Troubleshooting an Adhesion Problem

      Multiple layers of dissimilar products can create complicated adhesion issues. Here, finishers scratch their heads over one case example. September 10, 2007

Question
The following is the finishing schedule I used on a recent project.

1- sealcoat, 2- sand 220 grit, 3- clean/stain, 4- barrier coat, 5- topcoat, 6- sand/clean, 7- topcoat, 8- topcoat.

Dry times: 1- 1 hr, 3- 4-6 hrs, 4- 1-2 hrs, 5- 2 hrs, 7- 2 hrs, 8- 2-3 days prior to moving.

Shop temp varies but stays between 55-70. It's impossible to get more even with my current setup.

I am in the process of leading a finishing project for a new church, by far the largest project I have done. The trim and door jambs are done, and we are now starting on the doors. I have had a few volunteers working on this project, and I am also donating my labor and shop use. I have attempted to keep control over the process, but like everyone else, I also need money so I have not been able to be there all the time. This could be part of the problem.

The problem: One of the guys who is installing the trim approached me the other day and mentioned that a couple of the trim pieces had the finish scrape/peel off! I have never had that problem before, so I went to the location and verified that that was indeed the case. I then went around the building to check what had already been installed to see if there where further problems. I didn't find any. I am not saying that there aren't, though.

My initial thought is that the stain on a few of the trim pieces did not dry properly prior to the ensuing coats. Any other ideas? If my schedule is the problem, please suggest an alternative method.

Forum Responses
(Finishing Forum)
From contributor J:
You've neglected to mention what finish materials you're using. I think that might be useful information.



From contributor B:
Yes, what materials used, particularly steps 3 and 4? Top coats also would help.


From contributor L:
My first impression is that something is being introduced in the "clean" stage that is not compatible. If other people are doing this, they might not realize that they are using something to wipe the wood that will prevent adhesion in a later stage. Check and see what exactly they are doing on a sample piece.


From contributor G:
How deep is the peeling? Is it just the topcoat or is the stain coming up too? What kind of wood?


From the original questioner:
Wood - oak
Stain - Sherwin Williams Wood Classics
Sealcoat and barrier coat - Target Coatings wb shellac, sealcoat reduced 25%, barrier coat- straight
Topcoat - Target Coatings Superclear 9000 polyurethane

Peeling is through the topcoats. It's not coming off in sheets, but if you drag a fingernail down it, it is removed easily. As to cleaning, there haven't been other chemicals used that I am aware of, just clean rags and air.



From contributor R:
Oil stain, water based sealer, oil based topcoat. Me thinks the water based shellac is the problem, but it's just a guess.


From the original questioner:
Shellac is wb. Topcoat is wb. I have used the Ultraseal previously without any problems. Here is what the Target coatings website says about the wb shellac:

"Oxford UltraSeal-WB can be used on all interior wood surfaces that require undercoat conditioning, pre-stain sealing or sanding sealer applications. UltraSeal-WB also demonstrates excellent barrier coat capabilities on contaminated and smoke-damaged surfaces. UltraSeal-WB is compatible for use with all water-based lacquers, urethanes and latex paints. UltraSeal-WB demonstrates excellent bonding properties when used as a tie-coat between oil-based stains, glazes and topcoats. UltraSeal-WB can be tinted with a wide range of water-soluble aniline dyes and universal pigments."



From contributor R:
I stand corrected. Water based sealer, oil based stain, water based sealer, water based topcoat.

My guess it that the finish is failing at the first water based sealer coat. I think the oil stain wasn't dry enough before you applied the second sealer coat. Oak takes a good stain and won't blotch like maple or other hardwoods will. In the future I would be tempted to lose the initial seal coat when staining oak. Your choice of stains is from a very reputable company, so you might also consider sticking with the same manufacturer throughout your finishing schedule.



From contributor D:
I've never used the TC 9000 poly, but without researching it myself, I would guess that your 55 F degrees could be the problem. Most coatings are formulated to be used at about 77 F - 50% humidity. Whatever they formulated it at is considered the ideal for that coating. You can, of course, apply at a lower temp than that, but getting lower than 63-65 F during application or cure time can cause adhesion problems. If it is in fact not happening on everything topcoated, is there a chance that the areas that are peeling are the areas that were coated and/or curing when the temp was below 60F?


From contributor T:
I use waterbased finishes as well and have noticed that wb urethane (Fuhr 255) can have adhesion problems, especially on but not exclusively with oil-based stains. I am presently sealing my stain with acrylic wb, then using the urethane product. I've never had adhesion problems with acrylics. I like the feel of my wb urethane and will continue using it, just never over oil-based stain.


From contributor C:
If you haven't done so already, I would post your problem on the Target forum, including all the info you have given here. Jeff Weiss of Target is very good about responding to the questions posted, and should be able to offer a solution.


From contributor I:
SW Wood Classics stain... that's oil based. That's the problem with the wb products. Change stains. Why not use an industrial fast drying type of stain? SW's BAC stain would work most likely if you have to use solvent. But best if you used water based stain.


From the original questioner:
The idea of the stain not being dry is where I am leaning as well.

I think the idea of the temp being too low could also be part of the problem, if not the problem, with relation to drying and/or adhesion.

Got me thinking - because of the size of the project, I used some 2X4 stackers that on the initial few are rather close to the floor. I wonder if the pieces that have issues are those pieces that had been on the bottom few stackers? Temps probably were several degrees cooler on the bottom than toward the top. Even though the time used for drying purposes may have been long enough, the temp probably wasn't warm enough to allow proper drying of the coats.

If this is the case, will the coats cure over time underneath the last topcoat? If they do in fact cure, will the adhesion problem continue or will the coats adhere as they cure?



From the original questioner:
It's a bit late to change stains, as we are down to the doors. They will be getting a lot of extra dry time, and now the temps are considerably warmer than a few weeks ago. Humidity is an issue, though the shop does have an ac unit.


From contributor D:
I don't know for sure, but based on just two experiences I have had like this years ago, this is what I'm thinking. If the oil stain was not dry enough, I would expect you to have an oil blushing, like a slight whitish haze or what I call a hot spot problem where the coating on top of undried oil stain won't dry and stays sticky.

Once, when I sprayed CV over polyester and the temp was in the 50's, the CV failed - as in peeling when scraped. Once when I painted (latex) some trim in my own home before moving in, the temp was in the 50's and the same thing happened... peeling when scraped.

The trim in the house which was not redone will still peel today if you scrape it. I actually think it is not really an adhesion problem but more of the chemical curing process of the coating that was altered and compromised permanently at the time, due to the low temp, and the peeling is just a symptom.

Just a guess though. Didn't follow it up scientifically for answers, just didn't chance it again. 2 oops is enough for me. If I were you, I would run some tests.



From the original questioner:
Taking a general look at the pieces in question, it's hard to tell that the problem is there. I haven't seen any haze and the topcoat feels like it's normal. I did notice what looks like a droplet of water on oil, with the excess water removed. The circular pattern is there, if that makes any sense. On the pieces that I looked at, this was present on one of them. There very likely are more; I didn't go through the whole pile.

I guess we will have to go and test all the rest of the trim that hasn't been looked over to see how far the damages extend. The pieces with issues will obviously need to be redone. I just hope that it's a few instead of the majority.



From contributor D:
Do the circle effect areas have a slight rainbow color, like oil and water looks? Look carefully in good light from different angles. If it has a very slight pastel rainbow coloration, then that is what undried or heavily concentrated oil stain looks like under close scrutiny. You really only see it after you coat over it. Kind of looks like the rainbow effect you can sometimes see in a slab of ham. At least the ham my mom used to serve :) My mom made the best salmonella!

I described it as blush/haze because it is hard to describe to someone who hasn't seen it before. Sounds like those spots are small and may have had the stain not quite dry there. If the coating dried over it and did not stay sticky and it does not visually create a problem, you can probably ignore it. You just need to find out how much peeling is possible. If it is very minimal just here and there, then you could try to just deal with those spots or wait for them to fail some time in the future and touch them up as a maintenance program.

If you need to get back on schedule fast, you can always use a hairdryer to help flash off the solvents of your oil stain faster. Any kind of air movement, fan, across the piece will carry the solvents away faster. But try to get your top coats on and cured at temps above 65, preferably higher.



From the original questioner:
I will be stopping by the church site tomorrow, and will take a few outside and get a good look at them.


From contributor P:
I'd give oil stain a few days to cure, especially on oak, since it seems to continue to spit out stain from the pores hours after you wipe it off. I've done what you're doing successfully, but I've always used regular alcohol-based shellac (de-waxed of course) as my seal coat.


From contributor K:
The BAC stain from SW will help with the drying time and can be mixed in the same color. You can also add lacquer thinner to the stain to push the drying. Add 10% thinner and it will be dry in an hour.


From the original questioner:
I checked over the trim today, and the problem happened on the base trim. I took a bunch outside and the areas look more like a sunburn than water on oil like I originally thought. There are bubbles, like a blister, and then areas that are peeling. One piece of trim had a small area that felt a bit tacky. That spot appeared to have a milky look to it. Other than that spot, there wasn't any variation of color that I could see.

The topcoat on the affected pieces scrapes off with a fingernail scratch very easily, even in the areas on the piece that aren't peeling or bubbled. The stain remains underneath the areas that are peeled or scraped. Any ideas that differ from what has been mentioned already?



From the original questioner:
I am curious why the people at SW wouldn't bother to mention that they have other products available? I wasn't aware that they had the other line. The BAC product would have been preferable to what we used. At this point, though, I am going to stick with the Wood Classics since we already have it and give plenty of dry time to the doors.

I forgot to mention on the previous post that there were about 30 pieces that have issues, more than I was thought there would be. I imagine that if we sand off the current finish and touch up whatever stain gets damaged, we can recoat them? I haven't done refinishing before, so I am looking for suggestions again.



From contributor K:
I was not very clear in my previous post, but you can add a little lacquer thinner to the Wood Classics stain to speed up the drying time. It makes a huge difference.


From the original questioner:
Add up to 10%? Does it adjust the color? That will be a big help if it shortens the dry time considerably.

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