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the house is in the area of the northridge earthquake of a few years ago. the family room slab (appears to be 4″)suffered some cracks. there are now 3 pieces, where once there was one, with the the middle one about 1/8 lower the other two. my brother wants to tile over the concrete floor as is. won’t the cracks just telegraph thru the tile eventually? best solution?
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Paul,
With cracks in concrete slabs, you're taking a chance no matter what you do.
I've repaired 2 house foundation slabs that were cracked and approximately 15 years old at the time of repair. I've had the opportunity to follow up on both 8-9 years later. Both show no signs of the cracks reappearing. I've done others with no follow-up. Basically I opened up the cracks with a chisel to a "V" configuration. We do decorative concrete resurfacing now so I use a diamond crack chasing blade. I didn't have it back then. I then cleaned out the cracks - vacuumed & rinsed with clear water - let them dry and then filled them with a rigid epoxy. I did not do an acid wash as I didn't have the option of high pressure washing the cracks to remove the weakened material that acid washing leaves. Keeping the cracks filled was the most time consuming part as there were places where the epoxy just slowly oozed down - it seemed like forever. Eventually everything filled up. I then used a concrete leveling material to get a nice level surface and tiled over. The second slab we did not level, but we did tile. My preference is to level the floor first. It makes the tile job so much easier. Both jobs evidently were sound as no cracks transferred through the tiles, 8 years later.
NOTE: I do not solicit this type of work. I am not an engineer; however, I did start out in the business with Morrison-Knudsen as a union cement finisher back in 1965 doing repairs on the missile silos in N.D. and then worked with Otto J. Eikhoff (sp?) doing both concrete repairs and new pours. So I've done a wee bit of this type of work over the years. You may want to talk with an engineer to get a professional opinion, especially if you plan on living in the house for any extended period of time after you make the repairs.
Good luck,
Cliff.
*PAUL, The main issue is that it is structural. That the substrate, or ground beneath the concrete, has moved, and the concrete cracked, since it has no tensile strength to speak of.I imagine that their are no control joints in the floor, and as such, the weakest part of the concrete cracked.If it were a hairline crack, this would most likely be due to normal shrinkage, during initial hydration period, following the pour. Especially if their are no, or insufficient, or improperly placed or not deep enough control joints. This scenario you have described will normally allow an overlayment of something like tile, provided idea of a self leveler is used to match the newer elevation. You can only hope the movement does not continue or if it does, at a very slow rate.Sincerely,Brian T. Chaffee
*cliff's repair is just what we have done in the past...we used Abatron's epoxy repair kits..before you proceed , you have to determine if the crack is active or if it has reached equilibrium...one way this is done is to epoxy thin glass like microscope slides across the crack....structural engineers have these kits specially made for this purpose.. but the thin glass will accomplish the same thing....make a reference grid on the glass with a sharpie so you can tell which direction any movement is in..if you come back after a change in season and the glass is intact, the slab is PROBABLY at equilibrium and will not get worse..go ahead and make your repair.. if it is still moving , you have to figure out how to stop it before you should attempt a repair
*Paul:Check these guys out:www.concrete.comwww.eng-tips.com
*Cliff,Brian,Mike and Andy,thanks somuch for your help. i passed the info on to my brother and he is quite appreciative. after looking at the site Andy mentioned he is leaning toward resurfacing and stamping.Cliff, you mentioned a material for patching stucco in another post and he is also looking into it. thanks again.
*About 10 years ago I tiled a 20'x15' concrete slab entry way- the slab had numerous cracks up to 1/8" wide. I did not monitor over time to determine if cracks were active, but assumed there would atleast be seasonal movement as home is located in way north Michigan and entry not well heated. Obviously I was concerned about those cracks telegraphing through new tile so glued down #15 felt (as bond-breaker) to concrete and set quarry tile in thinset directly on felt.No cracks anywhere in tile or grout joints to this date, and I check it every time I visit my parents' home. There are thick membrane materials for use in place of the felt today, but the principle remains the same. Just some thoughts. Randy
*Paul,Glad to be of some help. I know what it's like to think that you are using first rate materials only to find out over time that they are second and third rate materials. Then there is the ensuing frustration that sets in as the "stuff" doesn't live up to the factory rep's. sales pitch and deteriorates prematurely leaving you holding the bag with an irrate customer - not to mention the ensuing loss when you have to go back to "make it right". As for some of the warranties and manufacturers' reps. promises - they are only as good as long as you can catch them, and some of those greasy so-and-so's can run very fast and are very very slippery.Good luck,Cliff.