# 64144

**URL:** <https://community.blackspectacles.com/t/topic/7934>\
**Category:** Project Planning & Design\
**Tags:** help\
**Created:** [October 14, 2026, 4:28am UTC](https://community.blackspectacles.com/t/topic/7934 "2026-10-14T04:28:07Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![xinruizhang](https://blackspectacles.com/uploads/images/8.png) [@xinruizhang](https://community.blackspectacles.com/u/xinruizhang)\
**Post date:** [October 14, 2026, 4:28am UTC](https://community.blackspectacles.com/t/topic/7934/1 "2026-10-14T04:28:07Z")

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question 64144 in PPD exam 1,

Can some explain why “Backfilling the excavation with limestone” is not correct?

I was thinking the voids between the stones will help with the hydrostatic pressure.

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**Author:** ![charles.broomfield](https://yyz1.discourse-cdn.com/flex029/user_avatar/community.blackspectacles.com/charles.broomfield/32/1959_2.png) [@charles.broomfield](https://community.blackspectacles.com/u/charles.broomfield)\
**Post date:** [October 14, 2026, 8:01pm UTC](https://community.blackspectacles.com/t/topic/7934/2 "2026-10-14T20:01:43Z")

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Hi @xinruizhang, thanks for the great question! I checked with Chris Hopstock, our architect, and here’s his take:

Filling with limestone backfill isn’t one of the best 3 options here for creating a waterproof basement because a drain tile, moisture barrier, and gravel beneath the foundation pour are all more effective and common practices. Limestone is not a common backfill material, and may be an expensive option depending on local conditions.

Thanks again for contributing to our community and good luck on PPD!

Charles Broomfield  
Community Manager  
**[Black Spectacles](https://www.blackspectacles.com/en-us/)**