We at Narrows Construction have put this fact information sheet together to assist in the understanding and education of inherent and normal properties that exist when using concrete for structural or Decorative purposes.
When working with Concrete it is important to remember that during the placement , Hydration , and curing of any concrete product there are variables at work that are not within human control.
Cracking: Unfortunately this is a fact that can not be avoided, even when following the strictest guidelines set forth by the American Concrete Institute , this is one of the inherent properties of concrete. Fortunately there are measures that can be taken to reduce unsightly cracks but not eliminated.
The Elements: Increased cracking may result when uncontrolled conditions appear during the placement, hydration , and curing of concrete such as excessive heat or cold , and heavy winds.
Concrete placement: After placement and Hydration begins there are more factors to understand. Concrete does not dry uniformly . The surface of a slab dries quicker than the bottom so there is a moisture gradient, resulting in Curling or Cupping at the surface which can cause shrink cracking, further more the moisture in the slab leaves the slab by way of moving towards the bottom and the surface, because the surface dries much faster than moisture can dissipate superficial cracks ( crazing cracking ) usually form and can be unsightly but never the less an integral part of any slab.
Hydration and Curing of Concrete: Water acts as a catalyst when mixed with cement causing the mixture to harden and gain strength. This is the Hydration process, once the initial hydration and strength has occurred the next phase comes to play called the curing process, this process will continue for many years to come. Initially there will be some shrinking that occurs which can also cause some cracks to form. We apply control joints to assist in the controlling of these cracks. These control joints also add a visual look to the finished product. These joints do not effect the strength of the concrete only the appearance.
Discoloration: Concrete is a natural product meaning that all the ingredients are found in nature and like nature the colors may not be consistent . Ready mix companies that supply the concrete do to availability may use rock, sand , cement from different sources all of which can effect the color , further, concrete does not dry and cure uniformly so there usually is some discoloration during the curing process Narrows Construction has no control over this discoloration which usually blends and cures out in a few month and shall not be held responsible, liable to remedy any discoloration in new Concrete.
Flat Slab Concrete: All flat slabs are susceptible to puddling , this can not be avoided . It is common and should be considered reasonable to see 1/4 inch pudding in approximately eight feet. Concrete slabs that are expected to drain should have fall in them. If you are considering having A job done in stamping or heavy texturing you should consider 1/4 fall for every foot of run. If you are thinking of maybe doing an exposed aggregate , broom finish or some other kind of surface that is of a smother nature , or perhaps a patio you might consider 1/8 inch per foot fall. The reason is that the heavier the texture the slower the water will drain and the more fall you will need, and for a Patio if you place to much fall in the slab this will reflect on the tables , and chairs placed upon it.
Rebar myth: Rebar as used for cracking. Thou the use of rebar is a very good idea costumers should consider that the use of rebar will add a considerable cost to the job and evaluate where and how , and if the cost out ways the risk. There are many different reasons that cause concrete to crack, rebar will only assist in reducing cracking in a few of them , it will not eliminate them.
Efflorescence: Efflorescence forms as a chalk like substance on the surface after placement. It is beyond the control of any contractor to prevent. It is usually white in color . It is caused by movement of soluble salts within the concrete to the surface. It usually appears within a day or two after placement or as long as a month or two later. It does not effect anything more than the appearance. It usually disappears over time. This is a normal occurrence Narrows Construction will not be responsible for the appearance of Efflorescence. Narrows Construction Will charge and addition cost to the job if a customer wishes to have it removed.
Overlay's: Are designed to go over Concrete, brick, and wood. For use inside or outside. They are an awesome way to repair existing concrete that have unsightly cracks and settling. Like concrete during the curing time you will see changes in the color , it is not uncommon to see colors that you did not want, give time to cure these colors will all blend to the approximate colors that were picked. From the samples we created or the color charts we provided. Because samples are unique Narrows Construction make no claim that they will be an exact match , only that they will represent a close proximity, to the colors selected.
Freshly poured concrete: We like to tell our customers not to walk on the new concrete for 72 hours and not to drive on a new driveway for two weeks and strongly recommend not driving on it for 30 day's the longer you stay off the concrete the more time it has to cure and the harder it gets. This will reduce the risk of promoting cracking, it also reduces scratches and marks left by any activity , although these superficial marks will usually disappear to the eye after a month or so.
Acid Stains: When it comes to Acid Stains it is very, very important to find a company that really knows how to apply this product. WE CAN NOT STRESS THIS ENOUGH. Unfortunately we see far to many jobs from commercial to residential that have been botched. After a company does a pour job with stains it is almost to late to repair and at the least can be very costly to do.
It starts with you the costumer. If you are thinking of having your project done in an Acid Stain finish , Please find a contractor that you trust before you proceed with any work. ( We would like to think that contractor would be us ) The reason is Acid Stains react with any chemical residue left on the slab during the coarse of construction, it does not matter if you can see this residue or not, it is still there. Merrily walking from the dirt on to your slab will leave a chemical print that can show later just after the Stain is applied. Protecting your slab is a must but merrily placing construction paper over the slab will not work completely. Picture your Plumber or electrician walking across your slab that you covered with paper and he spills his pop or his feet are wet because he stepped in water somewhere, That is all it takes to cause damage, every where he walk you will see a foot print after the stain has been applied.
This happens all to often as I said. To get your best results with stains the slab needs to be cleaned and degreased first , if you wait to hire a contractor for staining until after your sheet rock is in you have created another problem. Yes the floor can be cleaned after the sheet
rock is in but you have limited the contractor as to his approach to doing that. When cleaning the more water and degreaser that is used the better the results, with sheet rock in you risk damage to the rock most contractors will resort to sanding at this point and that will just not
give you the best results. We prefer to do the Staining before any other subs have started and long enough after the Concrete has had a chance to cure out , this might sound odd to you but if we do our work first and get the slab sealed than it will be better protected and it is much
easier to do some mirror patching and buffing than it is to remove damage that you can not see until the stain is applied. For more information please feel free to give us a call or send us and E-mail before you start your project. Narrows Construction 253-318-3978 firstname.lastname@example.org