Advice for how to harden wood before/during varnishing?

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Forum topic by christopolos posted 03-11-2018 08:20 PM 2992 views 3 times favorited 8 replies Add to Favorites Watch
View christopolos's profile


3 posts in 888 days

03-11-2018 08:20 PM

Topic tags/keywords: varnish finishing epoxy satin varnishing ply plywood

Hello lumberjocks,

I have been researching how to harden wood before or during the varnishing. And asking for advice on this forum.

I have made some chairs by laminating wpb/marine ply and osb, then rounding off the layers (pic included, is an oiled finish which I will take off to refinish)

The surface hardness isnt tough enough and scratches to easily. I am unsure if this piece will always have this problem because the materials used aren’t hardwood, or if there is a solution?

After researching online, what I might do is similar to what boat builders use. I am wondering about using epoxy resin to harden the material. Dilute the first coat with acetone to sink into the wood, then another coat of epoxy undiluted.
And then on top of this a varnish to give a satin finish as I dont want a high gloss that epoxy resin seams to give.

So do you guys know if epoxy resin hardens the wood? or do boat builders use this to seal and make it watertight.
Or if there is a better solution?

8 replies so far

View eflanders's profile


326 posts in 2627 days

#1 posted 03-11-2018 08:48 PM

Marine epoxy will not harden the wood to prevent scratches etc. It is used to prevent water penetration. Adding fiberglass or carbon fiber is what gives it strenothing but not necessarily hardness. The only way I know to make wood harder is by using heat. This process is fairly common in archery (bow and arrow) and bamboo fly rod builds. Using heat to harden wood is kind of tricky if you do not want any charing. The process does darken the wood and that is common indicator of when to start moving the heat. When I’ve done it, I used a commercial heat gun as a hair dryer does not quite get there. Old time rod builders used to store the wood in a sand box in a hot attic but it took years to do it this way. Bowyers use a heat gun or an insulated heat box using incandesent 100w light bulbs. The Bowyers bible #3 discusses the process in depth. Hardening the wood makes it react to bending in a quicker fashion. But adding heat to wood also is a way the bend wood permanently as it cools. So it is a bit of a tricky balancing act. Note: Native American Indians and some Amazon indians used heat to harden their wood arrow tips so they would be tougher. It looks like your bonding layers/using laminated wood. Adding heat to already laminated wood layers could cause the bond between layers to release.

View OSU55's profile


2648 posts in 2766 days

#2 posted 03-11-2018 09:50 PM

The low surface hardness is because of the oil finish. A varnish will be much harder, poly or other. Unfortunately the wood is already saturated with oil, which will somewhat reduce the impact resistance vs starting with varnish, but a varnish finish will still be much more scratch resistant vs the oil. Next time use thinned varnish from the beginning (how “thinned” depends on what warnish you are using, get it down to 20-25 % solids for 1st 2 coats). Apply it like the oil, flood it on keep it wet for 10-15 minutes, wipe off. Gradually increase solids after 2 coats. Can wipe or brush after 2 coats depends on film thickness you want. It is still only “skin” deep. There are also 2 part epoxies for rotted wood that may penetrate deeper, and then varnish over.

View dhazelton's profile


2839 posts in 3073 days

#3 posted 03-11-2018 10:07 PM

Minwax makes a wood hardener that is meant to help repair punky window sashes and the like – it soaks in and works great. You could try that on some scrap plywood edging.

View ArtMann's profile


1480 posts in 1592 days

#4 posted 03-12-2018 12:08 AM

I agree with eflanders. You can’t get epoxy or varnish to penetrate deep enough to make much difference. Mostly, what you are doing is providing a hard surface over the top of the material. That is probably all you need. Punky or rotten wood is another story. That is more like saturating a sponge.

I am familiar with modern epoxy plywood boat building processes. The builder laminates one or more layers of saturated woven fiberglass fabric over the wood and that is what provides the strength. The epoxy doesn’t penetrate the wood but can provide a tough barrier to the wood. That might be a good process for you to check out for future builds. You can find very good information on this web page.

I use their products and have been well satisfied but the information applies to other brands too.

View shipwright's profile


8560 posts in 3574 days

#5 posted 03-12-2018 04:26 AM

Check out System Three S1 Sealer. I have built a lot of boats and used a lot of epoxy. This one penetrates like diesel and then crosslinks.
This is exactly what you want. ..... IMHO

-- Paul M ..............the early bird may get the worm but it’s the second mouse that gets the cheese!

View Aj2's profile


3088 posts in 2574 days

#6 posted 03-12-2018 06:04 AM

That’s a very cool chair. I’m guessing you don’t have to worry about anyone copying it looks very difficult to make.
It has a sexiness about it. Much like Wendell castles work.
Good luck with finish.

-- Aj

View christopolos's profile


3 posts in 888 days

#7 posted 03-12-2018 10:14 PM

Thanks alot for the advice guys.

shipwright – That looks like a winner winner … chicken dinner : ) I will look for a supplier in the UK or an equivalent product. The fact it says penetrating on the tin and they say no need for a thinner is great.

Does crosslinks mean it will adhere well to another material on top of it?

I could ask a hundred questions but I wont.

eflanders – interesting method, haven’t heard of that but might be handy in the future. And as you said probably not suitable for the laminated materials used.

Aj – thanks.can I use that quote for any future promo pics ’ It has a sexiness about it’ Aj

View mahdee's profile


4291 posts in 2544 days

#8 posted 03-13-2018 12:23 AM

Total boat also has a similar product like system 3.


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