Water borne poly failure - Woodworking Talk - Woodworkers Forum
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post #1 of 11 Old 07-22-2017, 06:21 AM Thread Starter
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Water borne poly failure

Ok so I have an Amish built dining set, picked it up for $100. Normally I build my own stuff but, given the price, I thought I'd give refinishing a try. I tried lots of new techniques (new for me). Figured if I screwed it up the I'm only out $100 + time/materials.

Here is the issue... I bought it with some pretty bad water stains in the finish. Nothing that looks like it got all the way to the wood. After testing with a wet plate, it looks like it must have been shellac or laquer that was used. Finish was turned white after less that 2 min exposure.

Step 1, soda blasted the table leaves as test piece. Actually worked pretty well. A little depending of the grain but nothing to worry about.

Step 2, test stain absorbsion. Stain took well, left it at 1 coat. Dry time 3 days.

Step 3, dewaxed shellac sealer, sprayed with HVLP gun. Most prominent (Right remains to be seen) advice was shellac between oil stain and water-borne poly. This is a first. Usually use oil based stain and poly exclusively. Dry time 18 hours.

Step 4. Three coats (relatively heavy) of water based poly on table top surface. 3 hours dry time between, 24 hours full cure before testing.

I had it the kid tested this morning, 3 year old and a bowl of cereal... in my eyes it failed. After clean up there were white spots where the milk spills were, white ring under the bowl. The white went away after several minutes but given what I have seen I wouldn't test any longer exposure. Now I've heard so many people preach about water-borne poly being as good as oil for heat and water resistance. What went wrong?
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post #2 of 11 Old 07-22-2017, 07:14 AM
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There are a number of different things that might have happened. You shouldn't be using a soda blaster on wood. The air will inject the soda material into the wood. Unless the wood was very thoroughly sanded afterwards and blown off with compressed air that could have caused problems.

The stain if you applied the stain and just let it dry without thoroughly wiping off the excess that could have prevented the finish from sticking. The finish would adhere to the stain on the surface instead.

You don't necessarily have to use a dewaxed shellac between oil stain and a waterborne finish. It's just that waterborne finishes are not compatible with linseed oil contained in oil stain. You could use a dewaxed shellac as you did or let the stain dry a week so the linseed oil can fully cure.

After you applied the dewax shellac did you sand it before using the waterborne finish? Only a few finishes don't require a mechanical bond and the scratches left by sanding are necessary for the finish to bond. This is also true to sand between the coats of the waterborne finish. The only exception to this rule is finishes such as lacquer and shellac which have strong enough solvents it literally melts into previous dried coats.

Depending on temperature, humidity and the product you were using 3 hours drying time may not have been enough drying time with the finish. If the finish were rushed the underlying coats will take a lot longer to fully cure and harden. This takes most finishes a full month to do. Certainly not 24 hours. During this month extra care needs to be given protect a finish.

What you need to know about water based polyurethane is it's not polyurethane and shouldn't be confused with oil based polyurethane which is polyurethane. Paint companies are trying to sell finishes and are under pressure from the government to do away with VOC finishes. They come up with a completely different product which is an acrylic finish and call it water based polyurethane so people will think it's the same thing and just as good when in fact you are buying a substandard product. You will never get the same results and quality of finish using a waterborne. The only real benefit of using a waterborne is on light colored wood the finish will remain clear and not yellow over time like oil based finishes do.
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post #3 of 11 Old 07-22-2017, 08:33 AM
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I was experimenting with waterborne "lacquer" a while back. I sprayed several coats while adapting to a steep learning curve. I eventually got a good result and polished it to gloss. Just for fun, I made a cut toward the end of the board with a utility knife to see how it would chip. Cutting it like that caused the finish to lift a little, so I grabbed it and was able to peel off the entire coating in a single sheet. This was over bare wood sanded to 220, no stain , no nothing; although did put a drop of transtint in the finish to warm it up a little bit. I gave up on waterborne finishes that day, but I still hope a new generation will arrive soon. I'd rather avoid nitro if I could.
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post #4 of 11 Old 07-23-2017, 08:53 AM Thread Starter
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Originally Posted by Steve Neul View Post
There are a number of different things that might have happened. You shouldn't be using a soda blaster on wood. The air will inject the soda material into the wood. Unless the wood was very thoroughly sanded afterwards and blown off with compressed air that could have caused problems.

The stain if you applied the stain and just let it dry without thoroughly wiping off the excess that could have prevented the finish from sticking. The finish would adhere to the stain on the surface instead.

You don't necessarily have to use a dewaxed shellac between oil stain and a waterborne finish. It's just that waterborne finishes are not compatible with linseed oil contained in oil stain. You could use a dewaxed shellac as you did or let the stain dry a week so the linseed oil can fully cure.

After you applied the dewax shellac did you sand it before using the waterborne finish? Only a few finishes don't require a mechanical bond and the scratches left by sanding are necessary for the finish to bond. This is also true to sand between the coats of the waterborne finish. The only exception to this rule is finishes such as lacquer and shellac which have strong enough solvents it literally melts into previous dried coats.

Depending on temperature, humidity and the product you were using 3 hours drying time may not have been enough drying time with the finish. If the finish were rushed the underlying coats will take a lot longer to fully cure and harden. This takes most finishes a full month to do. Certainly not 24 hours. During this month extra care needs to be given protect a finish.

What you need to know about water based polyurethane is it's not polyurethane and shouldn't be confused with oil based polyurethane which is polyurethane. Paint companies are trying to sell finishes and are under pressure from the government to do away with VOC finishes. They come up with a completely different product which is an acrylic finish and call it water based polyurethane so people will think it's the same thing and just as good when in fact you are buying a substandard product. You will never get the same results and quality of finish using a waterborne. The only real benefit of using a waterborne is on light colored wood the finish will remain clear and not yellow over time like oil based finishes do.
Steve,

Appreciate the nice response. I'll try to tackle these one at a time.

Soda blaster is an experiment, seems fine so far, do NOT use an air compressor to blow it off. It's basically salt so even the smallest drops of water will cause reaction and horrible discoloration. You will be sanding it out. Use a shop vac, firm and med bristles. Will remove most of the soda from the grain. Sand and vac again. Wipe generously with mineral spirits to "wash" the surface. Mineral spirits won't react with salt like water does, so don't use a water based stain. Time will tell if there are reprocussions in the long run. Like I said, experiment...

Yes I wiped the excess stain, I doubt the moisture reached that deep since the white water marks disappeared after several minutes. The Varathane stain I'm using dries in 1 hour, not several like most. I used the white cloth test before shellac.

All coats were well sanded.

You are right about the poly, its acrylic urethane.
According to Rustoleum, the water based full cures in 72 hours. Actually, they claim the same for their oil based but I'd like to see that. I put the finish on in an air conditioned kitchen, humility should have been low (compared to outside) and temp stable at 72 degrees.

All this being said... 1 day may have been too soon as you mentioned. I'll have to test again in a couple days to see if I get the same reaction to moisture on the water based finish since it claims 72 hours to cure. Nevertheless, I'm prepared to either strip the table leaves and start again or oil poly over the water based... not sure I want to do that either... don't know how that would bond. Whatever I do, the rest has to be done to match.

Also, I know water will destroy a shellac finish, so will heat, but how does it react to cold? I will have to test that too... if a cold dry object like an ice pack will cause a temporary discoloration.
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post #5 of 11 Old 07-23-2017, 09:30 AM
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I think I would quit using the soda blaster altogether on wood. The salt it introduces into the wood may not all be cleaned off by sanding and can come back to haunt you. I knew an antique dealer which routinely stripped furniture in a salt solution. He asked me to finish one of the pieces he had stripped and even though I washed the furniture again and sanded it there were some spots the salt had lifted the finish before it left my shop. Then I heard he sold the furniture and it had come back and he refunded the people their money. The people wanted a film finish on it where this guy was just doing a Briwax finish on everything. That would work with the way they were dip stripping the furniture where the film finish failed. I wasn't there when the furniture was stripped though and don't know how well it was initially rinsed though.

I just mentioned the stain because I didn't know exactly how it was done. A lot of people use stain like it was paint and brush multiple coats on and just let it sit and dry. Stain doesn't have a binder in it which will allow you do to that. With multiple coats it's like mixing dirt and water and brush it on. It may stick initially but will eventually fall off. The finish will stick to the pigment on the surface and when it falls off take the finish with it.

About shellac in cold, it's pretty much unaffected like any other finish. If the furniture was kept below freezing there maybe the potential of it cracking if the wood were bent while frozen.

From what you are telling now I suspect the problem stems from the finish not being fully cured yet. It may not ever be completely waterproof but I think in time it will be water resistant you can easily live with.
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post #6 of 11 Old 07-23-2017, 09:34 PM
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I've had very good results with water based poly finishes. What kind did you use Phil? I am partial to General Finishes products for a lot of things. Never had a problem with anything they make. I agree with Steve, your drying times, especially with a heavy coat are not enough. I would lay off the heavy coats also. I spray a wet coat, but not heavy to the point where you'd worry about runs. Adhesion has not been a problem. In fact, I made a large lazy Susan out of Honduran Mahogany a few years ago for an outdoor pizza oven. I sprayed five coats of GF water based finish with UV inhibitors for exterior use. When I got done I noticed a few pencil marks I left on the bottom side which probably only I would ever see, but it bothered me. So I took a random orbital sander with 100 grit on it to sand through the finish on the bottom. It took me about a half hour. It had built up a decent film thickness and had dried for a few days, so it was pretty tough.
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post #7 of 11 Old 07-24-2017, 01:45 AM Thread Starter
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I've had very good results with water based poly finishes. What kind did you use Phil?
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post #8 of 11 Old 07-24-2017, 01:48 AM
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Just be sure to turn the can upright before you open it.
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post #9 of 11 Old 07-24-2017, 04:55 PM Thread Starter
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So I have decided to strip the table leaves I finished and use oil poly instead. I need to get the rest of the table finished and I don't want to waste too much of my time putting on a product that doesn't serve the purpose. The entire point of the strip and refinish was water stains in the existing finish. Makes no sense to keep working with water poly if after 4 days it's still vulnerable to water in normal use.

Thanks for the input guys, I'm sure water based poly has its place in furniture, I just wouldn't use it in the kitchen where water exposure is inevitable.
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post #10 of 11 Old 07-24-2017, 08:36 PM
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So I have decided to strip the table leaves I finished and use oil poly instead. I need to get the rest of the table finished and I don't want to waste too much of my time putting on a product that doesn't serve the purpose. The entire point of the strip and refinish was water stains in the existing finish. Makes no sense to keep working with water poly if after 4 days it's still vulnerable to water in normal use.

Thanks for the input guys, I'm sure water based poly has its place in furniture, I just wouldn't use it in the kitchen where water exposure is inevitable.
Just keep in mind that all oil based finishes have a certain amount of a yellow cast to them and they continue to yellow as they age. You don't really see it on medium to dark colored finishes but it shows up pretty bad on light colored projects. If you are alright with that aspect then the oil based poly will certainly do the job for you. I have it on a work bench and have spilled lacquer thinner on the table before and it didn't hurt the finish.
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post #11 of 11 Old 07-26-2017, 10:05 PM Thread Starter
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Just keep in mind that all oil based finishes have a certain amount of a yellow cast to them and they continue to yellow as they age. You don't really see it on medium to dark colored finishes but it shows up pretty bad on light colored projects. If you are alright with that aspect then the oil based poly will certainly do the job for you. I have it on a work bench and have spilled lacquer thinner on the table before and it didn't hurt the finish.
I prefer it on red oak. Really brings the stain/wood to life. Table is finished (except the leaves I have to redo). I coat gunstock stain, 6 coats oil based poly, 3 full strength, 3 at 60% or so. On to the chairs.
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