Reproduction Parts for 1916-1964 Chevrolet Passenger Cars & 1918-1987 Chevrolet & GMC Trucks


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Shade Tree Mechanic
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Good morning all

I wanted to ask the VCCA group their suggestions on Polyurethanes for protecting wood beds. What brand would weather best? My concern is if the paint film lets moisture vapor breathe. There is always some moisture in wood. When it goes out in the hot sun the moisture builds up pressure and I will be back to ordering another wooden kit much sooner. I would like to protect the wood the best way I can. The following link was helpful but still left me with many question. Any suggestions from members that treated / stain wood for their cars/ trucks?

https://www.paintdocs.com/docs/webP...ang=E&doctype=PDS&prodno=1545102



Am I looking into this to much?

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Urethane spar is probably the best coating to use. It is intended for wood on boats which see both moisture and sun on a daily basis. All coatings have some porosity or transfer rate for gas. Water vapor is a gas that can go where liquid water can't.


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Thank you I will research Urethane Spar. I believe many more coats will be applied with the Urethane Spar compared to the regular polyurethane.

Last edited by DreamChevy; 05/17/19 10:24 AM.
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Mar-K Manufacturing has done a fairly extensive test over a five year period using a variety of commonly available products. At least two I thought would be acceptable failed the test. They do state that results may vary depending on storage and/or local climate conditions The reports are available in their “Tricks and Tips” section on the company website, mar-k.com. It will be worth your time to read their technical articles.
Mar-K manufactures top quality reproduction truck beds and miscellaneous other parts for Chevrolet and two other American truck makers.

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Thank you for the information , I will read up on the technical articles for more insight.

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My first thought was "BOATS" like Chipper mentioned. Lots of work goes into finishing wood for boats. I worked for a boat builder for a summer when I was a teen and coated and sanded and coated and sanded....

Maybe have a look at some wooden boat forums and see what they are using in your area or state close by. Many products vary in quality based on what state you are in as many states have low VOC laws now.


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Interesting question and discussion.

We are debating what we will do to finish the bed of the '49 3100 we are getting back on the road.

My thinking is that the best "protection" for this scenario is a penetrating exterior stain. It lets the wood flex and breath and change size as the moisture changes without cracking. Plus it is easy to touch up.

If your desired result is a high gloss finish like a hardwood floor in a bed that will never have anything in it then the finishes for boats are probably a good choice.

I also agree with Tim' s comment about sanding between each coat. And I would be cautious about building up too many coats.



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Original wood in most Chevy truck beds was hard pine and not Oak or any similar hardwood sold these days as replacement. The wood was often dark brown or blackish with overspray on the edges from the body being painted. The original coating applied was much like a creosote but not as heavy. What many use now is linseed oil mixed with pine tar. Lay coat after coat on it until it stop absorbing into the wood for original type lasting protection. Wipe off and let dry. Now this is for an original finish. Most these days don't like the look as I mentioned, along with this finish, paint overspray around the edges is factory correct. Today this look is unacceptable for some reason. So, if one wants a nice clean look with some shine or satin look, I agree with the spar varnish. The main reason for spar varnish is the UV protection it offers. Polyurethane does not offer UV protection and neither does an epoxy finish. I did hours of research when restoring my 32' Olds wheels to the original look with the difference being I used spar varnish in the end rather than just linseed oil or tung oil for a longer lasting finish. I used the linseed oil/pine tar mixture to get the dark brown coloring that the cars of the era had. Today, many are bleaching then applying epoxy resin for a very white, shiny looking wheel. While it looks good, it's really not original and they still need a couple of coats of spar varnish over the epoxy or it will deteriorate from the sun.

A WORD OF CAUTION: If bleaching old wood with oxalic acid to remove iron staining, make sure to thoroughly flush the surface with clear water then neutralize with baking soda so the wood doesn't continue to "gas out' during the finishing process. If sanding the wood causes a burning in your nose or eyes, there is still acid present in the wood and it needs to be flushed/neutralized again. Also, if using the linseed oil/pine tar mixture for color, it will need to be allowed to soak in and dry at least two weeks before applying the spar varnish or the varnish will not dry properly. (Ask me how I know all this!)

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Very informative thank you very much. Everyone has been very insightful. It is great to have this platform to share knowledge among classic car / truck owners. Do you have photos of your finished project? I am curious to see how the linseed/ tung oil and pine tar mix turned out. This time I am going with the Spar varnish. I want to get my truck on the road it has been a two year restoration. I am sure Mr. Adler wants my truck out of his shop. The finish line is approaching just as the weather is getting better. Finish photos will be added later. Thank you all once again.

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Originally Posted by Chistech
The main reason for spar varnish is the UV protection it offers. Polyurethane does not offer UV protection and neither does an epoxy finish had.

Can spar varnish be applied over poly to achieve the UV protection? My Aero with Country Club kit already has the poly on the wood. Really don't want to get into removing the wood for stripping the poly off. Of course the car isn't outside much so maybe UV protection isn't a large factor in my situation ?????

Thanks; Dick

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I know Spar Varnish comes in a spray application. Please do your homework regarding the spray application.Reading your post I assumed this might be ideal for your situation. Minwax Helmsman offers a gloss Oil-based Spar Urethane Varnish this brand has great reviews for UV

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I will forgo a chemistry lesson but direct you to the following website to help understand that there are urethane coatings (including paints) that are extremely UV stable. Same for epoxy coatings. They just don't use the more common aromatic components that are NOT UV stable.

https://adi.americanchemistry.com/A...lained/What-Are-Aliphatic-Diisocyanates/



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What is the mix ratio of the linseed oil and pine tar?
Was this the final top coat?
Thanks.....

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I don't think you want to use pine tar but turpentine. A 50-50 mix is generally recommended. Make sure it is boiled linseed oil.


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So what you are really doing is to thin the linseed oil with turpentine so it soaks in better?
Will this mixture give me the black color of the original beds in trucks?

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The boiled linseed oil turpentine mix is to get the oil into the wood cells and protect against oxidation and deterioration. Any black color was a very dilute paint or stain that basically soaked into the wood surface. With age the wood will darken.


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The Pine Tar mixture sounds like "boat soup". There are a lot of different recipes. Usually some mixture of linseed oil, pine tar, turpentine, and japan drier.

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I ended up using Helmsman clear spar urethane gloss. Got the look I wanted and protection that is needed from the elements.

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I used 3 coats of boiled liseed /turpentin then exterior spar varnish . looks grt. brushed smooth , and I can put on another coat any time !!keeps getting better looking as it ages . I used yellow pine from my local lmbr yard $100.oo

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Do you have any photos to share? How long do you boil liseed/ turpentin?

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From the post above the mix is 50/50 and the linseed oil is purchased as "boiled linseed oil"-it is also sold "raw" .


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im new here and don't have a clue how to post pix . the boiled linseed comes that way .you don't have to boil it . I don't think its even boiled , just what its called .basically you let it set for a day or so each coat until the wood isn't sucking it up then remove all excess . wait a couple more days and apply the spar varnish . very user friendly .almost cant screw it up and like I said when it starts looking bad you hit it with steel wool and put on another coat

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Thank you for the information. I will keep you all posted when the truck is done.

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I used high quality pine tar from Japan, it’s hard to find, with boiled linseed oil, and turpentine to thin it and help it soak in on my Olds wheels. The mixture needs to dry for a few weeks and “gas out” if you want to apply a varnish or sealer type product. Yes, the mixture has been used on boats for years to preserve and color wood. Since the whaling ships were made right here in New England, that mixture has been used. Normal stain can be used but doesn’t work to seal the wood on itself like the pine tar does. The pine tar will actually gum up as it dies sealing the grain and a yearly reapplication make the wood look fresh again. Normal stain colors but leaves the grain open. Read up a fair amount on this before using the mixture on my Olds.

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Sealing the back side of the board and edges will help allot


tom cirjak
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