No sealer before polyurethane


Hi,
This article mentions "no sanding sealer before polyurethane", but it's the only article that I found that states that.
http://doityourself.com/info/furniturerefinseal.htm
Is that so? No sealer before polyurethane?
(How about a light sanding after stainer?)
Thanks!
Aaron Fude
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Don't believe everything you read on-line (including responses from this group). When in doubt, go to the manufacturers website and research the product you want to use.
Here is Minwaxes response:
http://www.minwax.com/products/woodprep/sand-seal.cfm
Dave
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My wife does our finishing work. She follows this procedure with excellent results.: Step 1 stain, Step 2 Sanding Sealer, Step 3 light sanding of sealer with steel wool, then begin to build up coats with more poly. Steel wool in between coats. Poly must be well dried or steel particles can get lodged in soft poly.
In addition to building custom cabinets we also restore classic mahogany boats. I do the boat finishing. I do not use sanding sealer, I use a 50% diluted solution of the poly varnish as a primer. Then apply two full strength coats of Poly before doing any sanding between coats. I apply 8 coats generally sanding between coats only when needed.
To sand seal or not in my opinion is all a matter of what process you work out that gives you the consistent results you are seeking and you just keep practicing to get good at it .
We do not sand after staining it could cause light and dark spots, especially on sharp edges.
Don Dando

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Don Dando wrote:

Truer words are rarely spoken. <G>
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Just like the warning on your lawnmower to keep your fingers out of the blade, the warning is given because some nimrod is likely to use a stearated sanding sealer and then complain. If you use a sealer, versus a sanding sealer, which is normally stearated, and even feels a little soapy, no problem.
Sanding after staining can really mess the surface. I'd rather scuff the first coat of dilute poly, which can be used as a sealer.
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George wrote:

As George says, a diluted coat of the finish itself can be used as an excellent sealer, if time is not a factor.
The OP should ask him or herself WHY a sealer?
Sanding sealers are typically used to speed the sanding / finish building process, before more expensive, less sandable, and sometimes much slower drying finish coats are applied. A good sealer can often be sanded within the hour.
If the final goal is an open-pored look on red oak, a sealer may not be necessary at all, or the diluted finish might be perfect. If I'm looking for a bowling alley mirrored surface, I might take most of the early coats of real sanding sealer off with 150 or 220 grit, before ending with a 320 or 400 grit scuff of the last coat. Genuine sealers let me do this in one day, diluted poly takes a lot longer, as each successive coat needs a lot more time to sand without "pilling".
I've found that the better sealers will mention right on the label if they are usable under polyurethane. For instance, Zinsser Quick 15 states right there on the label that it's stearated and lists the products it's intended to be used under. I'm pretty sure it even says "not for polyurethane" in bold face print.
My absolute favorite, truly universal, sanding sealer is Zinsser Seal Coat, which happens to be a simple premixed 2 lb. cut of dewaxed shellac. Seal Coat works GREAT under any finish where you'd use a sealer, and is well worth the time to learn to use. Learn it, and stock ONE product. It can be sprayed right out of the can, applied with a foam brush or rubbing pad, or a good quality paint brush.
I've dedicated several brushes to shellac (and Seal Coat). When I'm done using them, I let them dry. Before the next use, I drop them in alcohol, and in 15 minutes they're ready to go.
In most cases, with the exception of Seal Coat, I try to stick with one brand of finishing product on one project. For example, if I'm using Behlen (Mohawk) lacquer, whenever possible, I'll use their toners and stains. If I'm applying a Waterlox, Pratt & Lambert, Sherwin Williams, etc... varnish over someone else's stain, I'll make sure there's a barrier coat of Seal Coat between them.
As usual, PRACTICE on SCRAP! <G>
Any time you're unfamiliar with a process, keep a test board (of decent size, NOT 3"x4" <G>) available, do _every_ step to the test control, including sanding, and write the steps and notes on the back. ONLY when the step is successful on the test board should you do it on the project. Great finish? Save the board so you remember the steps next time, and to show the "customer" (even if it's yourself and the wife) what the finish will look like.
A good finish really makes your great work look as great as it really is, don't rush it. Take the time to really get to know what you're doing. Nowadays, I typically consider a project about half done when I start finishing. As a beginner, I was almost done!
Have fun!
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Barry, While not for furniture, I use SEAL COAT frequently. For me, the typical use it to coat & seal my hardboard templates. Both the 1/8in 'drawing' and the 1/4in 'router'. Extra 'protection' coats go on the edges.
Contrary to the 'experts' my favorite brushes are the 'disposable CHIP' brushes for Epoxy, and the foam ones for Varnish. {YES - goes against what all the 'pundits' say . . . but it's really technique & care that counts !}. When I first started to use the SEAL COAT, a foam brush was what I used. As I proceeded I noticed little BLACK bits in the finish . . . Turned out that the ALCOHOL was DISINTEGRATING the foam brush !!! I then switched to the 'chip' brushes and no problems.
So the question is . . . what 'type' of FOAM brush are you using ???
Regards & Thanks, Ron Magen Backyard Boatshop
SNIP

. . . applied with a foam brush . . . .
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Ron Magen wrote:

Good idea.

The black no-name ones I get from Coastal Tool in 36 brush boxes. I haven't had a problem, yet. <G>
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For other than utility furniture, and even some of that, think cabinet scraper rather than sanding. Much nicer job.
J
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snipped-for-privacy@sme-online.com wrote:

Even better, learn how to properly use both.
In addition to pre-finish preparation, cabinet scrapers are much better than sanding blocks for removing drips, runs, etc... in dried finishes.
Properly scraped and sanded surfaces will be virtually indistinguishable from each other, but sometimes, the scraper is so much nicer to use. On smaller projects I even find scrapers faster, since I don't need to swap grits.
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Hi,
Thank you everybody for responding!
I must admit that most of the responses went right over my head and I feel woefully overmatched. But to remedy that feeling, I might as well ask a couple of questions:
1. When you say "diluted poly" diluted with what? 2. When you talk about steel wool - what grade? I went to home depot and found several gradations. And what is the pupose of using steel weel between coats?
Thanks!
Aaron Fude
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snipped-for-privacy@gmail.com wrote:

Probably mineral spirits (paint thinner), but check the label under "Thinning". If label says "Do Not Thin", look under "Cleanup".

I don't use steel wool until the final rub out, so I'll defer to the person who mentioned it. I prefer lightly scuffing with 320 grit on a felt block between coats to knock down dust nibs and provide "tooth" for the next coat.
When you use steel wool, unfold it, and make sure the wool fibers go _across_ (as opposed to with) your rubbing direction. This allows the wool fibers to properly cut. If you rub parallel with the fibers, you risk creating deep scratches that may show through the final finish.
Don't forget the test board!
A lot of this stuff doesn't apply to water based poly.
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Paint thinner to if you're using oil-based poly. Don't know if the water-based responds well to thinning/dilution.
Avoid steel wool. Gets little stickers in your hand, leaves crap all over the place as it crumbles, and with some acid woods, can sneak in and turn an area black later.
Two things in sanding between coats. First is level, where you have brush strokes, bubbles and such to knock off. Best to use a backed sandpaper with a bit of lube to keep clean for this. Second is tooth, where you scuff to gain mechanical grip for the next coat. You may use the level method or a soft-backed flexible sanding sponge for this if you're level. You're just trying to destroy the gloss a smooth surface gives, so the next coat can adhere.
On the last coat, lots of people like to randomize the surface with some abrasive. Cuts down on surface reflection without introducing light-scatter in the finish itself as "satin" type varnishes do. I prefer to just use wax, where the polymer size gives me a bit of scatter, but the film is only a few thick.
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I have used the following process with very good results. I apply (liberally) Watco Danish Oil, following instructions on the can. After I wipe it down really well, I let it set for a day. Next day I apply a coat of polyurethane. (I use satin finish most of the time). If I've applied the poly in the morning, it's usually dry enough to sand in the late afternoon. I use 320 grit. I only sand enough to knock down the little fibers that stick up. I wipe it down thoroughly with a tack rag. and apply another coat of poly. I always apply thin coats and the number of coats depend on what the particular project is. I should mention that I've done some projects that I only use Danish oil on and I apply a couple of coats. There are those who say that anything past the first coat of Danish oil is superfluous but if that's the case then the extra rubbing must be what brings out the nicer finish.
Max
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