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control joints residential slabs on grade

control joints residential slabs on grade

control joints residential slabs on grade

(OP)
Do you specify control joints for residential slabs on grade for areas that will be covered by flooring?  

RE: control joints residential slabs on grade

Yes.

RE: control joints residential slabs on grade

(OP)
Since the main benefit of control joints in a s.o.g. is crack control, what other benefit does it provide since you don't see the cracks anyways?

RE: control joints residential slabs on grade

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.

http://www.nceng.com.au/
"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

RE: control joints residential slabs on grade

I always specify control joints, limiting them to 400 to 600 square feet in area, residential or otherwise.   

Mike McCann
MMC Engineering

 

RE: control joints residential slabs on grade

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.

RE: control joints residential slabs on grade

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.

RE: control joints residential slabs on grade

I assume there is a difference in the construction technique  between Australia and USA.  

http://www.nceng.com.au/
"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

RE: control joints residential slabs on grade

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.

RE: control joints residential slabs on grade

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.

RE: control joints residential slabs on grade

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

 

RE: control joints residential slabs on grade

The procedures must be different here.  Few of our houses on grade have jointing in the concrete slab, and tile cracking problems are rare.

RE: control joints residential slabs on grade

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.  

http://www.nceng.com.au/
"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

RE: control joints residential slabs on grade

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.   

RE: control joints residential slabs on grade

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.

RE: control joints residential slabs on grade

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

 

RE: control joints residential slabs on grade

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.

RE: control joints residential slabs on grade

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.

RE: control joints residential slabs on grade

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.  

RE: control joints residential slabs on grade

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

 

RE: control joints residential slabs on grade

Ron,
You're confusing me, so in the USA they normally don't joint or they do joint.

Interesting, polypropylene fibres wouldn't be allowed within 100m of my slabs.

The way our system works is that generally for any class of site above A,S you require footing at regular spacing's. This regular restraints position ensure that the cracking minor in nature. For A,S class sites I may consider a joint.
 

http://www.nceng.com.au/
"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

RE: control joints residential slabs on grade

Ron,
This is one of the main brands of tile adhesive used in Australia.  Recently changed its brand name from ABA to Ardex.  I don't know if it is available in the US, but there would be similar products there.  Per capita, Australia is a much bigger consumer of tiles than is the US, mostly because of the climate, but I would think Florida would be similar.

http://www.ardexaustralia.com/product_category_display.asp?catid=4

RE: control joints residential slabs on grade

Ron hit many a nail on the head, and we do similar forensic work it seems... I do inspections sometimes in several homes a week all over the state, and cracks in tile are often worrisome to the homeowners, but we usually chalk it up to cracks in the slab telegraphing through the tile, and sometimes possibly due to poor workmanship in mortar coverage that causes cracks due to foot traffic.

Hokie- The further south you go in Florida and the closer you are to water, the more tile you see. I am pretty sure its a cultural thin in South Florida with the Latino majority and their Spanish architectural traditions (many more tile roofs, CMU and stucco walls, etc.) Now tile is pretty much standard in wet rooms and in many common areas, with laminate and real wood flooring making in-roads, especially with the improvement of laminate flooring quality and low price of material and installation.

I rarely see control joints in residential construction, sometimes in garages but very rarely in the house. Structural engineers have been pretty well kept out of most residential construction, and if its not required by code its not likely many contractors would do it, or know how and where to do it correctly. It would take coordination with the architect to align the joints with flooring transitions or walls but it could be done. Or you could let the slab crack where it wants during curing and then chase the cracks with a grinder and epoxy them, but NOBODY is doing that.

When I do a forensic investigation and people are having tile problems because of cracks in the slab, I give them the options and also warn them about the lack of guarantees.

I've also seen a lot of tenting and de-bonding failures, but that is its own subject. Had it happen on a rental property of mine. I did 4-5 repairs and then gave up and removed all of the tile (myself), did laminate in one room and did an epoxy coating in the rest. It serves its purpose, which is as little maintenance as possible..

  

RE: control joints residential slabs on grade

Ron- For your current investigation with tile debond, slab "compression" or shrinkage due to PT stresses a possible contributing cause of the tenting tile, or is that confidential at this point? I have always thought with regular SOG that is on the low end of probably contributing causes of tile debonding. Workmanship is on the high end, and long-term tile expansion due to moisture re-absorption.

Sorry for the off topic post...

RE: control joints residential slabs on grade

I think one statement from the Oz structural brethren is worth repeating:
"...unjointed slab with 0.3% reinforcement in a 100mm thick slab..."
This will result in fewer visible cracks, and control of crack growth.
When residential slabs are indeed reinforced in the US (probably less than 1/2 the time), it is not anywhere near 0.3%.  More like 0.18%.  Maybe.

RE: control joints residential slabs on grade

a2...the PT has little to do with the debonding as it occurs in both directions; whereas the PT is one direction only.  Would be interesting to be able to measure strand relaxation and correlate to overall shrinkage to see whether the chicken or the egg came first.

I agree that more often the issue is workmanship; however, there is a correlation to the amount of volumetric shrinkage of the concrete (lots of water in the mix)and the incidence of debonding.

I will be installing floor tile in our master bath this summer, so I'm going to use adhesive instead of thinset to see how it works.  I anticipate it will work just fine...just don't know why it is discouraged by the tile industry in the US.

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