Powdered Lime as Epoxy Filler

[David Showalter]

I've read somewhere that Powdered Lime is an aceptable filler for epoxy. To be used like Silica or Wood Flour. What's the opinions out there?

[Cuyahoga Chuck]

Silica and wood flour are considered medium strength fillers. Chopped glass is considered high strength. Micro balloons is easy sanding and good for fairing. What's the good news about powdered lime?
Charlie

[igatenby]

Off topic, but, I know they use it to enhance the hit from Betel Nut in Papua New Guinea. It makes an awful mess of their teeth.

Ian

[Stiletto]

I think it would be fairly heavy for its volume compared to wood flour etc.

[Thorne]

Don't you also have the hydrophillic element to consider -- fillers that "love" water (like sawdust) will absorb more evil moisture than those that don't, like microballoons and glass.

And isn't lime an organic solvent of sorts -- used on dead bodies, right? Could that make working with it a bit hazardous?

[ 09-30-2005, 10:49 AM: Message edited by: Thorne ]

[Keith Wilson]

Lime? I think it was powdered limestone that was used as a hard filler. Lime is Calcium oxide, CaO, while limestone mostly is Calcium Carbonate, CaCO3 - much less reactive. Dave Carnell did some experiments on it a few years ago, and AFAIK he never endorses something without testing it pretty extensively himself. Here's the quote from his "epoxy knowhow" web page. (http://www.angelfire.com/nc3/davecarnell/epoxy.html)

FILLERS

Fillers are added to epoxy resin to make putties for two kinds of uses that have greatly different requirements. Those used for structural joints alone or in combination with fiberglass should be as strong as possible. Putties used for filling and fairing must sand easily.

The best filler for structural uses is pulverized limestone (flour fine, not gritty as ground limestone is). It mixes to a putty that doubles the resin volume and is dense and strong. It is universally available as a fertilizer material at under a nickel a pound. It is a real bear to sand. Portland cement is pretty much equivalent. Talc, another mineral, is as strong and sands easily. It also is thixotropic (the putty does not flow, but will spread). It is available from fiberglass supply houses at around a dollar a pound. For small amounts buy generic baby powder. Check that contents are talc and fragrance. For filling and fairing applications hollow bead type fillers sand most easily because they are hollow and break. There are three kinds of beads: thermoplastic (Microlight®) which can soften with heat; phenolic, which are usually dark-colored; and glass (Scotchlite®), which are white. The glass beads make the lowest density filler and are the lowest cost. White wheat flour from the kitchen is a pretty good filler for finishing putties.I haven't ever used it myself. I'm not fond of construction that uses fillets of epoxy, and I'm sloppy enough with goop that the difficulty of sanding limestone/epoxy seems like it would be significant. OTOH, it's VERY cheap compared to almost any other filler, and it certainly would be strong.

[ 09-30-2005, 11:02 AM: Message edited by: Keith Wilson ]

[Cuyahoga Chuck]

There are two kinds of lime that are available at any garden supply. Powdered limestone and hydrated lime. Both are relatively cheap and are used to change the acidity of soil. These products are fine powders and are sure to get in your nose on a windy day but are not particularly dangerous otherwise.
Other than being cheap their suitability as thixatropic agents should be based on some benefit that is not present in the thickeners we commonly use.
Does this stuff make a stronger product, have more abrasion resistance, is it easier to sand or whatever? If you pick up any can of West Systems thickeners there is a chart that states which of their thickeners is good for which particular use.
Why is anybody championing powdered lime as a thickener over portland cement, play sand, crushed egg shells, blasting grit or Bisquick?
Charlie

[Keith Wilson]

FWIW, hydrated lime is Calcium Hydroxide, Ca(OH)2. I have no idea if it's any good for epoxy filler.

I believe that Dave Carnell advocated using limestone because it is very cheap and, based on his experience, produces a strong structural fillet. Perhaps he can answer himself; he used to poke his nose in here from time to time.

[ 09-30-2005, 11:24 AM: Message edited by: Keith Wilson ]

[Cuyahoga Chuck]

Saying something is "strong" isn't very analytic. Stronger than what? How does any of the afore mentioned agents stack up against old standbys like chopped 'glass or wood flour.
In the few years I've followed S&G boatbuilding a lot of things have come and gone. Are these recomendations recent?
Charlie

[kc8pql]

I used to build R&D prototypes and patterns for Owens Corning Fiberglas. Limestone is a commonly used filler in polyester/glass pultrusions because it is cheap and dense. Bare parts soak up water and needed to be coated for exterior use. We used LPU.

Edited to add: I wouldn't use it for anything I can think of on a boat. The big cost savings came because of quantity. Tons not pounds. For the small amount needed to build a boat, the savings wouldn't be much. I build a 25,000 lb. boat and only used about 15 lbs. of Cabosil costing maybe 75 bucks. Compared to the total cost of the boat, that's nothing.

Ken

[ 09-30-2005, 09:34 PM: Message edited by: kc8pql ]

[ssor]

Also used is talc, asbestos( not a real good idea),lint from clothes dryers filters. You can use just about anything that you can blend with the resin but why set about to reinvent the wheel ( round is best)? There are several very good fillers on the market select one suitable for your purposes and use that.

[David Showalter]

Okay, sounds like limestone was the correct question. I agree that the best filler would be the traditional micro baloons, cabosil, etc. Thanks for the help.

[sdowney717]

I always thought diatomaceous earth would make a good filler. It can be bought for use as an insecticide fairly cheap. Also if you eat it you dont get sick, it kills bugs inside and outside.
http://www.pinnaclefarms.ca/Gaia_Tree/PhoebeDE.html
http://www.biconet.com/crawlers/DE.html
DE is odorless and nontoxic.

DE is composed of finely milled fossilized shells of minuscule organisms called diatoms. The microscopically fine, sharp edges desiccate the insects' exoskeleton upon contact and the pests dehydrate and die within hours. The insects also die when they eat the dust.