Brickman Consulting

Wood Flooring Solutions.

Calculating Shrink/Swell and Why It Matters

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Cross posted from Howard Brickman's article on Hardwood Floors Magazine: Inspector Blog.

Wood shrinks and swells when it loses and gains moisture content (MC). For example, if a piece of 2¼" wide plainsawn red oak flooring were to decrease in MC from 8% to 5%, the net change in MC would be 3%. Using standard values from the Wood Handbook Table 4-3 Shrinkage Values of Domestic Woods, the net change in dimension would be .021" (2.25" x .086 x .03 / .28 = .021"). Expressed as a fraction, .021" would be between 1/64" (.015625") and 1/32" (.03125").

How is this information useful? Let’s take a real-world scenario and show how a quantitative understanding of dimensional change helps us perform an analysis.

SCENARIO:
We look at a wood floor that we installed last year where the customer has called to complain about gaps between boards. As part of our normal procedure, we look at the surface of the floor to see if individual boards are flat, cupped (concave), or crowned (convex). In this case, the boards are still very flat. Then we determine the size, frequency and distribution of the gaps. We note the minimum and maximum gaps, then we eliminate the smallest and largest gaps to describe the range, which characterizes the majority of the gaps (80-90%). In statistics this is referred as “eliminating the outliers." Now we choose several locations where the gapping is the most severe and begin a series of accurate board-width measurements, along with MC of the individual boards. Our results are:

MC of all of the boards is less than 6%. We estimate the MC at 5% based on interior RH for the last three weeks using Wood Handbook Table 4-2 Moisture Content of Wood in Equilibrium With Stated Temperature and Relative Humidity. The widths of individual boards range from 1/64" to 1/32" less than the manufactured width of 2¼". The gaps are located between every board and range in size from 1/64" to 1/32".

Danger! FORMULA ALERT: IF YOU BECOME SHORT OF BREATH, BREAK OUT IN A COLD SWEAT, AND HAVE DILATED PUPILS WHEN YOU READ FORMULAS, please skip this section of the blog. For you brave souls, let’s proceed.

FIRST FORMULA (Change in Dimension)
Δ D (change in dimension) = Manufactured Width x St (Shrinkage factor from Wood Handbook) x Δ MC / .28

SECOND FORMULA (Change in Moisture Content)
Δ MC = [Δ D x .28] / [ Width x St ]

With these two formulas we can:

1 – Predict the amount that a board will swell or shrink (Δ D) and
2 – Estimate the magnitude of change in MC (Δ MC) based on the current width of the board.

IT’S SAFE TO START READING AGAIN. Danger over.

Now it’s time for some SHRINKAGE RULES:

Rule Numero Uno: If a board is less than its manufactured width, it has lost MC since it was manufactured.

Rule Numero Dos: If a board is exactly its manufactured width, it is at the same MC as at the time of manufacture.

Rule Numero Tres: If a board is greater than its manufactured width, it has gained MC since it was manufactured.

Applying Rule Numero Uno, we know that our boards that are smaller than the manufactured width have lost MC. Using the SECOND FORMULA for Δ MC, we can pretty accurately quantify the change in MC.

For boards that are 1/64" narrower than 2¼", the Δ MC is 2.26%:

Δ MC= [Δ D x .28 ] / [ Width x St ] Δ MC= [ 1/64" x .28 ] / [ 2.25" x .086 ] Δ MC= [ .015625" x .28 ] / [ 2.25" x .086 ] Δ MC= [ .004375 ] / [ .1935 ] Δ MC= .0226 = 2.26%

For boards that are 1/32" narrower than 2¼", the MC is 4.52%:

Δ MC= [Δ D x .28 ] / [ Width x St ] Δ MC= [ 1/32" x .28 ] / [ 2.25" x .086 ] Δ MC= [ .03125" x .28 ] / [ 2.25" x .086 ] Δ MC= [ .00875 ] / [ .1935 ] Δ MC= .0452 = 4.52%

If we add the Δ MC to our current 5%, the boards that are 1/64" narrow were originally at 7.26% (5% + 2.26% = 7.26%). The boards that are 1/32" narrow were originally at 9.42% (5% + 4.52% = 9.53%). This allows us to estimate MC at time of manufacture between 7.26% and 9.52%.

I find these quantitative methods to be useful tools when working through the analysis of a wood floor that has evidence of a change (or changes) in MC. In new construction there are frequently several MC changes, starting with the adsorption of excessive moisture from the subfloor, then the eventual drying during the following winter heating season.

Let’s explore how doing all this rigmarole calculating helps with analysis. Let’s change our scenario by a single factor: instead of gaps that range from 1/64" to 1/32", how about gaps that range from 1/32" to 3/64" with individual board shrinkage that ranges from 1/64" to 1/32"? We have already done the calculations on the board shrinkage, but that doesn’t account for the additional size of the gaps. SO… something besides seasonal low interior RH would have to be the cause of the increased size of the gaps. Maybe the flooring was left on the job to “acclimate" and picked up some excessive moisture before it was it was installed? Or… (to be continued)
 

Do You Need An Alibi?

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Cross posted from Howard Brickman's column in Hardwood Floors Magazine: Inspector Blog.

Only a guilty man needs to have an alibi prepared. Well, you are all guilty of being wood floor guys, so let’s get those alibis ready for prime time. And maybe the process of getting those alibis prepped will also provide a framework for preventing the need for an alibi.

Tool/Equipment List:

  • smartphone with camera
  • pin-type moisture meter
  • black Sharpie Marker
  • hammer
  • 6d and 8d finish nails
  • thermohygrometer
  • flashlight
  • spiral notebook
  • pencils and pens
  • string (fluorescent red, blue, green, or yellow)

Stuff To Do (or Not Do):

BEFORE WOOD FLOORING DELIVERY:

  • Do not sign a confession, err, I mean contract provided by the general contractor without carefully reviewing the provisions regarding warranties and terms of payment.
  • Check moisture content (MC) of the subfloor and inspect the crawl space. Use the Sharpie to write the MC readings directly on the subfloor with the date and your initials. Check MC near windows, plumbing, and doors, and by obvious signs of water staining or moisture intrusions. More readings are better. Record the readings in your notebook.
  • Make a label that lists the date, job address, and your name in large block letters for identifying pictures.
  • Take pictures of the high-MC readings with your smartphone. It will automatically time, date, and location-stamp the individual photos.
  • Take pictures of other non-compliant issues (e.g., missing windows or doors, tile saws on subfloor, unvented torpedo gas/kerosene heaters, etc.)
  • Check MC of joists and subfloor in basement and crawl space. Look for water, mold, and mildew, and take pictures.
  • Politely request that the GC or building owner correct any problems noted in a brief and concise e-mail (or using another method that documents the content and delivery of the request).

AFTER WOOD FLOORING DELIVERY:

  • Check subfloor MC again and verify the any problems observed during previous visits were corrected. If not, document them again.
  • Check wood flooring MC on at least 40 boards. Use the Sharpie to write MC and date on the back of boards. Record the readings in your notebook. Reject the flooring if it is outside the range from 6% to 9% MC.

BEFORE INSTALLING THE FLOORING:

  • Verify that you document everything that could negatively impact the wood floor. Use the list from the NWFA Installation Guidelines (the PDF is available free online for all NWFA members).
  • Communicate one last time to the GC if there are any issues. This is the point at which you need to present your disclaimer or waiver document for the GC to sign or at least acknowledge. This can be a delicate time in the job. You may want to tread lightly, because there is a fine line between being a concerned wood floor professional and being a pain in the neck who aggravates everyone else on the job, especially the GC. You know the deal. There are 10 flooring guys waiting on the sidewalk to come in and do the work without even “noticing” the all of the potential problems.
  • If you are called to help out a GC at the “last minute,” take a deep breath and try to figure out why the other floor guy that has been doing his work for the past three years is not available. Is there a money issue? Or what?
  • If you are installing a nail-down solid floor, there are some critical steps that help to inoculate you from problems during an inspection: 1) fasteners every 6”; 2) #15 asphalt-saturated felt; 3) Expansion space around the perimeter of the floor.

The typical inspector will check MC, expansion space, nailing, and will want to see your documentation. If you have done due diligence with your prep work, the chances of a job going South are greatly reduced. If it goes South, you should be certain that a really qualified person performs the inspection. The same qualities that make you a competent craftsman apply to the inspection craft: experience in the wood floor craft, experience in performing inspections, referrals from really knowledgeable people in the industry, and the proper temperament to stand up to the pressure from all of the associated parties. In addition to doing everything right, you have to be able to prove that you did everything right. Here’s to hoping that you never need that alibi. Good fortune favors the well prepared.

Ignorance, like Mr. Know-It-All

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Cross posted from Howard Brickman's article on Hardwood Floors Magazine: Inspector Blog.

Do you remember “Mr. Know It All” from “Rocky and Bullwinkle”? Bullwinkle would make some ridiculous remark that was completely wrong, but he said it with ultimate self-confidence and an assertive manner.

Do you know any “Mr. Know It Alls”? You know the type. They use their self-confidence and an assertive manner to bluff their way through every situation. The customers don’t know enough about the wood floor business to know if they are being given the straight scoop… or not. As long as everything goes as planned, the misinformation doesn’t seem to do any harm.

But let’s think about another approach that transforms Mr. Know-It-All into Mr. Knows-It-All. Think about how effective it would be to combine self-confidence and an assertive manner with actually knowing what you are talking about. This is done with some hard work by learning the important fundamentals. It starts by learning the technical vocabulary of 300 words… Learning how to properly spell and pronounce the words and their definitions… Then reading and reading and reading…

“The man who does not read good books has no advantage over the man who can't read them.” — Mark Twain. It’s a little late to be handing out a summer reading list, but here are some good books to put on your recommended reading list.

– Wood Handbook, published by the Forest Products Laboratory (PDFs of the chapters are available free here.)
– Drying Eastern Hardwood Lumber by John M. McMillen and Eugene M. Wengert (also available free on the Forest Product Laboratory website)
– Understanding Wood by Bruce Hoadley (Taunton Press)
– Identifying Wood by Bruce Hoadley (Taunton Press)

E-mail me when you get through these and need some more titles. Don’t get discouraged. Google the words that you don’t understand, or use a dictionary. I think that we still have dictionaries in the 21st century. I have been reading and rereading these and other books for over 30 years, and you never seem to really “Know-It-All”.

Are You Whimpering?

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Cross posted from Howard Brickman's article on Hardwood Floors Magazine: Inspector Blog.

“Sir, we clocked you installing a wood floor on a high moisture content subfloor. May I see your documentation on moisture content of the subfloor?”

You whimper, “But officer, it looked dry to me.”

This is the wood floor guy equivalent of getting bagged with the radar gun going 50 in the 30 mph speed zone. So, how do you protect yourself? Get a radar detector. It’s called a moisture meter. Here are the step by step instructions.

-Buy a proper moisture meter.
-Use the moisture meter.
-Learn how to take the right amount of moisture tests.
-Learn how to properly use your proper moisture meter.
-Take your proper moisture meter everywhere you go.

Now let’s break it down.

– Buy a proper moisture meter: I use the Delmhorst J-4 or BD-10 electrical resistance (pin type) meters and also keep a Moisture Content Standard (also sold by Delmhorst) to check the meter for accuracy every time I use it. I am not familiar with all of the other moisture meters currently available. And Mom used to say if you can’t say something nice, then don’t say anything.

– Use the moisture meter: Check every place where there could possibly be some excessive moisture, including near exterior doors and windows, plumbing, tile wet saw, masonry and plaster mixing locations. It is not the average of the MC readings that damages flooring, it is high MC locations. Your options are to dry or replace the wet subfloor.

– Learn how to take the right amount of moisture tests. You can probably stop when you get to 50 tests in 1500’. Even on small jobs you should take at least 15 readings. Another hint: Write the date, MC, and your initials on the subfloor with a black Sharpie. Test the flooring on the bottom face and also write the test results on the pieces of flooring. If the floor has to be replaced you will have the documentation there for the world to see. It is also a great idea to record these MC readings on the work order or flooring delivery ticket or other job related paperwork that can be tucked away in the job file.

– Learn how to properly use your proper moisture meter: What does the MC number mean? Learn what “normal” MC in subflooring and flooring is for your part of the world during different times of the year by testing existing houses. Get in the habit of constantly checking your own house. Push those pins to the full ¼”/ 5/16” depth and orient the pins with the longitudinal axis of the grain (with the grain). And what does variance of the number mean? If the MC varies by more than 1% there is something changing in the building. The greater the variance, the more substantial the changes that are in progress.

– Take your proper moisture meter everywhere you go. Please…. Pretty please with sugar on it…

The best source for information on moisture meters is our friends at the Forest Products Laboratory. One of my favorites is FPL-08 Electric Moisture Meters for Wood by William James. And you can download a copy from the FPL web site.

And remember the magic words: shrink and swell.