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Question DetailsAsked on 7/27/2016

we just completed the top portion of the shower pan thats on the liner . It cracked. Can we repair it ?

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You might need to response back with more info if I misunderstood you - using the Answer This Question yellow button right below your question, as if you were answering your own question - that will keep it all in this one "thread".

I infer you mean the mud coat or mortar bed, the porous concrete bed on top of the liner which will then receive the thinset and tile ?

I would certainly consider WHY it cracked - basically (never an absolute rule, is it ?) if the crack(s) are radial - radiating out from the drain, that is shrinkage cracking. If curcumferential (curved or straight segments forming a rough curve) around and outward from the drain or running straight across the bed from side to side, those would likely be settlement cracks, meaning the bed was not properly supported - so probably would mean is on a manufactured fiberglass or plastic liner pan which was not properly supported underneath, or that the subfloor is not strong enough.

If minor radial shrinkage cracks (reason I recommend reinforcing this bed layer), using a thinner mix of thinset or cement and water to fill the cracks to eliminate any gaps should not cause problems - because that layer is supposed to be porous and permeable to drain any leakage through the tile anyway - the reason the liner is under it. Wide cracks of course would be a concern about whether they were settlement cracks from the bed basicallyi "hanging" from the edges at the curb and lip.

Cracks across the bed (paralle to the sides of the shower) or circular around the drain (except right at the drain, where you will get a small shrinkage crack right around it) I would be much more concerned about whether this is indicative of more to come when the shower is in use and has a couple hundred or more additional pounds in it, or if this was due to inadequate subfloor strength.

The inadequate support question is tough to answer - I recommend a seamless sheet of 3/4" or even (if doesn't cause elevation issues) 1" marine plywood under showers and tile baths, because the weight of the mudbed is on the order of the design capacity load of normal flooring - even more in some code areas, and that is without anyone or any standing water in the shower/bath. A full bath is actually a substantial overload in many cases - the reason why in the old days the floor joists were commonly doubled up under them if not supported by an intermediate wall underneath and short-span.

IF you are in doubt, I guess you could put about 500# in there and see if it cracks more - that would be (and distribute it around a bit, not point load) about 8 sacks of sand (60# each usually), 5 sacks of portland cement (usually 94# each), or 12-13 5 gallon pails full of water, or 2-3 people standing in there. Or you might have tile boxes (variable weight, but labelled) you could stack in there. If 500# sitting for several hours does not crack it more, I would guess it was shrinkage cracking. Of course, if there is any vertical offset at the crack (one side higher than the other) then definitely settlement, and I would be starting over on the beds and liner unless you are willing to cross your fingers and hope the liner does not tear or the drain pipe break with the settlement over time.

Answered 3 years ago by LCD

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