Joining 2x Mdf boards?

[TheOriginalTableLeg]

Hi everyone,

Apologies for any incorrectly used words as I am not a carpenter.

How would somebody go about joining 2x Mdf boards edge to edge?

I have seen in other woods where dowels or biscuits have been used but wasn't sure if that applied to Mdf as it seems very different internally.

I really need the joint to be strong as the join will be filled, sanded and painted and then moved to a different location. Whilst moving I want to try and ensure that no movement occurs between the joint that will then crack the filler.

Any idea's?

Thanks in advance.

 

[Burnerman]

Dowels or biscuits will help with the location of the two sheets, but MDF has little inherent edge strength as it is.
The thicker the MDF the better, anyway.
Is there any way you can brace the sheets from the back, covering the join?
John

 

[big-all]

3 problems with 2 full sheets

weighs a ton

will need to be well supported and will delaminate in seconds with no or little movement whilst carrying

must be fully supported to avoid sagging in use

why not tell us exactly what your doing so we can offer practical solutions

 

[TheOriginalTableLeg]

Thanks for the replies.

My project is I'm building a floating wall to house my TV and wiring etc.

Because I could not make the wall out of one whole piece of board I had to use 3 pieces.

The edges of the wall protrude out from the framework approx. 2.5" at the left and right hand sides when viewed from the front.

In essence I have one whole piece full width above the Tv, one whole piece below and then a piece each side of the Tv up the outside bridging the section between the upper and lower sections.
This means I have 2x joints on either side of the TV at this point.

I realise typing this its not that easy to explain so I hope that makes sense.

The only options I could see to strengthen the joint was to either use something like a mending plate screwed onto the back of the joint, using an angle bracket wide enough to span either side of the join screwed in from the back or to try and cut a length of 2x2 at 45deg down its length and then fix this to the back either as a full length top to bottom or as 4" long sections just at the join.

 

[Flyingjockman]

You should do any filling/painting in situ, if that isn`t practical, how about making an external carrying case for transportation, you could fix a few lenghts of something like 2x1 across the join, to avoid wracking. Another piece of advice, avoid potholes/speedbumps/matchsticks on the way to the job.

 

[Flyingjockman]

How`s that for rubbish timing

 

[Deleted member 174758]

The only options I could see to strengthen the joint was to either use something like a mending plate screwed onto the back of the joint, using an angle bracket wide enough to span either side of the join screwed in from the back or to try and cut a length of 2x2 at 45deg down its length and then fix this to the back either as a full length top to bottom or as 4" long sections just at the join.

On department stores where I sometimes do this sort of job I groove the edges of the boards to take a plywood slip (6mm thick x 25 or 30mm wide) to locate the joint. The joints are pulled together using "banjo bolts" (as in kitchen worktop joints) every 400 to 500mm down the back of the joint - these will pull the joint in really tight. Without these you will struggle to get a tight near-invisible joint. Finally 18mm MDF cleats 350 to 400 mm wide are glued and screwed across almost the full length of the joints (at the back and stopping short so they can't be seen - so for a 4ft board, 3-1/2 feet long). Forget about mickey mouse repair plates or 2 x 2 softwood - too small, too weak and don't provide enough rigidity and strength in the joint

 

[TheOriginalTableLeg]

On department stores where I sometimes do this sort of job I groove the edges of the boards to take a plywood slip (6mm thick x 25 or 30mm wide) to locate the joint. The joints are pulled together using "banjo bolts" (as in kitchen worktop joints) every 400 to 500mm down the back of the joint - these will pull the joint in really tight. Without these you will struggle to get a tight near-invisible joint. Finally 18mm MDF cleats 350 to 400 mm wide are glued and screwed across almost the full length of the joints (at the back and stopping short so they can't be seen - so for a 4ft board, 3-1/2 feet long). Forget about mickey mouse repair plates or 2 x 2 softwood - too small, too weak and don't provide enough rigidity and strength in the joint

A comprehensive reply, thank you.

I can see I'm going to have to give this a bit more thought.

Many thanks again to all those who replied.

 

[foxhole]

Would help if you provided dimension, a MDF board is hardly very informative.

 

[Harbourwoodwork]

You can design your way out of this problem