slab edge splits

[phild01]

Hi
My slab is more than 3 weeks old and have just started framing. The roof is tile and I am nailing down bottom plates (45mm) with spaghetti and 90mm nails, 50 mm in from slab edge. Today I noticed that the slab edge is cracking free where these nails went in. The nails are the thicker gal bullet head and did take a bit of pounding. The thinner 75mm nails were gliding in too easily I thought. What am I doing wrong and can the edge be easily repaired. Thanks for any help.

[TermiMonster]

Without knowing the details, a couple of things spring to mind:
1: Up the drill bit size by 1/2 mm, so if you're using 6mm try 6.5mm, and..
2. Put the nails more to the inside of the bottom plate, ie 65-70mm in from slab edge.
TM

Also, make sure you're hole is deep enough, ie hole needs to be ~10mm deeper than nail.

[phild01]

Without knowing the details, a couple of things spring to mind:
1: Up the drill bit size by 1/2 mm, so if you're using 6mm try 6.5mm, and..
2. Put the nails more to the inside of the bottom plate, ie 65-70mm in from slab edge.
TM

Also, make sure you're hole is deep enough, ie hole needs to be ~10mm deeper than nail.

Yes, I was using a 6mm in a rotary drill and it was only just the length of the nail. I then used a 5mm long masonry bit in the hammer drill to go the extra 10mm. What is distressing me now is the damage to the slab edge and wonder what is an acceptable way of repairing this. It has happened where my jamb studs are. I suppose I will need to somehow pin into good concrete and patch with a bondcrete mix of cement! Just not sure.

[ringtail]

May I ask why are you nailing and not using the standard M12 gal stud chemset into the slab or M12 Dyna bolts ? Its pretty well mandatory up here for tie down. Nails wont pass the framing inspection in Brisbane and definitely wont pass the further north you go.

[Bloss]

May I ask why are you nailing and not using the standard M12 gal stud chemset into the slab or M12 Dyna bolts ? Its pretty well mandatory up here for tie down. Nails wont pass the framing inspection in Brisbane and definitely wont pass the further north you go.

:whs: or further South . . .

[phild01]

May I ask why are you nailing and not using the standard M12 gal stud chemset into the slab or M12 Dyna bolts ? Its pretty well mandatory up here for tie down. Nails wont pass the framing inspection in Brisbane and definitely wont pass the further north you go.
Brisbane is in a different zone to Sydney isn't it. Tie down is a consideration but as I said the roof is tile and wind uplift is negligible. I was too tight to use chemset and damage from the dynabolts would have been worse than the nails I drove in. I don't think using a rotary hammer helped much here either. Did discover a different type of fixing yesterday that is like a nail with a deformed end and countersunk type head. Anyway what I really need now is a way to fix the slab edge.

[ringtail]

But what are you building - a new house ? extension / renno ? what's the certifier / council inspector going to say about your lack of tie down or are you not getting it approved ? I'm not sure on the wind rating for Sydney but it wouldn't be much different to Brisbane. Its gets a more heavy duty from the fraser coast north but Sydney is just a prone to high wind as Brisbane.

[Cecile]

the slab edge is cracking free where these nails went in.

I'm not a builder, nor a concrete expert. My common sense though, for what it's worth, asks whether your concrete is the correct strength in the first place.

[phild01]

But what are you building - a new house ? extension / renno ? what's the certifier / council inspector going to say about your lack of tie down or are you not getting it approved ? I'm not sure on the wind rating for Sydney but it wouldn't be much different to Brisbane. Its gets a more heavy duty from the fraser coast north but Sydney is just a prone to high wind as Brisbane.
It is a basement two bedroom extension. To my knowledge Brisbane is in an intermediate wind zone area being region B extending down to Coffs Harbour. Sydney, I believe is Region A Normal. Brisbane is at greater risk of cyclonic winds which is what tie down is more about for tiled roof homes. Sheet roofs require tie down no matter the region. I am building to N3 but finding it hard to get a lot of information about this except for bracing. Yes I am going through a certifier. I would like to hear of any home in Sydney being blown apart that had a tiled roof! Could be wrong though.

[ringtail]

It is a basement two bedroom extension. To my knowledge Brisbane is in an intermediate wind zone area being region B extending down to Coffs Harbour. Sydney, I believe is Region A Normal. Brisbane is at greater risk of cyclonic winds which is what tie down is more about for tiled roof homes. Sheet roofs require tie down no matter the region. I am building to N3 but finding it hard to get a lot of information about this except for bracing. Yes I am going through a certifier. I would like to hear of any home in Sydney being blown apart that had a tiled roof! Could be wrong though.


Totally agree that a tiled roof house requires less tie down than a tin roof, but that doesn't mean no tie down, which is essentially what you have with hand driven nails and a cracking slab. Remember that the fixing of the bottom plate is vital to achieve adequate bracing too, not just tie down. If the bottom plate can move on the slab that alone will compromise the rest of the bracing. Wind load is a mighty beast. Regarding the cracking slab, did a concreter lay it and place all the steel properly ?

[phild01]

Totally agree that a tiled roof house requires less tie down than a tin roof, but that doesn't mean no tie down, which is essentially what you have with hand driven nails and a cracking slab. Remember that the fixing of the bottom plate is vital to achieve adequate bracing too, not just tie down. If the bottom plate can move on the slab that alone will compromise the rest of the bracing. Wind load is a mighty beast. Regarding the cracking slab, did a concreter lay it and place all the steel properly ?

I am still trying to find specific information regarding tie-down requirements for me. Personally, for where I am, I might be big on bracing but strongly doubt the benefits of anchoring to the slab. The wind can be strong but it has never budged the house of it's foundation by any amount. It is such a different thing when houses are built with wings (sheet roofs). As for the slab it is 32mpa with 72 mesh placed correctly.

[ringtail]

I am still trying to find specific information regarding tie-down requirements for me. Personally, for where I am, I might be big on bracing but strongly doubt the benefits of anchoring to the slab. The wind can be strong but it has never budged the house of it's foundation by any amount. It is such a different thing when houses are built with wings (sheet roofs). As for the slab it is 32mpa with 72 mesh placed correctly.


Cool. I know what you mean. My house is old as and has bugger all tie down ( with a sheet roof) and aint going anywhere, but, unfortunately what we think is fine is quite often not sufficient to satisfy council / certifier. Which is a PITA but rules is rules I guess.

[Bloss]

The type of bracing on a particular wall governs the tie down fixings for that wall - so it depends what your plans have specced for each wall.

The minimum or nominal fixing would be one 75mm masonary nail at not more than 1200mm centres (note it will be usually much less eg: 550mm) for no or type A bracing then and M10 bolt or other 13 kN (or greater) capacity connection at each end intermediately and at max.1200 mm centers for type B bracing.

In any case the results you have had with nails suggest you have no choice (and you are seriously saying you didn't go chemset because of the cost . . . mmm) but to go chemset - not because you need the uplift security, but because for whatever reason your green slab is not happy with the nails.

As to seeking examples of catastrophic failure or building movement . . . mmm, again. They might be minimum standards, but most abide by them - as think member interd6 said at one point one prior to the adoption of standard common practice was to add a safety margin, so slightly over engineering was the norm. CAD means that structures can now be designed to just comply (to save short term costs) so variations from plan at build are not always a great idea (not that I am suggesting you are).

[ringtail]

Ahhhh if only it was that easy up here. M12 chemset or dyna with 50 mm square washer ( not 30) every 600. M12 rod next to every window ( both sides no exceptions) and no more than 1200 between rods unless window or door opening is wider than 1200. Tin or tile makes no difference, this is what the certifier wants to see or the frame inspection will get knocked.

[phild01]

The type of bracing on a particular wall governs the tie down fixings for that wall - so it depends what your plans have specced for each wall.


In any case the results you have had with nails suggest you have no choice (and you are seriously saying you didn't go chemset because of the cost . . . mmm) but to go chemset - not because you need the uplift security, but because for whatever reason your green slab is not happy with the nails.



I drew the plans myself without a spec but using F22 4mm ply for external walls and metal brace internally (nominal). As for chemset, $30 - $40 per cartridge and spare nozzles at $5 does get over the top! With a bit more experience with slabs (first one) I would do this differently. As for the slab split I think I will remove the split, tediously square the void, chemset some gal rod and inlay a new coarse aggregate cement-mix.

[METRIX]

Hi.

Reading your post I would suggest you don't nail your bottom plate down if your slab does not like this, and opt for chemset method, this won't put any stress on the edge of the slab and give you a far superior hold, I know it cost's $40 a tube, but if your going to do a job, do it right as it will only cost you more in labour and fixups later.

On all new slab construction in Sydney [Region B / N2 Min spec we use], we use M12 galvanized Dyna's, or chemset [depending on the engineer's requirements] to hold down frames and have never had problems with splitting edges using dyna's, we commonly use powder fired 72mm nails to pin the frames in position, then fix off with M12 Dyna's [still no splitting of edges using powder fired nails].

I might suggest there is a problem with your concrete mix as a nail driven into a plug 50mm in from edge should not cause any cracking at the edge, unless the nail you are trying to force into the plug is severely oversized..

From your description I would also suggest you will have a problem getting the structure passed, if signs of cracking at the hold down points is evident, I can't see the certifier liking this.

I would be concerned with the ability of the structure to withstand any lateral forces put on it for the life of the structure, if there is cracking evident at the fixing points and these have been repaired by one method or another, the fixing point has been compromised and will not perform its job effectively.

I know your main question is NOT why the concrete is splitting, but how to repair the splits.

My question would be, why is the concrete splitting ? and what do I need to do to stop it splitting, my answer would be to choose another fixing method as the one you have chosen in not appropriate.

[phild01]

Hi.


I know your main question is NOT why the concrete is splitting, but how to repair the splits.

My question would be, why is the concrete splitting ? and what do I need to do to stop it splitting, my answer would be to choose another fixing method as the one you have chosen in not appropriate.


I will be redoing the fixing and will use chemset but I must address the damage done. Ripping up the slab and redoing is not an option anyone would want. I suspect I will have approx 50mm of the slab edge to repair which is right under a jamb stud. So the wall load will only be on 45mm of the original slab. I believe if I square off the damage, the replacement pinned cement/mortar mix will take a bearing down onto the existing slab. So not patching the sheared concrete edge but inserting a block of new mix to carry the offset load to existing cohesive slab. My options seem limited!

[ringtail]

Did you use a vibrator on the slab ? Can you post a few pics of the slab edge ?

[phild01]

Did you use a vibrator on the slab ? Can you post a few pics of the slab edge ?

The slab is 120mm on brick to sandstone
A vibrator was used!91024

[METRIX]

WOW, thats a sizable chunk one nail has taken out of the slab, best to switch to chemset and save the grief.
That will deffinetly be knocked back by the certifier if left in that state.

[phild01]

WOW, thats a sizable chunk one nail has taken out of the slab, best to switch to chemset and save the grief.
That will definetly be knocked back by the certifier if left in that state.

Definitely won't be leaving it like that. I am going to put on my dentistry cap and carefully create a level based void, pin it with chemset and gal then layer new cement mix to it. This crack occurred days after I drove the nail in.

[METRIX]

Sounds like a good idea, I hope you didn't do to many more nails which ended up like this, or you will be a very busy dentist :q