Wood hardening.

[mikegr]

What is the best way to harden wood? Let's say balsa 1-1.5 mm. CA glue? Epoxy? Polyester?

[Jaager]

The more efficient and satisfying way is to avoid this inappropriate species to begin with and use a species that is better suited.

In North America -  the most economical is construction Pine, then comes Yellow Poplar,  if you gotta, Soft Maple, Aspen or other Cottonwood.

These are soft, but are less prone to crush and hold trunnels; and sand without tearing.

Other geographic regions will have local species that serve. .

Edited November 15, 2021 by Jaager

[Charter33]

Hi Mike,

The best answer to your question probably depends on the reason behind why you need to harden the wood.

If you want to achieve a silky smooth surface that sands well enough to enable you to get a good quality surface to subsequently apply a painted finish to you will probably find that a good quality sanding sealer will do the job. 

If you're trying to toughen the wood to improve impact resistance you could try applying something that will give a good depth of penetration and bind the wood fibres together such as a wash of watered down PVA wood glue.

I think that I'd only resort to polyester or epoxy resins if I was hoping to achieve a waterproof finish, but here again it would depend on the size of the area being treated for reasons of cost if nothing else.

Wood varnishes, polyurethane and acrylic, will also improve surface hardness and reduce damage from scuffing and knocks etc.

Hope this helps....

Cheers,

Graham

[Roger Pellett]

The answer to your specific question might be a product called “git rot,” sold here in the US by marine supply houses to salvage rotted wood (it would be easier to answer questions if you guys would give us a rough location of where you live.). This is a very thin epoxy resin intended to penetrate the wood.  In the last few years there has been an explosion of other specialized epoxy resins intended to solve various problems, and you might find something that meets your needs, sold by companies like WestSystem and System 3. Intended for use by wooden boat builders and repairers, they can be expensive for modeling applications.

 

I second, Jaager’s suggestion to solve your problem by substituting a different species of wood,  IMHO, in the rush to build a model from what is considered to be “museum quality lumber, ordinary construction grade pine, not spruce or fir, is overlooked by many modelers.  If you sort through wood at your local lumberyard or big box home improvement store you will find a nice piece of pine for a fraction of what it will cost you to salvage the balsa.  Since most of our applications require small pieces, we can generally work around knots and checks.  This means that less select grades can work fine for us.

 

Roger

 

 

[mikegr]

 

I am looking for thin but durable wood sheets to make some parts like longer main decks etc.  I found only one supplier selling quality wood like lime, walnut, birch Air plywood from 0.4mm thick. But he's somewhat far. So at the moment only balsa is quite available around. While its easy to work with it is sometimes too fragile especially if less than 1.5 mm thick.

[Jaager]

1 hour ago, mikegr said:

I am looking for thin but durable wood sheets to make some parts like longer main decks etc.  I found only one supplier selling quality wood like lime, walnut, birch Air plywood from 0.4mm thick

I wrongly assumed that the Balsa was for a filler for POB.  I never dreamed that you intend to use it for something important.

For a deck or anything that shows  the only species that rates as "quality" is Birch.   Lime is better than its American brother Basswood but it is only sort of OK,   average kit sort of stuff.

North American Black Walnut is "quality" but not for our uses - it is open pore and does not scale.  Anything else called Walnut is there because it has a color that is sort of close.  All are also open pore, often coarse grain and or brittle.  None of it is scale appropriate.  aircraft plywood is suited for use as a sub flooring if a deck is then planked wth a scale appropriate veneer that is too thin to be a single layer.

 

If you can only find one supplier that is domestic to you, I would guess that you are not in either North America or Europe. Without you should tell us where you are, none of us can help you find a helpful source, or suggest species in your region that would be appropriate.

[mikegr]

13 minutes ago, Jaager said:

I wrongly assumed that the Balsa was for a filler for POB.  I never dreamed that you intend to use it for something important.

For a deck or anything that shows  the only species that rates as "quality" is Birch.   Lime is better than its American brother Basswood but it is only sort of OK,   average kit sort of stuff.

North American Black Walnut is "quality" but not for our uses - it is open pore and does not scale.  Anything else called Walnut is there because it has a color that is sort of close.  All are also open pore, often coarse grain and or brittle.  None of it is scale appropriate.  aircraft plywood is suited for use as a sub flooring if a deck is then planked wth a scale appropriate veneer that is too thin to be a single layer.

 

If you can only find one supplier that is domestic to you, I would guess that you are not in either North America or Europe. Without you should tell us where you are, none of us can help you find a helpful source, or suggest species in your region that would be appropriate.

I am based in Greece. Best access to wood is from North Europe, mostly Germany.  Shipping  though can be prohibited  because of their size and the recently increased rates.

Note that i work on modern ships so "quality wood" appearance is not an issue for me. In contrast, i have to convert all wood texture to a totally smooth surface before paint.  I also avoid to use styrene for large surface parts, i prefer wood.

From my theoritical research one way to  reinforce big and thin surfaces is by adding cloth and polyester at the back side of them,  of course i need to experiment as i haven't use resin/liquid polyester before

[Jaager]

We have very different imperatives it seems.   The avoid Balsa part still stands.  But you can use open pore hardwood - it just means using a sand-n-sealer to fill the pores.

 

Hobbymill - a new European supplier has more than suitable wood.  The premium species than he offers is best used with a clear finish.  Painting it hides what is being paid for.

If you have professional or amateur woodworkers nearby,  you can ways buy construction lumber and have someone with the required tools resaw it into a thickness that you can use.

 

[Snug Harbor Johnny]

  'Just can't resist this thread title ... I wonder if a Viagra solution would harden the wood 😉  (Johnny, don't quit your day job.)

[Roger Pellett]

If you are building modern steel hulled ships, this means that you’re going to be painting the wood so appearance is not a factor.  Thin craft grade plywood is readily available here in the US.  It comes in fractional inch thicknesses down to 1/64in which I believe is less than .5 mm.  A higher grade material in the same thickness range is also sold for model aircraft use.  It should be available in Europe and will work for structural applications.  

[mikegr]

3 hours ago, Jaager said:

We have very different imperatives it seems.   The avoid Balsa part still stands.  But you can use open pore hardwood - it just means using a sand-n-sealer to fill the pores.

 

Hobbymill - a new European supplier has more than suitable wood.  The premium species than he offers is best used with a clear finish.  Painting it hides what is being paid for.

If you have professional or amateur woodworkers nearby,  you can ways buy construction lumber and have someone with the required tools resaw it into a thickness that you can use.

 

What is exactly wrong with balsa?

It is used extensively in R/C airplanes as well as for high end models like the USS Indiana, built for the Indiana World War Museum in Indianapolis

[Roger Pellett]

Scratch building model ships requires ingenious use of the materials at hand. It’s the results that count, and no one can argue with the quality of the model in your photo.

 

I think that we’re trying to say that by using balsa you’re making life hard for yourself.  As a very soft porous wood, it is hard to hold crisp clean edges, it dents easily  and is  difficult to finish.  It is commonly used to build model aircraft because it is light, a property unimportant to ship modelers.  

 

I’ve never been to Greece but I believe that it has a robust wooden boat building industry.  See if you can track down one of the penetrating epoxies that I mentioned above.

 

Roger

[Bob Cleek]

I've had a lot of experience with penetrating epoxies in full-scale boatbuilding applications. "Git Rot," a U.S. product that's been around a long time is quite outdated technology at this time. It continues to sell for some reason. I suspect it's its trade name, which promises much more than it can ever accomplish. The industry standard penetrating epoxy sealer for the last few decades is "Clear Penetrating Epoxy Sealer," ("CPES"tm) manufactured by Smith and Company. Clear Penetrating Epoxy Sealer (smithandcompany.org) "Git Rot" is the consistency of honey. "CPES" is the consistency of water. "CPES" is an epoxy product which saturates the wood fibers and then cures, producing an epoxy saturated wood. It doesn't simply sit on the surface of the wood, like "Git Rot." "CPES" isn't simply "thinned epoxy," which can be easily mixed up by thinning epoxy resin with acetone. It contains serious-business solvents which you don't want to spend a lot of time inhaling in a closed area. "CPES" doesn't penetrate wood much deeper than water would, so a lot depends on the grain orientation and wood species in how deep the penetration goes. On flat-sawn surfaces, it can be as little as a 34th of an inch. Into edge-grain surfaces, it can easily penetrate a quarter inch or more and in open-grain species like white oak, penetration to the length of the grain is possible in pressurized or vacuum applications. All of which is to say that there's really no benefit to be had by laying a "crust" of epoxy saturated wood over the surface of a piece. The epoxy will not provide any substantial increase in strength or impact resistance and will be quite difficult to sand smooth, as well. In fact, in terms of surface hardness and sealing ability, a coating of thinned shellac will produce much the same result as penetrating epoxy for much less trouble, mess, and expense.

 

That said, I agree strongly with Roger Pellett's point that there is no reason not to use quality wood species suitable for the modeling purposes. In terms of cost, construction time, appearance, if that be an issue, and overall engineering suitability, there are any number of wood species anywhere one might be, short of Antarctica, that will serve the purpose better than balsa wood. Balsa is a very soft, light wood. It has very little strength compared to other species. It is difficult to work with because it does not hold a sharp, crisp edge when cut and it does not sand smooth without the use of a sanding sealer which adds additional steps to the finishing process. 

 

The quality of the materials that go into a ship model have a lot to do with how long that model survives. A quality model is more highly valued and appreciated than one made with inferior materials. Some modelers have expressed their belief that quality materials don't matter to them because they are only building for fun and that perspective has a certain commonsense appeal, to be sure. However, for the more anally inclined, I'd recommend Dan Wegner's classic article on "Ephemeral Materials in Ship Models" as the serious ship modeler's guide to modeling materials. Nautical Research Guild - Article - Ephemeral Materials in Ship Models (thenrg.org)

 

 

Edited November 16, 2021 by Bob Cleek

[Roger Pellett]

Ship model building flourished during the 1930’s and 40’s encouraged by serialized articles published in Popular Mechanics and Mechanics Illustrated Magazines and probably because it did not require a lot of expensive materials in depression era America and later during WWII.  These models featured hulls carved from solid blocks or laminated pieces of pine.

 

During the 1970’s there were a number of articles published in the Nautical Research Journal and Model Shipwright Magazine advocating use of today’s classic ship modeling woods; Boxwood, Pear, holly, etc.  This was in connection with making built up or Admiralty style models.  About this same time, POB model kits began to be imported into the US.  Heavily marketed, they displaced many of the traditional American solid hull kits.  Hooking on to the desire of the uninformed to build a “museum quality” model these kits often feature deluxe sounding but unsuitable Woods like a brown wood marketed as walnut.

 

I have two models built by my father with solid pine carved hulls.  One is over 70 years old and one is over 80, even though adhesives used today are much better than those available to him.  Both are in perfect condition.  The solid hull construction method using readily available inexpensive pine lumber should not be overlooked by scratch builders wanting to build a model that can be passed along to grandchildren and great grandchildren.

 

Roger

[wefalck]

When building models of steel or iron ships, I would rather go for some man-made sheet material. It is much easier to produce a convincing surface with these. If one does not like styrene for some reason, there are various alternatives, such as acrylic glass (down to 1 mm thickness), bakelite paper (down to 0.2 mm thickness), ABS (similar to styrene ...), PVC, and others.

 

At some stage in the 1980s it seems to have been fashionable among RC-boat builders, where top-weight is of concern, to reinforce balsa-wood by laminating on thin paper. This increases its impact resistance and the tensile strength. Also it seems to make it easier to cut clean edges on thin material.

 

[mtdoramike]

Your best answer would be to fiberglass the surface with cloth and resin. You will get a suitable result. Balsa is fine to use for hulls and decks where weight is a concern. I have built boats models primarily out of balsa more then a few times that are for R/C use, but I always use fiberglass cloth and resin, usually a 2oz cloth or even a 4oz cloth depending on strength needed. 

 

I have also skim coated hulls with auto body bondo, sanding smooth to give the balsa extra rigidity before glassing.

Edited November 17, 2021 by mtdoramike

[mikegr]

1 hour ago, wefalck said:

When building models of steel or iron ships, I would rather go for some man-made sheet material. It is much easier to produce a convincing surface with these. If one does not like styrene for some reason, there are various alternatives, such as acrylic glass (down to 1 mm thickness), bakelite paper (down to 0.2 mm thickness), ABS (similar to styrene ...), PVC, and others.

 

 

 

Υes there are. Carbon Fiber. More flexible, stronger and thinner that wood.

 

53 minutes ago, mtdoramike said:

Your best answer would be to fiberglass the surface with cloth and resin. You will get a suitable result. Balsa is fine to use for hulls and decks where weight is a concern. I have built boats models primarily out of balsa more then a few times that are for R/C use, but I always use fiberglass cloth and resin, usually a 2oz cloth or even a 4oz cloth depending on strength needed. 

 

I have also skim coated hulls with auto body bondo, sanding smooth to give the balsa extra rigidity before glassing.

When you say resin you mean epoxy or fiberglass resin? I understand that cloth is required to make the hull waterproof. Is it required on static models?

[wefalck]

In fiberglass reinforced resin, the fiberglass provides for tensile strength, not watertightness. The resin provides for compressive strength. The tensile strength is needed (probably) in RC models.

 

Carbon fibre is probably going to be very expensive and likely to be an overkill for a static model, where the tensile strenght provided by carbon fibre is not needed.

 

I would think carefully what you actually wanted to achieve with your layer of balsa-wood, what its intended function was. That then probably indicates what properties you are looking for in an alternative material. Is it supposed to be a structural material or just to provide a smooth surface.

[Roger Pellett]

For those not familiar with the Lake Freighter Model that I am currently building, inspired by Wefalck (impregnated paper) and Bob Cleek (shellac) I plated the hull with shellac saturated paper, glued on with common Titebond woodworking glue.  Primed with several coats of Tamiya spray can primer, the result has been a surprisingly durable surface.  I recently managed to set the plated hull down on a on a blob of glue left on a piece of cardboard.  When discovered, the glue had grabbed but not completely hardened.  The cardboard peeled right off without damaging the surface.

 

mikegr could cover his balsa hull the same way.

 

Roger

[Snug Harbor Johnny]

  A friend of mine made a fairly large scale hull model of an 18th c. English warship (Centurion) entirely out of balsa.  Most of the ship is painted, and it looks alright.  I've forgotten my model airplane work as a youth, and those were balsa flying models.  I 'hardened' the balsa by diluting model aircraft 'dope' 50/50 with Aerogloss dope thinner.  Then it would penetrate deeply into the balsa.  When all the solvent outgassed (dried), the structure was substantially strengthened and the surface was 'harder', could be sanded lightly and then accepted the silk or paper covering to be glued and ... doped.

 

  I don't know if they still sell those products, as they needed adequate ventilation to prevent one from feeling ... 'dopy' - which is where the name came from when a lot was used on WWI aircraft fabric coverings to make the fabric water proof, grease/fuel resistant and air tight.  I suup[ose one could used Duco cement thinned (acetone?) and it would do the same thing.  I used thinned Duco (a clear hard drying cement) to soak into Myocene Era shell fossils to keep them from crumbling.  Those were obtained from the fabled Calvert Cliffs of Maryland when one could still access the fossil bearing zones.  These days opportunities are highly limited.

[Roger Pellett]

During the depression my father, a recent aeronautical engineering graduate, and my mother started the short lived  Viking Aircraft Co to supplement his meager salary.  My father designed model air craft, drew the plans, and produced the kits; balsa sheet, strips, and tissue paper.  The kits included a bottle of model airplane Dope, homemade by dissolving celluloid in acetone.  When painted on the model, the acetone evaporated leaving the celluloid.  Model airplane cement was supposedly a thicker version of the same stuff.

 

Roger

[mikegr]

16 hours ago, wefalck said:

In fiberglass reinforced resin, the fiberglass provides for tensile strength, not watertightness. The resin provides for compressive strength. The tensile strength is needed (probably) in RC models.

 

Carbon fibre is probably going to be very expensive and likely to be an overkill for a static model, where the tensile strenght provided by carbon fibre is not needed.

 

I would think carefully what you actually wanted to achieve with your layer of balsa-wood, what its intended function was. That then probably indicates what properties you are looking for in an alternative material. Is it supposed to be a structural material or just to provide a smooth surface.

Even talking about static models i am concerned about weight distribution, for an unknown reason i want my projects to be built not top heavy. Maybe later decide to make an R/C project.

For frame and bulkheads i would use a thicker and strong wood. But everything from main deck and above must be  lightweight and durable.

For smaller superstructure parts i have a lot of options. Aluminum, styrene and balsa sheets will do just fine. But for main deck  that can be from 50 to  100+cm long i would rather use something strong but also flexible so it can keep up with the curves of the hull.

Carbon fibre is expensive only if used extensively, making my own sheets is possible. Besides ordering high quality wood from Europe is 60€+ minimum shipping even for minimum order cause of the item dimensions. So at the moment i need either to improve what i have and learn how to use it functionally or need to find substantial materials.

[wefalck]

I think your problem will be that a deck is actually curved in two directions, something that carbon-fibre sheets don't like too much I believe.

 

Not sure, whether you actually would need the deck to add strength to the model, if the hull structure itself is already quite substantial as it seems. Maybe a sheet of 1 mm aluminium would be sufficient. It's relatively cheep and would not need a lot of surface preparation.

 

In the old days aircraft models were built with a balsa-wood frame and silk-span (either silk fabric or 'Japan' paper) cover. It was attached with a fast-drying varnish that also shrunk during the drying process, thus producing a sort of 'pre-stressed' structure. It was also practice to not only cover the wings in this way, but the planked balsa-wood hull for added strength. However, such processes would require a lot of work to achieve a surface that can pass for sheet iron/steel.

[Bob Cleek]

18 hours ago, wefalck said:

Carbon fibre is probably going to be very expensive and likely to be an overkill for a static model, where the tensile strenght provided by carbon fibre is not needed.

In my experience, resin bonded carbon fiber is one of the nastiest materials I've ever seen worked. When fairing it smooth, the sanding dust is indistinguishable from sanded pencil lead dust, and lots of it. It gets everywhere on everything. You end up looking like you've been working in an old-time coal mine all day. Clean-up is a nightmare.

[Bob Cleek]

1 hour ago, mikegr said:

Even talking about static models i am concerned about weight distribution, for an unknown reason i want my projects to be built not top heavy.

I would expect this to be an issue easily addressed by adding some inside lead ballast to the hull. 

[mtdoramike]

23 hours ago, mikegr said:

Υes there are. Carbon Fiber. More flexible, stronger and thinner that wood.

 

When you say resin you mean epoxy or fiberglass resin? I understand that cloth is required to make the hull waterproof. Is it required on static models?

Fiber glass cloth and epoxy resin. This is not a requirement for static, BUT if you are building the model primarily from balsa, you will need to re-enforce the wood due to the softness of balsa. You could just give the balsa a couple of coats of epoxy resin, but you will still be able to dent the wood with your finger nail quite easily. Why is carbon fiber or other woods even mentioned in this thread, the op asked about wood hardening. He's talking about a model, I think carbon fiber is a tad over kill.  

[mtaylor]

11 hours ago, Bob Cleek said:

In my experience, resin bonded carbon fiber is one of the nastiest materials I've ever seen worked. When fairing it smooth, the sanding dust is indistinguishable from sanded pencil lead dust, and lots of it. It gets everywhere on everything. You end up looking like you've been working in an old-time coal mine all day. Clean-up is a nightmare.

Add to this that the dust is NOT something you want in your shop, garage, or house or anywhere there's people, pets, etc..   Very nasty stuff healthwise.

[GAStan]

Check out Cactus Juice Stabilizing Resin, www.turntex.com.  Knife makers use it to stabilize wood they use for handles.  Available thru Amazon.

 

It's a heat cured resin.  Typically it is used with a vacuum for total penetration but I think with the thin wood you are using soaking it for a day or two would work.

 

Glenn

 

Edit:  I'm not affiliated in any way.  I have used it with good results.  It's consistency is thin, similar to water.

Edited November 19, 2021 by GAStan
Added more info at bottom of post.

[mtdoramike]

Thanks for the tip Glenn, I'm going to get me some of it and try it out.

[mikegr]

16 hours ago, GAStan said:

Check out Cactus Juice Stabilizing Resin, www.turntex.com.  Knife makers use it to stabilize wood they use for handles.  Available thru Amazon.

 

It's a heat cured resin.  Typically it is used with a vacuum for total penetration but I think with the thin wood you are using soaking it for a day or two would work.

 

Glenn

 

Edit:  I'm not affiliated in any way.  I have used it with good results.  It's consistency is thin, similar to water.

I found it also on a domestic seller, kind unusual. About 100usd per half gallon.

I also found this, it comes at 500 ml can. If does what promises might be a solution.

https://bormawachs.com/dettaglio_new.php?idprod=0641&cat1=2&lang=2

A friend who owns hardware store, gave me some polyester, he insist that soak the wood in it, will solve my problem. I get i will do some experiments and if doesn't work i will buy a specialized product.