mortise and tenon joints on oak framed barn

[bobp8623]

Hello all

Grateful for some advice please. We have an oak framed barn at the house which is in reasonably good condition. Some very large oak beams provide the basis of the framework. Over time some of the smaller beams have been replaced with softwood whilst others have deteriorated and not been replaced.

My question - is there a technique for replacing the in situ mortise and tenon joints including those which have deteriorated. The larger beams which the mortices are cut into cannot be moved as they in turn are fixed into other very large beams

Many thanks for any help that you are able to offer

Bob

 

[Sgian Dubh]

Slip, slot or loose tenons are the answer. Essentially you create two mortices, one in each member. The mortice in the new beam will have to extend all the way through to one edge or the other. Then you make an L shaped slip of wood that 'slips' into the mortice in the existing fixed beam or stud, or other frame member. The grain direction of the slip runs the vertical length of the L as viewed on the monitor here, or written on a piece of paper. The other end of the slip, the bottom end of the L, sticks out and you slide the new or replacement member on to this. You may need to include cross dowels to lock the lot together, particularly if you have to slide the new member up into place rather than down or sideways. Finally, trim the bit of the slip that sticks out of the edge of the new member and tidy it all up. Slainte.

 

[pip1954]

so are you saying a double tong one into exsisting mortice and one in end of beam?
pip

 

[Sgian Dubh]

Essentially that. A double length tenon that fits into two mortices, one worked in one piece and the other worked in the second member. If the replacement part is, for example a middle rail in a frame that can't be taken apart you have to slide the new rail down between the frame stiles over the slip tenons sticking out of the mortices in the stiles. This is why the slip tenon may need to be L shaped so that the excess wood can later be trimmed off flush with the edge of the replacement rail. Slainte.

 

[zb1]

Before you do anything you should make sure that the barn is not listed. If it is then you will need the approval of your local conservation officer. They may not be happy with the softwood being replaced as this could be considered to be detrimental to the historical value of the building. I know it sounds strange but this is the way it is. Buildings are no longer restored they are conserved using "honest" repairs. It always looks odd scarfing a great chunk of square green 200x200 oak onto the bottom of a rotten post that was once probably 8"x8" and square but hasn't been that way for a century or two.

 

[Sgian Dubh]

As a postscript I intended to include these two sketches in my previous post, but after I'd created, scanned and resized them I couldn't upload anything to Photobucket for some unknown reason. I think there was a glitch at Photobucket's end, but I could be wrong. However, it all seems to be working again, so, a bit late, here are the additional explanatory sketches for pip1954 and bobp8623. Slainte.