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  • Proper application of polyurethane - Need help

    I am no expert when it comes to finishing. I am working on my coffee table subwoofer. Last night I applied one coat of minwax semi-gloss poly spray and then 1 hour later applied one coat of brush on minwax poly.

    Should I add another coat?
    Should I sand in between?

  • #2
    Re: Proper application of polyurethane - Need help

    I would sand before I put on anymore finish. I would use 220 or finer if you like. If it doesn't powder up when you sand give it more dry time. I would put as many coats until you get the desired build up. Three is usually good. Remember careful on the edges you can sand through very easy. Using a sanding block helps a lot.
    http://www.pellegreneacoustics.com/

    Trench Seam Method for MDF
    https://picasaweb.google.com/101632266659473725850

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    • #3
      Re: Proper application of polyurethane - Need help

      On my latest speakers, Marcato, I applied 4 coats of gloss, Minwax polyurethane. I applied the first 3 coats with a brush to get really thick covering, sanding after the first 2 coats with 320-grit sandpaper. After the third coat I used fine steel wool to just dull the surface, and the last coat was a wipe-on of gloss Minwax which gave a very smooth, even and super glossy finish. I suspect just two brushed-on coats with one wipe-on coat would be fine, too.
      Paul

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      • #4
        Re: Proper application of polyurethane - Need help

        Originally posted by davepellegrene View Post
        I would sand before I put on anymore finish. I would use 220 or finer if you like. If it doesn't powder up when you sand give it more dry time. I would put as many coats until you get the desired build up. Three is usually good. Remember careful on the edges you can sand through very easy. Using a sanding block helps a lot.
        Absolutely great call on the sanding block! Knock down the hills and helps keep your fingers pressure from sanding through at the corners. Tack cloth very well between coats so you don't have any grit on your next coat and allow a few minutes after tacking to make sure that the surface has no haze of thinner around. I run the back of my hand across the surface to check right before I recoat. As Dave implies, several thin coats is better than less thick coats. When spraying, I like to keep a wet edge, always move forward so the overspray will be in an area about to be sprayed as this helps minimize little bumps that can drive you nuts. And I like a light buff with 0000 steel wool before my last coat.
        When you run make sure you run,
        to something not away from, cause lies don't need an aeroplane to chase you anywhere.

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        • #5
          Re: Proper application of polyurethane - Need help

          I have never felt good about my hand sanding technique, especially around corners. I ended up using 000 steel wool to smooth things out and applied a thin brush coat this morning. I imagine that I will use 0000 and try one final coat. I really like a thick build. I imagine it is likely to be a little more durable, with the build.

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          • #6
            Re: Proper application of polyurethane - Need help

            Another source for finishing wood with a clear finish and no yellowing of the wood is Enviornmental Technology Inc's. "Envirotex Lite". This stuff is expensive ($22.69 a Qt.) and stinks to high heaven, but leaves a shinny as glass finish. Pour on or brush on and flows out to leave no streaks. Takes time to dry, but leaves a plastic or glass finsih that is clear as a bell!

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            • #7
              Re: Proper application of polyurethane - Need help

              Originally posted by jerryanderson View Post
              Another source for finishing wood with a clear finish and no yellowing of the wood is Enviornmental Technology Inc's. "Envirotex Lite". This stuff is expensive ($22.69 a Qt.) and stinks to high heaven, but leaves a shinny as glass finish. Pour on or brush on and flows out to leave no streaks. Takes time to dry, but leaves a plastic or glass finsih that is clear as a bell!

              I wonder if it has low off gassing... It sounds like it stinks but that may go away. Does it build nicely?

              BTW: Where did you purchase this product.

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              • #8
                Re: Proper application of polyurethane - Need help

                The Envirotex Lite is an epoxy finish that is primarily made for things like table tops or bars and is generally intended to be poured on and left to flow out evenly. I would think you would have problems using it on something like speakers where you need to cover multiple sides. But it might be worth a try. Google it and read up on it if you want to know more.

                As far as finishing with poly is concerned, I like the oil based versions much better than the water based. Although some of the water based material is getting pretty good and has it's advantages. The oil based poly is a top coat material that needs to be sanded between coats to improve adhesion. It sticks to the previous layer, unlike lacquer which actually dissolves the under coat and becomes one with it, so to speak. It works best if you thin the first coat so that it sinks in and seals the wood, this improves the bond as well. Subsequent coats can be applied at full thickness, assuming you are brushing it on.

                It's generally recommended to use gloss poly on all the build coats and only use a satin (assuming you want that type of finish) on the last coat. The additive(s) that are used to reduce the shine from gloss to satin also blocks some of the light causing the poly to be less transparent. After multiple coats this can become substantial.

                I like to wet sand my final coat with 600 grit or finer sand paper, working up to 1500 or so and then polishing with rubbing compound. If you aren't trying to get a super fine finish like a piano black, you don't need to use a polishing compound. This will leave a slightly dull surface, like a satin finish. If you want a super shiny finish like a Piano Black, you need to use polishing compounds as well and this process will become a lot of work as you will need to spend a little (lot) more time at each consecutive level of sanding/polishing to get all the imperfections out.

                Brian Walter

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                • #9
                  Re: Proper application of polyurethane - Need help

                  Originally posted by brianpowers27 View Post
                  I have never felt good about my hand sanding technique, especially around corners. I ended up using 000 steel wool to smooth things out and applied a thin brush coat this morning. I imagine that I will use 0000 and try one final coat. I really like a thick build. I imagine it is likely to be a little more durable, with the build.
                  Instead of steel wool I like to use a red scotch brite pad. You don't get the little pieces of metal. Like Bif said even lightly sanding will take out the bumps and give you a smoother finish. The steel wool or scotch bright pad wont do that. If you want a hand rubbed finish after your last coat you can buff it with the 0000 steel wool then wax it to bring the shine back.

                  I have found on finishes, especially auto finishes, the thicker they are the easier they will chip.
                  http://www.pellegreneacoustics.com/

                  Trench Seam Method for MDF
                  https://picasaweb.google.com/101632266659473725850

                  Comment


                  • #10
                    Re: Proper application of polyurethane - Need help

                    get yourself a couple of small mason jars and mix your poly with thinner 50/50 and use it as your first coat, seals and dries very fast. put a couple of undiluted allowing to dry completely and use the gray scotch brite pad, i get mine at home depot, use it with a block of wood. make sure you have very good light for this. tack well, then wipe on the last coat with the mix. or spray on. if you just cant get it to dry without nubs and bumps. then buff once more with the grey or if you can find it the white pad. the get som paste wax, cut a couple of inches off one of your white socks, put a little of the wax in it and rub the sock on your surface the wax will seep through and leave just enough on your surface. let dry buff well. i use a pad on my ramdom orbit sander.
                    " To me, the soundstage presentation is more about phase and distortion and less about size. However, when you talk about bass extension, there's no replacement for displacement". Tyger23. 4.2015

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                    • #11
                      Re: Proper application of polyurethane - Need help

                      Originally posted by brianpowers27 View Post
                      I wonder if it has low off gassing... It sounds like it stinks but that may go away. Does it build nicely?

                      BTW: Where did you purchase this product.
                      It can be built up! Has many uses...I found out about it through my other hobby, model railroading. Modlers use it to model lakes and streams on their layouts and you can build it up. I know bars use it to protect the wood from water stains or patrons crying in their beer??? Other have used it for decopage! I have used it for small streams on my layout and it dries very clear! It smoothes out by its self...no streaks!! It can be brushed on, but be careful with a second coat! Allways keep the applied surface flat and even!
                      It does take some time to set up and dry, so on speaker cabinets its one side at a time! Patience is required with this stuff, but the payoff can be quite stunning! It can be purchased through your local hobby shop. Ask if they have it on hand or look through the Walther's Model Rairoad Catalog. Its in the scenery section of the HO scale catalog or go on line to www.walthers.com and order direct from them. They have an excellent online/mail order system!
                      You might try your serach engine and see if you can find Enviornmental Technologies Inc. online! You could also try local hardware stores etc. and see if they have it!

                      Comment


                      • #12
                        Re: Proper application of polyurethane - Need help

                        Originally posted by jerryanderson View Post
                        It can be built up! Has many uses...I found out about it through my other hobby, model railroading. Modlers use it to model lakes and streams on their layouts and you can build it up. I know bars use it to protect the wood from water stains or patrons crying in their beer??? Other have used it for decopage! I have used it for small streams on my layout and it dries very clear! It smoothes out by its self...no streaks!!
                        It does take some time to set up and dry, so on speaker cabinets its one side at a time! Patience is required with this stuff, but the payoff can be quite stunning! It can be purchased through your local hobby shop. Ask if they have it on hand or look through the Walther's Model Rairoad Catalog. Its in the scenery section of the HO scale catalog or go on line to www.walthers.com and order direct from them. They have an excellent online/mail order system!
                        You might try your serach engine and see if you can find Enviornmental Technologies Inc. online! You could also try local hardware stores etc. and see if they have it!
                        My local Home Depot has it.
                        http://www.pellegreneacoustics.com/

                        Trench Seam Method for MDF
                        https://picasaweb.google.com/101632266659473725850

                        Comment


                        • #13
                          Re: Proper application of polyurethane - Need help

                          Originally posted by davepellegrene View Post
                          My local Home Depot has it.
                          It would be an interesting project. I may get a smaller quantity and do a little finishing on some scrap woods I have laying around and see how it works!

                          Comment


                          • #14
                            Re: Proper application of polyurethane - Need help

                            Originally posted by jerryanderson View Post
                            It would be an interesting project. I may get a smaller quantity and do a little finishing on some scrap woods I have laying around and see how it works!
                            I have been doing a lot of projects using epoxy. I now you can spray it with the right equipment. I just used an epoxy with a 90 minute set time. I used it to fill in between pieces of granite. It seemed to flow out really nice. Made me think you could probably roll it onto a project and it would have time to flow out smooth. You can also add color to it. I am getting ready to put a new surface on my water ski jump. I will be using sheets of cdx plywood coated on all sides and edges with an epoxy prime then probably two coats of epoxy. This will be a good place to see how it flows with a roller.
                            http://www.pellegreneacoustics.com/

                            Trench Seam Method for MDF
                            https://picasaweb.google.com/101632266659473725850

                            Comment


                            • #15
                              Re: Proper application of polyurethane - Need help

                              Originally posted by davepellegrene View Post
                              I have been doing a lot of projects using epoxy. I now you can spray it with the right equipment. I just used an epoxy with a 90 minute set time. I used it to fill in between pieces of granite. It seemed to flow out really nice. Made me think you could probably roll it onto a project and it would have time to flow out smooth. You can also add color to it. I am getting ready to put a new surface on my water ski jump. I will be using sheets of cdx plywood coated on all sides and edges with an epoxy prime then probably two coats of epoxy. This will be a good place to see how it flows with a roller.
                              I assume this would be some kind of sponge or foam rubber roller?? Would one like a small decorative roller be used for small projects? I will pursue this further when the weather gets a little warmer around here!

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