Replies

1. 
   Sgian_Dubh | Feb 17, 2002 05:14pm | #1

   *
   It sounds like you might be spraying over an open grained timber such as oak. Would you be more specific about this? The problem you describe has occurred to me on such timbers. My conclusion is that the polish partially sinks into the open grain, but that trapped air works its way out causing the bubbles, but this is only my conclusion. I've used two or three of strategies to reduce the chance of this happening when you want an open grained look, but they're not an absolute guarantee of success.
   *Thin the first coat of pre-cat with lacquer thinner, perhaps even as much as 25%, and apply a light coat that will cling and conform to the open grain.
   *Add some lacquer retarder to the polish and again apply a fairly thin coat. I'm not so fond of this as the polish
   b can
   remain 'imprint' soft for a long time, even as long as a week rather than imprint free after just overnight.
   *Apply a thin coat or two of dewaxed blonde shellac to initially seal the timber trapping the air. I've been hearing good things about a fairly new product from Zinnser called Seal-Cote (I think) which is a blonde dewaxed shellac as I understand, but I've not had opportunity to try it myself.
   *Another option might be to fill the grain or I've been known to do a semi-fill.

   Yes, you can cut back imperfections in pre-cat and spray over. Subsequent coats will re-melt the lower coat so that it becomes part of the new coat, but if you create a hollow in removing the blemish, the next layer might tend to follow the hollow, which might matter on a horizontal surface. You have to be careful not to apply pre-cat too heavily; 5 mils I think is generally advised as the combined thickness of all the coats, which means two, and three coats only at a push if you are just denibbing between coats. Thick finished layers of pre-cat usually craze or end up with 'chinese writing' 6- 12 months down the road. Slainte, RJ.

1. 
   Jerry_Thompson | Feb 17, 2002 05:22pm | #2

   *The wood is not open grain and I have two coats of dewaxed shellac on it. After thinking about it some I think I am putting it on too thick.Today is another day and I am going to sand it all level and start over.Thanks.

1. 
   Jerry_Thompson | Feb 17, 2002 10:39pm | #3

   *That was the problem. I put it on too thick. I tried the spraying out on a piece of cardboard. It may be putting it on a little thin but I have no bubbles and I will have to do several coats before I rub it out.Is there any "best" water based lacquer or are they all about the same?Jerry

1. 
   Sgian_Dubh | Feb 17, 2002 10:50pm | #4

   *Well, it seems I was barking up the wrong tree altogether after all, but it didn't take long to type what I did, and I'm pleased to hear that you seem to have ascertained the problem anyway. Be careful of spraying multiple coats of pre-cat lacquer for the reasons I described in my first post. I can't help you much with water based finishes I'm afraid. I haven't used them for several years. Slainte, RJ.

1. 
   Jerry_Thompson | Feb 18, 2002 05:35am | #5

   *Sgian;Thanks for the info. Now, how do it tell if I have 5 mils of finish on the piece? Secondly, I have small crack like blemishes on the ends of the wood. This appeared with the first coat. Am I going to have to take it all off and start over?What kind of lacquer do you use? I sprayed Deft on on project and it looks good. The project has about 6 coats on it and I have no idea how thick it is. I plan on using pumice and rotten stone to polish it. It seems to me that this would reduce the mil thickness somewhat.Thank you for your help. I am just getting a feel for all of this and cannot decide to use the water base or solvent type yet. I have heard from both sides of the fence and one swears by one type and one will not use the other.Jerry

2. 
   Sgian_Dubh | Feb 18, 2002 05:45am | #6

   *Your polish house should be able to supply you with a little aluminium gauge with a series of notches cut around the edge which are marked in mils. Dip the edge of the gauge into some freshly applied polish to see how thick a coat you are putting on.I can't hazard a good guess for the end grain cracking. It's one of those things I'd need to see, and anything else would just be speculation unless you are able to be more specific in your routine, from timber preparation to polish application.I'm not sure but I think the Deft product you mentioned is a nitrocellulose lacquer as opposed to a pre-cat or post-cat lacquer, and if this is correct, then it is one member of this specific family of polishes that can safely be built up coat upon coat. In my experience there is the right and wrong place to use every polish. Pre-cats have their strengths and weaknesses as do all finishes. Pre-catalysed lacquers are quick to apply, but have something of a reputation for lack of long term durability, and are hard to fix without spray equipment. Slainte, RJ.

3. 
   Jerry_Thompson | Feb 19, 2002 12:48am | #7

   *Sgian;I went on line to the fellow at Target Coatings. He said it was a problem called "crazing." This happens when pre-cat lacquers do not have enough catalyst in them or in some case too much.So much for pre-cat lacquers. I now have to take the finish off of these items and start over.Thank you for your help.Jerry

4. 
   Ron_Brese | Feb 19, 2002 06:41am | #8

   *b From the Workshop of Ron BreseJerry what type hvlp unit are you using to apply the waterborne material? It seems that the general concensus is that turbines don't spray waterbornes very well at all. I am assuming that the adjustments you made to spray lighter coats was to reduce the fluid flow. This adjustment would have probably increased the guns ability to atomize the material, therefore improving your results. So it may not have been that you were applying too much material, you may have just been sending more material thru the gun than it had the ability to atomize. I have a compressor driven Asturo and with waterborne finishes I still have to be careful not to force too much material thru the gun at too high a rate. You have to find those adjustments that give you good atomization and decent material flow.Sgian may have misunderstood that Target Coatings doesn't sell the Hydrocote resisthane, they do however sell the Oxford PSL lacquer with which I have had good results spraying over shellac.Ron

5. 
   Sgian_Dubh | Feb 19, 2002 06:46am | #9

   *I guess it's a learning process Jerry. Crazing and chinese writing are the same thing as I alluded to in an earlier post. It's not at all a case of too much or two little catalyst. It's sold as a b pre-catalysed product so your man essentially admitted that they sell a product that is formulated incorrectly, i.e., with too much, or too little catalyst. You can't mess with the formulation they sell. You can thin it, which is just a solvent, but it's b their formulation. Personally, I don't think you got an answer that makes any sense at all, and in my book, cracking- with the grain- is a different fault to chinese writing; always has been, and always will be. Slainte, RJ.

6. 
   Sgian_Dubh | Feb 19, 2002 04:19pm | #10

   *Sorry Jerry. I missed that question on which products I use. I use mostly ML Campbell products if I'm using the nitrocellulose family of finishes, which includes pre-cat and post-cat lacquers, and some of their stains, tinters and so on. Slainte, RJ.

7. 
   Sgian_Dubh | Feb 19, 2002 04:23pm | #11

   *Ron, I don't know anything about Target coatings I agree. I thought Jerry was asking about problems with pre-catalysed lacquer, as that was the term he used in his opening question. It seems I might be barking up the wrong tree again then! Twice in one topic. Darn. I'd better keep away from this from now on. ;-) Slainte, RJ.

8. 
   Jerry_Thompson | Feb 20, 2002 02:28am | #12

   *Ron;I am using an old Croix HVLP. It has not been used much as I have had it for years and got out of wood working for some time and now I am back into it.I use a 1.4mm nozzle. I do believe I put the material down too thick. I had a lot of bubbles which I knocked down with sand paper. I tried a bare board and messed around with the air and trigger settings and I am able to put down a thin coat and I do not see crazing and only a couple of bubbles.I have a full day coming up where I can take my time and after taking off the previous finish I am going to give it another try. I know I can get it and I thank you and Sgian for all of you help. I will keep you posted.Thanks.Jerry