everything you see on Holmes on Homes;
                        http://forum.canadianwoodworking.com...lems-with-them

                        Comment


                        • #13

                          Re: a MUST if using MDF

                          Re: a MUST if using MDF

                          I've done a lot of MDF base and crown and never experienced outside miters opening up. My miters are cut tight and glued with carpenters glue and clamped or glued with miter bond on self returns and I fold the edges over with a nail set. If it opens up anywhere it's going to be the inside copes which are designed to move. If miters aren't tight and clamped you won't get a good glue bond and movement will show at the outside miters. You're not going to stop seasonal movement but you can control where it takes place. Copes are used to allow for movement.

                          Comment


                          • #14

                            Re: a MUST if using MDF

                            Re: a MUST if using MDF

                            Originally posted by dave_k View Post
                            I've done a lot of MDF base and crown and never experienced outside miters opening up. My miters are cut tight and glued with carpenters glue and clamped or glued with miter bond on self returns and I fold the edges over with a nail set. If it opens up anywhere it's going to be the inside copes which are designed to move. If miters aren't tight and clamped you won't get a good glue bond and movement will show at the outside miters. You're not going to stop seasonal movement but you can control where it takes place. Copes are used to allow for movement.
                            Hey Dave,

                            It's the inside miters that opened. All the outside miters are perfect (tight joints glued and pin nailed)... I couldn't cope the inside corners due to the shape of this baseboard, and honestly, I can't see any cope that would hide a baseboard backing off 1/4" from where it started. I also sprung these inside mitres into place, so they were tight as well...BUT i didn't glue those inside miters. yeh, i should have, but I'm not sure even that would have helped.

                            Thanks for the reply.

                            Mitch
                            Last edited by mitch hrycan; 03-03-2013, 10:10 PM.

                            Comment


                            • #15

                              Re: a MUST if using MDF

                              Re: a MUST if using MDF

                              Originally posted by mitch hrycan View Post
                              Hey Dave,

                              It's the inside miters that opened. All the outside miters are perfect (tight joints glued and pin nailed)... I couldn't cope the inside corners due to the shape of this baseboard, and honestly, I can't see any cope that would hide a baseboard backing off 1/4" from where it started. I also sprung these inside mitres into place, so they were tight as well...BUT i didn't glue those inside miters. yeh, i should have, but I'm not sure even that would have helped.

                              Thanks for the reply.

                              Mitch
                              If the baseboard was coped that 1/4" would have been 1/8" because you would only have seen the movement from one side instead of 2. The piece behind the cope moves but you don't see it in the joint. 1/8" is still a lot of movement, on painted MDF I get hairline cracks on a caulked joint at worst. On painted base I caulk the inside joints regardless of how tight they are. There has to be enough caulk in the joint that it allows for movement without tearing. I use Alex + siliconized painters caulk.

                              You also plan your copes for sight lines. The coped pieces face the focal point of the room so you are always looking at the cope rather than into the joint. It's easy to do. I just measure up the room and write the measurements on a little sketch with a graphical notation of whether the end is a cope, by or self return along with measured angles of any mitres.

                              You can't fight movement in building materials, it's going to happen. You have to plan and work the materials to allow for movement in all phases of construction to either minimize movement, provide a gasket or control joint to allow for movement and then plan your work so the movement isn't as obvious.
                              Last edited by dave_k; 03-04-2013, 04:03 AM.

                              Comment

                              Working...
                              X