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How hard/resistant should precat be?

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  • How hard/resistant should precat be?

    Hello

    I know my question may be hard to answer but I will try my best to describe it how I test hardness/resistance

    My product of comparison is a floor polyurethane varnish (non catalysed, hardware store type). Now even if the look may have been "ok" the resistance was phenomenal! To scratch to the finish bare wood I would need a penny and press real hard. I suppose this is what you would expect for a floor polyurethane


    I have now switched to a precat lacquer(duracoat precat from mohawk). I knew it would be less scratch resistant that poly but I am confused as to whether is supposed to be THAT MUCH less resistant.

    I first tried self sealing (all products are from mohawk) :

    -dye
    -precat Washcoat (5% solid)
    -pigment stain
    -precat sealcoat (5%)
    -Full coat (18% not reduced)
    -Grain filler
    -Sand 320-600 to get smooth)
    - Precat coat (10-12% solid)

    this has left me a fantastic look but a light scratch with my nail(without denting the wood) would remove all the finish up to the dye/first washcoat easily. Some people have pointed to me that the pigment stain could be the problem as self sealing on natural has given me better result.

    So I decided to go with the recommended vinyl sealer :

    -dye
    -Vinyl 5%
    -sand
    -Pigment stain
    -Unreduced vinyl coat (17-18%)
    -Grain Filler

    (Havent completed the next steps but they will go as follow)

    -Sand
    -Vinyl sealer(tinted or not)
    -Precat coat ( 18%)

    Up to the grain filler step I got a big improvement on resistance. In order to lift the vinyl sealer I must scratch to the point where I dent the wood and if the wood is too hard then I won't be able to lift the vinyl without scratching a lot. I estimate I must use about 100% more pressure to damage the vinyl. I am now waiting for the grain filler to dry (oïl) before applying the lacquer coats. I went ''by the book" using the recommended products on the tech sheets.

    For those who have experience with precat "how" would you describe it's resistance/hardness. Whats considered acceptable. How can I stain wood if finish can't stick to it. Does mineral spirits/solvent from grain filler damage the vinyl?

    Confused newbie here. Don't want to give up on proff. finishing systems since their look is fantastic and they are so easy to work with.
    Last edited by stgpascal; 11-20-2019, 11:28 PM.
  • Thread Continues Below...

  • #2

    Re: How hard/resistant should precat be?

    I should add that the test pieces are made from bare ash (no refinishing). The least resistant ones are the one where I used mineral spirits to clean the grain filler. Maybe it weakened the vinyl sealer.

    Comment


    • #3

      Re: How hard/resistant should precat be?

      On a scale of 1 to 10, I would put pre-cat lacquers somewhere in the 4 to 5 range, being more durable than wax, oil (0 to 1), shellac(1 to 2) or nitrocellulose lacquer(3 to 4) and much less durable than post cat (7 to 8), which itself is less durable than 2K poly or the UV/heat cured finishes (9 to 10). Floor finishes vary depending if they are catalysed or not, but I would put them in the 7 to 10 range).

      These numbers are purely subjective based on my own experiences as I have never bothered to quantify anything.
      I'm sure a finish chemist could give you a more detailed answer based on extensive industry tests and way more quantitative date than I have access to. I just know what works for me!

      On the topic of mineral spirits affecting the durability, it shouldn't interfere with any of the curing processes AS LONG AS IT IS COMPLETELY DRY before being topcoated.

      If you are getting white spots and areas of peeling, especially in deeper grain, (as per your pic on Woodweb) it suggests to me that something in your finishing process is not completely dry before you are coating it. FWIW I leave grain filler to dry overnight and will give solvent based stains a minimum of 3hr after wiping them, then the first coat of sealer is only a spit coat before either a tone coat (if the colour needs tweaking) or another coat of sealer prior to topcoat.

      Paul
      Last edited by Paul O in Paris; 11-21-2019, 10:35 AM.

      Comment


      • #4

        Re: How hard/resistant should precat be?

        Pascal,
        How long did you let the finish cure before testing the hardness? I know that some of the finishes I use take days and maybe several weeks to fully cure and reach their maximum hardness.

        David

        Comment


        • #5

          Re: How hard/resistant should precat be?

          Originally posted by Paul O in Paris View Post

          If you are getting white spots and areas of peeling, especially in deeper grain, (as per your pic on Woodweb) it suggests to me that something in your finishing process is not completely dry before you are coating it. FWIW I leave grain filler to dry overnight and will give solvent based stains a minimum of 3hr after wiping them, then the first coat of sealer is only a spit coat before either a tone coat (if the colour needs tweaking) or another coat of sealer prior to topcoat.

          Paul

          Haha busted

          This problem was when using precat as selfsealing. Since then I have switched to a proper grain filler as you have suggested to.

          Again your help is invaluable. I would say your numbers represent pretty accuratly what I am getting when using precat over vinyl compared to poly. Maybe I was misled by some people on forums that told that precat where hard to scratch and almost as resistant as poly.

          david the test was made on the vinyl ealer after 48h on the vinyl but as said there is still some steps to do tonight since I was waiting foe the filler to dry

          Comment


          • #6

            Re: How hard/resistant should precat be?

            Not all precats are created equal. The numbers you list for solids are very low. This indicates low build and fast dry. I would look into a higher solid more modern formulation. Your coating supplier should be able to walk you through a recommended process to deal with each of your steps. Grain Filler, stain sealer and lacquer all work together to give you the desired results. I would look for a high build product to avoid the grain filling which I have never found to be an enjoyable process. I would look into material from Axalta, Chemcraft or Becker Acroma which I would say are the leaders in this field
            Mark
            www.masterfinishing.ca

            Comment

            • Thread Continues Below...

            • #7

              Re: How hard/resistant should precat be?

              Mark,

              I'd like your take on Sayerlack, which is being marketed by Sherwin-Williams.
              All the best,

              Marty

              Secretary of Kingston Wood Artisans Inc. https://kwoodartca.wordpress.com/

              Master Mistake Fixer (because I've made them all... at least once)

              Comment


              • #8

                Re: How hard/resistant should precat be?

                So I have completed the test pieces. THe grain filler has cured and put on another full coat of vinyl sealer than full coat of precat. It's been now 24+ hours and the pieces seems to have become more fragile than ever but some spots are more resistant than others wich raises the Following question:


                -Have I applied too thick of a finish (Vinyl washcoat + vinyl full coat + grain fille + vinyl full coat + lacquer full coat + sometimes even toners)? I Don't have specialized equipement to measure but since it seems the more coats I Added the more fragile it became maybe I applied the finish too thick (4-5 tho is damn thin if you look at a feeler gauge and it's easy to go overboard). I know about the crazing and all but could this be an early symptom?

                - Have I recoated too soon or too late? My vinyl spec sheets ask for a 45min dry time than scuff sand but isn't catalysed and mention no recoat window. I may wait a few hours to a full 48h depending on my Schedule. Since It need sanding I also assume that sealers don't "burn in".

                My bets are on the finish being too thick. I have a test piece wich I did not liked the color so ended up stopping spraying after only 1 vinyl coat and guess what...they were damn hard to scratch


                EDIT : people have pointed to me that the oil based wiping stain could be the culprit. Mohawk specifies that is it compatible with ALL their top coats and that it is ready to topcoat in 30 min. Should I Apply it directly over the dye without washcoat (and live with the blotching) and would it be better If I waited 72h before topcoating (like those hardware store type stain)
                Last edited by stgpascal; 11-22-2019, 05:14 PM.

                Comment


                • #9

                  Re: How hard/resistant should precat be?


                  Since I Don't want to give up on precat I remade 2 test pieces from ash. Since the wiping stain (or the stain being over a washcoat) is likely the culprit I will try 2 Schedule.

                  -Both will have a black dye stain (wich is in fact really dark redish)

                  I stained directly over the Dye on the first one. Blotched a bit but the also hid the red tint of the dye quite well. Hope it did note lift too much of the dye (acetone based)

                  The second one was stained after a washcoat. It was very uniform but kept a black redish tint (will need a green toner).

                  Althout this wiping stain is supposed to be ready to topcoat in 30min (well according to the spec sheet) i will give it 72h to dry.

                  as of now the only difference I see is that the stain over the wascoat still ooze oil from ash pores and the smell scream mineral spirits. As for the stain on bare wood the smell is already almost gone.

                  Although is is not specified in the spec sheets I suspected the 30min dry time may be for an application over bare closed pore wood.

                  Anyway I will take these at home for 72h and continue the Schedule. If the wiping stain did not cure over the washcoat after that I gess I will have to trade a bit of blotchiness for a more durable finish.

                  Comment


                  • #10

                    Re: How hard/resistant should precat be?

                    Marty, Sayerlack makes some excellent products. European technology tends to be ahead of us here in North America. SW bought them a few years now. One of the things I have heard (no personal experience) is can be hard to get in the SW store locations in small quantities.

                    I also believe and please correct me if I am wrong Sayerlack does not offer acid cure products in North America. I have seen their waterbase and urethane/polyesters but I have not seen "lacquer" from them. I assume SW would supply their own lacquer than Sayerlack.
                    Mark
                    www.masterfinishing.ca

                    Comment


                    • #11

                      Re: How hard/resistant should precat be?

                      Pascal, IMO you have too many coats of vinyl sealer in the mix and are creating "sandwiches" of soft materials that will affect the durability of the final finish.

                      When I first started using vinyl, it was explained to me that the product was intended purely as a sealer or "isolante", ie something to go between the topcoats and what is underneath them if there was a chance that adhesion would be compromised by contaminants. I was also recommended not to use more than one coat of sealer under most circumstances.
                      Exceptions to the one coat directive could be accommodated by diluting the vinyl sealer heavily and applying as a "spit coat" eg over grain that was wild and would blotch when stain is applied. Recommended dilution was 6 parts thinners to 1 part vinyl and application was basically a dry coat. It was also recommended I use this ratio for any tone coats I needed if I wasn't going to use a diluted topcoat for this purpose.
                      Been doing this for about 17yrs in refinishing and can quite honestly say that I could count the number of problems I've had on one hand. I also use a post cat CV for topcoat so I have to keep the total dry mils of finish within a certain limit.

                      If you want a blotch free end product then you may want to change the methodology you are using by not using stain. Ask your distributor for a shading lacquer. They should be able to mix one to your specified colour. It will look different, but IMO this is the best way to really cut back on the blotching. However, as I always tell customers, a little blotching is just nature's way of showing them that they have real wood and not some plastic wanabee! But I also offer alternatives.
                      If you want to stick with stain, then get some clear stain base and apply that as a sealer to the bare wood before the stain. This way you only need the vinyl sealer between stain and topcoat if you are concerned about potential colour bleed.
                      Lots of ways to skin the cat lol!

                      In the end the durability of the final finish is dependent not only on it's own cured hardness but also on the hardness of what's underneath it.

                      Comment

                      • Thread Continues Below...

                      • #12

                        Re: How hard/resistant should precat be?

                        Thanks Paul.

                        While trying to give the wiping stain more time to cure I was wondering also how to cut back on coats. Are Spitcoart and washcoat basically the same thing?

                        My vinyl is 17.something solid undiluted. I use a 2 part thinner/vinyl to get a 6% washcoat (Nothing scientific, read on many forum to shoot for 5-10%). Your recipe would give me about 3% wich is more like commercial conditionners you can buy (read minwax crap here!). I will keep that in my mind if I have some other test pieces since it would be a more bare wood stain application.

                        I will see how those 2 samples goes. I will probably trade some blotching for a finish that doesnt scratch like a lottery ticket. Hey, even our high end(store bought) birch table has blotching all over it's top but i supect they used black toners since it still looks great.

                        Regarding toners also how would you mix them. Not the color but the thinner to finish ratio and if I follow you idea I am better using my lacquer than my vinyl sealer right?

                        Comment


                        • #13

                          Re: How hard/resistant should precat be?

                          Pascal, when I refer to a spitcoat I mean a coat that is applied with the fluid volume turned way down at the gun and as a fast pass. It dries real fast and feels rough to the bare hand. A light scuff with 320 leaves enough material in the pores to reduce blotching in problem areas. A washcoat is something I apply with more fluid at the gun and a slower pass. It leaves a very thin wet layer that, when dry, can be smoothed out by a light scuffing with 320 if needed. I often use this before application of toner coats just to limit any potential colour bleed.
                          Both these coats use my 6:1 ratio, as do my tone coats because I am trying to keep the total thickness of finish material below the topcoats to a minimum. You could easily use your lacquer for a tonecoat as it is precat and not so sensitive to total dry mil thickness as the post cats I use.

                          I don't know if those are recognised definitions in the finishing industry. I suspect not and I imagine everyone has their own definition of what each term means. But as I said before, that's what works for me and I'm passing it on in the hope it works for you too.

                          Have you had a detailed discussion with your supplier about what you are trying to achieve and the problems you are having?
                          Suppliers are usually a far better source of practical information than the internet as they will have seen all kinds of problems from their customers and have therefore gained a lot of troubleshooting knowledge over the years. They also (should) know what their products are capable of and what processes should be avoided. If you don't get any satisfaction, change suppliers as there really isn't a lot of difference between the day to day products of the major manufacturers these days. IMO, and experience, a knowledgeable and helpful supplier is a critical factor in determining your success.

                          Good luck
                          Paul
                          Last edited by Paul O in Paris; 11-24-2019, 11:48 AM.

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