Joist hangers with lime mortar and old bricks

[nishnish]

Hi,
Got rotten joists to replace in an 1890 cellar. Looks like the ends have fallen foul of the usual wet rot (they are embedded in the external walls, with only half a brick protection from the elements). I can see that almost all the others have already been replaced for likely this same reason (probably been done many times?).
The ones in there are 60x180mm, so these days it looks like 47x175 is the closest.
Reading on here I see recommendations to use joist hangers to avoid the damp joist end issue.
Though all hangers seem to specify a certain strength of masonry. Like these do:

http://www.toolstation.com/shop/p42476

Will the old masonry be able to cope with these?
One issue I see is that the current holes will need to be bricked up and then a wait of weeks for the lime mortar to harden. Even after weeks, I'm not sure it will be very strong, judging by the other lime mortar (no cement) I've used around the house.
What about something like these, bolted into the surrounding bricks?

http://www.toolstation.com/shop/p96448

Thanks.

 

[hotrod]

I would forget the hangers and build the new joists into the masonry. Wrap the joist ends in DPC.

Ensure the new joists are pressure treated. Treat any cut ends on site with a trade preservative.

 

[nishnish]

Thought so. Thanks for the reply.
Getting a treated 7x2 to replace. Got a tin of the stuff to treat the sawn ends too.
You've ruled out the hangers, because of the limited strength of the bricks and mortar?

 

[hotrod]

I prefer joists to be built in. If the masonry is suspect you can often struggle getting a fixing for the hanger.

Plus, if you build it in and need to meet existing levels you can always pack the underside of the new joist up, off the existing masonry, with slate/tile to ensure it is at the correct level/height.

hth

 

[nishnish]

I prefer joists to be built in. If the masonry is suspect you can often struggle getting a fixing for the hanger.

The masonry certainly is suspect. It's a bit of a hotch potch. Especially on the inner leaf below ground. The cellars themselves are better, but under one room is a crawl space and it looks like they built the inner leaf from a bag o' brick bits in the dark.

Plus, if you build it in and need to meet existing levels you can always pack the underside of the new joist up, off the existing masonry, with slate/tile to ensure it is at the correct level/height.

Yeah, the hangers seem like a sleek efficient answer, especially on the perfect masonry they show in the examples. Suppose it'd be possible if all the joists were replaced and the hangers could sit elsewhere, in the better masonry, rather than bits that have been mashed about over a 100yrs with different joist replacements.
I thought you could just pack the bottom of the joist in a hanger? Or am I way off?
Some of the joists in that room have been packed up with bits of timber. Which even have their own little DPM wrapping

 

[hotrod]

Yeah, the hangers seem like a sleek efficient answer, especially on the perfect masonry they show in the examples. Suppose it'd be possible if all the joists were replaced and the hangers could sit elsewhere, in the better masonry, rather than bits that have been mashed about over a 100yrs with different joist replacements.
I thought you could just pack the bottom of the joist in a hanger? Or am I way off?
Some of the joists in that room have been packed up with bits of timber. Which even have their own little DPM wrapping

Yes, if your masonry was new and level you could use built-in hangers and it would make the job a lot easier. I wouldn't advise packing the bottom of the joist hanger 'shoe' with timber to get the correct level - the hangers are designed for you to "notch down".

I like that they went to the trouble of wrapping the timber packers in DPM .

 

[leew2]

I've seen ready made plastic caps at builders merchants designed to go over the ends of joists to prevent rot.

If using a smaller joist size, make sure it is still strong enough for the expected loads (may need an SE here). If your joists are a non standard size then most timber merchants will be able to take the next size up and cut it down to whatever size you need, in this case a 75x200.

 

[nishnish]

I've seen ready made plastic caps at builders merchants designed to go over the ends of joists to prevent rot.

You mean something like these?

http://www.easyjoist.co.uk/product.php

How much are they compared to DPM?
Isn't the usual method to nail two strips of DPM to the joist ends? I do always wonder about the joist corners where the dpm gives worst coverage and must inevitably let a bit of moisture through? Or is there some standard better way to wrap?

If using a smaller joist size, make sure it is still strong enough for the expected loads (may need an SE here). If your joists are a non standard size then most timber merchants will be able to take the next size up and cut it down to whatever size you need, in this case a 75x200.

These are old replacement joists. They are slightly wider than those used on the 1st floor, where the joists are various widths so I suspect are original (these are a uniform 60x180mm). I expect whomever replaced just used what was similar, without regard to loading etc.
I doubt they are anywhere near the strength of modern C16 graded joists.
From looking at C16 span tables, 47x175mm can span much more than the 2.6m of the square bay window that it'll be used across. The joist centres average about 38cm. As it's a bay, with radiator, it's also less likely to be as loaded as joists elsewhere in the room, due to an absence of furniture.
Please advise if you think my logic is flawed?
Thanks.

 

[^woody^]

I'd bolt a bearer timber to the wall with polythene between, and then hang the joists off this

No damp problems then, and no air leakage either

 

[nishnish]

Thanks for reply.
Some images may help.
Looking from cellar the 2nd joist from left (painted blue) has rotten ends:

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Close-up:

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Close-up from other side. Rotten end resting on board carrying electrical distribution unit:

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• nishnish
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Better views of space available for bearer:

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I've since propped the joist with some 4x2 to raise it off the board.
Is there enough space there to fit wooden bearer?
It will have to be made of 7x2 also? I suppose I could cut part of it away to avoid the cables?
You mean then using a joist hanger off the bearer?
Thanks.

 

[nishnish]

So there's not enough space for a bearer woody?

 

[^woody^]

Well TBH, its only a small vertical load from a joist, and not going anywhere so by just putting in a hanger on a couple of sound bricks it will be OK irrespective of the general condition of the wall - after all the wall is holding the house up!

 

[nishnish]

Thanks woody.
Which type of hanger?
Would the multi truss type;

http://www.toolstation.com/shop/p96448

bolted onto the wall, be a stronger fixing than the normal hanger which gets mortared in?
Or are multi truss hangers for something entirely different?
I suppose I could prop those floorboards up for a few weeks whilst the lime mortar gains some strength.
Cheers.

 

[^woody^]

That hanger is really for timber.

Might be a bit awkward trying to drill all those holes close together and the bricks may not like it.

I'd stick with a proper masonry hanger like item 26815 or similar

 

[nishnish]

Ok. Cheers woody.