How much water-based poly is too much?

StPaulGalDecember 16, 2013

Hi all,

I am a total amateur and I could use some help from someone who knows what they are doing.

I am restoring an old factory/railroad cart, and I have finally arrived at the finishing stage. I chose a water-based poly for ease of cleanup and crystal clear coating. My question is this: how many coats is too many?

The instructions suggest 3 coats, but the internet seems to have a massive amount of variation with regard to how many coats are optimal. I have read everything from "should not need more than two" to "water-based versions could require as many as 10 or 20."

I think I would prefer about 5 coats, because the surface of the wood is very uneven and I would like to mitigate that a bit with my finish. (I don't want to sand it smooth because the beauty of the piece, in my opinion, are the pits/scuffs/burn marks from a hundred years of industrial use. But I also want a surface that feels smooth and silky.) However, the last thing I want is a cloudy mess.

So long story short: how much water-based poly is too much?

Thanks in advance for the help!

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klem1

Too much is any more than it says on the can to use. Why are you trying an end around on the people that made your finish? You can read the net until you are blind and never find better directions than those furnished by the manufacture.

    Bookmark   December 16, 2013 at 12:17PM
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StPaulGal

I am certainly not trying to do an end run around the manufacturer. I am just trying to understand the significance of their suggestion to use three coats. Does that mean "at least three" or "never more than three" or "always exactly three" or something entirely different.

    Bookmark   December 16, 2013 at 1:00PM
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aidan_m

The number of coats is completely irrelevant. It depends on the product. It depends on the method of application.

The important thing is to read and follow the directions provided by the manufacturer. For water base finishes, there are a couple of rules that you MUST follow:

1. Do not apply water base finishes at temperatures below 65 F. That is the most important rule to follow! Many things will go wrong if the temperatures are too cold. A white or cloudy appearance is from the cold. Be sure everything is at the proper temperature: the work piece, the finish, and the air.

2. Allow each coat to dry properly before recoating. If you can't sand the previous coat of finish and produce powder, it is not dry enough. Do not attempt to put on all the coats the same day, even if the can says one hour recoat. Two coats per day is the max!

3. Choose the application method based on how thick of a coating you desire. Wiping on a finish leaves the thinnest coat. More coats are necessary to build a durable film. Brushes lay on a thicker coating that levels out as it dries. If you brush too thin, it leaves brush marks; brush too heavy and you get runs. I doubt you'll be using spray equipment, so I won't go there. I'd say that 3 wet coats applied with a brush would be ideal. With a rag, you may need 5 or more coats to achieve a durable film.

    Bookmark   December 16, 2013 at 1:39PM
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StPaulGal

Thank you so much for your helpful response!

I am using Varathane Water-Based Interior Polyurethane in a gloss finish and I am brushing it on. I have done 2 coats at this point, and I waited about 6 hours between coats. (The can said at least 2, but not more than 2 per 24 hours). I plan on adding one more coat tonight. With the additional information I have given, can anyone suggest whether 4 coats total would be okay? Or should I stick with 3?

Thanks again!

    Bookmark   December 16, 2013 at 2:01PM
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klem1

When useing for an application the manufacture approves the product for use on,if they don't say otherwise,it means exactly. Some products say until finish drys to an even gloss plus one coat. Some give other guides but all will give you guidance one way or another. The most common cause of failure is using product for unapproved applications without consulting mfgrs desk. Normaly any coats additional do nothing for performance but often make it pron to cracking,chipping and aligatoring. If your finish does'nt specifily state for outdoor use,call # on container first,if it says it;s suitable,3 coats it is. Don't overlook dry time between coats and wherther to sand between.

    Bookmark   December 16, 2013 at 2:02PM
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bobismyuncle

In addition to the above, each manufacturer will have recommended "wet-mil" (thickness in 0.001" when applied) and / or "dry-mil"(thickness of dried coat(s)) recommendations.

In general, too thick an application can lead to problems like
- looking plasticky
- rounding over pores of ring-porous woods like oak, ash, etc. Your distressed piece may also look funny with too much finish rounding over the dents and dings.
- prone to chipping
- incorrect curing (most acrylic (w/b) finishes need about 3 weeks to fully cure by coalescence of molecules of finish) Dry to the touch does not mean fully cured.

That said, I normally apply 3 or 4 coats by spraying.

Your project, a RR cart, should not have a thick, glossy finish, that is more appropriate for a highly formal piece like a Chippendale dining set.

    Bookmark   December 16, 2013 at 3:21PM
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StPaulGal

Thank you all so much for your help! I applied the third coat last night, and I will stop there. I appreciate everyone who took the time to answer my question.

    Bookmark   December 17, 2013 at 7:22PM
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Linelle

Be sure to give it time to cure. I used 6 coats on a desktop recently, and, although it felt very dry, I was cautioned to wait at least two weeks before using it.

    Bookmark   December 28, 2013 at 3:22PM
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