Cell-O-Fill

[Howard]

How many have tried and/or switched to the cellulose thixotropic that is being touted as a replacement for fumed silica?

 

Seems MAS and those that sell it are touting it's benefits. I have questions.

[cprinos]

I'm using it for my cs17. I used silica for my panel scarfs because I had ordered some with my epoxy and I didn't want to change what I was used to for the very first glue ups in the boat, but after that I've only been using the cellofill. I figure it takes about 2/3, maybe less to thicken epoxy compared to cabosil. It is also not as billowy as cabosil and doesn't fly all over at the slightest provocation. I've used it for all other gluing operations including laminations and have no complaints. My shop (garage) is connected to my house, so I figured the fewer toxic things I can employ the better. I did not do any kind of extensive testing, but I did do a simple joint failure test with both at the beginning and couldn't tell any difference.

[Howard]

It may work fine. Since the cabosil (fumed silica) is a mineral, it offers some structural properties in addition to working as a thickener. This cell-o-fill is a cellulose product, but then so is wood flour. Just curious if it offers the same structural benefits in places like fillets as the fumed silica does.

 

What I'm intending to do is develop a workable blend of thickeners to mix in bulk, then a ratio of epoxy to thickener mix so I can quickly make consistent batches, without it being a seat of the pants, trial and error process each time. It will also go faster, meaning I can get each batch out of the mixing cup sooner, with less danger of having large batches go off before I'm ready.

 

The fumed silica does blow everyone and does float on the epoxy and I always wear a mask working it. Would not mind switching to something else as long as I don't give up the structural benefits.

[Hirilonde]

Howard, when you say fumed silica is structura filler, what do you mean exactly? And why does it being a mineral make it so?

 

I have never considered any epoxy/filler mixture to be structural at all.  That it is an adhesive of structural materials (when used as a glue), or a binder of them (when it totally saturates and surrounds and binds  them together) is how I see it's contribution to the process.  But it is the other materials, wood, glass or carbon cloth. FRP etc.. that are the structural materials.  West System 406, aka colloidal silica is an ahesive filler and considered one of the strongest due to density and that it is inhert.  It comes as a very light weight appearing powder, but most of what is in the can is air. It thickens the epoxy to a good gap filler without any significant weakening of it as a bonding agent.  The hardened or cured version of the mush is actually quite brittle.

 

I have no knowledge of Cell-O-Fill, what it is or how well it performs as an adhesive filler.  I would want to see some sort of report by a known entity before I used it.

[hokeyhydro]

colloidal silica IS fumed silica.

[Howard]

Fumed silica goes by many names, such as the generic colloidal silica and the brand names Cab-o-sil and Aerosil. While they all appear to do the same thing, if you start digging into it, they are somewhat different. Some are said to be hydrophilic (attract moisture) and others hydrophobic (repel) moisture. Having said that, I'd think 99.9% of us would all use them the same way and not be able to tell the difference. I think the key feature is they help create a stronger, denser, thicker and compared to some similar products (such as wood flour) smoother spreading epoxy. Most of us who have tried to fair out a mistake made with silica know how hard it is to sand (vs. something like microballons or talc). Fumed silica is also an inert mineral.

 

The cell-o-fill, by comparison, is a cellulose (type unknown) that appears to have many of the same properties, except for the density part. I also don't know about the smoother spreading part, nor the strength of the resulting structural part. I've always related strength to density, so my first thought is to group a less dense cellulose product closer to either wood flour, talc or even microballons. The latter two will thicken epoxy too, but not something I'd want in my structural fillets.

 

Fumed silica is light and fluffy and does go airborne pretty easily and not something I'd care to breath, but at the same time, it does offer some benefits and I'd hate to give those up if the replacement isn't as good or better.

 

BTW, the fillet blend I'm working on is 2:1:1, wood flour, fumed silica and milled poly fibers. Going to be doing some tests of this blend against the same thing with the cellulose. Curious to see how it turns out.

 

To anyone still curious, this from the MAS epoxy site:

 

Fillers & Additives

Fumed Colloidal Silica (also known as CAB-0-SIL)
When a hard solid with high density is needed.
Application: structural bonding, filling and filleting

MSDS Sheet

Milled Fibers (1/32" milled fiberglass)
Provides extremely high strength.
Application: enhanced strength fillets and bonding

MSDS Sheet

Phenolic Micro Balloons (organic phenolic hollow spheres)
When low density, light weight, sandable, paint ready surfaces are required.
Application: fairing and filling

MSDS Sheet

Wood Flour
When a hard solid for filling and filleting is needed.
Application: wood gluing, filleting and bonding

MSDS Sheet

Cell-O-Fill
Non toxic, non-carcinogenic. For use in place of Colloidal Silica when high strength and low density are required.
Application: bonding, filling and filleting

[cprinos]

for filleting applications, filler density affects the recommended fillet radius (see p. 103 of http://www.westsystem.com/ss/assets/HowTo-Publications/GougeonBook%20061205.pdf

)... so wood flour fillets need a larger radius vs silica.  Mixing cellofill in wood flour has the same effect as mixing in silica --- it tends to make the the fillet slurry a little smoother than just wood flour alone. I did some test joints as described in that section of the gougeon book using same size fillets for silica and cellofill and they both had correct failure modes (e.g. broke in the wood, not the fillet). I didn't try to find the absolute minimum fillet size for each....I imagine the silica would allow the smallest radius.

[Howard]

I did some similar tests a few years back, but this was with fillets and glass tape. My tests were of 3/4 inch fir plywood held in a 90 degree orientation, with fillet on one side, fillet on two sides and various tape configurations. In almost every instance, the plywood was the weak link. Even a small fillet and single layer of 6 oz tape was stronger than the plywood, which failed at the cellular level of the wood that formed the plys. Has always made me wonder about the necessity of 3, 4 or 5 layers of tape on joint when even one layer is stronger than the wood below it. I still do it when spec'd, but smile when I do it.

 

Good to hear the cellulose filler is that strong too. If it is strong, and works smooth and avoids the nasty issues, maybe there is a good reason whey they recommend using it?

[Blkskmr]

 I did an informal test. I epoxied two 2 x 3/4" x 12" long boards at a 90 degree angle to two 1 x 6 x 12" planks.   One joint was made with a cellulose fiber filler and the other was with colloidal silica.  The purpose of the test was to determine relative strength of one versus the other.  Would cellulose fibers make an acceptable replacement for colloidal silica? Most data suggest colloidal silica makes a stronger joint. The colloidal silica joint failed at 30.4 ft/lbs.   The cellulosic fiber joint failed at 44 ft/lbs. 

( I would like to post photos but can't figure out how to attach photos)

 

Notes and caveats:

1) This is one data point so the results are almost meaningless.... but it was a fun test to do.

2) I tried to make the fillets on each equal, but I can see that the colloidal silica joint was not as broad

3) The colloidal silica joint failed  at the fillet.

4) The cellulose fiber fillet failed at the wood.  The wood failed. 

 

Summary:  All data in the market place suggest colloidal silica is stronger than cellulose fibers and I agree.  I  was pleased to see that I could make a cellulose fiber fillet joint that would be stronger than the wood.  That is what I wanted to know but I did the comparison just for fun.  I feel comfortable using the cellulose fibers on my fillet joints on my boat.   My reason for wanting to use the cellulose is due to the fact my wife and I both have asthma and she has had another serious life threatening illness.  
We do wear respirator like masks.  My thought is if we can make joints that are stronger than the wood we are joining using a material that seems to have fewer potential adverse health affects, then we should.  We will still wear our masks.

[Tom Lathrop]

I did some similar tests a few years back, but this was with fillets and glass tape. My tests were of 3/4 inch fir plywood held in a 90 degree orientation, with fillet on one side, fillet on two sides and various tape configurations. In almost every instance, the plywood was the weak link. Even a small fillet and single layer of 6 oz tape was stronger than the plywood, which failed at the cellular level of the wood that formed the plys. Has always made me wonder about the necessity of 3, 4 or 5 layers of tape on joint when even one layer is stronger than the wood below it. I still do it when spec'd, but smile when I do it.

 

Good to hear the cellulose filler is that strong too. If it is strong, and works smooth and avoids the nasty issues, maybe there is a good reason whey they recommend using it?

 

Glad to hear someone else say so Howard.  My testing shows that multiple layers of glass tape rarely provide greater strength to a fileted joint.  The failure mode is almost always braking of the wood or sheer failure of the tape to wood interface.  In a side load on a "T" joint, failure is usually a hinging about one edge of a filet and ripping of the opposite layer of glass from the wood in sheer.  These failures will seldom be prevented by adding more glass layers.  Still, most people have been taught to use and expect to see multiple layers and so most designers will specify that.  I'm being a bit uncertain because there are instances where thickness of the glass adds strength.  In many cases a filet alone is perfectly adequate.  Motor mounting joints get multiple layers for me.  Can't be too careful there.

 

I have found that wood flour is often thixotropic also. 

[PeterP]

Thick and Thixotropic are two different concepts. Thixotropic refers to a fluid whose rheological properties change with application of shear stress. It forms a pseudo gell structure (thickens) which breaks down with application of force and it becomes runny. Ketchup is a great example - it is thick yet you skake the bottle and it becomes runny -every time. In contrast when you thicken epoxy it stays thick no matter how hard you stir it and then it sets up (permanently). Not the same thing! PeterP

[Ken_Potts]

   Anyone who is concerned about the safety of using colloidal silica should read the MSDS (material safety data sheet) - Actually, anybody who ISN'T worried about it really ought to take a look.  And while you're at it you really should look at the MSDS for epoxy hardener too.  It seems like a lot of people think it's safe to drink the stuff just because it doesn't stink .  The West Systems website has downloadable MSDSs for their products.  I'm sure other companies make the information available too.

   There are safe ways to handle these materials and it's easier to be safe if you know the hazards.

[Blkskmr]

Thank you for the responses.  I agree it is important to read the MSDS and to wear appropriate protective equipment. 

Regards to all. 

R Johnson

[PAR]

Ken, I don't know anyone with half a brain that likes to or tries to swim in epoxy. Fully cured it's quite inert (body imbedded medical electronics, like pacemakers are sealed with epoxy), but unfortunately we tend to play with it when it's not. Silica on the other hand is used in all sorts of stuff from food, to makeup and everything between, so don't get too excited about what you see on a MSDS, unless you understand the realities of the chemistry or physical properties of the materials involved. Assuming reasonable precautions, not excess mind you, most will not have any issues.

[LennieG]

I have ended up with some serious lung issues which show up numerous spots on a cat scan. Basically, it seems like there is a foreign substance surrounded by inflammation in many places. This lead to numerous (false it would seem) diagnoses of pneumonia over the winter, and long story short, a large amount of a bacteria deep on my lungs. It is not cancer. It is a household bacteria that attacks vulnerable hosts, and I have preexisting lung issues.The treatment is 3 heavy duty antibiotics for up to a year, each with their own problematic potential side effects.

The reason I bring it up:

It seems like a bit of a mystery to the Doc or medical community how I got this, but epoxy is th easy answer because it is known to be toxic and not really understood. The Doc has read the MSDS info.

In the 20 page booklet that was given to me relating to my disease( which has fancy names and different flavors) Silica seems to be a known culprit.

If I am you, I use Cell-a-fill and wear a respirator more than usual. I trust my condition is treatable and I will get better.

As I recall John Harris made an analogy at WBS that cabosil is a little stronger , but both are 10 times stronger than you need.

[Ken_Potts]

   PAR - I probably shouldn't have made the joke about swimming.  Over the years I have seen many comments about how epoxy seems safer than other things like polyester resin because it doesn't smell as bad but the actual MSDS for epoxy hardener offers some food for thought (and procedures to safely handle a dangerous substance).

   The advice I offered was simply to read the MSDS and I stand by that.  Howard was good enough to post links to several filler materials and to that I'll add a link to the MSDS for West Systems 205 hardener - http://www.westsystem.com/ss/assets/MSDS/MSDS205.pdf- I think it is far better to read the actual document than to listen to my (or any other layman's) advice.

   As far as whether I understand the realities of chemistry, the actual reason for the existence of something called a Material Safety Data Sheet is so non-chemists can handle a material safely.  If you'd like I'll be more than happy to check with a chemist about whether cured epoxy is "inert" and report back here.  I have my suspicions but I won't speculate.

   And to all - I'm sorry for the hijack of this thread about the strength of fillers.  I just wasn't able to keep from rising to the challenge of "...don't get too excited about what you see on an MSDS, unless you understand the realities..."  I've added the link to the MSDS and if I think I need to say anything else about the subject I'll start a different discussion.

[Howard]

Ken:

 

Your note about the unknown dangers of working with these chemicals is well taken. I was a farm kid back in the late 60's, early 70's and farmers of all stripes readily signed on to the concept of better living through chemistry. One in particular was a broadleaf herbicide known as Lorox. As my uncle once told me, we were lead to believe it wasn't dangerous at all.......safe enough to drink. That wasn't the case. It was quite common for me to get a horrible sunburn on days when I was tasked with spraying the stuff and never thought anything about it until I overheard another farmer mentioning that he was suffering from the blistered lips, nose, etc. from that chemical, which made a person photosensitive. Could be coincidence, but I've been under the knife for skin cancer about 4 or 5 times. Almost every farmer over the age of 70 has seen twice that. Not really the chemical companies fault, exactly, they created and offered a valuable product, and we just didn't know about the dangers of using it. So, like a lot of things, realize there may be dangers with this stuff and to the extent possible, use abundance of caution and don't take chances. Don't not do it, but don't go out and roll in the stuff either.

 

My personal fear is the fiberglass. Not using it, but sanding it. I shudder to think that all those little microscopic shards of glass are flowing into my lungs when I'm sanding the stuff. Full filtered respirator at all times. Ear protection.......for the sound and to keep all that airborne crap out of my ear canals. Really should be doing something better than safety glasses for my eyes and that is WITH a vacuum hose attached to my sander at all times. It gets most of it, but not all.

 

On the cell-0-fill, I'm going to be using it. On any fillets, I'm also using poly fibers, which I'm told function more or less like re-bar in concrete. Not much chance the fillets and epoxy are going to fail, but what to do about the multiple layers of glass (see Tom's comment about post 10).

 

Case in point would be the glass schedule for the Princess CB trunk. Plans suggest as many as 3 or 4 layers of 1208 biaxial glass tape staggered on both sides of the CB trunk at it's join with the bottom panels. I'm not a designer, but as a builder, I sometimes ask, what purpose does this serve? I look at that and think to myself at that particular junction, the fulcrum point is the bottom panels themselves, so there is very little side stress that much tape is going to need to overcome. But then you realize that unless the CB trunk is supported somewhere else, the force created by the long lever that is the CB itself passes through that joint and up to the top of the CB trunk, putting those taped joints under tremendous strain of tension and compression during tacks, and even more so if there is a grounding. But going back to Tom's comment, what good is 4 layers of tape if the underlying wood is going to peel first anyway? Plenty, if if prevents the trunk from moving at all. But that may also presume it's not going to be supported by any other means, and in my situation, that won't be the case (no pun intended). That case will have several divider panels attached to it forming a number of structural I-beams connected to the bottom panel and topsides on the outboard side, so when it is done, it couldn't move if it wanted to. The more dividers and panels we add, with taped fillets, the stronger this gets.

 

As for me, again I have to trust the designer, so this gets the full tape schedule as per plans, plus whatever I add to the sides. I'm fairly certain it will be strong enough the CB itself will snap before this gives out........which if something has to fail, that is how I'd want it to happen.

[PAR]

The perils of epoxy are pretty well known and documented. While still chemically active (about 3 weeks after hard cure) it's toxic. This is where most of use are sanding it, finishing it, etc. and when you can get cured, but still chemically active goo in our lungs. It acts in two ways against us, first is as a hard particulate, imbedded into lung tissue and mucus membranes of the bronchial tracts. This is much like black lung that coal miners experience and an exposure thing that's easily handled with good particulate masks. The second and more difficult issue is what happens once it is in the lungs and chemically active or if it's forced into the blood stream with a solvent wipe. This is a mainline to the brain and create a potential for a number of problems. The fix for this is to not use a solvent to get it off your skin, don't eat it, butter your toast with it, etc. The biggest problems boat builders face is the airborne dust of chemically active, but dry goo. This brings both issues up, but a good mask will stop all but the most sensitive from contracting anything. Dust collection is a good idea and this can be a simple home made thing with a shop vac and a work area hood or funnel, to suck off sanding dust as it's being created.

 

Yes, epoxy is used on medical devices implanted in the human body. It typically is an "F" or "P" formulation, instead of the typical "A" formulation we boat builders employ, but it's still the same molecule (mostly). There are a number of epoxy formulations (several), but we use mostly the A mix with some using the F, unless you're into infusion and or prepeg formulations.

[Don Silsbe]

Great discussion! I've always felt that if I have the safety equipment hanging on a hook in my shop, and I don't use it, that's just plain foolish. At least that's what I tell myself when I fin myself thickening "just a small" batch of goop. And even though epoxy is nearly odorless in the liquid state, I still find that I've got a headache when I don't wear a respirator. And I do have a friend who "swims" in epoxy-- he doesn't wear gloves!!! He's not concerned, because he can clean up with vinegar. You should see his hands. So we need to discipline ourselves to use our safety equipment. At least that's what I keep telling myself.

[Steve W]

I am scared to the point I wear a full respirator with dust covers. I have full dust collection and use a sander attached to a vacuum with a fine bag filter. I mix my batches outside so the loose dust isn't blowing around my basement shop. How long does this all take and cost? Not much really compared to one health problem. Howard is right about farming. the amount of junk used in modern farming is scary and yet nobody pays attention. I eat from an organic co-op, but it cost a lot of money to eat that way. Great discussion.

 

Take Care,

Steve