Spot Repairs in Post-Catalyzed Lacquers

      Spray touch-up techniques for minor dings and scratches. May 11, 2006

Occasionally we make small repairs in our finish to blemishes that have occurred during handling or assembly. One method we use is to lightly sand the area with 1200, then 2000 grit paper. This will often polish out a small mark, but leaves the area with a higher sheen than the rest of the door or gable. We use S.W. post -at lacquer with a 40 sheen. I hear about rubbing out a finish to reduce the shine. What is the process and will it work in our circumstance?

Forum Responses
(Finishing Forum)
From contributor L:
Use a lower grit paper until you find one that matches the sheen you use (ie:1000 grit).

From contributor M:
One way is to buy pre-cat aerosols that will match the sheen of your finish. In some cases, you may not need to sand some minor defects.

From contributor S:
Contributor M is exactly correct - the pre-cat will rewet and flow the imperfection out. Also, one thing we use is "No Blush Blender Flat." It is just a solvent that will rewet the finish and flow out scratches, fingerprints, and minor dings you get during install without raising the sheen, and you never have to sand a thing. Mohawk makes it.

From contributor A:
How is it that a pre-cat will re-wet a conversion varnish?

From contributor M:
The pre-cat will cover most defects, and it will adhere to the CV and other coatings. Another technique that would work would be the micro-mesh abrasive and polishing pads. You can polish up or scratch down to adjust the sheens.

From contributor S:
Pre-cat would not re-wet a CV. The questioner said he used post-cat lacquer, which will re-wet easily for the first few days after it is sprayed. Pre-cat and post-cat are basically the same product, except the post-cat has a much stronger cat.

From contributor M:
At one time, a pre-cat was a coating where the catalyst was added when the coating was produced. Whereas, in a post-cat the catalyst was mixed into the coating just before the coating was applied by the finisher or sprayer. In fact, the amount of catalyst was the same for both the pre and post. Things may have changed now. I know that some manufacturers preferred the post-cats because when they were selling pre-cats, they had a very short shelf life and they would lose a lot of product because they would harden right in the containers.

From contributor A:
My mistake. I thought the questioner used a CV, however most post-cat lacquers don't respond to re-wetting unless it's a short window of time. He mentions handling and assembling.

Konig has excellent aerosol products. I worked for a millwork shop some years ago and they used the products there. My experience at that time was Mohawk products. We were using a conversion varnish on a large panel job. Some of the panels had superficial scratches on them. I was the new guy, so I was mum, but one of the finishers grabbed a piece of sandpaper, hit it lightly, grabbed a yellow can, shook, sprayed. I thought for sure you would see the halo. The problem area was center of panel. I was blown away.

From contributor S:
By saying the post-cat had a stronger catalyst, I meant it will catalyze quicker, so it is added by the consumer instead of the slow acting pre-cat, which is put in at the factory. I use a lot of post-cat because I like the hardness and don't have to change solvents like I do with the CV.

From contributor R:
Our installers usually carry a little of the topcoat material with them to the job site. If they need to do any spraying for touchup reasons, they pour a little of this material (which is thinned, of course) into one of the Prevall units. These are a combination of a sealed air unit and a glass jar. Simply pour in the liquid, attach the air unit to it and spray. These units can be bought at any good paint store and cost just a few bucks. One thing to be careful of is mixing and trying to match the sheens of different manufacturers. I myself use a Sherwin Williams product and I know that they don't put any of their product into small spray cans. By using the Prevall, I'm sure of the compatibility of my coatings, be it a sealer or a topcoat.

From contributor D:
I prefer the Mohawk pre-cat aerosol for spot spraying these types of repairs. I read that at Steelcase, they also use the Mohawk pre-cat aerosol. For a spot repair this is fine. For larger repairs, which might require coating the whole surface, the same coating might be better. If the repair is made on some molding, then I prefer to use Mohawk's Finish Up, which is a wipe-on waterbase polyurethane. I also use the wipe-on waterbase to seal in a burn in, which I then topcoat with Mohawk's pre-cat after the WB is dry.

From contributor R:
Aside from Steelcase, using or not using a Mohawk product, or if using a water based product over a molding is okay or not okay, will you please explain why you prefer to have two or three other products on hand to use when you can simply use the same product applied at the shop in a simple to use spray gun like the Prevall spray unit for a simple on-the-job touchup? Let's leave aside those larger repairs, which probably will be brought back to a shop to be rectified in a proper manner. Rather than toting a whole bunch of Mohawks spray bombs in various sheens, what's wrong with using the same product all throughout the finishing schedule, be it at the shop or at a job site?

From contributor D:
Spraying the same material over a repair might be fine for a small part or a small shape, but on a flat area where spot spraying will leave a halo, that's not okay with me. I do not use the Preval units because buying a unit to use once in a great while does not fit my budget. Rather, buying the different sheens of Mohawk pre-cat and the different sheens of Konig's Special Repair Lacquer, both of which I know do not leave halos when done just right, is in line with my materials cost. As a repair technician, I have an operating kit. I am not going out on one job to solve one problem. My kit must be diverse to tackle many types of problems. I drive around equipped to handle them all, time being the only constraint that I ever hope to run up against. But as I opened with, it is the chance of a halo that keeps me away from spraying the same product.

I cannot hope to formulate my own spray better than Mohawk or Konig. They have access to the technologies of just the right mix of solvents to use in their sprays. The sad part of it all is that once upon a time, there was methylene chloride in the aerosols. The presence of this great material helped the aerosols to lay down really good. I miss the old Star aerosols and I still have many cans left that I use. Those were miraculously halo-free as well.

From contributor R:
I agree with you in that a furniture finishing technician should have the products on hand to repair any finish he or she may come upon, but that wasn't the question the questioner
asked. For his particular circumstance, there is nothing wrong with a Prevall spray unit, into which has been poured the same material that he used at his shop, which in this case happens to be Sherwin Williams Post-Cat Lacquer with a 40 sheen.

From the original questioner:
We do use Mohawk products in our shop for repairs. They are amazingly halo-free and have quickly solved many repair issues. I guess what I discovered most was that our repair method might not be the best. Our extremely fine sandpaper is polishing out the defects, but is probably leaving a poor surface for any next coat that must be applied. We are not using the aerosols to their full extent, only using them for very small touchups. We will start test new procedures immediately. Thanks for all of the responses.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor J:
I have similar problems with the "halo" issue. I haven't found a magic cure for this yet, either, but I do have another way to apply touchup in the field. I purchased a spray paint loader from my finish supplier. When I'm done spraying, I load up two cans with whatever material I sprayed the job with and fill up two cans. One is for me to keep if I'm ever called back to fix a scratch and the other is for the client to keep for their own use. Another added benefit to this technique is that the material is preserved almost indefinitely in the pressurized air tight can so you can spray it out in another couple of years to do a color match if the client requests another piece/door/drawer front.

My ML Campbell lacquers have a shelf life of about 120 days before I have to toss them out, which means I will have a tough time matching the exact color years down the road without some of the original product. The loader was expensive, but the preloaded aerosols are only a couple of bucks and you can put anything in there - primer, topcoat, stain and dye. And you can customize the tip too for the application. I use them to spot prime after the first coat on any sandthroughs, runs or other tough to reach areas that you don't want to load the gun up for.

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