Floordude

“What is the best way to handle an expansion joint in a concrete slab?”

Flooring manufacturers recommend that you “honor” a concrete expansion joint. By this, they mean the joint needs to be allowed to move with temperature changes. A concrete slab will move approximately 1/8 inch per 100 linear feet per five degrees Fahrenheit. The joint needs to either be covered with an expansion cover or be filled with elastomeric joint filler and left exposed.



Types of Concrete Joints

Isolation or Expansion Joints
Isolation or expansion joints should be used wherever complete freedom of vertical and horizontal movement is required between the floor and adjoining building elements. Isolation joints should be used at junctions with walls, (not requiring lateral restraints from the slab), columns, drains, manholes and stairways. Isolation joints are formed by the insertion of preformed joint filler between the floor and the adjacent element. The joint material should extend the full depth of the slab and not protrude above it. Isolation joint are usually active joints and are rarely without movement as they permit independent vertical and horizontal movement between adjoining parts of the structure.

Construction Joints
Construction joints – are placed in a slab to define the extent of individual placements, generally in conformity with a predetermined joint layout. They are typically placed at the end of a day’s work but may be required when concrete placement is stopped for longer than the setting time of concrete. Construction joints may be doweled, keyed or butted depending upon the intended usage of the slab. Regardless of the usage, construction joints are generally active and should be treated as such.

Construction Joints
Sawcut Contraction joints (control joints) are used to limit random, out of floor joint, floor slab cracking. These joints are usually on column lines, with intermediate joints located at equal spaces between column lines. These joints must be carefully designed and properly constructed if uncontrolled cracking of concrete slabs are to be avoided. Depending upon the size of the large aggregate, the maximum spacing of contraction joints should be 24 to 36 times the thickness of the slab. For example, in a 4-inch (100mm) thick slab the joint spacing should be about 10 feet (3 m). It is further recommended that joint spacing be limited to a maximum of 15 feet (4.5 m). The depth of the sawcut should be a minimum of 1/4 the depth of the thickness of the slab and/or a minimum of 1 inch (25mm). All construction joints should be square or nearly so and L-shaped panels should be avoided. Sawcut joints are generally cut 4-12 hours after the concrete has been finished. Contraction/control joints can be either active or dormant. Active contraction joints are caused by the slab not being dry or stabilized by temperature and humidity.

Slab curling can make this situation worse. If the slab curls after the joint is cut and then relaxes after the floor covering is placed, that movement can also cause the joint filler to bulge upward. Most floor covering installers choose to repair this problem by removing the row (or strip) of covering directly above the joint bulge and using a razor blade to trim the joint filler that has bulged. If this solution is implemented before the slab moisture is in equilibrium, additional moisture movement may cause the joint to bulge further and require a second repair.

The following is a series of events that happen to the slab starting with the pour and ending with a bulge occurring in the finished floor.

Flooring contractors will send their installation crew out and start the floor preparation with no idea of wither there is any potential for movement at the concrete joints. First of all, a calcium chloride test, done to ASTM F-1869 standards, will give you no indication of the amount of moisture down in the slab they measure moisture movement at the surface of the slab down as far as about ¾”. The hygrometer probe test, (in-situ), done to ASTM F-2170 standards, will give you a more realistic look at the internal moisture content. If you were to do both tests and the calcium chloride was indicating a slab dry enough to install over and the hygrometer probe test was high, you could expect the slab to be curled and the joints to be active. Any high compressive Portland-based filler, used to fill any active joints, will be pushed up showing through the finished floor, only to be found on the deficiency (punch) list.


One of the most perplexing segments of the commercial flooring installation is how to handle joints in a concrete slab. Flooring manufacturers insist that flooring contractors “honor” all joints that are active (moving) and to cover all dormant (non-moving) joints. The general contractor, architects, designers or owners do not want to place a joint cover down the middle of the room just to accommodate the flooring manufacture, nor do they want to deal with the aesthetics left by the joint cover. With fast-track construction and a lack of environmental controls, concrete joints are going to keep moving long after the structure is occupied. Just how do you know whether a concrete joint is active or dormant? You cannot look at a concrete joint and make that determination. Just how long will the concrete movement be a problem? We know that 80 percent of the concrete movement peaks once the slab is stabilizes normally in 6 – 9 months, but has been known to move for as long as 3 years after the temperature and humidity has been stabilized. In this article we are going to look at this dilemma and what needs to be done with joints. Cracks in concrete cannot be prevented entirely, but they can be controlled and minimized by properly designed joints.

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Anti-wingnut

Very good points Floordude. You are absolutely correct. The problems start because control joints are seldom designed. The GC will perform saw cuts based on various stress risers in the building. Seldom if ever are the locations of these saw cuts ever officially designed and committed to paper by the architect. Subsequent designers and architects will layout floor cover based on the needs of the tenet, with little or no thought to preexisting conditions. The contractors must install the floor, and often there is no easy way to rectify the needs of existing control joints, budget, schedule and aesthetics into the floor layout. Typically what happens is the joints get Raeco'ed, and the floor gets laid.

Architects should be responsible for designing a reasonable crack management system which the contractors can follow. Then subsequent architects, designers, and contractors would have access to these plans, and hopefully could incorporate at least modicum of thought to protecting the future floor.

But it won't happen, and GC's and flooring contractors will continually be painted into a corner

BKM Resilient

Hi Floordude
Have you done much BIG commercial vinyl work?
You have to know all the basics of concrete to survive thirty years of laying vinyl floors in multi-million dollar projects. The customer's architect draws the plans up and we are contracted to COVER the floor. We patch and lay over the floor basically "as is" and exclude structural failure, moisture problems and major preparation in every standard contract. We're not dealing with the Little Old Lady From Pasadena so our customers can't plead ignorance of what our contract implies. THEY are experts in structural design and concrete. We are expert in covering the floor. Anything they want related to that stuff that's BEYOND OUR CONTROL is negotiable as an extra to our scope of work and liability. If he want's cuts every 15-20' at the sawcut they would have to draw the plan with that detail included. I've never seen it or heard of it. For those customers who are not general contractors or Fortune 500 corporations our contract language is clear and simple and will hold up in court.

Mike Costello

I would say as a whole I agree.

But I have had architetcs spec expansion joints in the past. We use what amounts to a extra large vinyl snap in at the expansion joints on vct jobs

ian@prosource

I have had to do that as well, for a large hall that was on a concrete raft that was built on a flood plain,

The wide cover bar we had was fixed down with a very heavy duty thin sticky foam pad fixing along just one edge. This aloud the floor to move and as we did not have to fix into the crete, reduced the chances of the crete edge from breaking down over time & use

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ian@prosurceab.ca
www.prosourcefloors.ca
11204-178st Edmonton Alberta Canada T5S 1P2
The views expressed are personal and should not be taken as offical ProSource floorcoverings policy

Floordude

Yes, 100's of thousands, of it. Chased the dragon, on a few, before I got edjewmakated.

I'm also the guy that gets called to investigate, when there is a failure. I see the cause and effect of this, at least 3 times a week. Guess who gets the blame... Believe it or not, your the guy the flooring manufacturer is relying on to install to their specifications, and honor all expansion and isolation joints. The GC and his concrete guys are suppose to know about the concrete, You can argue all you want, but in the end, if there is a flooring failure caused by an isolation or expansion joint, it is going to be the floorguys butt and wallet on the line. I have run into this, and sat down with the architect, to rewrite the specs, in mid construction. All you have to do, is have the certifications, for the architect to respect you and your documented stance on the matter. If your just some bum looking installer, the architect won't give you the time of day.

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BKM Resilient

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What distinguishes a contractor from some "bum looking installer" is how the contract language is written and how well the company knows how to protect itself from inevitable job failures. There are standard exclusions that any hard surface shop knows about. Basically that covers major floor prep, seismic/slab movement, moisture, abuse and any other "pre-existing" conditions beyond the flooring contractors scope of work. We don't have to grovel to the architect. Screw that nonsense.

It's really a simple concept. Earl Scheib will paint any car for $99, remember that? Nothing but the paint is included. They will barely buff the scratches out of the old paint job. People think they deserve a thousand dollars of body work for $99. Guess what? Earl Scheib has been around a LONG time because he knows how to write a contract and how to paint cars.

All we do is COVER the floor, get it?