I am trying to refinish the surface of a dinner table. Based on the test that I did on the existing finish of the dinner table, I believe it has a coat of ploy on it. I light sand the surface and put a coat of poly on it. Unfortunately for me, I see that ploy beans up on the surface along the tree ring area.
Does this mean that the original finish is not poly and is not compatible with poly?
Can I "fix" this problem by lightly sanding the area where the poly cannot stick to?
Do I have to sand down the entire surface to remove _all_ the finish and start this over again?
If the original finish is poly, yes, just sand a bit to scuff the surface and new poly will work fine. If the original finish is not poly, you should sand it off and start with a clean surface.
Are you absolutely certain that there is no polish, silicone-based product, or oil that may have been spilled on the table top? Just sanding will not remove oil or silicone residue unless you get into fresh wood which will hurt the stain, etc. It sounds to me as if there is a chemical incompatibility.
___________________________ Keep the whole world singing. . . . DanG
You may be onto something. The dining table is extensible where the middle two sections are removable. And my friend, who gave me the table, told me that they rarely ever use those two removable sections. The problem seems to be mainly affecting the table surface on the non-removable sections of the table. The problem don't seem to affect the removable sections (that are rarely used). Sound like the non-removable sections may have some grease or oil from food or from hands that get trapped in the tree ring area. If this is true, I will have to remove all the finish including the stain either by sanding or by chemical. Oh well...
I will assume that you have never refinished a dining room table before. Unless you are really good with a brush or you have a spray rig, you will not be getting a dining room table smooth finish.
Before stripping the piece, try wiping down the surface with a lot of clean rags and mineral spirits to remove as much of the contamination as possible. Scuff sand the surface and then apply a sealer coat of shellac. This will seal in the contaminants. You will have to spray the shellac so you do not stir up the contaminants to the surface. Once the shellac dries, very lightly sand it such that you do not remove it. Apply your topcoat of choice.
For hundreds of years, large tables were finished in dusty environments , without spray gear.
The OP should study "wet sanding" and "polishing" a varnish finish. "Fine Woodworking" magazine has had many articles over the years detailing the flattening and rubbing out of varnishes. Modern, high-end, silicone free automotive products are fantastic for rubbing out flattened, brush applied varnishes, and are very easy to find in many locales. Seek out "Meguires", "3M" or "Mother's" professional auto finishing products.
That said, I use a high quality HVLP spray rig and M.L. Cambell lacquers for SPEED, not necessarily for quality. An as-beautiful-as-rubbed-lacquer table top can be achieved with varnish, a brush, and sweat, it just takes more time!
You are correct in that a finish can eventually be rubbed out to a high gloss. However, you are not going to get a modern high gloss finish as seen on mass produced dining table tops unless you have a rubbing sander and it will never look as glossy as an off the gun finish. Varnish will also never achieve the same level of gloss as, say, lacquer due to the difference in hardness and brittleness of the two finishes. If the goal is to achieve the same level of gloss as a dining room table achieved several hundred years ago, try French polishing. Very labor intensive and will not hold up to modern table use.
A good, hard, phenolic varnish, like Pratt & Lambert or Behlen's Rockhard, can be leveled via wet sanding with a hardwood block and rubbed to a spectacular gloss, you just need to wait a lot longer before you can do it.
A while back, David Sorg did an article in Fine Woodworking demonstrating the procedure and the results. I'd post a link, but's pay-only.
Finally, I sprayed two coats of dewax shellac on the dining table (the local home center only sells dewax shellac in a spray can anyway). The dry shellac surface looked quite nice and didn't have any problem that I had when I used poly. I thought I would be home free. I light sanded the surface and then applied a coat of poly. Unfortunately, the problem was still there. Admittedly, the problem was not as bad as before using shellac; but the problem was still bad enough that I had to swipe away the poly.
I might have sanded away too much of the shellac. But I doubt this because I only slightly sanded the surface. Moreover, the problem is only happening in the wood grain area; I believe that the wood grain area tends to be lower than the rest of the surface and is hard to sand into anyway.
What should I do? Should I spray a couple more coats of dewax shellac before applying poly?
About the only difference I've noticed with Zinnser shellac, whether it be called "Seal Coat", "Shellac - finish and sealer", "Sanding Sealer", or the spray can Shellac, is the color and cut .... Amber or Clear, and 2# or 3# cut, dewaxed, with the spray can cut not designated last time I looked.
My painter's generally buy the gallon size of Zinnser's "Sanding Sealer" before spraying cabinets. Last time I looked at that label (last week), and despite the different name, it was 2# cut, dewaxed shellac, with the same "contents description" on the can as Zinnser "Shellac - finish and sealer", which is generally 3# cut in the quart cans.
Since I generally spray 2# cut as the final three or four coats, I've been buying the gallon cans of "Sanding Sealer" and cutting it for the first couple of coats down to around 1 1/2# cut, since it is a bit more cost effective.
A Zinnser quart of the 3# cut variety at the BORG is around $10 here, while a gallon of the "Sanding Sealer" was around $27 at Sherwin Williams last week ... not a big savings considering the amount of shellac you get, but easier and a bit less costly to cut to where I like to spray it, which is in itself dependent upon the temperature and humidity hereabouts.
Finally, the problem is fixed after I have sprayed six-coats of dewaxed shellac over the wood surface. Now, I have applied the first coat of poly and everything is fine.
Good thing I don't need to sand between coats of shellac as long as I start spraying as soon as the shellac has become tacky. Otherwise, applying six-coats of shellac would have taken me a long time.
There is some controversy about the nature of the shellac in Zinnser spray cans. In theory, it should be dewaxed since the wax should clog the spray nozzle. In practice, the can does not state that the shellac is dewaxed. Given Zinnser's marketing of their Seal Coat dewaxed shellac, I would think they would want to highlight the shellac in their spray cans if it is dewaxed.
You appear to have a severe contamination problem. When this has happened to me, I do the following:
Clean the surface with a dilute solution of Dawn dishwashing liquid - one capful per gallon of warm water. Use lots of fresh rags so you are removing the contaminant, not just smearing it around. Rinse with water using fresh rags and then dry with more fresh rags.
Go over the top with a cloth meant for removing silicone polish from cars. You should be able to get one at an auto supply store. If you can't, don't worry about it. Use lot of fresh rags and mineral spirits.
Get some shellac that is clearly labeled dewaxed. Mail order some Seal Coat or dewaxed shellac flakes if you must.
Using a 1.5 pound cut, you will have to dilute whatever you buy accordingly, spray it on in very light coats using a Preval spray head or equivalent. These spray heads are pressurized heads with a spray nozzle. Hardware stores usually have them. You simply fill the jar with whatever you want to spray, screw on the head and go to it. It is not cheap if you do a lot of spraying but it sounds like a good idea for your single project.
Spray on total of at least two light coats. The idea is to completely seal the wood without forming a very thick coat of shellac. Thin coats will also dry faster and may be less likely to enable the floating of any residual contaminants to the surface.
Go over the top very lightly with some 0000 steel wool. This will provide a tooth for the top coats. Remove the steel wool dust with a tack rag.
Apply a very light first coat of polyurethane. If you want, you can thin it out sufficiently to spray it which would be the best method in this case. The idea is to put down a light coat without overworking it. You don't want to bring the contaminants to the top.
If you are still having a problems, and you will know immediately, wipe of the still wet poly.
Add a tiny amount of silicone to the poly. One brand is Smoothie. It is also called fish eye remover. What this will do is make the poly more like the contaminant so it will stick to the residual stuff.
Apply the additive containing poly.
If what I have described still doesn't work, there may be something in your brushes or rags that recontaminates the surface when you use them. Wash everything with soap and water and let dry before using them.
Thanks for the advice. What you have suggested makes sense to me. Next time, I will try to use your approach.
I had tried to solve the problem by spraying degreaser over the surface, and used clean paper towels to clean the surface, and spray two coats of dewaxed shellac. But that didn't help. I probably didn't put enough effort in cleaning the surface because I didn't use water to wash the surface; I was afraid of putting too much water over the wood surface might trap water under the surface and might delaminate the table top. Luckily, six coats of shellac have fixed the problem. Now, I have applied 4 coats of poly over the shellac and the dining table surface is getting smoother after each coat of poly.
My goal is to put enough poly over the surface to make the wood grain to go away. Then I can clean the surface easily after each meal. I am hoping that I can sand the surface flat during the weekend and apply two final coats of ploy and I will be done.
As you have learned, sometimes many light misting coats of shellac is what it takes to seal in contaminants.
I suggest that before you put down any more coats of polyurethane, you level the finish as best you can. You will almost certainly rub through the topmost poly layer to give "lacing". It looks like a piece of lace was placed on the surface because the rub through is not even across the surface. Poly does not burn into the previous coat so lacing can occur. A fresh coat of poly will make it disappear. The purpose for leveling is to provide a perfectly smooth surface for the final topcoats. This is done by using a sanding block and progressively finer sandpaper so that you eventually attain an even scratch pattern on the surface of the piece.
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