How long for Poly to cure?

[bluthart]

I am finally about finished with my son's crib, except for some polyurethane on a few parts. If he will not/cannot be in contact with any wood surfaces, then is it OK to put him in it fairly soon? Will the poly give off any harmful fumes for any length of time after it is dry? My wife plans on putting a "bumper" around the inside, so he won't be able to come into contact with any of the wood surfaces for a few months. I used Minwax Fast-drying Polyurethane, semi-gloss. Thanks for any help!

 

[SteveColes]

I don't think it is necessary, but I make it a practice to let it cure for at least a week. In this case, both for safety and durability. Also, putting a bumper on the piece also means you should give it some time.

I say at least a week. This article says up to a week.

I think Howard may say even longer

 

[SteveHall]

Volatile Organic Compounds (VOC) can have serious health implications for children, you'll want to play it safe. (Of course, everyone has their own tolerances for safety, so the definition of safe is pretty broad. I make paintings with lead, cadmium, and magnesium based artist's paints and use OMS, but I'm also confident in the many measures I use to avoid contamination.) On to three facts...

1. According to the product MSDS, Minwax Fast-Drying Polyurethane contains 446 grams/liter of VOC. This is four times what indoor paint contains.

2. You can use the State of California VOC limits to see a comparison of various coating products.

3. Another reference is the USGBC LEED 2.2 (page 67, credit EQ 4.2) limits clear wood finish varnishes to 350 g/L.

VOCs are gone when the product is cured. But they don't evaporate in a linear fashion, something can be dry to the touch but take 10x longer to really cure/dry for use.

So given that Minwax recommends not placing carpet on the product for 7 days, I'd bet it might be 14-28 days before most of the VOCs are gone. If it were me, I'd probably let the crib cure somewhere outside of the living space (garage, attic) at least that long before using, especially considering the risks.

I hope this little bit of research and opinion helps, it would be nice to hear a chemist's opinion.

 

[kooshball]

There is a difference between drying and curing. Your VOCs will leave the coating during drying and can be aided by temperature or air-flow but curing this type of coating will take time; 1-3 weeks.

 

[Joe Scharle]

Is shellac an option?
I use shellac for as many things as I can since I discovered that a box I finished in the late 90s still has a varnish smell when opened!

 

[manfre]

The bumper could be more dangerous to the baby than the VOCs. If you do get one, make sure it easily allows air to pass through to prevent a suffocation risk.

 

[Skymaster]

You can use the water based Poly. Stuff is fantastic,1 hr between coats, and is even available in a bowling alley strength.

 

[bluthart]

Is shellac an option?
I use shellac for as many things as I can since I discovered that a box I finished in the late 90s still has a varnish smell when opened!

Joe - I already have put poly on most of it.

 

[richlife]

It probably will take much longer than you expect for a full cure of polyurethane -- but that may not matter for this application. Bob Flexner in his great book on Finishing (as well as other sources), says that if you are planning to "finish the finish" on poly, you should wait at least 30 days for the poly to fully cure and harden.

Now, "finishing the finish" means that you will burnish the final poly coating to whatever luster you want by using water or mineral spirits as a lubricant and rub with successively finer abrasives (starting with 400 grit and going to at least 1200 grit -- I went to 8000 grit on one project). So enough about the process, the point for curing or hardening is that, poly remains in a "liquid" state for a very long time (up to 30 days). Applying the "finish the finish" process after two weeks, for example, will likely result in the poly flowing together and thereby eliminating all the very hard work of obtaining the finish you wanted to start with. In the case of the 8000 grit finish I did, it took hours of effort to obtain a true mirror finish (comparable to a French Polish with shellac) on a toybox. Years later with all it's abuse, you can still identify that finish.

So after a week a two, your poly finish will look and feel hard, but still will be "flowing" microscopically. That may well not matter for your crib, but I would still go for at least two weeks to get the good "hard" protective finish that polyurethane can provide.

Rich

 

[richlife]

You can use the water based Poly. Stuff is fantastic,1 hr between coats, and is even available in a bowling alley strength.

I'm sorry, but I would have to disagree with using water based poly. I'd be happy to have contradicting experiences, but I've found that water based poly is not stable at all in situations where it may have contact with water. We did the trim for our entire house with water based poly (and now regret it). In every instance that the trim has contact with water (window sills, plant shelves, bathroom baseboard) the water has damaged the poly coating (basically dissolved it -- it IS the solvent for water based poly). If your crib might be chewed on by a teething toddler or get water or other liquids spilled on it (leaky bottles), the water based poly just may not hold up.

Now our house was done 20 years ago, but I redid the bath baseboards about 7 years ago and the same problem occurred. I just have no faith in water based poly in these conditions.

Rich

 

[lbtripp]

You won't have the water problems if you use a pre-cat water based material. The only problem is the shelf life is short (60 days). At $ 76.00 a gallon it isn't cost effective for everyone. You need to have enough projects to spray to use up the gallon.

 

[kooshball]

The difference isn't so much water-based vs. oil based but rather the type of polymer backbone that is used as well as the level of cross-linking (or curing). Ropes that hold oil-rigs to the bottom of the ocean floor are coated with water-based polyurethane systems and they are designed not to hydrolyze.

Point being; make sure you select the correct system for the job (water-based or oil-based) and if you can, get a catalyzed system for maximum chemical / water resistance.

I'm sorry, but I would have to disagree with using water based poly. I'd be happy to have contradicting experiences, but I've found that water based poly is not stable at all in situations where it may have contact with water. We did the trim for our entire house with water based poly (and now regret it). In every instance that the trim has contact with water (window sills, plant shelves, bathroom baseboard) the water has damaged the poly coating (basically dissolved it -- it IS the solvent for water based poly). If your crib might be chewed on by a teething toddler or get water or other liquids spilled on it (leaky bottles), the water based poly just may not hold up.

Now our house was done 20 years ago, but I redid the bath baseboards about 7 years ago and the same problem occurred. I just have no faith in water based poly in these conditions.

Rich

 

[Mike Davis]

I would wait at least 7 days before using and 30 before allowing any contact.

Allergies are cumulative, the more exposure one gets the more likely to develop a sensitivity. Don't take chances with an infant.

 

[CrealBilly]

If in a enclosed place like the inside of a box or drawer oil based poly will still smell after years and gets worse with heat. A bookcase I made for my sister took well over a month to stop smelling.

I like the oil look of poly so I mix it 50/50 with mineral spirits and rub it in with a rag, wait a few days sand with 600 grit and give it another coat, wait a few more days sand again with 600. Then build up the finsih with water based poly. I really like the water based poly that Ace Hardware sells. It's works great in the spary gun and dries in a few hours, I can usually get several coats on in a days time. I don't know who makes the Ace Hardware brand water base poly, but it works well for me.

 

[Gofor]

Under normal conditions (70 degree temp, 50% humidity, and open to air), most oil-based varnishes (furniture poly included) finish off-gassing any solvents in 30 days. When you no longer smell it (the solvents) its pretty much cured. Enclosed spaces like drawers and interior of cabinets takes longer because there is no air flow. Putting the padding on a crib will stop the air flow where it touches, so the solvents can't evaporate. They also may start to react with the padding, giving off other fumes.

Overcoating it with something that partially seals it will only slow down the evaporation, taking it longer.

To speed up the cure you want air flow and higher temps. If your shop or garage is heated, let it set there with a fan blowing to keep the air circulating around it. Outdoors during the day in the sunlight and wind will also speed things up if the garage/shop isn't heated.

HTHs

Go

Not to put too fine a point on it, but if you can't smell the poly readily, it is probably no worse than the new plastic on the mattress liner. That smell of new plastic is also fumes. "New car smell" is the fumes from all the urethanes, plastic and adhesives used in the car's manufacture. They are what put that hard to remove film on the inside of the windshield.

 

[Howard Acheson]

To answer your question, oil based finishes can take 3-4 weeks to fully cure. By that time most off-gassing will be finished.

 

[Tom Rioux]

Those early days are so precious I wouldn't want any kids sleeping in a crib surrounded by something as toxic as polyurethane.

Poly takes a long time to cure. Even after a month the off gassing still happens, stinking up the whole house. Some have measured voc coming off a film over two years later. Poly is a hard double urethane bond, it's going to trap solvent within it and release it slowly as the coalescing process squeezes tighter and tighter. The film will be harder after 3 months than it was after a month. That's because it is still curing, to a deeper level. Curing and hardening can continue 6-12 months from what I've seen.

Poly is made with isocyanates. Oceans of Isocyanates are made every year, poisoning the earth for profit and performance. A lot of this foolish poisoning is because garbage poly is made with it and therefore doesn't last long. Aliphatic Urethane or poly made with triisocyanates is much better and lasts far longer but it's still expensive poison. If the performance is vital like a water tank or metal roof there are better options. Zero VOC Epoxy for example. A crib just doesn't need poly.

Minwax says they have 46% of 64742−88−7 (medium aliphatic naphtha) mineral spirits, 3% Odorless Mineral Spirits. That is a lot of minerals spirits to come off through the film. The poly is low viscosity stuff and dries fast so I wonder what the other 30% is because it looks like only 20% resin to me.

Minwax MSDS

Section 3 −− HAZARDS IDENTIFICATION
−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−
ROUTES OF EXPOSURE
INHALATION of vapor or spray mist.
EYE or SKIN contact with the product, vapor or spray mist.
EFFECTS OF OVEREXPOSURE
EYES: Irritation.
SKIN: Prolonged or repeated exposure may cause irritation.
INHALATION: Irritation of the upper respiratory system.
May cause nervous system depression. Extreme overexposure may result in
unconsciousness and possibly death.
SIGNS AND SYMPTOMS OF OVEREXPOSURE
Headache, dizziness, nausea, and loss of coordination are indications of
excessive exposure to vapors or spray mists.
Redness and itching or burning sensation may indicate eye or excessive
skin exposure.
MEDICAL CONDITIONS AGGRAVATED BY EXPOSURE
None generally recognized.
CANCER INFORMATION
For complete discussion of toxicology data refer to Section 11.

 

[kooshball]

Isocyanates are used in the process of manufacturing a polyurethane in a sealed reactor and are not present in the final formulation; have you done an IR spectrum analysis and found an NCO peak? If so, what brand/type product was it found in?

I agree that free isocyanate is not something that you want around but believe me, you want the products that are properly made from it. Our military, hospital patients and traveling public are kept safe with the use of polyurethanes.

A well made (premium) polyurethane (which is what most people have been recommending) will not have any left over isocyanate in it.

 

[Tom Rioux]

I want to say thanks for your response Kooshball. You’ve gotten me to revisit the whole polyurethane topic which is worthwhile and I appreciate your insight. So, I welcome any corrections to my opinions.

I wouldn’t go so far as to say we are keeping the world safe with Polyurethane but there’s a place for it. Not in wood finishing and cribs since I find it to be lacking and toxic. I don’t want poly, it’s additives, solvents, minerals spirits near an infants lungs.

Agreed on the point of quality. Premium poly is better and less likely to have residual isocyanate. I don’t have poly mentioned for the crib on my list of premium poly. There may be more reliable processes than spectroscopy to insure no free isocyanates remain in a coating. It’s a whole extra process, expensive to do. It just doesn’t happen much. Those who do it usually talk about it because it makes a better product and raises costs.

I believe over indexing is the standard in the polyurethane industry; adding a little more isocyanate than is necessary to insure maximum creation of the urethane bond.
I talked it over with a manufacturer, Chemical Engineer I know in the industry; it seems that even if ATR Spectroscopy is used throughout the process it’s still an art and takes a real master. Apparently residual isocyanate is plausible even when measuring n-c-o levels and rate of isocyanate consumption; that even without error residual isocyanate is not unlikely because of over indexing and the fact that spectroscopy might not pick it all up.

Another thing someone brought up today is that with a polyurethane dispersion, like the one mentioned for the crib, blockers are typically employed in these situations, this helps block the reaction. It has been questioned if even NMR would pick up residual isocyanate effectively in this scenario. I don't know what to think here but it does raise an interesting question.

Nobody really knows what trace isocyanate amounts are actually doing and more needs to be revealed. I wouldn’t bet my kids health on the idea that batches go through without trace yet unhealthy amounts of isocyanate. Especially, when they are churned out in high production batches for big box and trade sales. Bayer is the first and now biggest poly maker but I’m more impressed with the lengths Wasser goes through to address isocyanates. Check out this link http://www.polymer-services.com/Isocyan-2000.pdf

Bottom line, unless the manufacturer is specifically quantifying no free isocyanates I don’t buy it.