FHB Logo Facebook LinkedIn Email Pinterest Twitter X Instagram Tiktok YouTube Plus Icon Close Icon Navigation Search Icon Navigation Search Icon Arrow Down Icon Video Guide Icon Article Guide Icon Modal Close Icon Guide Search Icon Skip to content
Subscribe
Log In
  • How-To
  • Design
  • Tools & Materials
  • Restoration
  • Videos
  • Blogs
  • Forum
  • Magazine
  • Members
  • FHB House
  • Podcast
Log In

Discussion Forum

Discussion Forum

why sand under concrete?

| Posted in General Discussion on August 18, 2004 09:23am

I’m preparing to pour a finish concrete foor, slab on grade. The structural plans call for 4″ compacted gravel base, insul-tarp vapor barrier, 2″ of sand and 4″ of concrete. What purpose other than a base for the concrete does the sand serve? Why use it when yopu have thick insul-tarp?

Reply
  • X
  • facebook
  • linkedin
  • pinterest
  • email
  • add to favorites Log in or Sign up to save your favorite articles

Replies

  1. brownbagg | Aug 18, 2004 09:53pm | #1

    its a local decision, some people use the sand so water will migrate under the concrete, some for freeze protection, here we do not use sand. Nothing wrong with it, just not needed here.

  2. User avater
    CapnMac | Aug 18, 2004 10:17pm | #2

    What purpose other than a base for the concrete does the sand serve?

    In the dark ages (before the internet, CDs & the like), I was taught that you used sand because is has a fine grain which meant it could be shaped precisely.  This better let a person control things like concrete thickness, which controls volume, etc.  Also, sand has "engineering" qualities like known compression, etc. which vary less between jobs.

    Or, in the field:  "Ya kin pour over dirt, but dirt ain't even; an' dirt ain't the same everys place." <g>

    Occupational hazard of my occupation not being around (sorry Bubba)
    1. sungod | Aug 19, 2004 07:28am | #6

      Here in Southern Calif. where there is hard clay dirt, sand will give tree roots a easy time, so it can pop up the patio or sidewalk.

      Sand on top of visqueen help remove the water in concrete so it sets faster.

      Sand does provide a homogeneous surface so the concrete will cure evenly (not crack).

  3. User avater
    BillHartmann | Aug 18, 2004 10:43pm | #3

    http://www.buildingscience.com/resources/foundations/sand_layer_under_slab.htm

    1. User avater
      CapnMac | Aug 19, 2004 12:49am | #4

      I'm glad you posted that link--I don't believe I've ever seen anyone visqueen under the sand base before.  Now, I've got printed reasons to "not to."Occupational hazard of my occupation not being around (sorry Bubba)

  4. remodelerdw | Aug 19, 2004 06:11am | #5

    We commonly use pea fill here, sand is rare for concrete work.  Primarily because pea-fill is self compacting and sand has to be jetted or it will settle unevely.  Run a hammer across concrete poured on sand after a year and you'll hear the hollows.

    reodeler

  5. fredsmart48 | Aug 19, 2004 08:18am | #7

    My understand and the big reason for the sand between the plastic and concrete is so concrete company can get by with a 5 or 6 inch slump instead of 3 inch slump. That is so they don’t need to hire 2 or 3 or 5 extra people to move the concrete when it just sits in one spot after it is placed and won’t self level.

    And Why is that a problem? As I am told with the plastic directly under ninth the concrete all the water in a 5 inch slump has to go up and as it moves up and sits on top of the concrete to evaporate you get separation in the concrete because the water sits on top of it to long. The concrete will not get to be the strongest it could be.

    1. brownbagg | Aug 19, 2004 01:34pm | #8

      it will also make the slab crack

  6. dIrishInMe | Aug 19, 2004 02:15pm | #9

    Just out of curiosity, what location is the slab to be in... Garage? basement? driveway? comercial building? etc?  

      

    Matt
    1. Rojoho | Aug 19, 2004 10:24pm | #10

      We're talking about1500 sq.ft. of ground level residental with radiant heating, two story victorian near San Francisco.

      By the way, Insul-tarp specifies "optional" granular fill on the insul-tarp, which is on 6" - 8" open drain rock. I plan to mechanically compact the rock base.

Log in or create an account to post a comment.

Sign up Log in

Become a member and get full access to FineHomebuilding.com

Video Shorts

Categories

  • Business
  • Code Questions
  • Construction Techniques
  • Energy, Heating & Insulation
  • General Discussion
  • Help/Work Wanted
  • Photo Gallery
  • Reader Classified
  • Tools for Home Building

Discussion Forum

Recent Posts and Replies

  • |
  • |
  • |
  • |
  • |
  • |
View More Create Post

Up Next

Video Shorts

Featured Story

FHB Summit 2025 — Design, Build, Business

Join some of the most experienced and recognized building professionals for two days of presentations, panel discussions, networking, and more.

Featured Video

How to Install Exterior Window Trim

Learn how to measure, cut, and build window casing made of cellular PVC, solid wood, poly-ash boards, or any common molding material. Plus, get tips for a clean and solid installation.

Related Stories

  • Podcast Episode 686: Brick Steps, Ground-Source Heat Pumps, and Greenhouses in Nova Scotia
  • FHB Podcast Segment: Efficient HVAC for a New Build
  • Affordable Scans, Accurate Plans
  • FHB Summit 2025 — Design, Build, Business

Highlights

Fine Homebuilding All Access
Fine Homebuilding Podcast
Tool Tech
Plus, get an extra 20% off with code GIFT20

"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Fine Homebuilding Magazine

  • Issue 331 - June 2025
    • A More Resilient Roof
    • Tool Test: You Need a Drywall Sander
    • Ducted vs. Ductless Heat Pumps
  • Issue 330 - April/May 2025
    • Deck Details for Durability
    • FAQs on HPWHs
    • 10 Tips for a Long-Lasting Paint Job
  • Issue 329 - Feb/Mar 2025
    • Smart Foundation for a Small Addition
    • A Kominka Comes West
    • Making Small Kitchens Work
  • Issue 328 - Dec/Jan 2024
    • How a Pro Replaces Columns
    • Passive House 3.0
    • Tool Test: Compact Line Lasers
  • Issue 327 - November 2024
    • Repairing Damaged Walls and Ceilings
    • Plumbing Protection
    • Talking Shop

Fine Home Building

Newsletter Sign-up

  • Fine Homebuilding

    Home building tips, offers, and expert advice in your inbox.

  • Green Building Advisor

    Building science and energy efficiency advice, plus special offers, in your inbox.

  • Old House Journal

    Repair, renovation, and restoration tips, plus special offers, in your inbox.

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters

Follow

  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X
  • Fine Homebuilding

    Dig into cutting-edge approaches and decades of proven solutions with total access to our experts and tradespeople.

    Start Free Trial Now
    • Facebook
    • Instagram
    • X
    • LinkedIn
  • GBA Prime

    Get instant access to the latest developments in green building, research, and reports from the field.

    Start Free Trial Now
    • Facebook
    • YouTube
  • Old House Journal

    Learn how to restore, repair, update, and decorate your home.

    Subscribe Now
    • Facebook
    • Instagram
    • X

Membership & Magazine

  • Online Archive
  • Start Free Trial
  • Magazine Subscription
  • Magazine Renewal
  • Gift a Subscription
  • Customer Support
  • Privacy Preferences
  • About
  • Contact
  • Advertise
  • Careers
  • Terms of Use
  • Site Map
  • Do not sell or share my information
  • Privacy Policy
  • Accessibility
  • California Privacy Rights

© 2025 Active Interest Media. All rights reserved.

Fine Homebuilding receives a commission for items purchased through links on this site, including Amazon Associates and other affiliate advertising programs.

  • Home Group
  • Antique Trader
  • Arts & Crafts Homes
  • Bank Note Reporter
  • Cabin Life
  • Cuisine at Home
  • Fine Gardening
  • Fine Woodworking
  • Green Building Advisor
  • Garden Gate
  • Horticulture
  • Keep Craft Alive
  • Log Home Living
  • Military Trader/Vehicles
  • Numismatic News
  • Numismaster
  • Old Cars Weekly
  • Old House Journal
  • Period Homes
  • Popular Woodworking
  • Script
  • ShopNotes
  • Sports Collectors Digest
  • Threads
  • Timber Home Living
  • Traditional Building
  • Woodsmith
  • World Coin News
  • Writer's Digest
Active Interest Media logo
X
X
This is a dialog window which overlays the main content of the page. The modal window is a 'site map' of the most critical areas of the site. Pressing the Escape (ESC) button will close the modal and bring you back to where you were on the page.

Main Menu

  • How-To
  • Design
  • Tools & Materials
  • Video
  • Blogs
  • Forum
  • Project Guides
  • Reader Projects
  • Magazine
  • Members
  • FHB House

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Podcasts

  • FHB Podcast
  • ProTalk

Webinars

  • Upcoming and On-Demand

Popular Topics

  • Kitchens
  • Business
  • Bedrooms
  • Roofs
  • Architecture and Design
  • Green Building
  • Decks
  • Framing
  • Safety
  • Remodeling
  • Bathrooms
  • Windows
  • Tilework
  • Ceilings
  • HVAC

Magazine

  • Current Issue
  • Past Issues
  • Magazine Index
  • Subscribe
  • Online Archive
  • Author Guidelines

All Access

  • Member Home
  • Start Free Trial
  • Gift Membership

Online Learning

  • Courses
  • Project Guides
  • Reader Projects
  • Podcast

More

  • FHB Ambassadors
  • FHB House
  • Customer Support

Account

  • Log In
  • Join

Newsletter

Get home building tips, offers, and expert advice in your inbox

Signing you up...

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
See all newsletters
See all newsletters

Follow

  • X
  • YouTube
  • instagram
  • facebook
  • pinterest
  • Tiktok

Join All Access

Become a member and get instant access to thousands of videos, how-tos, tool reviews, and design features.

Start Your Free Trial

Subscribe

FHB Magazine

Start your subscription today and save up to 70%

Subscribe

Enjoy unlimited access to Fine Homebuilding. Join Now

Already a member? Log in

We hope you’ve enjoyed your free articles. To keep reading, become a member today.

Get complete site access to expert advice, how-to videos, Code Check, and more, plus the print magazine.

Start your FREE trial

Already a member? Log in

Privacy Policy Update

We use cookies, pixels, script and other tracking technologies to analyze and improve our service, to improve and personalize content, and for advertising to you. We also share information about your use of our site with third-party social media, advertising and analytics partners. You can view our Privacy Policy here and our Terms of Use here.

Cookies

Analytics

These cookies help us track site metrics to improve our sites and provide a better user experience.

Advertising/Social Media

These cookies are used to serve advertisements aligned with your interests.

Essential

These cookies are required to provide basic functions like page navigation and access to secure areas of the website.

Delete My Data

Delete all cookies and associated data