Replies

1. 
   jako17 | Jan 05, 2004 07:00pm | #1

   Several coats of shellac

2. 
   JBD | Jan 05, 2004 11:16pm | #2

   Shellac is Ok, but epoxy is superior for waterproofing, and swell prevention. 

   For the best seal/filler for MDF edges as prep for paint, I use the new brushable/pourable polyester glaze (two part) that you can get at automotive stores.  It's easy to apply, cures quickly, fills better than ANYTHING, and sands like a dream.

    

   "The furniture designer is an architect." - Maurice DuFrenes (French Art Deco furniture designer, contemporary of Ruhlmann)

   http://www.pbase.com/dr_dichro

3. 
   Novy | Jan 05, 2004 11:17pm | #3

   Put the same laminate on the underside.

   On a hill by the harbour

    

   PS. don't worry about the edges of the hole unless your shop is a defective submarine

   
   

   ---

   Edited 1/5/2004 3:19:15 PM ET by NOVY_7

1. 
   alanplanesaw | Jan 06, 2004 12:23am | #5

   If by the harbour means you live by a large body of water (ocean?) then I understand your need to seal MDF.

   But, what I don't understand, is that if I need to seal the underside, I would think I need to worry even more about the sides of the hole in the middle.  The underneath side is a factory surface -- not perfectly sealed I know.  But, where I cut the hole has breached that surface and the cut surface would allow more humidity than the underneath side.

   I live in Pennsylvania, where we are having an unusually rainey year, but the shop is relatively dry.  Drier than the garage, but maybe a little more humidity than the house.  I don't want to have to worry about this table top at all so I will probably seal any exposed MDF surface.

   Thanks,

   Alan - planesaw

1. 
   Novy | Jan 07, 2004 10:57pm | #11

   Alan,

    John W actually explains quite nicely (post #8) the reason for laminating both sides. That being said my shop is located about 200 yards from the harbour & I never seal mdf worksurfaces or jigs. Unless someone spills their beer on them they will expand & contract evenly with humidity changes.

   On a hill by the harbour

   Edited 1/7/2004 2:59:53 PM ET by NOVY_7

1. 
   alanplanesaw | Jan 08, 2004 06:07am | #13

   Novy_7  Thanks.  Alan

4. 
   PlaneWood | Jan 05, 2004 11:20pm | #4

   I used poly.

   PlaneWood by Mike_in_Katy (maker of fine sawdust!)
   PlaneWood

1. 
   alanplanesaw | Jan 06, 2004 12:25am | #6

   Mike,

   Having lived in Las Veagas for about 10 years, I would assume its dryness is somewhat similar to Katy.  When you say poly, I also assume you mean polyurethane.  Any particular type?

   Thanks,

   Alan - planesaw

1. 
   PlaneWood | Jan 06, 2004 02:19am | #8

   Dryness?  You are kidding, right?  Down here if you want a drink you breathe a little faster!  Right now the humidity is hovering around 99%.

   Poly - the cheapest u can find.

   PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood

5. 
   JohnWW | Jan 06, 2004 02:02am | #7

   MDF expands and contracts with moisture changes, laminate doesn't.  Because of this, the laminated side of the top won't be able to move as much as the unfaced underside which will cause stress that can lead to the top warping.  The solution is to laminate both surfaces of the top if it is important that the top stay flat.  

   Whether or not the top gains and loses moisture isn't as important as keeping the stresses in balance.  As long as the stresses are in balance the top can gain and lose moisture without warping.  In any case it is impossible to perfectly seal the top to eliminate moisture gain and loss, so balanced construction is a must.

   Faced or not, MDF is very weak under a load.  To keep the top from sagging downward in the center it is important to support the top as close to the sides of the cut out as possible.

   John W.

1. 
   alanplanesaw | Jan 06, 2004 02:28am | #9

   Thanks for the explanation.  Helps when I understand why I am doing something.

   Also, yes, I have added support right around the hole for the router plate.  Although there is "adequate" thickness, I would believe that over time and use, the vibration of the router cutting wood, along with its own weight and pressure holding the wood down, that the MDF will gradually give to some degree.  I am using glue and screws to attach some oak pieces that will fully support the weight of the router&plate.

   Thanks,

   Alan - planesaw

6. 
   billl6 | Jan 06, 2004 05:15am | #10

   Alan, I use tung oil two or three coats and then wax if I want a super slick surface. Edges soak up a lot of oil, but you can seal them with a coat of diluted white glue.

   Bill
7. 
   bill_1010 | Jan 08, 2004 05:53am | #12

   type 2 woodglue thinned down 5 parts water 1 part glue.  Makes a sizing per se.  however, id just laminate the other side and seal the edges with the sizing or epoxy or just some varnish.