NEW! Faster Search Option

Clear epoxy for filling drying cracks

Rooms's picture

I have some great wood for slab table tops, but there are a few small ½-¾" wide cracks 2-4" long. I'm thinking of filling and stabilizing them with epoxy and contrasting butterflies (or Dutchmen).


I don't have any experience with epoxy fillers. I'd like to go with a clear material if possible. What is a good brand? Must it be built-up in layers to eliminate bubbles? How do you finish/polish it? Long story short, what do I need to know?


Thanks,


Rooms

Scooter1's picture

(post #85415, reply #1 of 19)

West Systems have a nice product with a powder (than can be dyed) to match the finish) that fills cracks. You can also use saw dust, but the powders work better.

Regards,

Scooter

"I may be drunk, but you're crazy, and I'll be sober tomorrow." WC Fields, "Its a Gift" 1934

Regards, Scooter "I may be drunk, but you're crazy, and I'll be sober tomorrow." WC Fields, "Its a Gift" 1934
Quickstep's picture

(post #85415, reply #2 of 19)

I've used West epoxy for similar applications.  I have not added fillers, but simply put tape on the underside where the epoxy would leak out and created a dam on the top side to keep the epoxy in the intended area and literally poured the epoxy slowly into the void. The West epoxy is amber in color and blends well enough with surrounding wood for me and I like the way it looks in its transparent state better than making it opaque with colorants. Stirring the epoxy creates bubbles, but they settle to the top fairly rapidly. As the epoxy is absorbed by the surrounding wood, the air in the pores that the epoxy replaces creates bubbles. If you use the slow hardener, these will percolate to the surface where some attention with the stir stick will make them go away. If you're filling a large area, be careful about mixing large batches as they tend to cure too quickly. I've always overfilled so that the bubbles that came to the surface afterward got sanded out during the leveling process. I've read that letting the flame of a torch dance over the bubbles will make them expand and burst, but I've never tried it. Something about flames and wood........ The downside I've discovered is that finishing options become somewhat limited because the part filled with the epoxy responds differently to the finish than the rest of the board because it doesn't absorb anything. For me this meant stain and oil finishes were out. Varnish worked fine. Also, as I varnished, the epoxy filled area built gloss faster than the rest of the board.


Lastly, the epoxy will eventually get hazy if exposed to direct sunlight for extended periods. This is usually not a problem indoors unless the piece is left in a window.

forestgirl's picture

(post #85415, reply #5 of 19)

Quickstep, how do you create your "dam?"  That topside always gets me.

forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-) 

forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-) 

Quickstep's picture

(post #85415, reply #7 of 19)

To create the dam, I build up a couple layers of masking tape around the area to be filled. If you're a little careful while pouring, the surface tension at the edge of the tape will let the epoxy form a bit of a "pillow". Even without that, a couple of layers is usually enough since you really need to be only a tinch above the surface of the wood, since the epoxy doesn't shrink when it hardens. You do need to watch to ensure that the wood doesn't keep absorbing the epoxy and create a concave area in the fill.


PS, I occasionally do the fill while the lumber is still rough so there's more opportunity to level the epoxy during the final planing/jointing process. If you do this, make sure the epoxy is fully cured, otherwise it will gum up your blades.

forestgirl's picture

(post #85415, reply #8 of 19)

Great idea to do it before planing.  Is there ever a problem with epoxy not curing completely, say over a day's time?

forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-) 

forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-) 

Hendo's picture

(post #85415, reply #9 of 19)

Greetings.


Perhaps I'm not understanding this thread, but it sounds like the voids we are discussing are fairly large;  a quarter inch or larger.


The epoxy is quite hard when it dries.  Won't the  hard epoxy fills affect the planer/jointer surface finish, or reduce blade life?


I've used WEST System epoxy around boats for many years and it is great stuff.  I've sanded it, and drilled through it without difficulty.  But slicing it with a jointer or planer seems like it might be a different animal.


I'm a newbie, and hopefully others with more experience will chime in, but I would be concerned about how the jointer/planer would react to the hard epoxy fills... 


-Tom Henderson, Ventura, CA

Quickstep's picture

(post #85415, reply #12 of 19)

Depending on temperature, and type of hardener, the epoxy can sometimes take longer than a day to get fully cured. As a general test, if it powders when sanded it's cured. West Systems technical publications have pretty good information about the characteristics of their products and the use of the various hardeners. I like epoxy in general because it's cure rate is fairly predictable. I use the slow hardener for most things because it allows extra time. There's also an issue with epoxy that if you mix a large batch, as it begins the chemical reaction that causes it to cure it generates heat; the heat speeds the reaction, generates more heat and so on. Once this starts, the batch is ruined. I've even heard that it can start a fire. For me, this is just another reason to go with the slow hardener unless I'm doing something small. In general, the faster epoxy cures, the harder and more brittle it is. The slow hardener produces a softer epoxy which is better able to respond to movement in the wood. Sort of like the difference between regular varnish and spar varnish. Lastly, yes, the cured epoxy is a little tough on blades, more so if there's filler in it like colloidal silica. I try to get most of the excess off before sending through the planer. I often use a belt sander, but again, caution is called for; epoxy doesn't like heat.


West's website (http://www.westsystem.com/)has lots of info and some of their publications are good as well (some at least used to be free). Their magazine, while self-promoting has some interesting articles about things people have done with epoxy and other high-tech materials like kevlar and carbon fiber. They're mostly in boating applications, but some of those translate to our stuff too.

forestgirl's picture

(post #85415, reply #13 of 19)

Thanks for the detailed information.  Didn't know about the differences related to quick/slow cure mixes.

forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-) 

forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-) 

Rooms's picture

(post #85415, reply #14 of 19)

Thank you to all of you. You've given me what I needed to know and a few extra pointers as well!


Rooms

JeffHeath's picture

(post #85415, reply #15 of 19)

One more to add.  I use System 3's T-88 2 part structural adhesive epoxy.  It comes in two bottles and is in gel form.  I squeeze even amounts out of each in whatever amount I need, and mix with a spackling knife.  I use fine sawdust for filling voids, and use it all the time on slab table tops for filling knots and checks, especially in crotch wood.  It works great, and takes finish (at least what I use) very well.  When complete, you can't even tell.  I lay it in the void a little heavy, and let dry 24 hours.  Scrape to flat the next day, and you're done.


Jeff

A distinguished graduate of the School of Hard Knocks
forestgirl's picture

(post #85415, reply #17 of 19)

May be needing some epoxy on curent project, and have a question.  This one will be painted.  There are two places, one is about the size of a nickle, kinda dug out spot, the other is more linear, along an edge, quite narrow (say 1/8-3/16").  The reason I don't just eliminate them while cutting stock is that the way things lay out, I'd loose an entire 3' part by doing so.


(a) Do I need to sand those spots and at what grit?  I'm thinking "Yes" and "220"
(b) Is the fill located on an edge likely to hold fast?  The stock will be 3/4" thick.  I'd make that edge an underneath-edge, and in the back of the cupboard-type unit. 


forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-) 

forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-) 

sapwood's picture

(post #85415, reply #19 of 19)

For painted work you have easy choices. 1. Any good wood filler. These will shrink, however, so overfill and sand off the excess. 2. Bondo or other brand of polyester filler. These stink like crazy and give me a headache so I don't use them except outside. 3. Spot putty used by the car repair guys. This will feather to a very fine edge but it also shrinks. 4. Any epoxy with or without a filler will work well. You can get the hardware store variety or fancy stuff elsewhere. I use 5 minute epoxy a lot. For deep fills that need strength use cabosil for a filler. For deep fills that don't need strength and that may need shaping, use micro-balloons as a filler. If you cannot or choose to not acquire either of those, you can use fine sawdust as a filler or even shredded steel wool (think little tiny strands of re-bar).

I wouldn't sand these spots prior to filling. That will feather the edges and make for thinner fills.

RickL's picture

(post #85415, reply #11 of 19)

Try the aluminum foil tape found in hardware stores for dams. It's $6 to $10 a roll.  We use the West Systems 5 min epoxy for production work. It's now available in a tube to fit a standard caulking gun with a spiral mixing tube. Less chance of bubbles this way. The flashing with a propane torch does work well. Try it. We are about to use a new polyurethane material for filling cracks. Sets up in 60 seconds and is the consistency of maple syrup. Much more flexible we thing than the epoxy so it should work well.  It's new and won;t be available until June.  Have also used super glue for crack filling and feather checks. With accellerator it's almost immediate. Still has to cure a bit.  There a taiwan source that's half the price of www.fastcap.com super glue.


Edited 5/4/2007 8:40 am ET by RickL

grainwise's picture

(post #85415, reply #18 of 19)

snip <I've read that letting the flame of a torch dance over the bubbles will make them expand and burst, but I've never tried it.>

Quickstep, I’ve done this before, but I use a bic lighter. I keep the flame about a quarter inch off the surface. It does work well, just don’t stay in one spot too long or you’ll scorch the epoxy. I’d imagine that a heat gun would work too, but never tried it.

-Kevin

-If you didn't learn something new today, you're not looking hard enough!
OldGreen's picture

(post #85415, reply #3 of 19)

Rooms,

I've had good luck using System 3"s Clear Coat epoxy on cracks. It's viscosity is very thin and it seems to flow into the crack faster. On darker woods like walnut, I've added a little black dye to the epoxy and thought it looked pretty good.

Matt

www.oldgreenwoodworking.com

sapwood's picture

(post #85415, reply #4 of 19)

You should consider leaving the cracks unfilled. They can be cleaned out and lightly sanded inside. The addition of a butterfly might be appropriate and look cool also. I've left cracks like this before. It seems more honest to me. Filling would be the thing to do if that area is used for a particular purpose that needed to be smooth.

RRav's picture

(post #85415, reply #6 of 19)

West System expoxy, with a cabosill additive, for filling larger areas.
I've used this quite successfully on the canoe I've been building.
dries CLEAR

r2

medicmike's picture

(post #85415, reply #10 of 19)

If the tables are going to be in an area thats exposed to sunlight, or any UV rays, you must protect it or the epoxy will yellow rapidly. Spar varnish does the job.


Mike

wdrite's picture

(post #85415, reply #16 of 19)

I agree with Sapwood,  particularly  if the cracks are at the ends.  Cracks that are 1/2 to 3/4 inch wide  are too wide to fill with anything other than wood.  Anything else will have a different rate of expansion and contraction due to temperature and humidity changes and will eventually cause separation problems.  You could fill with wood patches or just leave them as they are.  Cracks in slabs due to drying shrinkage are characteristic of slabs.