# Spar Urethane Question



## Tom5151

Hello,

I am going to be finishing some shop cabinets that I have just built. I am going to use Helmsman Spar Urethane by Minwax (Semi-gloss) since I recently got a very good deal on a lot of it. My question is about thinning this product. I am curious to know if there are any adverse effects to doing so since the directions on the can do not address it at all. If I was to thin it, what ratio should I use as a starting point? 10%...more? less?....are mineral spirits sufficient as the thinning agent?

Thanks


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## Dominick

Tom5151 said:


> Hello,
> 
> I am going to be finishing some shop cabinets that I have just built. I am going to use Helmsman Spar Urethane by Minwax (Semi-gloss) since I recently got a very good deal on a lot of it. My question is about thinning this product. I am curious to know if there are any adverse effects to doing so since the directions on the can do not address it at all. If I was to thin it, what ratio should I use as a starting point? 10%...more? less?....are mineral spirits sufficient as the thinning agent?
> 
> Thanks


I personally don't like that stuff. It is thick. 
Defiantly thin it out at least the first couple of coats 50/50 then you can reduce it to like 75/25. Depending how thick & however many coats you want. 
This stuff is meant for outdoors,so the finish I believe doesn't give a hard durable finish, like a oil based poly because being a spar urithane for outdoors it will remain flexible for changing temps and rain/humidity.
Yes mineral spirits.


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## cabinetman

Dominick said:


> I personally don't like that stuff. It is thick.
> Defiantly thin it out at least the first couple of coats 50/50 then you can reduce it to like 75/25. Depending how thick & however many coats you want.
> This stuff is meant for outdoors,so the finish I believe doesn't give a hard durable finish, like a oil based poly because being a spar urithane for outdoors it will remain flexible for changing temps and rain/humidity.
> Yes mineral spirits.


+1.:yes: I agree. Dominick hit the proverbial nail on the head, and used a nail set to seat it. Spars in general aren't intended for indoor use. It could take weeks to dry and never really get hard. It stinks aplenty, and can remain sticky.

It has a longer (higher) oil ratio, and UV additives, which IMO are unnecessary for interior finishing.











 







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## Dominick

Hence.... spar = marine varnish.


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## Dominick

Wow I'm flattered that you actually agree with me :laughing: 
I'll have to save that post for reference.


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## cabinetman

Dominick said:


> Wow I'm flattered that you actually agree with me :laughing:
> I'll have to save that post for reference.


But that doesn't mean we are right.:laughing::laughing:










 







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## Dominick

cabinetman said:


> But that doesn't mean we are right.:laughing::laughing:
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Yea.... At least your right about that.


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## Tom5151

Hello gents and thank you as always.......the reason I was considering it on this project is due to the fact that the cabinets will be in an unheated unconditioned garage where the humidity and temps fluctuate all the time. Given that, would I still be better off just using a good oil based poly? If so, is it a good idea to thin regular indoor oil based poly? If so, what ratios are a good starting point?

Thanks.


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## cabinetman

Tom5151 said:


> Hello gents and thank you as always.......the reason I was considering it on this project is due to the fact that the cabinets will be in an unheated unconditioned garage where the humidity and temps fluctuate all the time. Given that, would I still be better off just using a good oil based poly? If so, is it a good idea to thin regular indoor oil based poly? If so, what ratios are a good starting point?
> 
> Thanks.


If you can spray...use waterbased polyurethane. If not wipe it on. If you have to use oil base polyurethane, thin the first coat or two 25%, and then full strength. Use VM&P Naptha as a thinner. Wipe on.










 







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## Tom5151

cabinetman said:


> If you can spray...use waterbased polyurethane. If not wipe it on. If you have to use oil base polyurethane, thin the first coat or two 25%, and then full strength. Use VM&P Naptha as a thinner. Wipe on.
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Got it.....I love WB but wanted to just give oil based a try since this is just a couple of shop carts and cabinets for myself. I scored a great deal on some oil based products including the Spar so wanted to just give it a shot and see. But it sounds like Spar would not be the way to go. I have some oil based poly that I will thin and try out.....just really experimenting in this case.

Thanks again


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## TimPa

our finishing dept uses exclusively the stuff you describe, did before i got here. initially, my intent was to change over to something else. but, i've bought into the product. yes - thick, can't use foam brushes. tough to get a smooooooth finish (brushing). but, it is durable on interior projects.


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## chemmy

There seems to be confusion over urethane and oil types here. 

The old long oil varnishes made with fossil resins, used in early spar work, needed the large amount of oil to plasticize the congo or other resin for good flexability. Later, the phenolic types used until recently were just the opposite have high concentrations of Phenol resins and low oil content, this was a great improvement over the former. The current class of polyurethanes also contain small amounts of oil [in comparison] there flexibility is from the addtion of polyols, normally acrylate types, which varying amounts will give either rigidity or flex. depnding on the mole to mole ratio. 

If helmsman were of a true oil type they could not be recoated in "4" hours, as per instructions, even non spar urethanes can be though. This is why you can use them for both interior or exrerior work with the same durability as the interior only has plus the added benifits of more uv protection. This is also why places like TimPa is mentioning have no problem with it's use. Thanks Tim.

Chemmy.


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## sailorman

A somewhat related question; can you spray water based poly over Minwax Spar Varnish? Last year, I made a new, folding table for the cabin on my sailboat (interior). I sprayed it with rattle can spar varnish; finish looks great, but as you advised, it smelled_ forever_. After living with the table for awhile, I need to bring it home and put something like a 3/8" wide rounded over edging on it, as the sharp angle with the iron on edging is uncomfortable to lean on. I'll need to refinish it, and I'd rather not endure months of smelling that stuff again, so I'd prefer to spray water based poly. I assume I'd need to sand it quite a bit to prep the surface.


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## Tom5151

chemmy said:


> There seems to be confusion over urethane and oil types here.
> 
> The old long oil varnishes made with fossil resins, used in early spar work, needed the large amount of oil to plasticize the congo or other resin for good flexability. Later, the phenolic types used until recently were just the opposite have high concentrations of Phenol resins and low oil content, this was a great improvement over the former. The current class of polyurethanes also contain small amounts of oil [in comparison] there flexibility is from the addtion of polyols, normally acrylate types, which varying amounts will give either rigidity or flex. depnding on the mole to mole ratio.
> 
> If helmsman were of a true oil type they could not be recoated in "4" hours, as per instructions, even non spar urethanes can be though. This is why you can use them for both interior or exrerior work with the same durability as the interior only has plus the added benifits of more uv protection. This is also why places like TimPa is mentioning have no problem with it's use. Thanks Tim.
> 
> Chemmy.


I am going to give both of them (Sapr and interior Poly) a shot just to see how the results compare. I am still assuming however that I should thin the Spar. Is that a correct assumption?

Thanks


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## chemmy

either can be thinned. though personally i don't find it necessary.


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## cabinetman

sailorman said:


> A somewhat related question; can you spray water based poly over Minwax Spar Varnish? Last year, I made a new, folding table for the cabin on my sailboat (interior). I sprayed it with rattle can spar varnish; finish looks great, but as you advised, it smelled_ forever_. After living with the table for awhile, I need to bring it home and put something like a 3/8" wide rounded over edging on it, as the sharp angle with the iron on edging is uncomfortable to lean on. I'll need to refinish it, and I'd rather not endure months of smelling that stuff again, so I'd prefer to spray water based poly. I assume I'd need to sand it quite a bit to prep the surface.


Scuff sand with 320x and you can spray water base poly. Thin applications work best.










 







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## cabinetman

Tom5151 said:


> I am going to give both of them (Sapr and interior Poly) a shot just to see how the results compare. I am still assuming however that I should thin the Spar. Is that a correct assumption?
> 
> Thanks


Thinning would make for a better wiping finish.










 







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## Tom5151

As you guys can likely tell, I know very little when it comes to finishing. I have had some good results on a few projects but I think that's more from luck than any level of expertise or skill. I have read what I can but the volume of information is a bit intimidating at least to me.

Having said that, can I ask what the main purpose of thinning is? Is it essentially to get the product being applied to flow better? Does it make a difference in the overall look or reult of the finishing process? For example, will a semi-gloss oil based poly "look better" in it's finished state if it is thinned? I am sure there are a multiitude of variables that come in to play but all things being equal, will I get a better looking finish using it right out of the can vs it being appropriately thinned? 

Is it accurate to say that only specific thinning agents should be used with a given product? I am speaking here just about oil based product.


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## cabinetman

Tom5151 said:


> As you guys can likely tell, I know very little when it comes to finishing. I have had some good results on a few projects but I think that's more from luck than any level of expertise or skill. I have read what I can but the volume of information is a bit intimidating at least to me.
> 
> Having said that, can I ask what the main purpose of thinning is? Is it essentially to get the product being applied to flow better? Does it make a difference in the overall look or reult of the finishing process? For example, will a semi-gloss oil based poly "look better" in it's finished state if it is thinned? I am sure there are a multiitude of variables that come in to play but all things being equal, will I get a better looking finish using it right out of the can vs it being appropriately thinned?
> 
> Is it accurate to say that only specific thinning agents should be used with a given product? I am speaking here just about oil based product.


Thinning will give a better flow, and will dry faster. For oil base polyurethane, I would use mineral spirits, or for a faster dry...Naptha. Thinned media IMO doesn't change the look over full strength.










 







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## chemmy

Tom5151 said:


> As you guys can likely tell, I know very little when it comes to finishing. I have had some good results on a few projects but I think that's more from luck than any level of expertise or skill. I have read what I can but the volume of information is a bit intimidating at least to me.
> 
> Having said that, can I ask what the main purpose of thinning is? Is it essentially to get the product being applied to flow better? Does it make a difference in the overall look or result of the finishing process? For example, will a semi-gloss oil based poly "look better" in it's finished state if it is thinned? I am sure there are a multitude of variables that come in to play but all things being equal, will I get a better looking finish using it right out of the can vs it being appropriately thinned?
> 
> Is it accurate to say that only specific thinning agents should be used with a given product? I am speaking here just about oil based product.


Several thing here may help you tom. First, if you search for the MSDS [material safety data sheet] on any or all of what you have you will see listed the volatiles, [mineral spirits/xylol/acetone etc.]
With your products, mineral spirits would be the main viscosity adjusting hydrocarbon and would read something like 30-40% of the overall products weight. 

That translates into approx. 25-35% by volume. So your product already has about 1/3 MS content as packaged. Some msds sheets will actually tell you both the weight and volume of each voc listed.

So what we have then, is a coating already thinned for application, that you can thin more if you so desire, [strictly up to you and the environment, [temp/humidity], and how deft you are at laying the material on by brush or other means. A good spar-man can lay a heavy coat of varnish on with no brush mark that is even thicker than what you are using, for example. But that takes a lot of practice. Believe me i know. 

So, in thinning your products, what is happening is the changing of the materials "viscosity" meaning the more you reduce it, the easier it is to brush or rag or spray because you have changed it's abiblity to flow more easily, that's all. 

What takes place after your application, is that the diluent evaporate and thus the resins become thicker once again till they reach a cured condition ok?

Each of your products, once dry, will look no better than your application of them be it spray/rag/or brush, if all are thinned equal amounts to the same solids contents and applied at the same thickness, ok? Usually the coatings are chosen by their performance characteristics more so then their thinness or thickness, except for ones meant specifically for high build applications,[ epoxy/polyester/etc.. ]

Chemmy


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## HowardAcheson

>>>> would I still be better off just using a good oil based poly?

Yes, interior rated poly varnish is more protective than exterior rated. It is harder, more water and water vapor resistant. As said before, exterior rated poly varnish contains a higher percentage of oil and UV protecturants. The higher amount of oil reduces the water resistance of the finish, makes it softer, more flexible and more easily damaged. But given that you already have the Minwax and that these are interior and shop cabinetry, there is no reason not to use the Helmsman. It's a good way to get rid of it.

One thing you want to do is avoid poly varnish for any exterior application. Urethanes are quickly attacked by the UV in sunlight. They become cloudy, then crack and peel. For the longest lasting exterior clear protection, use a non-poly true marine varnish. Go to a real marine supply store and look for varnish brands like Pettit, Wolsey, Interlux and, best of all, Epifanes.


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## Tom5151

Thank you men...

As I will likely be brushing and/or wiping all of the oil-based product (at least for the time being) I believe I will experiment with thinning the product down a bit to help with material flow. I am hopeful that this will give me a bit more margin for error than if I was spraying right off the bat.


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## gary1

Thining out Spar is dumb. The whole purpose of using a Spar is to protect outdoor stuff. Spar is more elastic than your harder finishes and when the wood expands and contracts like any piece of wood will do outside, spar stays solid and attached to the wood. When you thin Spar it becomes harder when it dries, causing it to crack faster. If you want to use spar use it, but if you thin it then you can use any thing really it would be the same thing.


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## Steve Neul

GaryPR said:


> Thining out Spar is dumb. The whole purpose of using a Spar is to protect outdoor stuff. Spar is more elastic than your harder finishes and when the wood expands and contracts like any piece of wood will do outside, spar stays solid and attached to the wood. When you thin Spar it becomes harder when it dries, causing it to crack faster. If you want to use spar use it, but if you thin it then you can use any thing really it would be the same thing.


You can thin a spar varnish however everything has limits. You just have to use the right solvents in the right amount. Generally I don't thin a varnish unless it's a little old or if I'm spraying it.


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