# MDF Joints - Hiding the seam



## mako1 (Jan 7, 2014)

How are you joining them together to start with?I would build it like a countertop substrate.Rip some narrow pieces and screw and glue them to the perimeter of the bottom.Of course this will give you a 1.5" top which may not be what you want.
Need a little more information to give an informed answer.


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## HTFreak (Mar 24, 2014)

There will be wood (either plywood or 2 x 4s) below the MDF. The MDF will be screwed into the foundation structure below (plywood or 2 x 4s). Therefore the MDF pieces will sit on the plywood/2 x 4s. 

The areas in red below are where the MDF will go (the area to the right against the side wall is a concrete bench that has 1/2 plywood on top). The MDF will attach and sit on the plywood. The MDF will also sit and attach to the framing structure near the screen.


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## ddawg16 (Aug 15, 2011)

If the MDF is going to be the 'bench', as in a sitting or working surface, then expect it to last a very short time. 

Even painted, it's pretty soft and will be easily damaged. 

My personal opinion is you will regret your decision very quickly.


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## HTFreak (Mar 24, 2014)

ddawg16 said:


> If the MDF is going to be the 'bench', as in a sitting or working surface, then expect it to last a very short time.
> 
> Even painted, it's pretty soft and will be easily damaged.
> 
> My personal opinion is you will regret your decision very quickly.


Thanks. I don't plan on putting seat cushions on it and I should reframe the
purpose of it from bench to something else. I don't plan on using it to allow people to sit on. I guess I plan on integrating the side area into an extension of the stage at the front of the room near the screen.

If I did want to change my mind and turn it into a seating "bench", what material should I use?

I'd like to stay on topic though about my issue with how to hide the seam between MDF pieces.


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## mako1 (Jan 7, 2014)

I asked for more info and got it!Wish everyone could do that.I'm an old cabinetmaker and mdf is not my favorite but have worked with tons of it on commercial jobs.It does work easy but makes all kinds of dust and is heavy and stinky.Looks like a very nice setup and don't know why you would want to paint a countertop in place of using some laminate but I'll try and answer your question.As I stated in me original post I would make it a double layer with 3" strips on all the joints screwed and glued to the top piece .tis does make it 1.5" thick but reinforces the joints and gives you the thickness of a regular countertop.You could skip the plywood and attach directly to the cabinets.
On to the question about using a single layer of 3/4" mdf with invisible seams.When you cut the joints clean and butt them there is not room really for any filler and unless the substrate is perfectly flat and level you will see a joint after painting sooner or later.I would use some biscuits on the joints for alignment when gluing them together.You need someway to pull the joints together while the glue sets the way you are going about it.You could hot glue some blocks to the top for some clamps but you'll have to watch the clamp pressure so you get the joint pulled together with out pulling the blocks loose.After the glue in the joints set the blocks can be taken off with a sharp chisel.The way you are proposing to do this project it will have to be done in place.Now you have all of the mdf joined and there is no real room for any filler in the joints but they will still show thru your paint.
Take a router with a V groove bit and run down the center of each joint 1/4 or so deep and fill with epoxy then sand flush.This groove will give the epoxy a surface to bond to.
A bit "out of the box thinking" but after many years of experience and your paramiters I believe this would work.
I would still go with making a traditional laminate top.Probably cost effective and a better result in the end and whole lot less trouble.


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## HTFreak (Mar 24, 2014)

mako1 said:


> I asked for more info and got it!Wish everyone could do that.I'm an old cabinetmaker and mdf is not my favorite but have worked with tons of it on commercial jobs.It does work easy but makes all kinds of dust and is heavy and stinky.Looks like a very nice setup and don't know why you would want to paint a countertop in place of using some laminate but I'll try and answer your question.As I stated in me original post I would make it a double layer with 3" strips on all the joints screwed and glued to the top piece .tis does make it 1.5" thick but reinforces the joints and gives you the thickness of a regular countertop.You could skip the plywood and attach directly to the cabinets.
> On to the question about using a single layer of 3/4" mdf with invisible seams.When you cut the joints clean and butt them there is not room really for any filler and unless the substrate is perfectly flat and level you will see a joint after painting sooner or later.I would use some biscuits on the joints for alignment when gluing them together.You need someway to pull the joints together while the glue sets the way you are going about it.You could hot glue some blocks to the top for some clamps but you'll have to watch the clamp pressure so you get the joint pulled together with out pulling the blocks loose.After the glue in the joints set the blocks can be taken off with a sharp chisel.The way you are proposing to do this project it will have to be done in place.Now you have all of the mdf joined and there is no real room for any filler in the joints but they will still show thru your paint.
> Take a router with a V groove bit and run down the center of each joint 1/4 or so deep and fill with epoxy then sand flush.This groove will give the epoxy a surface to bond to.
> A bit "out of the box thinking" but after many years of experience and your paramiters I believe this would work.
> I would still go with making a traditional laminate top.Probably cost effective and a better result in the end and whole lot less trouble.


Thanks. Is laminate some kind of veneer?


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## mako1 (Jan 7, 2014)

You could call it "some kind of veneer". http://www.wilsonart.com/laminate/design-library Laminate like they use on countertops.Paint is not going to hold up long on what you want and the way you are proposing to build it will have to be built in place and will be a real PITA with mediocre to poor results.


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## Millertyme (Apr 20, 2010)

You need to make sure the seems stays tight. Do so by either half lapping joint, or scab the under side with a scrap piece of plywood and glueing and screwing it from underneath. If joint isn't tight fill any gap with bondo and sand flat and prime.


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## woodworkbykirk (Sep 25, 2011)

what miller describes is the method i typically use. bondo dries much harder and wont crack like wood filler will do sometimes.. if the joint is still very nice and tight i will put some wood glue on it and sand it to fill the small voids.

on the face of the bench making a frame that allows for joints can hide it and dress it up at the same time.


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