Cracking of wood due to strong humidity deviations – need help

[vossiewulf]

9 hours ago, paulsutcliffe said:

Expansion can then become just as big a problem though as the shrinkage, my cheerful hull below after a year in the garage the wood is holly and was dry and seasoned but has obviously swollen after fitting and painting with watered down acrylic

 

I saw that in I guess your build log for it? I can't look at those pictures, it's like a scene from a 1960s Driver's Ed movie. Not to mention that's a few dollars of holly unless you milled it yourself. In which case the time and machines cost a lot. Either way a seriously bad day.

[Srodbro]

Bob Cleek:

 

”Acoating of white shellac is an excellent sealer for model parts.”

 

When would one apply the shellac?  Must be after planking, since we need moisture in the planks to form to the hull ( less so for a deck). But, If after planking, which is after adding blocking between ribs, how does sealer get to the underside of the plank?  The blocking should be coated as well, before planking?

 

Or, is the idea that you seal as much as you can , and continue to hope?

[druxey]

I suspect that humidity control is far more effective than any sealer.

[Bob Cleek]

3 hours ago, Srodbro said:

When would one apply the shellac?  Must be after planking, since we need moisture in the planks to form to the hull ( less so for a deck). But, If after planking, which is after adding blocking between ribs, how does sealer get to the underside of the plank?  The blocking should be coated as well, before planking?

 

Or, is the idea that you seal as much as you can , and continue to hope?

The latter. You do the best you can sealing, depending on the circumstances, and hope for the best. Usually, an element, such as a deckhouse, can be sealed as it's completed and before installing. Sealing is best done just before painting, or what would be painting if not left natural. Planking, of course, is sealed after the topsides are faired and the job is done. The shellac should be thin so that it soaks into the wood readily and doesn't leave any visible build-up after it's dry.

 

There will always be ambient moisture in the wood. I'm not sure, however, from where the misconception comes that it is necessary to wet wood to bend it, though. It's the heat that's necessary. Moisture, whether it be boiling water or steam, is simply one convenient way to convey heat from its origin to the wood you want to bend. The gondola builders in Venice actually bend their planks over a live fire, taking care not to burn the wood.

 

Some experienced modelers use other types of sealers. Minwax "wipe on" finishes seem popular. I'm not sure how Minwax compares to shellac in terms of a moisture barrier, but it will serve the same sealing effect to one degree or another.  It would provide a soft satin finish, and bring out the wood's color and figuring, better than shellac as it's intended as a visible finish. Shellac is capable of doing the same, but that requires a lot of hand rubbing and repeated applications, as is done with fine classic furniture, and their delicacy makes miniatures poor candidates for a traditional "French polished" finish. I can't comment on the archival properties of Minwax and other modern and often synthetic finishes. Like many materials available today, they simply haven't been around long enough for us to know. Shellac's longevity, on the other hand, is well established by the archaeological record.

1 hour ago, druxey said:

I suspect that humidity control is far more effective than any sealer.

Absolutely! That's the first line of defense. Moisture always seeks an equilibrium. The value of a sealer is that it slows the rate of absorption and evaporation and so "levels out" the cycling between high and low humidity. That retards the amount of movement. The cyclic movement of the parts will weaken the structure over time. The less movement, the longer the structure stays strong and tight.

Edited February 7, 2019 by Bob Cleek

[Drazen]

Well, spraying very thinned shellac is possible with my airbrush(es). I can do several thin layers after the first one has been set and soaked into the wood, the next one comes to make the sealing more tight.

What actually  is the problem with airbrushing, is that you have an airflow which must hit the surface in order to leave paint there. The areas, where the spray is not circulating (e.g. corners) will be covered not so well. But, I must try with a stronger amount of medium. I can make a big mess inside my gunports since they are more or less closed on the lover decks.

I will leave the 50% humidity till spring and when it starts to go over the 50% by itself, I will take my gun (airbrush-gun I mean) and do this job.

 

Bob, a very nice explanation., Thank you!

 

Drazen

[Bob Cleek]

4 hours ago, Drazen said:

Well, spraying very thinned shellac is possible with my airbrush(es). I can do several thin layers after the first one has been set and soaked into the wood, the next one comes to make the sealing more tight.

An airbrush will work, but I use a brush simply because I don't have to worry about masking and overspray or getting into the cracks and corners. I only apply a single coat, as thinned shellac will penetrate bare wood rather well. Adding more shellac on top of what's already soaked into the wood is really only gilding the lily. Thin as the shellac is, or should be, there aren't any problems with brush strokes mucking up the smoothness of the surface. It's barely noticeable when dried... or should be.

[Drazen]

Bob,

 

I do also apply shellac by brush on the areas which are accessible to the hand-brush.

The whole idea on airbrushing shellac was to protect the inner areas of the ship by airbrushing through gunports. The wood has not been protected from inside, but only from outside (this by hand brushing shellac or Golden GAC100). Still, the ship hull is getting or loosing moisture from inside and this happens for instance through the gunports. I think the most of the harm has been happened by non-protected inside and exchange through gunports.

I cannot reach every corner of the inside of the ship by brush - by airbrush probably better.

 

Please, check the previous photos of the ship in different stages in order to understand what I mean. Here again also the link to my build:

 

Drazen

Edited February 9, 2019 by Drazen

[paulsutcliffe]

My hms Sirius model is in the same garage as the cheerful Hull and I have had no problems with cracking or shrinking, it has been out there for years now, even through our latest hottest summer for years, however each layer as I have been building from the orlop up has been coated in layers of Tung oil thinned with spirits for the first coat 50/50

I'm not sure if this is what's made the difference to this model or not

Regards

Paul

[druxey]

Specie of wood also make a difference!

[Bob Cleek]

9 hours ago, Drazen said:

The whole idea on airbrushing shellac was to protect the inner areas of the ship by airbrushing through gunports. The wood has not been protected from inside, but only from outside (this by hand brushing shellac or Golden GAC100). Still, the ship hull is getting or loosing moisture from inside and this happens for instance through the gunports. I think the most of the harm has been happened by non-protected inside and exchange through gunports.

I cannot reach every corner of the inside of the ship by brush - by airbrush probably better.

Got it. The airbrush would be a better option. Applying the shellac to areas before they are closed up will prevent that in the future, of course.

[Drazen]

Let me now explain my strategy how to deal with my problem.

 

1..Get the humidity to approx 50% and keep it there by humidifier in winter and dehumidifier in summer.

 

2. After the wood has been acclimatised (e.g. 2 months), I am going to spray few very thinned layers shellac through the gunports. For this, I will probably close all, other openings to get the area filled well. I want to get shellac also in the corners inside of the hull.

 

3. Than, depending on how much the cracks went back/recovered, I am going to pour epoxy into the gaps where wood cracked.

 

4. Repairing of the decks if needed. I have some vital parts on the decks damaged (frames of the gratings) which are not so easy to be made again. Better would be not to need to repair this. Let us see.

 

What I am still unsure is if it makes sense to spray thinned epoxy instead of shellac inside of the hull. Epoxy would make the whole thing very solid, but I must check if there are good thinner in order to be able to clean the airbrush afterwards. Also, the toxicity of epoxy is an issue. But, for this I have a very good mask which has a very good filter build in.

 

Any comments on this?

 

Drazen

[Bob Cleek]

5 hours ago, Drazen said:

3. Than, depending on how much the cracks went back/recovered, I am going to pour epoxy into the gaps where wood cracked.

 

Filling cracks with anything that is as inflexible as epoxy resin isn't a good idea. If and when the wood swells up again, it will be pressing against that inflexible cured epoxy and cause greater cracking further down the crack. You'd be much better off to replace the cracked piece entirely, if at all possible, with properly dried wood of the same species.

 

5 hours ago, Drazen said:

What I am still unsure is if it makes sense to spray thinned epoxy instead of shellac inside of the hull. Epoxy would make the whole thing very solid, but I must check if there are good thinner in order to be able to clean the airbrush afterwards. Also, the toxicity of epoxy is an issue. But, for this I have a very good mask which has a very good filter build in.

As you seem to realize, atomizing epoxy resin isn't a good idea. Inhaling it isn't at all recommended. (And this advice is coming from a guy that isn't a sissy about such things.) Epoxy isn't going to make things much more solid unless you build up a rather thick coating and standard cured epoxy resin is quite brittle. (WEST Systems epoxy markets a brand of epoxy known as "G-flex" which cures to a somewhat flexible state. It's now being used as an adhesive in full-sized wooden boatbuilding, but I don't think would do you any good in this instance. As a structural material, epoxy has to be used in a matrix of stronger material, such as glass or carbon fiber fabric or matting. Again, I'm afraid a "do over" of the damaged parts is what is required to restore your model in this case.

 

Most epoxies can be thinned with alcohol or acetone, but I shudder to think what gunked up epoxy would do to an airbrush!

[Richard Griffith]

I agree with Bob.  Never mind that the air brush will be ruined, but your lungs and nervous system will be too.

 

Controlling the humidity is the best strategy, then replacing the cracked planks should 'solve' the problem.

 

BTW, Longridge's HMS Victory develop cracks in its hull planking……..        Duff

[vossiewulf]

Agree. luthiers use epoxy resin all the time as their grain-filler, but they spread it squeegee-style with plastic spreaders, I've never heard of anyone trying to spray it.

 

Also Bob is correct that you need to account for the relative flexibility of the glue, epoxy once fully cured is very rigid and replacement of the wood is a better idea. If it's not possible, use yellow glue as it remains flexible to a degree after curing. There are also some (apparently) good newer CA glues that remain flexible after curing, but they don't have much of a track record yet, and that's important in a model intended to last for decades at least.

[druxey]

The bottom line to all this discussion is, WOOD WILL MOVE. All you can do is minimize this by humidity control and not making any part too large. As suggested, painful as the thought may be, it is now a matter of re-doing some of the work by replacing the fractured pieces.

[Drazen]

On 2/10/2019 at 12:41 AM, Y.T. said:

Hi Drazen , is there a way you could thin the bulkiness of wood off the hull through ports? Like making your structure more as POB (planks on bulkheads) instead of solid hull you currently have?  My belief is that removing material from the structure, making it weigh less, reducing the structure to only a skeleton of a hull - same as real ship hulls were made - this makes the structure less susceptible  to humidity variations. Imagine a real ship made in the ship yard. They made it in dry air environment and when ready they dropped whole thing in the water. I think main trick is making ships of THIN  wood as real ships were made. Protecting with chemicals may help but .... for this-  there is no proven theory.

I am afraid this is in that stage no more possible. Please, check my build log. Changing basic structure would mean starting building from the beginning. But, please see my build process and if you have any ideas, maybe you see it from another perspective.

 

The solid hull was meant to get a solid ground base for the planking. This showed to be of great benefit. Still, it brings some drawbacks with it, as you see - the sensitivity to humidity. The idea of solid hull was not mine and not new. Some top builders are using it for their ships all the time. It seems that several "small" differences did accumulated and made the system to "tip over": I definitely have extreme variations in my work room, the hull is relatively large, I did not protect inside of the hull during building the hull, De 7 Provincien has in the middle a large area with gratings (so, there is an "U-shape" which means that the upper part wants to widen when the wood contracts)... Just some aspects.

 

Drazen

[Drazen]

On 2/10/2019 at 5:24 AM, Bob Cleek said:

Filling cracks with anything that is as inflexible as epoxy resin isn't a good idea. If and when the wood swells up again, it will be pressing against that inflexible cured epoxy and cause greater cracking further down the crack. You'd be much better off to replace the cracked piece entirely, if at all possible, with properly dried wood of the same species.

 

As you seem to realize, atomizing epoxy resin isn't a good idea. Inhaling it isn't at all recommended. (And this advice is coming from a guy that isn't a sissy about such things.) Epoxy isn't going to make things much more solid unless you build up a rather thick coating and standard cured epoxy resin is quite brittle. (WEST Systems epoxy markets a brand of epoxy known as "G-flex" which cures to a somewhat flexible state. It's now being used as an adhesive in full-sized wooden boatbuilding, but I don't think would do you any good in this instance. As a structural material, epoxy has to be used in a matrix of stronger material, such as glass or carbon fiber fabric or matting. Again, I'm afraid a "do over" of the damaged parts is what is required to restore your model in this case.

 

Most epoxies can be thinned with alcohol or acetone, but I shudder to think what gunked up epoxy would do to an airbrush!

When I was a student, a very good friend and me were restoring an old small sailing boat (Finn class). It was wooden and I can remember, we have had a diluting/cleaning medium for epoxy and for cleaning our tools. However, we did not use airbrush, but manual tools to apply epoxy. The whole ship hull was soaked with epoxy to prevent water coming in and to stiffen the structure. When sailing regattas (what we did), it was very important to have a very stiff hull which does not flex. We did not have money to buy a new boat made of new materials, but had to be innovative. 🙂

 

I think, I will protect inside of the hull with shellac than.

 

Drazen

[Drazen]

On 2/10/2019 at 11:18 PM, druxey said:

The bottom line to all this discussion is, WOOD WILL MOVE. All you can do is minimize this by humidity control and not making any part too large. As suggested, painful as the thought may be, it is now a matter of re-doing some of the work by replacing the fractured pieces.

Yup! The humidity control, i already do.

 

Drazen

[Drazen]

On 2/10/2019 at 9:50 PM, vossiewulf said:

Agree. luthiers use epoxy resin all the time as their grain-filler, but they spread it squeegee-style with plastic spreaders, I've never heard of anyone trying to spray it.

 

Also Bob is correct that you need to account for the relative flexibility of the glue, epoxy once fully cured is very rigid and replacement of the wood is a better idea. If it's not possible, use yellow glue as it remains flexible to a degree after curing. There are also some (apparently) good newer CA glues that remain flexible after curing, but they don't have much of a track record yet, and that's important in a model intended to last for decades at least.

What is a "yellow glue"? I know the "white glue" should be PVA-glue what carpenter are commonly using.

We have in Europe some sometimes other names and brands.

 

Just a note: Be careful with CA-glue + maple! It will leave a yellow film/shade near the bonds, which may only be removed by leaving the model staying on the sun for several weeks (something like letting plastic models near the window after the decals got a yellow shade). Wit e.g. pear wood, this is not the problem - no yellowing.

 

Drazen

[vossiewulf]

1 hour ago, Drazen said:

What is a "yellow glue"?

High strength PVA glues designed for woodworking. Here the most common is Titebond.

 

Are you sure the yellow shade from CA isn't a very thin layer of CA near the joint? I've seen that with several light woods, but only when there was an actual layer of CA on the surface. 

[Drazen]

OK, I think I know which glue you mean. I am using the D3 glue for professional and industry use, not the one which can be both in common building supplies stores. It is water resistant, but not meant for outside being left in the rain. There are wood glues from D1 as the lowest resistance, up to D4 with complete resistance on water. Since my model is not meant to swim, the D3 is more than enough.

 

Concerning CA: Please, please see the photos. A single water spout has been made here of 8 pieces and glued with CA gel glue from the back side. No glue on the visible side. I guess the fumes did the yellowing effect. CA fumes are strong and can ruin for instance a canopy on the plastic plane model. I have had many of this on gratings and got it away by letting them behind the window glass. To remove the effect here, I will try with an UV-lamp.

 

Drazen

[vossiewulf]

3 hours ago, Drazen said:

Concerning CA: Please, please see the photos. A single water spout has been made here of 8 pieces and glued with CA gel glue from the back side. No glue on the visible side. I guess the fumes did the yellowing effect.

Interesting, you're right but I have honestly never seen that, and I've used CA on maple before. I suggest trying a different CA glue if you can and see if it does the same thing before you totally rule it out for future use.