# Tips / Advice for Applying Moisture Curing Urethanes



## Joe67

I started a thread on the general forum about painting exotic hardwoods (http://www.painttalk.com/f2/painting-exotic-brazilain-hardwoods-68530/), and I am still interested in general discussion of that. But for a current job, the decision of what coating to use has been made by the client. It will be a moisture curing urethane - specifically, SW Armorseal Rexthane I (http://www.sherwin-williams.com/pai.../armorseal-rexthane-i-moisture-cure-urethane/)

So now I am also interested in discussion / advice from people who have experience with MCUs. I have applied plenty of oil paints, varnishes, urethanes, etc., but had never even heard of MCUs until now.

Apparently, they are dicey. I know at least a few things. One is not to do anything without a respirator. Another is China bristle only. No cheating with synthetics. And set-up speed can be a problem.

The set up speed is what makes me paranoid, and the biggest reason is that I am in central Virginia. It is August. And I have to put this stuff on new exterior deck boards. I'm dealing with temps in the 90s and humidity that starts out in the 90+% range and bottoms out in the afternoons at 50-60%. (Dew points generally 70-75. Chance of thunderstorms - perpetual).

Anyway, I always want to do new stuff and learn new stuff. (Rolling yet another wall with standard latex gets boring after a while, as most of us know, I'm sure). So I'm into figuring this out. If anyone has any experience and advice with MCUs I'd be thrilled to hear about it.


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## Rbriggs82

I have a lot of experience with Rexthane but never on wood, I've only used it on garage floors. I've also used it in the condition you've described and it was fine. I never had a problem with it drying too fast for me and setting up.. 

China brush is good and if I was you I'd use a mohair roller sleeve. The first time I ever used it the guy at SW had me use it and it worked fine, but for garage floors I thought it put it on a little too thin so now I use a heavier nap. For what you're doing I'd go back to the mohair. 

The smell is nasty, if you have a pick up I suggest using that and tossing everything in the back when you're done. If you only have a van throw everything into a five and put a lid on it. Clean up wise, I just toss everything (sleeve, handle, grid, bucket, and brush) I don't even attempt to wash it. 

I've always found it easy to work with but like I said I've never used it in the application you are.


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## kdpaint

I have zip to add, but I want to bump this and see what others think (other than why anyone would spend $$$$ for that type of wood...and then paint it?)


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## Joe67

Rbriggs, thanks much for that response. Given that you're in SC, I'm sure you also have these conditions all summer and its good to know that its workable enough despite heat and humidity. In terms of set-up/tack times I doubt wood vs. concrete matters all that much. Just the prep will be different. I believe it will get an 80 grit scuff sand and wipedown with acetone just prior to coating. 

I was actually thinking of skipping a roller altogether and just straight brushing the whole thing out. It's only about 300 sqft total and its a "spare no expense" job so if I take my time on it, no big deal. It has to be back brushed either way and I often feel much more in control of coat thickness with a brush. But if anyone thinks there is good reason to roll and brush out I'm glad to hear about it. I'll have some mohair on hand, either way, probably 4" though and feel it out once I get started.

How well does the material in a work pot hold up over the course of a few hours of work? And do you ever find occasion to thin it a little? I haven't looked yet at what the Rexthane literature says about thinning yet.
@kdpaint, I can't answer why people do such things, but I suspect marketing. People get the idea that stuff like this won't ever rot. It's "high quality" or whatever. So they want *that* wood regardless. And for some people the money isn't such an issue. I can tell you that the company I am working with would never choose to do this. We all love wood too much. It doesn't make me happy to do it. What's going on here is that there are 3 porches. One is only 3 yrs old and was done by someone else using Ipe topped with Rexthane. The other two have rot issues and all of the floors/stairs are being replaced and its all supposed to match. The 3yr old porch was done by a different contractor, so we have no idea how the initial decisions were made.


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## Rbriggs82

Joe67 said:


> Rbriggs, thanks much for that response. Given that you're in SC, I'm sure you also have these conditions all summer and its good to know that its workable enough despite heat and humidity. In terms of set-up/tack times I doubt wood vs. concrete matters all that much. Just the prep will be different. I believe it will get an 80 grit scuff sand and wipedown with acetone just prior to coating.
> 
> I was actually thinking of skipping a roller altogether and just straight brushing the whole thing out. It's only about 300 sqft total and its a "spare no expense" job so if I take my time on it, no big deal. It has to be back brushed either way and I often feel much more in control of coat thickness with a brush. But if anyone thinks there is good reason to roll and brush out I'm glad to hear about it. I'll have some mohair on hand, either way, probably 4" though and feel it out once I get started.
> 
> How well does the material in a work pot hold up over the course of a few hours of work? And do you ever find occasion to thin it a little? I haven't looked yet at what the Rexthane literature says about thinning yet.
> @kdpaint, I can't answer why people do such things, but I suspect marketing. People get the idea that stuff like this won't ever rot. It's "high quality" or whatever. So they want *that* wood regardless. And for some people the money isn't such an issue. I can tell you that the company I am working with would never choose to do this. We all love wood too much. It doesn't make me happy to do it. What's going on here is that there are 3 porches. One is only 3 yrs old and was done by someone else using Ipe topped with Rexthane. The other two have rot issues and all of the floors/stairs are being replaced and its all supposed to match. The 3yr old porch was done by a different contractor, so we have no idea how the initial decisions were made.


I never had the need to thin it down and don't really know how to go about it, I've never needed to. As far as pot life, I don't think I've ever used it for more than 2 hours straight and at that point it was fine. I'm not sure about how it's cut life is after that.


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## NACE

Rbriggs82 said:


> I never had the need to thin it down and don't really know how to go about it, I've never needed to. As far as pot life, I don't think I've ever used it for more than 2 hours straight and at that point it was fine. I'm not sure about how it's cut life is after that.


Pot life is only an issue with MCU after it's been opened. Once moisture gets in it will harden or get very jelly like. There is a special reducer for MCU. Brushing is fine for 300 sq ft.


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## Joe67

NACE said:


> Pot life is only an issue with MCU after it's been opened. Once moisture gets in it will harden or get very jelly like. There is a special reducer for MCU. Brushing is fine for 300 sq ft.


I was thinking of my work pot life - the orginal product will be sealed back up in the can, though it apparently has about a 7 day life after being opened. (Anyone ever hear of or use bloxygen, by the way? I don't know if it's relevant for MCUs in any case).

The questions about humidity and such are relate. While curing isn't the same as tack time, I was worried about high humidity creating fast tack times given that its an MCU. If a work pot had a short life, then I would put less in it and revisit the can more often. But if Rbiggs has no problem over a couple of hours then I'm not so worried.


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