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I have a wipe on poly question...

3K views 21 replies 14 participants last post by  bluekingfisher 
#1 · (Edited by Moderator)
Hey there gang, I have a question in concern with my wipe on poly. When I buy my wipe on poly, due to its small pouring tip on the tin can, I buy a paint can to pour it in but what my question is about is when I am finishing a project and the lid has been open either for too long or just too many times and the poly gets tacky and thicker slowly. So instead of wasting the rest of it can I thin it out at all and get the same results? I hate buying a new can of it every so often when I dont have to.
 
#2 ·
It seems to me, since wipe on is simply poly cut 50-50 with mineral spirits, that you can thin it out again. I just use regular poly in a gal. can, then mix what I think I need for a job. I have a special coffee can dedicated to wipe on.

I'm curious, why do you get the pre-mixed?
 
#3 ·
Some expert will probably refute me, but here is my guess. Your poly starts getting thick when the solvents start to evaporate out of it. So by adding a little more solvent, you are basically just getting back to where you were. In other words, no problem.
 
#8 ·
Here is the trick to keep your varnishes good for a much longer time. Buy a large bag of small glass marbles. Fill the can with marbles every time you use the poly. This will keep the air to a minimum. You can them just wash the marbles with thinner to clean them when the can is empty and you a ready to use them again.
 
#13 · (Edited by Moderator)
Mark, once the poly starts to thicken and skins over it is beginning to polymerize and there is nothing you can do to reverse the process since this is a chemical reaction between the urethane resins and oxygen in the air. When my poly gets in this shape I will generally toss it since it is not worth screwing up the finish on project to save a few bucks.

You can't stop this process but you can slow it down by limiting the headspace over the poly once you open the container or pour it into another can. This can be done by pouring into smaller containers. John's suggestion is also a good one for limiting the headspace. Another way to help forestall this is to use bloxygen. This is simply a can of argon gas which is heavier than air. Spraying it in the container of poly is supposed to displace the air in the container and thereby slowing any further polymerization of the urethane resins.

I would recommend staying away from a plastic container and use only metal or glass for storage of your poly mixture. And, as always, I usually suggest making your own wiping varnish by cutting poly 50:50 with mineral spirits. This will save you some money since by buying commercial wiping products you are paying a premium price for mineral spirits.
 
#14 ·
Mark, as is usual, I occasionally get in a mind set about a topic and forget to think about other angles. It is possible that your poly is thickening due to solvent evaporation and adding more solvent will correct the problem, particularly if the wiping product was formulated with a solvent such as naphtha, which evaporates much quicker than mineral spirits.

But, in general, I have found that once poly begins to thicken and reaches the viscosity of honey, for instance, it has begun to polymerize with oxygen and this process is not reversible. I feel it is better, as I said, to simply toss it and start with fresh poly rather than ruin the finish. For what it is worth, I have found that a wiping poly will last far longer than the concentrate. I have kept wiping mixtures as long as two years without any evidence of skimming or thickening. This is generally enough time for me to use them up (I generally mix it in 2 gallon batches) and mix up a fresh batch.
 
#17 ·
Some good advie from your fellow jocks there Mark.
I use a lot of wipe on poly.
The tins available now have a plastic click down lid which is a big improvement from the metal screw down lid that tended to gum up.
I don't leave the lid open for more time than necessary.
To avoid the contents going off I keep the can handy & give it a shake once a day. Never had a problem since.
 
#20 ·
I have been using 50/50 mineral spirits and Gloss Poly at the school for 4 years. It works great! Dries fast. Easy to apply.

I mix the stuff in a 5 gallon paint can. I then pour it into old milk containers or windshield washer solvent containers (I like those the best; the lids are better!). My students will go through about 4 gallons of this a semester. I have to buy the poly, but I get the mineral spirits for free from the bus barn (they buy it by the barrell). Really cuts down on my finishing costs.

Students apply the finish with old sheets and tea towels I acquire (garage sales, good will etc). I have the kids put the saturated rags in a zip lock bag. They'll keep several days and can be reused this way. At the end of the week, I simply toss the bag in the trash. Come Monday, we break out new rags.

No brushes to clean out. Works pretty good so far!
 
#21 ·
There is a product in an spray can that is a heavy gas. When you use you product you spray a shot and it prevents evaporation and oxygen from getting on your product. I cant remember who. sorry to be so vague.
 
#22 · (Edited by Moderator)
Another means of prolonging the life of the poly is to turn the can on its head when not in use. That way the poly fills the head space and can't evaporate. You will have to make sure the seal is tight to prevent leaks of course. I use this method with oil paint cans and never had it skim over. It's a simple and inexpensive fix
 
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