Technical Data

MM80 - Crack & Joint Repair

MM80 10

INTRODUCTION

Metzger/McGuire and Norton Construction Products are pleased to provide this guide on a number of common floor problems and our recommended “common sense” correction methods. These field proven methods and materials were developed through years of experience as restoration/repair specialists.

FIVE PRINCIPLES FOR SUCCESSFUL REPAIR

Determine CauseDid slab movement cause or contribute to the problem?Can a change in your operation (different wheels etc) ease future damage? Is the concrete itself adequate?

Match Materials To ProblemDon’t use high strength concrete in joints/cracks that are likely to move. Would a liquid or mortar best fill the defect? Does the cure time match the limits you have?

Match Materials to Methods How deep must material be applied? What tools are required to obtain that depth? Can you wet saw cut, or must the floor be totally dry for maximum adhesion?

Match System to ConditionsWill dry cutting create unacceptable dust? Will odour from epoxy or solvent be a problem? Us epoxy cure time adequate for the type of work involved?

Preparation Is VitalNever feather edge! Always make a vertical edge at the end of the repair. Remove all foreign substances and structurally unsound concrete to ensure best bonding.

FILLER SEPARATION

MM80 is installed long before a slab has completed its shrinkage and may separate adhesively as joints open. Gaps can be filled with Crack Fill if MM80 is firmly in place.

A Norton Construction Products Guide

Fig 1. Typical Failure

Fig 2. Saw cut past the edge of breakage

Width (mm) Depth (mm) 3-30 12-20 30-100 20-25

Fig 3. Preparation

Clean out debris, blow out and choke off base with silica sand.

Fig 4. Install MM80 flush/slightlycrowned

Width (mm) Filler (%) <12 0 >12 250

Fig 5.Severe Damage > 30mm wide

Brush apply a primer coat of epoxy. Install filled epoxy. Inset expansion strip making sure bot-tom extends below epoxy and it is vertical

Fig 6. Typical Failure

Fig 7. Saw Cut

Saw cut past the edge of breakage to a depth of 25mm

Fig 8. Preparation

Clean out debris, flow MM80 liquid into any cracks.

MM80

Fig 9. Install MM80

Width (mm) Depth (mm) Filler (%) <30 25 250 >30 refer to Fig 5.

TYPICAL SPALLED JOINTS/CRACK KEYWAY JOINTS

Fig 10. Filler separation

MM80 is installed long before a slab has ompleted its shrinkage. Where MM80 separates adhesively but is still firmly in place, voids can be filled with Crack fill.

Crack Fill

BETTER SOLUTIONS FOR CONCRETE FLOORS

MM80 - Crack & Joint Repair

Fig 11. Typical Failure

SPALLS WITH PREMOULDED FILLER

Fig 12. Saw cut to 20-25 mm deep Fig 13. Prepare the Surface

Remove filler and concrete laitance to a depth of 25-30 mm. Form a barrier by applying tape or a thin layer of sand.

Tape or sand

Fig 14. Install MM80

Width (mm) Depth (mm) Filler (%) <30 25 250 >30 25 500

CRACKS & DETERIORATED JOINTS IN YOURCONCRETE FLOOR

Do you remember when you first moved into your warehouse or distribution centre? The joints were sharp and narrow, and you had only a few isolated , random cracks. Now as you walk through the facility you see that all the joint edges are severely

crumbled and random cracks are everywhere. What happened? How did your great new floor turn into a nightmare that causes materials handling vehicles to slow down and wheels to deteriorate?

This article will help you understand concrete floors in general, and more specifically, why floors crack and joints deteriorate. To do justice to the subject would fill a book, so I’ll focus on just the most common problems we see in our company. Hopefully the condensed information contained here will help you avoid the same problems on future floors and offer some solutions to make your present floor tolerable.Floor deterioration causes generally fall into one or more of the following categories:• Deficiencyindesign• Deficiencyinconstruction• Owner(ortenant)abuseorneglect.

This article will focus on design and construction deficiencies since they are by far the most prevalent cause of deteriorated floors. A high quality floor can tolerate some owner neglect, but even top notch maintenance can not overcome built in problems.

A PRIMER ON CONCRETE

Concrete is basically a combination of Portland Cement, large aggregate (rocks), fine aggregate (sand), and water. Sometimes additives may be used to accomplish certain objectives such as workability, etc. For concrete to prove durable, all components must be in a proper balance. Too much or too little of any component can cause problems later. For example, let’s look at the water component.

Water serves to react (hydrate) the cement, make the mix homogeneous and make the concrete workable and placeable. But too much water can result in excessive shrinkage and weakened concrete.

CRACKS

If a crack has no “islands”, no edge chipping and is less than a credit card thickness it should not be saw cut open. Brush apply a protective coating of liquid MM80.

If wider than credit card thicknesses apply a bead of Crack Fill and allow to seep into the crack. Reapply until no further penetration. Allow to cure. Razor cut of excess.

SURFACE SPALLS

Make cuts a minimum of 12mm deep at edges. Remove concrete within cut area to at least 12mm depth. Remove all dust and loose concrete. Mix and brush in liquid MM80 as a primer coat. Add 500% silica sand to MM80 liquid to make a mortar and apply. Trowel smooth or broom finish during epoxy cure for non-skid texture.

REPAIRS TO PLASTIC JOINTS

Spalls often occur where plastic zip strips are used as control joints. Saw cut both sides of the T joint along edge of spall to a depthof12-20mm.Removeconcreterubbleandzipstrip.Overfillresulting joint with MM80 and grind flush. If joint width exceeds 12mm, mix MM80 with 250% silica sand to form a mortar.

Technical Data MM80 10

All concrete mixes contain more water than is actually needed to hydrate the cement. The excess water eventually evaporates. Oneprimaryobjectiveistoretainthewateruntilthecementis fully hydrated, then let it evaporate slowly over a prolonged period of time. This moisture retention process is called “curing” the concrete.

As concrete loses moisture it shrinks in dimension, usually at the rate of 3mm in every 6m of slab. If concrete were left as it is placed, it would crack in random crack patterns. To avoid random cracking we create joints at regularly spaced intervals, thus weakening the slab in a grid pattern. These joints, called control (or contraction) joints force the cracking to occur in straight lines beneath the joint , so actually producing a designed crack.

Concrete slabs shrink at a relatively slow rate because all the moisture must evaporate through the top of the slab. A reasonable shrinkage rate estimate is: 30% in the first 30 days50-60% in the next 335 days80-90% in the first year

In other words, the slab is still shrinking long after you have taken occupancy. Thus joints will continue to open up and new random cracks may occur at any point in the first year or two.

When we create the control joints we caused interruptions in what would otherwise ideally be a continuous surface. To restore the floor’s surface continuity for the purpose of material handling vehicle flow, we must refill the joints. The filler must accommodate two conflicting objectives:• Behardenoughtosupporthard-wheeledtraffic• Allowthejointtocontinuetoopenuntilthe shrinkage process is complete

SO WHAT WENT WRONG WITH YOUR FLOOR?

In the design and construction process there are literally hundreds of mistakes that can be made. The following are the most common that we encounter.

Common causes of Random CrackingShallow JointsThe joints were not cut deep enough to induce the crack, leaving the slab to crack randomly. Slab ThicknessIf the slab thickness varies, the slab contraction will encounter restraint, causing the slab to crack.

Joint SpacingJoints were spaced too far apart and the concrete cracked between the joints rather than at the joints.

Delayed JointingThe shrinkage stresses in the slab exceeded the strength of the concrete before the joints were cut.

Inadequate BaseThe base under the slab must be smooth and evenly, densely compacted. Uneven bases create restraint, causing the slab to crack.

Additional Causes Of Cracking• Concretemixtooweak(toomuchwateretc)• Additivesmaycauseexcessivecurl• Slabwassubjectedtowindorsun,causingrapiddrying and early stresses• Steelreinforcingwasimproperlypositioned• Floorwasdesignedforlightloads,butoperationsimposed are heavy loads• Slabwasnotproperlycuredtoprolongwaterretention• Basewasnotadequatelycompacted,especiallycommon near foundation walls, docks, RR sidings.

Joint RestraintIf the dowels at construction joints are misaligned, or if rebar is used instead of smooth, greased dowels, the joints will be restrained and random cracks will occur, usually parallel to the joints.

Imposed LoadsIn tilt-up construction the crane’s outrigger may rest on a panel corner and break it off.

Curled EdgesAll concrete curls upward at the end of the pours. If this curl is severe enough , leaving the panel end cantilevered, the slab may crack when loads are imposed.

Re-entrant CornersIrregular corners cause irregular stress points that will cause cracking.

Common causes of Joint DeteriorationInsert JointsInstead of saw cutting joints some contractors use insert-type joints. If these inserts are out -of-plumb, the joint edges break off.

Metal KeysMetal left-in-place key forms create cantilevered nosings that break off under loads.

Weak EdgesIf the edges of joints were not properly cured, they may be inherently weak. Another cause of weak joint edges is cutting too early, causing micro-fractures in the edges.

BETTER SOLUTIONS FOR CONCRETE FLOORS

MM80 - Crack & Joint Repair

Unfilled JointsJoints must be filled to restore surface continuity and eliminate impact points from hard wheels.

Inadequate FillersThe filler is installed too early, severe separation may occur between the filler and concrete, leaving edges exposed to impact.

Filling Too EarlyIf the filler is installed too early , severe separation may occur between the filler and concrete, leaving edges exposed to impact.

Cheap FillersSome cheap fillers become brittle in as soon as 6-12 months. Oncebrittle,thefillerdeterioratesandfailstoprotectjointedges.

Shallow fillingTo properly support traffic, the filler must be installed full depth in saw cuts and 5mm deep in thru-slab construction joints. If the filler depth is inadequate, the filler will drop and leave joint edges exposed.

Rocking SlabsIf slab curl is severe, and joints are not dowelled, the slab panel may “rock” as traffic crosses. This rocking will see one panel drop as the opposite panel remains high, exposing it to wheel impact.

High Strength FillerFillers must allow slab panels to move. High-strength fillers weld slab sections together, causing adjacent concrete edges break off.

CORRECTIONS OF CRACKS

There is no one correct way to repair cracks. Considerations include:• Ageofslab• Causeofcracking• Widthofcrack• Isthecrackacleansnap,ordoesithaveislands,fractures,etc.• Isthecrackposingstructuralproblems?• Doesslabrockatthecrack?• Relativestrengthofconcrete

The basic principles of crack repair are as follows:Don’t make condition worseIf the crack is of hairline width, it is usually better to leave it alone. For additional protection against deterioration apply an epoxy coating over crack.

Cut out only when necessaryIf the crack snapped cleanly, with no islands, and if the edges of the crack have not spalled, merely fill the crack with a proper epoxy (semi-rigid).

Cut out as narrow as possibleDon’t use a cutting tool (router, etc) that will create a 25mm wide repair of a 3mm wide crack.

Cut out deep enoughWhen cutting out cracks, always go at least 25mm deep to provide enough “bite” for the epoxy along the joint walls.

Note: Surveys show that 70 - 90% of all joint filling is deficient!

Intentional or not, deficient floor joint filling has reached epidemic proportions in South Africa and worldwide. Im-proper installation can result in severe floor damage once

in use and can cost a facility owner a lifetime of floor repairs and reduced productivity. To find out how you can prevent

cheating call Norton/CLF and ask for the article “How to avoid deficient Joint Filler Installations”

Don’t weld the crackMost cracks in slabs-on-grade do not present structural problems. Welding the slab together at the crack may merely result in another crack occurring adjacent to the first. Use a semi-rigid epoxy for most crack repairs, especially for the first two years.

Don’t feather-edge repairsTo feather means to taper to -0- thickness. Instead, create a vertical edge of a least 25mm deep on all crack repairs.

REPAIR OF DETERIORATED JOINTS

Don’t feather edge repairsJoints are designed to accommodate slab movement. If the joint opens after a feather-edged repair, the thin section of the repair epoxy will break off under load.

Use semi-rigid epoxiesJoints may open and close as seasonal temperatures vary. Semi-rigid epoxies will allow for movement. Joint repairs are best done in cold weather when joints are at their widest.

Remove all previous fillersMost fillers will not adhere well to themselves or other fillers. It is critical that the epoxy bond directly to bare concrete.

Refill to proper depthTo function as an edge protector the filler must be installed full depth in saw cut joints, taking advantage of the support provided by the base of the cut. In thru-slab construction joints install the filler 50mm deep to make up for the lack of base support.

Wide deterioration may require special treatmentSeek assistance from repair product manufacturers, consultants or contractors before attempting wide repairs (over 25mm etc.). Different defects may require different products and procedures . Also, it is important to analyse why the deterioration got so wide.

CONCLUSION

The causes of cracking and joint deterioration are numerous. So to are the techniques and products required to perform permanent floor repairs. It is vital that you have an understanding of what caused the problem before you decide on a corrective approach.

Norton/CLF publishes a “Guide to Basic Floor Repairs” that is available upon request, with no cost or obligation. Your floor is a critical part of your warehouse or distribution centre’s operational productivity. Simply put, better floors equal greater productivity.

Technical Data MM80 10

SURFACE SPALLING OR DETERIORATION

REPAIR PROCEDURES

Surface Spalling or Delamination Basic preparation Advanced preparation

Prepared Area Filled Area

Make two cuts at outer edges of spalling, 10mm deep min.

Remove as shown

1. Make two cuts at outer edges of spalling, 10mm deep min. After cuts are made, deepen the defect to the depth shown with a bush hammer or other means. Remove all dust and loose concrete.

2. Mix MM80 epoxy. Add aggregate to liquid epoxy. Mix per instructions and apply. Compact mortar with trowel from kit to ensure full contact. Trowel smoother broom finish during epoxy cure non-skid texture.

Bulked MM 80

TYPICAL SPALLED JOINTS AND CRACKS

Typical Spalled Joint Repaired Joint

For defects up to 35mm wide

This detail shows our standard method of dealing with all spalled joints or cracks.

NEVER FEATHER EDGE A REPAIR

OPTION: SPAL-PRO 2000, Polyurea repair Polymer can be used if access time is critical

BETTER SOLUTIONS FOR CONCRETE FLOORS

MM80 - Crack & Joint Repair

REPAIR PROCEDURES

1. Make two cuts at the ends of spalls and remove as shown. Cuts should be minimum of 10mm deep (20mm is preferred). Clear out debris and loose elements with narrow tools. Vacuum or blow clear with compressed air.

2. Choke off base with silica sand. Install Spal-Pro 2000 (if access time is critical) or MM80 flush to the floor or slightly crowned.

MM80Remove

CutSilica Sand

NOTE: For joints up to 10 mm wide use MM-80 as a liquid. For wider repairs, use sand-modified MM-80. Mix MM-80 thoroughly; then add 1 part of silica sand by volume to make a mortar. This will give more deflection resistance to the MM-80 and extend material yield.

SEVERE SPALLING AT JOINT

REPAIR PROCEDURES

MM 80 Repair with perspex strip MM80 Repair Bad Repair

Major Spall (35mm Plus) Prepared Spall

1. Make 20mm deep cuts just beyond spalls and remove concrete as shown Fill joint space below newly cut slot with sand. Mix BINDER 3 liquid and brush-apply a prime coat to concrete. Modify remaining BINDER 3 with silica sand at a ratio of 4-5 parts silica (by volume) to create a mortar.

2. Fill slot with BINDER 3 mortar. Insert M/M’s EXPANSTRIP as shown, making sure the bottom of the strip extends lower than the epoxy. Tool epoxy flush with surface. Allow epoxy to fully harden. Snap off exposed strip. Grind or sand surface flush if necessary.

OPTION: MM-80 or SPAL-PRO 2000 may be used instead of Binder 3. When using either of these products it is not necessary to use a divider strip unless excessive movement is expected. Please see “Typical Spalling” for basic repair procedures.

Remove

Cut

For defects up to 35mm or wider

Technical Data MM80 10

KEYWAY CONSTRUCTION JOINT,SPALLS ON BOTH SIDES

Most metal forms cast in place are impossible to remove. They must be isolated from the concrete to prevent harmful vibration.

1. Make cuts just past the spalling and remove. Cuts should be 25mm minimum.

Remove

Cut

2. Allow MM80 liquid to flow into cracks 3. Then use sand modified MM80 and fill void flush floor. Straighten metal as much as possible.

REPAIR OF PLASTIC “T” JOINT

1. Plastic zip-strips as control joints are common in many parts of the world, but they can cause spalling, as shown.

2. Saw cut both spalled edges and joint. Cuts should be 15 mm deep minimum. (20mm min. is preferable).

3. Remove concrete laitance, zip strip and debris.

4. Overfill resulting joint with MM-80 and grind flush to floor level.

NOTE: If joint width exceeds 15mm modify MM-80 with 2 1/2 parts of silica sand.

MM80 Mortar

HAIRLINE RANDOM CRACKS

1. Rake out debris with knife, wire, etc. Vacuum clear

2. Apply a bead of our Spal-Pro 2000 Rapid Set Polyurea and allow it to seep into crack. Re-apply until seepage stops. Allow to cure. Razor off excess.

Greater than credit card widthIf a crack is credit card thickness or wider, it should be repaired to prevent hard wheel damage.

NOTE: If edge chipping or islands are present, treat as shown in “Typical Spalled Joints and Cracks”.

MM80

BETTER SOLUTIONS FOR CONCRETE FLOORS

The information given is based on knowledge and performance of the material. Every precaution is taken in the manufacture of the product and the responsibility is limited to the quality of supplies, with no guarantee of results in the field as Norton Construction Products has no control over site conditions or execution of works.

Technical Data

CLF Concrete Laser Flooring Pty (Ltd)POBox2589,Witkoppen,Johannesburg,SA•www.concreteflooring.co.zaTel:+27117045557•Fax:+27114621456•E-mail:peter@concreteflooring.co.za

MM80 10MM80 - Crack & Joint Repair

THE WORKS

If your floor resembles this picture, we’d like to help. The repair procedures outlined in other parts of the Guide to Basic Floor Repairs cover most of the issues encountered in this scenario but we would encourage you to call or email us to discuss having a Norton/CLF representative visit the site and make specific recommendations for repairs.

Major spalling and corner break. Prepared area

Finishing work and finished product.