Soil pipe deposit.

In our bathroom, the loo is against an internal wall and discharges into a near horizontal 110mm soil pipe run (2.5degree fall) about 2.5 metres long before joining the top of a vertical soil stack via a bend fitted with an inspection/rodding point.
I had a quick look in the other day (for the first time) and saw that the bottom of the horizontal pipe has about 20mm thick deposit, not soft, shit like stuff but a hard crusty layer which I can chip away, a bit like a weak mortar bed. Clearly any lack of smoothness in this run will slow down the flow and allow it to build up. I seem to recall reading about self cleaning velocities in pipes carrying mixed liquids and solids and it sounds logical.
I got a 1m steel rod and hammer to it but that was as far as I could reach.
We do have fairly hard water so is this likely to be some form of horizontal stalactite / stalagmite being formed over the 30 years since installation?
Having chipped it away, I can't provide a photo of course. DOH!
I wonder about fitting a temporary plug where it joins the stack and pouring brick acid down the loo to dissolve the rest over night>
Any thoughts?
TIA
Bob
PS It is not a viable proposition to re-plumb to get rid of the horizontal run and it still works after 30 years
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On 11/07/2016 2:05 PM, Bob Minchin wrote:

From my experience of washing my potholing gear in the bath, yes, it is like to be calcium based. Hard as rock! The plumber said he had never seen the likes of it before in all his experiences and wondered what it was. And, I now knowing why the U-bend was blocked, didn't explain it to him.
Besides, 'hard as shit' has credibility.
As an aside, there was a few places where people would spike an object into a mountain stream in order to calcite it. I believe it didn't take too long. In my early months of pot-holing I wore a heavy wool jumper. This would aften stiffen up if left too long in the drying process.
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And the erst. Did this once years ago. Probably spent more time and acid than a new toilet would have cost me
It does work. Acid, chip, flush, acid, chip,flush...
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On Monday, 11 July 2016 14:05:45 UTC+1, Bob Minchin wrote:

Lime. Mechanical action/turbulence causes it to be deposited. Chip it out & then clean the pan regularly with Harpic or similar.
When I removed the WC from my present house, the outlet pipe was half filled (a D shape0 with lime.
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On 11/07/2016 5:20 PM, harry wrote:

If it is a PVC pipe, small sharp shocks may bring it undone?
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On 11/07/2016 14:05, Bob Minchin wrote:

I've lost the plot here. The toilet runs away okay and has done so for 30 years. So, why are you bothering?
You can get Harpic in a black bottle that has extra acid in it. We use that, and our toilets are nice and clean. I imagine our pipes have marginally less scale too.
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GB wrote:

Our toilet is also squeaky clean but the pipe isn't. It is called preventative maintenance
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On 11/07/2016 20:42, Bob Minchin wrote:

My point is that you do not really know: a) Whether the scale layer is increasing, and b) If so, how long it will take to cause a problem.
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