I'm working with Red Oak. On the table tops I'm trying to get a smooth finish. I am applying poly U and sanding between each coat. But no matter how smooth I get it between coats the next coat raises the grain again. Is there a sealer I could use to stop this action?
There is certainly something wrong with that picture. You'd have to really work at it to have that happen on purpose.
You do not say whether you are using water based poly or oil based but let us assume worst case (for grain raising) situation and you are using water based.
Even if you chose not to pre dampen, let dry, scuff off the fuzz, apply finish and apply the poly, let it cure, then scuff off the fuzz the wood should be more then sufficiently sealed to halt any further fuzz rising.
The only thing I can think of that would cause what you have happening is if you were grossly over sanding the first coat.
Raising the grain is really a misnomer. The purpose of the exercise is to lightly dampen the wood and it will swell. You let it dry and the cells shrink back to their normal size. When they do severed strands of wood remain proud of the surface giving the wood a fuzzy feel and appearance. You then LIGHTLY sand or scrape off the fuzz. Sand or scrape too hard and guess what, you sever more strands and you are right back where you started from. In addition, if you sand to soon the more absorbent part of the wood, which will swell more then the less absorbent, will be, when they shrink back to size, lower then the harder less absorbent parts of the grain. You end up with a distinct grain showing through your finish, think sand stone erosion or drift wood, and you have to take the whole thing down again and start over.
Now, if you are putting on a coat of poly and letting it cure fully, then, when cured, other then the fuzz left standing at that point, there is no way for more to raise with the second coat unless you are sanding right through that first coat.The first coat of poly would be acting as the only sealer you would need.
what you need is a good pore filler. There are some water based and solvent based. I like the stuff that I bought for floors; trowelable Zar latex based Red Oak. I fill the pores BEFORE staining, because this product takes the stain well so that the filled pores don't look weird. There are lots of pore filling techniques. I suggest you Google, or wait for more knowledgeable folks tell you how they do it. Trying to fill oak pores with poly is a true PITA and a time waster.
I fill the pores by rubbing it on with a coarse cloth and rub off the excess; it dries super fast. When it's truly dried ( a few hours at most) I sand with 220. On the floor I used 80 grit. Then stain as usual ( I use an oil based product; I'm sure you could use water based) and apply the finish coats.
Leon will probably answer your question better than I can...
dave
Ev> I'm working with Red Oak. On the table tops I'm trying to get a smooth
Is this water-based poly, or oil-based?
-- Doug Miller (alphageek at milmac dot com)
How come we choose from just two people to run for president and 50 for Miss America?
oops! I goofed again. I thought you had an issue with getting the poly to fill in the pores. I'm often guilty of scanning a post too fast. Ignore my previous "tips". :)
dave
Bay Area Dave wrote:
If you are using a water based poly you can use a sealer first. You might want to try clear de-waxed shellac on a scrap of oak. Let it dry and try the water based poly. I think you will find it works.
Neither the water based poly nor the clear de-waxed shellac will yellow the wood. Don't use orange or waxed shellac. They won't work.
Joe.....
You should have used a grain filler, sand it down and then applied the finish. I hope you don't mind doing a little stripping!
I'm assuming it's a water based poly correct? If it's an oil based poly, you should not be having this problem. If it is water based poly you're using, it's an easy fix. Stop sanding so hard. Instead of taking the "fur" of that's poking out the top coat of poly, you're actually removing the poly and exposing the raw wood each time you sand. Next coat of poly raises the grain all over again, so you sand again. Vicious circle huh?
After you apply the poly, use a sanding block on the panel surfaces and only use "hand held" paper if you absolutely have to. Doing this allows any pressure you're applying to be evenly distributed across the sanding block and greatly reduces any chance of a "sand through". When you sand (between coats), "scuff" with 220. Go over it once, maybe twice, and lightly at that. Apply a second coat, repeat the "scuffing" process. Apply a third coat and change your 220 paper to 320 if you choose. You can now sand a bit harder, but be careful of "point" pressure. Apply as many coats as you want now, using 320 paper between them. If you break through the hardened film at any point and expose raw wood, the grain will raise again.
To answer your other question, yes, there's a sealer you can use. Zinsser had developed a de-waxed shellac (de-waxed is vital if you plan on putting another substance over top of it) in a can. It's brand name is "Seal Coat". Please note that this is not the same product as "Stain Blocker" or any other Zinsser product. This one is special as it's the only de-waxed ready-made shellac on the market. Use it as is (you can cut it if you wish, but it's a 2lb cut out of the can) and apply a nice even coat. Because shellac is alcohol based it, like water will raise the grain of the wood and cause fur. Sand it off (as described above) and carry on with poly or stain or whatever you're using. Of course you can also roll your own shellac and de-cant it if you wish...nothing wrong with that at all and in fact f you want any color other than blonde, you'll have to do exactly that.
good luck Rob
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