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  1. #1
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    no control joints in slab?

    It appears house slabs in Thailand don't use control joints. I was reading this also appears to be the case in Australia (ref: AS 2870 specification). This is strange because in the US control joints are considered crucial and used prolifically. Can anyone compare the two methods and are there times not to use one versus the other? I would like to know specifically if slabs without control joints are compatible with a ceramic tile floor laid across the entirety and in this case whether control joints are advised at the ceramic tile layer.

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    Joints

    I could be wrong but I thought they were for expansion due to freezing/thawing, or at least a greater range between high and low temps diurnally.

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    ^Correct NN. Thermal expansion and contraction. Since most of the time temperatures range from 24 to 35 C here in Thailand no need for x-joints. I would suspect in Oz they use them in the more extreme temperature zones where snowfall is common.

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    Thailand Expat superman's Avatar
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    Control joints and expansion joints are 2 different things.
    Control joints (often confused with expansion joints) are cut into the concrete or asphalt, and are different from expansion joints
    Expansion joint - Wikipedia, the free encyclopedia

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    Quote Originally Posted by canopy View Post
    It appears house slabs in Thailand don't use control joints. I was reading this also appears to be the case in Australia (ref: AS 2870 specification). This is strange because in the US control joints are considered crucial and used prolifically. Can anyone compare the two methods and are there times not to use one versus the other? I would like to know specifically if slabs without control joints are compatible with a ceramic tile floor laid across the entirety and in this case whether control joints are advised at the ceramic tile layer.
    I cant see a problem cutting in some control joints (we always called them expansion joints in aus) where you think they may be needed , such as the top of a driveway rise or every 3m or so of 100mm load bearing concrete. Its not going to hurt is it?
    For a house slab thats shaded , and on settled, firm substrate in Thailand its not going to hurt either.
    If the slab is going to crack for any reason it will hopefully do so in the joints which u can fill with silicone to prevent ants/etc using them to access the house.
    Just tile the floor normally as you would any slab, and if you want to gety really fussy can use a rubber based tile adhesive for the whole floor or just for those tiles that cover the expansion /control joint.
    My guess is its not common practice here as theres not so much temp variation , although theres upwards of 20degC variation in a 24hr period in some northern provinces.
    Its so easy to do i cant see any reason not to.

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    Thailand Expat superman's Avatar
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    Quote Originally Posted by shaggersback
    If the slab is going to crack for any reason it will hopefully do so in the joints
    How can a slab crack in the joint ? That's what the expansion joint is for, expansion, to avoid cracking.

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    we just had a Driveway put down, 140 square mt. after the pour had set they cut 2 cross cut across the Length! would have been easier to mark and cut a Line when it was Wet! but then I'm not one to ask ''do it my way''

    Also Different Sub soil types require foundations! Adelaide South Australia has 'Bay of Biscay'' type soil, that is its has a tendency to move after a few years, wall crack and Foundations shift inches,

    look a Anchor Wat, built on a Swamp and a Hydraulic foundation, moves like an Ocean, all Man made.

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    Quote Originally Posted by superman View Post
    Quote Originally Posted by shaggersback
    If the slab is going to crack for any reason it will hopefully do so in the joints
    How can a slab crack in the joint ? That's what the expansion joint is for, expansion, to avoid cracking.
    Should i say bend? Cant see concrete "bending" too easily either.
    The joint will allow movement. I had my driveway done in aus as a continuous pour over 25 meters. The exp joints were cut in two days later with a concrete saw that was set to a cutting depth of 70mm. So indeed the concrete would "crack" at this point if there was movement , as the concrete was 100mm thick.
    Hope thats clear enuff for you Superdude.
    Saying that , theres no gaurantee its going to "crack" in the place you want it to either.

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    Actually, there is a very good reason to use control joints, as I found out last year with a guesthouse building in Phuket. The guestroom floors were laid with large 60x60cm floor tiles, but with minimal grouting between each tile.

    In the middle of one night, there was a terrible cracking sound, which scared the crap out of the guests in that room. Upon inspection, two complete rows of floor tiles, stretching 20 metres from the front of the building to the back had been forced up away from the floor.

    what happened was that a minor earthquake had occurred - the guesthouse building had moved ever so slightly, but the floor tiles had no expansion joint to absorb this movement - so they moved in the only direction left to them ==> upwards!!
    Groping women when you're old is fine - everyone thinks you're senile

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    As concrete dries, it shrinks. Cracks form due to the uneven nature of this shrinkage. Control joints are used to define where cracks occur. When laying tile an expansion joint instead of the normal grout joint is used over these control joints.

    I wish to use the slab as a termite barrier so cracks need to be small. I am in a pickle whether to use control joints and manage the controlled cracks or follow AS 2870 that when properly executed (a very difficult ask in Thailand) all cracks are sufficiently small.

  11. #11
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    we put 'expansion' joints in our slab for the new house here in SE QLD OZZIE, and sure enough i spotted a hair line fracture on one of the corners, fortunately not structural problem

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    Quote Originally Posted by mingmong View Post
    we just had a Driveway put down, 140 square mt. after the pour had set they cut 2 cross cut across the Length! would have been easier to mark and cut a Line when it was Wet! but then I'm not one to ask ''do it my way''
    They probably knew what they were doing. Cutting wet concrete requires specialized, expensive green concrete early entry saws that may not even be available in Thailand. Cutting with a normal diamond blade is risky because you have to wait long enough until there is enough hardening, but not too long when cracks form.

    Control joints can also be formed using a hand groover on wet concrete. I don't know why Thai's wouldn't use this method as it would seem the cheapest way. The only place I found that sells these is Watsadu, but curiously the blade is only 1cm deep. Since control joint depth needs to be minimum 1/4 the slab thickness I don't understand what these are for since they are too shallow.

  13. #13
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    Yes I have the Hand tools here, you can buy too but I brought a couple over from Dad's House

    they have a habit of leaving the Edges razor sharp! like its the first part to crack is the edge falls off, it's the Thai way or the Hi-way

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