Rule #1 For Foundation Performance: Proper Hydration

December 9, 2014

Rule #1 of foundation performance is to maintain consistent hydration to the soil around and below the slab foundation. This means the plumbing drains need to be checked for leaks, every 5-10 years minimum and especially each time a house is purchased. Rule #2 of foundation maintenance is to refer to rule #1.

Today, I want to share images of the evolution of a plumbing leak.

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Here, a slab foundation is formed up on a sloped lot. (Same system on a flat lot, just less form board height needed).

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Back fill is brought in to minimize the amount of concrete needed to make the slab. Bags of sand/dirt hold up the fill so the concrete beams or structure of the slab are resting on original soils. Plumbing drain lines are installed, supported by the fill dirt.

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The pipes are now resting on poor long term support and really should be suspended from the poured concrete above with stainless steel hanging brackets. Installing drain pipes without hangers is 100% typical and normal but also is a poor practice as the fill dirt will move independently of the slab. This system has the pipes under tension causing failure.

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After the plumbing is installed, a plastic moisture barrier is installed and then the structural components are installed. In this case, the structure is post tension cables and re-bar. Next the concrete will be placed to complete the slab foundation.

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Soil supporting the pipes settles over time and the pipe joints separate because the horizontal runs of the pipes are too heavy for the vertical connections to stayed glued. Note: Rarely does the PVC pipes break in the pipe runs. Typically it is the joints that disconnect. This picture is the bath tub fixture that disconnected, but also the toilet and sink in this bathroom disconnected too. Another point to note is that once a slow leak occurs at one fixture, it helps compact the fill dirt causing more stress on the connective joints of other fixtures which causes more leaks.

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This is a great photo of the typical situation of the “slab-on-grade” actually not sitting on the fill dirt. The structural beams of the home are supporting the slab sections between the structural beams, not the fill dirt. The design engineer knew the fill was not going to be supporting the concrete long term that is why he approved the foundation plan. Too bad most engineers do not consider how the plumbing is supported.

Most every slab foundation we work on is performing identical to this slab.The fortunate thing for this home owner is the structural beams are resting on surface bedrock as this home is in the hill country. If this home was built on expansive clay soil with little or no bedrock, the foundation may have failed too and would need repairs that could cost additional thousands of dollars, not to mention all the sheet rock and cosmetic finishes of the home that would have failed.

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This is the floor plan of the home highlighting the tunnel it took to access the drain lines. All the new repaired pipes are now connected to the slab with stainless steel hangers for long term support and performance. Note: cost of repairs: $26,000.00

Remember, rule #1 of foundation performance is to maintain consistent hydration to the soil around and below the slab foundation. Remember to check the plumbing outflow from your home needs to be checked for leaks every 5-10 years minimum and especially each time a house is purchased.

What’s rule #2 of foundation maintenance?

Easy. ALWAYS refer to rule #1.