Replies

1. 
   forestgirl | Oct 02, 2003 08:19pm | #1

   I can't give you the kind of technical info you're asking from Jon, but in terms of practical approaches, 'twere I undertaking your task I'd make the first couple of wetsanding coats pretty thin and use more like 220 or 300 grit paper to put it on.  I've wetsanded red oak with Watco and gotten virtually no weeping.  The idea is to produce a bit of a slurry with the wetsanding and not have so much Watco that there's too much for the pores to handle.

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

1. 
   parrothead | Oct 03, 2003 03:27pm | #5

   Hello forestgirl and jazzdogg, thanks for the response. If I start wet sanding at 220 or 300 what should I sand the pieces to before I start? Then what should be my final wet sanding grit 400, 600. Right now I dry sand to 400 and then wet sand to 600, I do this only when I use an oil finish, mostly cherry. Other woods that I finish in poly are sanded to 220 and then stain, sanding sealer and poly go on, dry sanding between coats.

   Finishing has always been my down fall. After I figured that I need to spend as much time on the finish as actually building the piece it is getting better, but I am still not very good.

   Thanks Mike We are the people our parents warned us about. J. Buffett

1. 
   forestgirl | Oct 03, 2003 07:02pm | #8

   I'd stop my dry sanding at the same grit that the wet-sanding starts at, but keep in mind I'm a neonate when it comes to finishing experience.  It's hard for me to imagine taking sanding past the 400-grit stage and getting any visible difference.

   It could well be that at least half the cause of the excessive bleeding you're experiencing is too much oil.  I spread a thin coat on the area, and then dip a small piece of sandpaper in the oil container, and sand, trying to keep just enough oil to have no "drag" but not so much that the paper is gliding.  When it starts to glide, that's too much oil, IMO.

   And, I don't let it sit on the surface -- I sand quite a bit, but then wipe off right away, especially the first 2 or 3 coats.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl   ;-)

2. 
   jazzdogg | Oct 03, 2003 11:40pm | #9

   Mike,

   I use a scraper followed by 220-grit before applying the oil. BTW, when I sand-in an oil finish, I sand with some vigor - the friction warms up the oil, which seems to help it penetrate. I've cut through a few oiled test pieces and observed penetration of about 1/4 inch. You might want to read about Thomas Moser's technique - from what I recall, he warms his oil to about 130-degrees before application.

   Good luck,Paul

2. 
   jazzdogg | Oct 02, 2003 08:35pm | #2

   Mike,

   It's "normal" for the oil to percolate out of the pores after applying an oil finish. I generally start sanding-in an oil finish with 220-grit silicon carbide abrasive, working my way up a grit every day of two. Even though the sanding slurry fills the open pores a little more with each successive coat, bleedback still occurs. I usually check the wood about once an hour after applying the oil, wiping up any bleedback before it hardens and contaminates the finish. This is particularly critical on the final coat, which I'll let cure for at least a week before waxing.

   FWIW, I prefer to use Liberon finishing oil - it seems to polymerize a little more quickly, and coats seem to build a little better than "pure oils" that remain thinner and liquid a little longer.

   Hope this is helpful,
   Paul

1. 
   Elcoholic | Oct 02, 2003 11:16pm | #3

   Just a guess on my part.  The oil drying/curing process generates heat and therefore the oil expands and weeps.  (Think spontaneous combustion)  Besides wet sanding the slurry into the pores I use 50/50 BLO and mineral spirits with a shot of Japan drier.  It doesn't eliminate bleeding, but it seems to speed things up.John O'Connell - JKO Handcrafted Woodworking

   Life is tough.  It's tougher if you're stupid - John Wayne

3. 
   ron61 | Oct 03, 2003 12:40am | #4

   Or you could only put on a small amount with a rag just enough to color the wood and not have the weeping.

   Who Ever Has The Biggest Pile Of Tools When You Die Wins

4. 
   Crunk | Oct 03, 2003 04:15pm | #6

   Make sure your shop is warm.  Make sure the oil is warm.  Wet sand in smaller amounts (don't flood the project) and buff like a demon.  Some weeping is unavoidable, but this ought to help.

5. 
   jonsherryl | Oct 03, 2003 06:24pm | #7

   Mike, sorry to be so late in jumping into your thread here, but I just found it. As for oil puddles, about all I can offer are some theoretical insights based on my personal experience...but anyway, here's my take on it: 

   First of all, I suspect one of the reasons oils tend to weep (and this would be the case regardless of the species) is that, as the dry wood absorbs the oil, the oil causes the wood tissue to expand slightly (as if the wood were being rehydrated.) As this happens, it constricts the capacity of the cell cavities and causes some of the oil to burp out. This theory would seem to make sense, since the effect seems to diminish with progressive coats of oil. In other words, once the wood is saturated with oil, the tissue's expansion stabilizes and successive applications of the oil tend to remain on the surface, rather than going in and coming out.

   As for cherry specifically, this is a truly strange species in that it virtually never has uniform porosity and, to some degree, it tends to accept all finishes in a sort of patchy fashion. I suspect the primary reason is that cherry virtually always has some waviness in its grain. Sometimes it is pronounced enough to produce a noticeable and attractive curl, but when the waviness is extremely subtle, it can cause finishing problems. This slightly undulating figure presents what amounts to exposed sections of oblique end grain on the flat sawn surface, which have varying porosity. The more perpendicular the grain is to the surface, the more it absorbs.

   I've also noticed that commercially steamed cherry (a procedure the mills often use now to make the wood's color a little more uniform) seems to exhibit this problem much more than does air dried cherry...so, I suspect there is yet another devil in the details. The extractives in Cherry are rather gummy and I suspect steaming this species may cause these gums to migrate and gather in an uneven fashion that affects the wood's subsequent porosity...but that's just a theory born in desperation, since I don't know what else could explain it (?) 

1. 
   Jeffj | Oct 10, 2003 06:05pm | #10

   The chemical explanation has to do with something called surface tension, contractile forces in liquids that cause them to either be repelled (assume the shape of a bead) or wet out a solid surface they contact. Think of water applied to a waxed surface. The water beads up because of high surface tension disparities bewteen the wax (low surface tension) and the water (high surface tension). The water does this because it has to expend less energy when in it's the shape of a bead. Water applied to glass does the same, unless you apply something called a surfactant (surface active agent) to the water to lower it's surface tension. Ammonia, detergents and soap added to water will all do this and allow the water to wet the glass better.

   When you apply an oil/mineral spirits (low surface tension) mixture to an open grained wood, the first part to evaporate is right at the surface. The open pore retains the mix of oil/solvent and what happens physically is a disparity in surface tension between the still wet oil/solvent in the pore and the surface of the wood where it meets air. The wet oil in the pore "wants to crawl out" (for lack of a better term) and form a bead or sphere. Note that the mineral spirits solvent is the culprit here, which gives the mixture very low surface tension. Weeping does not happen with 100% linseed or tung oil.

   To eliminate weeping on open grained wood, apply a thinner first coat and wipe the excess off immediately. Don't flood and let the oil sit. Or apply a sealer coat of shellac (1/2 pound cut) first. Both methods eliminate the retention of the oil/solvent in the open pores.

   Also - this can happen with closed grained figured woods like cherry or maple, the more absorbant figured areas acting like resevoirs for the oil/solvent.

   Jeff

   Edited 10/10/2003 12:21:21 PM ET by Jeff

1. 
   forestgirl | Oct 10, 2003 07:02pm | #11

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

2. 
   jonsherryl | Oct 10, 2003 09:08pm | #12

   Good, thorough explanation, Jeff. Do you have any insights on why the weeping and beading seems to diminish with subsequent coats? Is it due to the polymerization of the oil? I know I notice it less with Tung than with linseed and I think tung has the better polymerizing characteristics.

   Also, since you seem to be really up to speed on the chemistry aspects of this, have you run across what it is about penetrating oil sealer coats (or oil stains) that tends to retard the drying time of a polyurethane top coat? I've had experiences where the first poly top coat has taken literally days to cure, while the old-formula alkyd resin varnishes (and/or shellac) I usually use over oil doesn't seem to have the same problem. Once the finishing regime gets down to poly-on-poly, the problem goes away...but it sure is a pain waiting out that first poly top coat.

1. 
   Jeffj | Oct 11, 2003 07:19pm | #14

   <<Do you have any insights on why the weeping and beading seems to diminish with subsequent coats? Is it due to the polymerization of the oil? I know I notice it less with Tung than with linseed and I think tung has the better polymerizing characteristics.>>

   When the porous/figured areas or pore cavity is sealed, it won't happen as less liquid is retained (it's pulled off when you wipe away the excess)

   <<Also, since you seem to be really up to speed on the chemistry aspects of this, have you run across what it is about penetrating oil sealer coats (or oil stains) that tends to retard the drying time of a polyurethane top coat? I've had experiences where the first poly top coat has taken literally days to cure, while the old-formula alkyd resin varnishes (and/or shellac) I usually use over oil doesn't seem to have the same problem. Once the finishing regime gets down to poly-on-poly, the problem goes away...but it sure is a pain waiting out that first poly top coat.>>

   Most consumer brand stains are long oil formulas and have changed over the past ten years to comply with the Clean Air Act of 1990. To get the stains down to a manageable VOC content most manufacturers changed to different resin systems as well as exempt mineral spirit solvents. It's probable these formulations are having a retarding action on the first poly coat, probably due to migration of some of the stain components into the poly or perhaps they act as oxygen inhibitors.

   JJ

3. 
   parrothead | Oct 10, 2003 09:25pm | #13

   Jeff, thanks for the reply. What a great answer in terms that I can understand. I guess that Jon brings up a good point that you elude to, why do subequent coats minimize the effect. Second if I use a sealer coat of shellac, would that prevent the absorbtion of the oil into the wood that I am trying to get?

   Thanks again MikeWe are the people our parents warned us about. J. Buffett