Flooring Joint Profiles

      Is it okay to saw strip flooring with a flat shoulder joint instead of a V groove? June 4, 2012

Iím preparing to do some alder tongue and groove, 3/4" thick by approximately 4" wide, and the customer wants to change the typical "v" groove to a 1/16" square reveal. They want a thin tight line. I am extremely concerned about expansion and the contractor taking that 1/16" from 0" to 1/8", and/or the alder buckling. What is the movement of alder solid in a building once HVAC is going and the wood is properly sealed both sides?

Forum Responses
(Architectural Woodworking Forum)
From contributor J:
It depends on how stable the humidity is, but each 4" board is likely to move 1/32" or less over a typical season, which shouldn't be a big problem. You're more likely to get into trouble if the wood is excessively wet or dry at install time, so acclimate carefully. It won't be easy to hold an even 1/16" gap over long joints.

From Carl Hagstrom, Systems Administrator at WOODWEB
You can use the WOODWEB wood shrinkage calculator to accurately predict the movement. Keep in mind that wood movement is controlled by a number of factors: change in humidity, species, and grain orientation. Typical assumptions for "in place" moisture content (MC) changes is 5% (from the drier heated winter environment to the more humid summer environment). Assuming that you'll have some flat sawn material, four inch wide alder boards will change 1/16th of an inch when the MC changes 5% (from 6% to 11%).

However, if you measure the MC of the wood when you install it (and you should definitely have a moisture meter and be using it), and the MC is 7.5%, then the boards will shrink 1/32 of an inch when they acclimate at 6%, or expand 1/32 of an inch when they acclimate to the higher MC of 11% in the summer.

Of course, if there is climate control year round that maintains a constant humidity, then the boards won't move at all. As appealing as that sounds, though, it's important to keep in mind that all it would take is a week or two of a malfunctioning humidifier to create movement.

As Contributor J mentions, the most important aspect is the MC of the material at installation (and maybe the client's perception of what is visually acceptable regarding movement). A link to the calculator is below - hope this helps.

WOODWEB's Wood Shrinkage Calculator

From contributor S:
You didn't actually say you were using this for flooring, so I am going to assume you are. If you do a square reveal you are making a flat bottom channel, which dirt will pack into. Even sweeping will not always get all the dirt out. The "V" groove doesn't allow for the dust, etc. to get trapped, making it a little easier to clean.

From Gene Wengert, forum technical advisor:
Carl has indeed given you the correct info. Consider that the floor (if it is a floor) is about 20 feet wide and you have flatsawn alder. Further, if we assume that in the wintertime the EMC conditions about be 6.0% EMC (30% RH) and in the summertime about 9% EMC (50% RH), then the alder will change 3% MC seasonally. This is about 0.7% movement or for a 2" wide piece, 0.014" movement.

So, in the wintertime, you will have a crack between each piece of 0.014. Actually, what will happen is that three pieces or more will stick together, so the crack will be every third piece and will be 0.042" which is over 1/32". Now, if the floor has a stain to it, when the crack develops, you might see a white, unfinished area. Then as mentioned, if you get some dirt in it, then in the summertime it will not close and the next winter it might even be a bit wider. (Note that I assumed 30% Rh to 50% RH. It could be drier at times and wetter at times, which would just make things worse.)

I would be remiss if I did not mention that alder is not a good flooring material as it is quite soft. So maybe this is for a wall. If so, things may be even worse, as the cracks will be right at eye level. Is there any chance that you could edge glue the pieces together and then let the entire section float? The change in size could be covered with appropriate molding.

Note that wood can never be sealed well enough to prevent the moisture changes seasonally. An excellent vapor sealer (rare) will act as a buffer for extreme, short term conditions.

It is also important to understand that it will take perhaps four weeks for properly KD alder to adjust itself to the house's RH, once the HVAC is turned on and all the dry wall and paint is dry and concrete dry. For some reason, some folks think a few days will do the trick. I wish that wood dried that fast. We would not need lumber dry kilns.

Would you like to add information to this article?
Interested in writing or submitting an article?
Have a question about this article?

Have you reviewed the related Knowledge Base areas below?
  • KnowledgeBase: Knowledge Base

  • KnowledgeBase: Architectural Millwork

  • KnowledgeBase: Architectural Millwork: Flooring

    Would you like to add information to this article? ... Click Here

    If you have a question regarding a Knowledge Base article, your best chance at uncovering an answer is to search the entire Knowledge Base for related articles or to post your question at the appropriate WOODWEB Forum. Before posting your message, be sure to
    review our Forum Guidelines.

    Questions entered in the Knowledge Base Article comment form will not generate responses! A list of WOODWEB Forums can be found at WOODWEB's Site Map.

    When you post your question at the Forum, be sure to include references to the Knowledge Base article that inspired your question. The more information you provide with your question, the better your chances are of receiving responses.

    Return to beginning of article.

    Refer a Friend || Read This Important Information || Site Map || Privacy Policy || Site User Agreement

    Letters, questions or comments? E-Mail us and let us know what you think. Be sure to review our Frequently Asked Questions page.

    Contact us to discuss advertising or to report problems with this site.

    To report a problem, send an e-mail to our Webmaster

    Copyright © 1996-2020 - WOODWEB ® Inc.
    All rights reserved. No part of this publication may be reproduced in any manner without permission of the Editor.
    Review WOODWEB's Copyright Policy.

    The editors, writers, and staff at WOODWEB try to promote safe practices. What is safe for one woodworker under certain conditions may not be safe for others in different circumstances. Readers should undertake the use of materials and methods discussed at WOODWEB after considerate evaluation, and at their own risk.

    WOODWEB, Inc.
    335 Bedell Road
    Montrose, PA 18801

    Contact WOODWEB

  • WOODWEB - the leading resource for professional woodworkers

      Home » Knowledge Base » Knowledge Base Article