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Water Polyurethane Cause Warping?

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  • Water Polyurethane Cause Warping?

    Hi all
    I finished a table top with water based poly and it almost immediately turned convex on the top that was finished. After flattening and finishing the other side, I again applied poly and the exact same thing happened on the other side.
    The only conclusion I can come to is that the water based poly caused this. Is this possible/ common?
    The wood is approximately 9 percent and has been in the same environment for many weeks.

    Thanks
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  • #2

    Re: Water Polyurethane Cause Warping?

    How thick is the top? Seems unlikely a finish would cause that if the top is a reasonable thickness.

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    • #3

      Re: Water Polyurethane Cause Warping?

      1.5" maple

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      • #4

        Re: Water Polyurethane Cause Warping?

        What poly are you using?
        What temperature are you applying it?

        I think its highly unlikely that water based poly would cause warping if the wood was dry and stable.
        My guess would be inherent stress in the wood since you have 9 percent moisture.

        How long did it sit after it was cut/jointed/planed etc?

        Do you have a pic of the cupping?

        Nathan

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        • #5

          Re: Water Polyurethane Cause Warping?

          The same thing happened to me several years back when I was spraying a 5/8" thick cherry coffee table top outside on a hot, humid August day. The way I got it back to flattish was to lay the unsprayed side on the grass to let it soak up some moisture from the ground. It didn't flatten out perfectly but it was back to within 1/8" and after spraying the top side and screwing to the table frame it all flattened out perfectly in the end. The moral of this story is to suggest that a fine mist on the cupped side may very well help and will certainly do no harm.
          The only water in the Forest is the river.

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          • #6

            Re: Water Polyurethane Cause Warping?

            Thanks for the replies and helpful info.

            I will try to get a picture of the top.

            If I am dealing with drying stress, how could this be dealt with? I understood that after kiln drying it should be conditioned with steam. If this is not an option, would the stress "relieve" itself if it sits long enough?
            Thanks for the help, I am pretty new to working with wood in this way!

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            • #7

              Re: Water Polyurethane Cause Warping?

              Conditioned with steam huh? Yep that should put enough moisture in it. Must be pulling our leg! Nice one.
              JimPTBO likes this.
              "Do it Right!"

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              • #8

                Re: Water Polyurethane Cause Warping?

                I am new but most articles I have read talk about the last stage of kiln drying is to condition the wood to prevent case hardening stress by introducing a humid environment to equalize the outer and inner sections of wood. I have seen people take about a water misting system or steam.
                Maybe I am missing something or wasn't clear what I meant!
                http://www.woodweb.com/knowledge_bas...ditioning.html

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                • #9

                  Re: Water Polyurethane Cause Warping?

                  You are correct in that steam is used during the drying process not just for stability but also for colour. Imho you need to be looking at your processes. If your wood is that reactive that a WB coating is causing cupping there is something more in play here. I just can't see how you could safely mill 1.5 "maple without something bad happening due internal stress.

                  Is it a glued up top or a live edge slab?

                  Last edited by JimPTBO; 01-22-2019, 07:10 PM. Reason: Push wrong button

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                  • #10

                    Re: Water Polyurethane Cause Warping?

                    Originally posted by Jtd1983 View Post
                    I am new but most articles I have read talk about the last stage of kiln drying is to condition the wood to prevent case hardening stress by introducing a humid environment to equalize the outer and inner sections of wood. I have seen people take about a water misting system or steam.
                    Maybe I am missing something or wasn't clear what I meant!
                    http://www.woodweb.com/knowledge_bas...ditioning.html
                    I understand you to be saying you preconditioned the wood with steam. Did I misread what you wrote? I honestly thought you were pulling our leg.
                    "Do it Right!"

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                    • #11

                      Re: Water Polyurethane Cause Warping?

                      Jtd1983, you're going to have give us some more information of what we can help you with beyond what you have stated. The article you refer to is about the use of atomized water as opposed to expensive to run steam system in a wood drying kiln.

                      Questions for you;

                      Do you have your own drying kiln and process your own lumber?

                      What size of table top did you build?

                      Hard maple or soft?

                      Is it a laminated top or a slab?

                      Did you buy a batch of wood reportly kiln dried and are looking for backup to get compensation?

                      Here are some links concerning steam and drying wood;

                      https://www.woodworkingnetwork.com/b...teaming-lumber

                      https://www.fpl.fs.fed.us/documnts/usda/ah528.pdf.

                      Would like to assist but issue is not very clear.

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                      • #12

                        Re: Water Polyurethane Cause Warping?

                        Regarding the OP's original question about waterborne polyurethane causing a 6/4" tabletop to warp, the simple answer is "yes". The fact of the matter is that when you apply any waterborne finish to only one side of a panel (tabletop, gable, whatever...) you are essentially wetting down only that side. So, of course the panel will swell up!

                        But such warpage would only be temporary as it would be counteracted when you apply finish to the other side of the panel. To clarify, apply finish on the first side then allow that side to dry to the touch - which usually takes only 45 minutes to an hour - then flip it over and apply finish to the other side. Allow that one to dry, then sand both sides to get rid of any "nubbies" (aka "whiskers") which were caused by the water component of the finish to raise the grain fibers. Continue alternating applying finish in this manner until you're happy with the results. Oh, and for the record, I apply a coat of sander/sealer on the bare wood before applying the topcoat (the polyurethane in this example), which will usually be two or perhaps three coats if using polyurethane.

                        As an example of how waterborne finishes affect, I should mention here that in my formative years (most who know me will tell you that I'm still at that stage!) I sprayed a 1/4" thick solid wood cherry panel thich I wanted to use for the bottom of a drawer. As soon as the first coat of finish (a waterborne sander/sealer) was applied, the panel warped very severely and I was quite alarmed. Fortunately my wife called me for lunch right then, so I left it on the drying rack. When I came back to the shop two hours later (hey, I'm old and need a nap abter having lunch, so don't give me a hard time), the warpage had mostly dissipated, so I left things as they were and sprayed the other side. Bingo! The panel leveled itself off... and in fact, it warped the other way... but only until the finish on that side had dried. After sanding both sides, I continued on to apply the top coats, and although the first side exhibited some warpage when the finish was first applied, the warpage went away as the drying took place. Again, the coat on the flip side seemed to resolve matters. The second coat of top coat exhibited no warpage whatsoever, which proved to me that such temporary warpage wasn't a concern at all because it goes away.

                        Sorry for the rambling, but like most questions related to finishes, the answer is seldom a simple yes or no.
                        Beaverfever1988, JimPTBO and nnieman like this.
                        All the best,

                        Marty

                        President of Kingston Wood Artisans https://kwoodartca.wordpress.com/

                        Proud member of the Wadkin Blockhead Club

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                        • #13

                          Re: Water Polyurethane Cause Warping?

                          I remain sceptical that a thin coat of finish will cause a 1 1/2 thick board to change shape. A finish will penetrate maybe 1/32nd which is about 2% of a 1 1/2 inch board. Will 2% move 98%? I have several 1/4 inch panels in process now and I agree they can be temperamental but the thickness is the difference.
                          JimPTBO likes this.

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                          • #14

                            Re: Water Polyurethane Cause Warping?

                            A friend of my made slab tables for quite a few years. He tells me that Maple was the most likely species to move on him long after he had made and delivered the table. Many of them moved. Other species were more stable. He even tried to get me to avoid maple and make my first tables out of douglas fir or cedar.
                            He convinced me to make a steel frame for the maple table top to be attached to in the hope of keeping it from moving. Even with all of that there has been movement on the first maple table I made. I used solvent based poly on it.

                            Maybe its just the water based product and that it is maple. I would try Marty's idea above and see if it works.

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                            • #15

                              Re: Water Polyurethane Cause Warping?

                              Originally posted by Randydb View Post
                              A friend of my made slab tables for quite a few years. He tells me that Maple was the most likely species to move on him long after he had made and delivered the table. Many of them moved. Other species were more stable. He even tried to get me to avoid maple and make my first tables out of douglas fir or cedar.
                              He convinced me to make a steel frame for the maple table top to be attached to in the hope of keeping it from moving. Even with all of that there has been movement on the first maple table I made. I used solvent based poly on it.

                              Maybe its just the water based product and that it is maple. I would try Marty's idea above and see if it works.
                              Got curious and looked up maple on wood-database.com. Maple's T/R Ratio is reported as 2.1 - she going move! Douglas fir for comparison being pretty damn stable has a T/R Ratio of 1.6. Poplar has 1.8.
                              Whether this in combination the water base coating is the root cause, hard to say.

                              My gut feeling still is there is a combination of factors at play in this case. Hopefully the OP can provide some updates. Pictures and some more details would be real helpful if we are going to be able to lend some assistance. I know I would not be too keen on building solid maple table top. Just the weight alone, wrestling 1- 1/2" x ? maple boards around the shop.....I'll pass thanks....getting old.

                              Oh, and I hope I did not come across too strong in my previous post. I honestly feel for the OP. It is probably fair to say not one of us on this site, be a pro or hobbyist, at least once has not had that gut wrenching experience of putting in the time and effort only to have a project go south at the finish stage. I know I have and yes still do on occasion, thankfully less than when I started out

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