I am lifting the roof on an old pig farrowing barn to accommodate a furniture restorer.
The roof is heavy but can be moved in one piece. So far I have raised one side on Acrows and intend to lay two courses of brick to gain the height needed.
What is a reasonable time to wait before heavily loading fresh brickwork? I am particularly nervous of any side thrust encountered as I start to jack up the other side.
regards
I would leave it 48Hrs ... 24 Hrs is no problem if a simple daed load, but as you point out there is side thrust, and bricks not particularly strong in that direction.
use a good 3:1 mix and suitable bricks, deep frog frettons as a minimum, laid frog up, and fully filled ... or engineering if you have them.
That seems very, very short.
Watching my brickies recently take off a couple of courses where they'd made a mistake on a chimney stack, 2 days after they'd gone on
- they had not the slightest difficulty in such green mortar - still very easy to clean off.
ISTR - a long, long time ago when I worked for Costain - the cure time for mass concrete (in the Summer) was 4 weeks after the shutters came off. Certainly when I'm using concrete, I'm surprised how easy it is to chip for the first week or two - compared to how hard it gets eventually.
In the current cold weather I'd plan on doing some other job - before putting, as you say, a significant sheer load on your new courses.
You might find useful manufacturers data here - certainly their advice on concrete I found useful:
OK. The brickwork will be Flettons for the first course and semi-engineering for the top. Basically because that is what I have lying about the farm:-) I can easily wait 3 days as I also have to fit a wider door and re-plumb the electrical conduit.
regards
In message , " snipped-for-privacy@gglz.com" writes
They give 2 days = 16-26 N/mm2
7 days= 27-37 N/mm2 28 days= 37-47 N/mm2for compressive strength on CEM 1 product.
I should be able to wait 5 days and get roughly half final strength.
regards
encountered as I
particularly
Tim,
Very temperature dependant: I've just laid 8 cu m of RC40 concrete and it took two days in the current cold snap to 'not' take a finger impression. Earlier in the year I laid a batch of the very same stuff on a blazing hot day and we couldn't finish tamping before it set solid (perhaps 1.5 hours from delivery)
Cement re-hydradtion (ie setting) is a chemical reaction and thus very dependent on the temp. When it starts to go off though it is exothermic - ie gives off heat.
AWEM
In message , Andrew Mawson writes
Hmm.. only a few degrees above freezing for the next few days:-(
I suppose I could make a temporary timber frame to support side 1 while I move the acrows to side 2. Lots of extra work though.
I think I will avoid bricks with a high moisture content (stored outside) and try poking the mortar after a few days. The wall plate will be strapped down anyway. Temporary buttresses could be screwed to various bits of concrete if it still looks dodgy.
Thanks all.
regards
If the cement dries out too quickly it won't set to full strength. Ensure it remains damp for a few days. Covering with polythene may do it.
In message , snipped-for-privacy@privacy.net writes
This is a *damp* agricultural wall. No roof gutters, doubtful damp course and probably impregnated with years of pig excrement. Drying too quickly is unlikely to be an issue:-)
regards
>
The heat given off can be an issue with bulk concrete (they incorporated cooling pipes in the Hoover Dam), but it's extremely likely to be detectable for mortar joints between bricks - there just isn't enough of it!
(But the point about temperature dependance is /very/ relevant.)
Indeed. 2 hours to 2 days to just go 'crunchy' is the variation I have noted. Over 0C-30C temp range.
Tim .... my comment about 48 Hrs is a practical one, if you are using an OPC & sand mix .... it would have enough partial strength after 48 Hrs. If you have any doubt use rapid set cement ... or an accelerator additive.
If you can leave it longer then all the better.
Some of the other comments about exothernmic reactions, and time to compressive strength are valid for bulk concrete, but not that relevant for coursed brickwork.
Obviously the longer you leave it the more strength it has, but courses and lintols (=dead load) are built up next working day on site.
would it be practical to add temporary wooden legs to the roof structure so it sits on the original brickwork, then the fill-in brickwork doesn't support the load. At a later date the legs could be cut away and brickwork finished. Or perhaps timber legs, if they ever deteriorate the roof will already be sitting on the newer fully cured brickwork by then.
NT
Certainly practical. Is it necessary?
Work is rarely scheduled on farms so there is always something waiting to be done. Even in the current *overnight frost* weather it looks as though half compressive strength will be reached after 5 days. My plan is to get the brickwork done today (snow was melting off the roof yesterday and dripping down my neck!) and get on with other things.
I see the danger point as when I start to jack up the other side to match. The only thing preventing the whole roof sliding sideways will be the new brickwork and wall straps. Elsewhere I have secured some strong angle iron to the concrete floor and a wall and then used an acrow to straighten the wall which was *leaning* from the damp course. I suppose something similar could be done with a couple of timber braces/buttresses to provide reassurance:-)
The mortar from a superficial pier I finished yesterday evening is
*biscuity* this morning.regards
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