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RE: Slab floor damage

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I would suggest that he client hire a geotechnical company first to rule out soil problems such as roots or voids formed from broken plumbing lines. Your comment about 1-inch elevation changes on the crack concerns me that there is something below grade causing the problem and before you can address he slab, you need to find out what is happening below the slab.

As Scott Maxwell would say – concrete cracks. There are usually cracks in slabs on grade because builders really don’t take the care necessary to keep the concrete moist as it cures to prevent temperature cracking. Therefore, if we eliminate geotechnical problems then the issue is how to prevent the cracks from radiating through the hard surface floor.

I’ve always used a Pascoe Membrane over all cracks which will absorb the expansion and contraction of the slab so that the crack will not radiate to the tile or hard floor. A contactor recently told me of a roll on product called C-Cure ( which is much less expensive than the Pascoe membrane. Essentially the C-cure product is a roll on Elastomeric sealant on the slab that the tile attaches to. It is thick enough and expands sufficiently to absorb the slab movement.

Builders used to use the Blue builders paper that was commonly used below stucco, but the problem is that the thinset adhesives bleed through this and the tile is not able to float or move over the slab (like a slip sheet). Crack prevention membranes or the products like C-Cure do the job really well.

I used the Pascoe membrane on all cracks in my home which is about 2100 square feet of Saltillo pavers. Not one crack has radiated through the Pavers in 8 years since we laid the tiles.

I believe in these products and include the spec in my general notes or on my foundation plan to make sure that if the client decides to use a hard surface floor material he/she will be forewarned that there are products that will minimize cracks from radiating through the slab.


Best Regards,


From: ENGRLAINES(--nospam--at) [mailto:ENGRLAINES(--nospam--at)]
Sent: Thursday, June 22, 2006 1:06 PM
To: seaint(--nospam--at)
Subject: Slab floor damage


40-year old single story house w/ 4" slab-on-grade foundation/floor, most likely cut and fill pad, water seepage in nearby street but not under house, trees in side yards. Floor tiles cracked (tight cracks) and buckled approximately 1-inch high near the edge of the floor (but not at the edge) in a 5-foot line perpendicular to cut/fill line and to base of slope. No damage to plaster walls, ceilings. Moderate temperatures (Los Angeles). No recent shaking (construction, earthquakes). Wha’s up?

Charles Laine, S.E.

Long Beach, CA