Hydraulic or not?

[MDE]

I have finally got round to repairing the hayloft in my (300-year old?) rubble stone barn. I have managed to source and cut some green oak joists. These go into the walls at each side of the barn and rest on a substantial beam in the centre. One end of the beam goes into an outside wall and the other end rests on an internal wall that needs repairing. I was planning on resting the ends of the joists that go into the walls on some lime mortar pads.
Questions: Should I use hydraulic lime (pozzolan added to my home-made lime mortar) for repairing the internal wall? What about for the mortar pads (these will be 4 to 8 inches into the wall)? Also, should I mortar round the sides and top of the joists (as seems to have been done previously) or should I simply wedge them in place? The wall on the "weather" side does suffer from a bit of damp (I suspect condensation as much as penetration).
BTW, I'm going to wait for it to warm up a bit, first!

 

[chuckey]

I would mortar the joist all round unless you want a hole so vermin and draughts can get in. It will also help to stop the stones at the sides and top of the hole moving about. I reckon that the most importent thing is that the bottom of the new joists sit on the middle of a stone and not across a joint, so the flooring loads are spread fairly across the wall and are not just on the edge of one stone, so as to tend to rotate it.
Viz-a-viz setting the new joist up, if you level them up with wedges inside plastic bags, under the ends, then wack the mortar in around the ends, when its gone off, pull out the wedges and make good the holes. Or balance the joists on acro props :roll:
Frank

 

[caliwag]

I know what I like

http://myweb.tiscali.co.uk/diesels/ :roll:

 

[middi]

A word of advise ( gained from experience).

A beam end ( or sole plate) lasts a lot longer if it is just "sitting" on a dwarf wall and not encased into the masonary. If there is no other option but to encase it in masonary and the masonary is not of a very porous contruction the beam(s) will will also suffer in the long run.

Adding pozzolan to the rich lime mix will make the rich lime mix less porous thefore less suitable.

The objective is to emove the surface moisture from the oak beams face (s)as fast as possible

 

[MDE]

Thanks, middi. Since it is a barn, appearance is not paramount. Following your advice, I'm thinking about just using slate or oak wedges to adjust the heights and not bothering to mortar except for any very large holes. The joists fit pretty well anyway as I cut the ends of them to go into the holes from the old joists. In any case, the tenons at the beam end plus the floorboards should prevent twisting.
As regards rebuilding the end wall (parallel to the joists), my understanding is that I need to use hydraulic lime otherwise the mortar inside the wall (which is 18" thick) may not harden. Is this true, or is it only a matter of time? I only need to rebuild the top couple of feet or so.

 

[Jon Maine]

Thanks, middi. Since it is a barn, appearance is not paramount. Following your advice, I'm thinking about just using slate or oak wedges to adjust the heights and not bothering to mortar except for any very large holes. The joists fit pretty well anyway as I cut the ends of them to go into the holes from the old joists. In any case, the tenons at the beam end plus the floorboards should prevent twisting.
As regards rebuilding the end wall (parallel to the joists), my understanding is that I need to use hydraulic lime otherwise the mortar inside the wall (which is 18" thick) may not harden. Is this true, or is it only a matter of time? I only need to rebuild the top couple of feet or so.

It will harden over time, of course there were more impurities in the mortars made on site centuries ago that they probably were pozolanic anyway. Depending on how fast you wish to work it may pay to use hydraulic if not putty lime will do just fine.

 

[middi]

Another point to take into consideration is that whilst it is perfectly ok ( also preferable and cheaper)to use "green" oak, the annoying disadvantage is that it tends to shrink over a period of 2 to 4 years or longer which can leave a gap large enough ( depending on beam size) to slide your fingers in the gap between joists and mortar. Nothing much you can do about that but to keep reponting with lime mortar if you have to.