Course outline
Floor flatness and prep: qualifying the substrate you'll accept
Resilient flooring and tile need a flat substrate, and manufacturers publish the maximum deviation they allow over a given distance — large-format tile and LVT are especially sensitive. Concrete is usually specified and measured differently, with F-numbers under ASTM E1155, so a slab can meet its own spec and still be too rough for your floor. Price a stated amount of prep, state the tolerance it assumes, and put anything beyond it on a unit price.
By Michael Reddy, IntelBid
After this lesson you can
- Explain the gap between concrete flatness specs and flooring tolerances
- Recognize the substrate conditions that need preparation
- Qualify prep so work beyond your allowance is paid
Why can a “flat” slab still be a problem?
| Concrete specification | Flooring manufacturer | |
|---|---|---|
| Typical measure | F-numbers (FF for flatness, FL for levelness) per ASTM E1155 | Maximum deviation over a distance, checked with a straightedge |
| When it's measured | Usually soon after the slab is placed | When you're ready to install |
| What it describes | Statistical flatness across the whole floor | Local dips and humps your floor will show |
A slab can pass its F-number requirement overall and still have local dips and humps outside the flooring tolerance — and slabs can change after placement as they cure and other trades work on them. That's the gap your qualification has to cover.
What prep conditions should you plan for?
| Condition | Typical fix | How to price it |
|---|---|---|
| High spots and humps | Grinding | Unit price per SF |
| Low spots and dips | Patching or self-leveling underlayment | Included amount plus unit price |
| Cracks and control joints | Fill non-moving cracks; honor moving joints | LF, or included within limits |
| Curing compounds, sealers, paint | Removal by grinding or chemical methods | Excluded or unit price |
| Old adhesive residue | Scraping or grinding | Unit price, or in removal scope |
| Contamination (oil, grease) | Cleaning or grinding | Excluded or unit price |
Sample prep qualification
“Price includes floor preparation limited to patching and skim-coating up to 5% of the floor area and filling of non-moving cracks. Price assumes the substrate is within the flooring manufacturer's published flatness tolerance and is free of curing compounds, sealers, coatings and contaminants. Grinding, self-leveling underlayment beyond areas shown, and removal of compounds, sealers or coatings are excluded and available at the unit prices listed.”
— Example to adapt — set your own limits
Inspect before you install
Many specs say that starting installation means you accept the substrate. Before installing in each area, inspect it, and give the GC written notice of unacceptable conditions — with photos and locations — while it's still their problem to fix or pay for.
Who is responsible for leveling a floor before flooring installation?
It depends on the contract. Specs often put preparation on the flooring contractor, so state in your proposal how much prep is included and price additional leveling or grinding as unit prices.
What are FF and FL numbers?
F-numbers measured under ASTM E1155 describe concrete floor flatness (FF) and levelness (FL) statistically across a floor. They don't guarantee a slab meets a flooring manufacturer's local flatness tolerance.
Does installing flooring mean accepting the substrate?
Many specifications say so. Inspect each area before installing and give written notice of unacceptable conditions first.
Key points
- A slab can meet its concrete spec and still fail your flooring tolerance.
- Include a stated amount of prep; price the rest as unit prices.
- Inspect and give written notice before installing.
Prep that's visible on the proposal
Add floor prep, grinding and self-leveling underlayment as their own lines with units and prices — or as Add alt lines — and state the included amount in a note on the proposal, so what's covered and what costs extra is clear on the proposal the GC levels.
Try it in IntelBidA 2-minute guided tour on a sample project — nothing touches real data. New to IntelBid? You'll start a free trial first.
Get new lessons, plus $100 toward IntelBid
New modules as they're published. Confirm your email and we'll send a $100 credit toward your IntelBid membership.
About the author. Michael Reddy builds IntelBid, bid management software for commercial flooring subcontractors. These lessons come from the bid desk: how the work is priced, won and paid for.