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control joints residential slabs on grade
- Thread starter jeng123
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rowingengineer
Structural
I don't specify joints for internal residential slabs on grade, generally I use a raft system to control settlement. Joints will reduce the effectiveness of the raft system.
"A safe structure will be the one whose weakest link is never overloaded by the greatest force to which the structure is subjected” Petroski 1992
"A safe structure will be the one whose weakest link is never overloaded by the greatest force to which the structure is subjected” Petroski 1992
msquared48
Structural
I always specify control joints, limiting them to 400 to 600 square feet in area, residential or otherwise.
Mike McCann
MMC Engineering
Mike McCann
MMC Engineering
Altho typical tract home builders and subs cheat any way they can to make more profit, it is a good idea to insist on control joints because if there are none, a large gap opens up between the slab edge and inside face of exterior stem wall (as in my house)...due to concrete shrinkage occuring long-term (my house about 15 yrs old).
I am also assuming you would have more problems with hard tile floors.
I am also assuming you would have more problems with hard tile floors.
The joints are there for a reason...control of cracking. Most homes do not have carpet everywhere. Under carpet, no big deal. Under tile or adhered vinyl...big deal.
If you have control joints, then subsequent floor coverings can be put in place without fear of further "random" cracking. Concrete shrinks for a long time...particularly residential concrete that often has a higher water-cement ratio than commercial concrete and less quality control on its placement, finishing and curing.
If you have control joints, then subsequent floor coverings can be put in place without fear of further "random" cracking. Concrete shrinks for a long time...particularly residential concrete that often has a higher water-cement ratio than commercial concrete and less quality control on its placement, finishing and curing.
rowingengineer
Structural
I assume there is a difference in the construction technique between Australia and USA.
"A safe structure will be the one whose weakest link is never overloaded by the greatest force to which the structure is subjected” Petroski 1992
"A safe structure will be the one whose weakest link is never overloaded by the greatest force to which the structure is subjected” Petroski 1992
I would require slab joints only at reentrant corners, as cracks starting there can be nasty. Otherwise, I think the joints are more a nuisance than a help. Normal shrinkage cracks don't reflect through ceramic tiles if flexible adhesive is used.
hokie66...normal concrete shrinkage will routinely debond tile and where tile bond is good, it will crack right through the tile. Thinset adhesive for floor tile is not flexible. Wall tile adhesive is flexible.
I would be interested to know if the procedures in Oz are different than in the US for tile placement.
I would be interested to know if the procedures in Oz are different than in the US for tile placement.
msquared48
Structural
Sorry Hokie, but I have to agree with Ron here. I have seen too much cracked floor tile and mortar joints too.
Mike McCann
MMC Engineering
Mike McCann
MMC Engineering
rowingengineer
Structural
I think we reinforce our slabs more, if you allow a large joint to open up how do you handle termites. Very rarely do I see a joint in the residential slabs with a raft system being used, the extra reinforcing required to maintain continuity at the footing locations would be hard to enforce.
"A safe structure will be the one whose weakest link is never overloaded by the greatest force to which the structure is subjected” Petroski 1992
"A safe structure will be the one whose weakest link is never overloaded by the greatest force to which the structure is subjected” Petroski 1992
Even with strip footings and a 100 slab, we don't tend to joint residential slabs, except where reentrant corners occur. However, we DO use flexible adhesive for ceramic floor tiles. My house is about 20 metres long, fully tiled, no joints, no cracks. Actually, the adhesive companies do recommend joints, but it doesn't happen, and problems are infrequent.
As another Oz eng I support Hokie's and RE's comments.
Our standard residential raft slab design allows up to 30m length of unjointed slab with 0.3% reinforcement in a 100mm thick slab.
A commonly used flexible floor tile adhesive claims to be able to cope with 0.9mm wide cracking. That's probably why we rarely see cracked tiles.
Our standard residential raft slab design allows up to 30m length of unjointed slab with 0.3% reinforcement in a 100mm thick slab.
A commonly used flexible floor tile adhesive claims to be able to cope with 0.9mm wide cracking. That's probably why we rarely see cracked tiles.
msquared48
Structural
Interesting. Thanks for the insight guys.
I guess that due to gravity and OZ being down under, the cracks tend to stay closed?
Mike McCann
MMC Engineering
I guess that due to gravity and OZ being down under, the cracks tend to stay closed?
Mike McCann
MMC Engineering
If you US folks joint slabs on ground, how do you align the joints in the tiles? Surely you don't cut all the tiles at the joints. My wife wouldn't have that. And don't tell me that you lay out the joints to suit the tiles, because she is going to change the tile selection.
How do you handle ceramic tiles on suspended floors? They crack as well, and you can't joint them very often.
How do you handle ceramic tiles on suspended floors? They crack as well, and you can't joint them very often.
Here in the US, tile on floor slabs is handled a bit differently...
First, slabs are not usually jointed. Secondly, they are not usually reinforced enough to prevent cracks or to hold the cracks to reasonable widths. I just personally recommend it and now the contractors are starting to do it more often, mostly because of the cracking problems with tile.
We are currently working on a tile debonding failure in a post-tensioned structure.
If you don't cut in joints, the crack width is larger because of the concentration of shrinkage at the joints. Another problem is that polypropylene fibers are often used in residential slabs, thus increasing the space between cracks but also increasing their widths when they occur.
Joint patterns can be chosen so as to highly reduce the probability of wide cracks occurring under anticipated tile application (kitchens, baths, foyers)....sometimes that results in irregular joint spacing and configuration, but it works.
I recommend using a crack mitigation membrane on top of the slab and under tile. This reduces the shear transfer between the slab and the tile adhesive....probably much in the same manner as your flexible adhesive.
I see no reason that flexible adhesives would not work here as well, other than manufacturers and the Tile Council of America do not recommend them, thus putting the design professional outside a defined standard of care (thus increasing liability) if designed so. The standard is a cementitious thinset adhesive.
One problem that we encounter with flexible adhesives on floor slabs in the US is re-emulsification due to high alkalinity and moisture transmission. Non-latex adhesives would probably be fine.
As for aligning tile with joints, that's rarely done except in long, narrow applications. Though the Tile Council requires the design professional to designate joints and locations, it is not often done. Either the membrane is used or you just don't worry about it and let the tile debond if it so desires.
What are some of the brands of flexible adhesives that you use in Oz? I'll give it a shot on my own house first, to see how it works.
First, slabs are not usually jointed. Secondly, they are not usually reinforced enough to prevent cracks or to hold the cracks to reasonable widths. I just personally recommend it and now the contractors are starting to do it more often, mostly because of the cracking problems with tile.
We are currently working on a tile debonding failure in a post-tensioned structure.
If you don't cut in joints, the crack width is larger because of the concentration of shrinkage at the joints. Another problem is that polypropylene fibers are often used in residential slabs, thus increasing the space between cracks but also increasing their widths when they occur.
Joint patterns can be chosen so as to highly reduce the probability of wide cracks occurring under anticipated tile application (kitchens, baths, foyers)....sometimes that results in irregular joint spacing and configuration, but it works.
I recommend using a crack mitigation membrane on top of the slab and under tile. This reduces the shear transfer between the slab and the tile adhesive....probably much in the same manner as your flexible adhesive.
I see no reason that flexible adhesives would not work here as well, other than manufacturers and the Tile Council of America do not recommend them, thus putting the design professional outside a defined standard of care (thus increasing liability) if designed so. The standard is a cementitious thinset adhesive.
One problem that we encounter with flexible adhesives on floor slabs in the US is re-emulsification due to high alkalinity and moisture transmission. Non-latex adhesives would probably be fine.
As for aligning tile with joints, that's rarely done except in long, narrow applications. Though the Tile Council requires the design professional to designate joints and locations, it is not often done. Either the membrane is used or you just don't worry about it and let the tile debond if it so desires.
What are some of the brands of flexible adhesives that you use in Oz? I'll give it a shot on my own house first, to see how it works.
There are some very good tile thinsets out there that are flexible.
The one that I prefer is made by Laticrete and when used with a latex additive, the thinset is very flexible.
IMO, the premix wall tile adhesives are pretty much all junk.
The one that I prefer is made by Laticrete and when used with a latex additive, the thinset is very flexible.
IMO, the premix wall tile adhesives are pretty much all junk.
msquared48
Structural
Had a chance to muse on this last night and remembered the tile floors we saw in resorts in Mazatlan and Cancun in years past when we had a little extra to spend. they were loarge expanses, and had no cracks, and were grouted with non-flexible grout. So either the mastic adhesive must have been flexible, or the cement base was very, very special...
Sold me on the masonry ability of the Mexicans.
Mike McCann
MMC Engineering
Sold me on the masonry ability of the Mexicans.
Mike McCann
MMC Engineering
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