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Thread: Sanding Sealer -When to use- Confusion/clarification needed please.

  1. #16
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    Quote Originally Posted by Stan Calow View Post
    Aren't many of the sanding sealers (and primers) basically shellac?
    I use both shellac and lacquer based sanding sealers on wood turnings, depending. I usually thin, depending on the wood and the reason for the sealer. (Sanding sealer appears to be thinned finish anyway.)

    I don't stain so I have nothing to say about that except if I did stain I'd first try it both ways on sanded pieces of exactly the same wood, both side and end grain. I dislike unpleasant surprises.

  2. #17
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    I may be a bit different from the rest in opinion and usage. I bought a Furniture Medic Franchise about 3 years ago and started refinishing items where I had no reference as to how they had been used.

    For my own past projects I rarely used sanding sealer and/or shellac and was using mostly solvent based stains and finish.

    One of my first paying jobs was to refinish a table top. I was only sanding and refinishing the top. I decided to use shellac as a barrier and a waterborne finish (General Finishes pre-Cat urethane) as a top coat. I had contamination problems which caused crazing. In retrospect, I think I had sanded through the shellac in spots which casused or aggravated the issue. General Finishes told me that I had to use GF sanding sealer not shellac since teh Pre-Cat shrinks as it cures. I swithcehd to that and was able to seal in the contaminants. it took multiple coats but it worked. i suspect the shellac would have worked too.

    Anyway, as a result, I now always apply stain (GF water based), GF sanding sealer and then finish (GF waterborne). I almost never have trouble. The sanding sealer also seems to have more solids so it fills faster and sands very easily. I had trouble once (on a table). I use a lot of extender since it is so dry in CO and last spring i did a table and it was a litle more humid. I noticed my finish coat took a while to dry. or at least skin over. I think the extended drying time allowed some contamintates to interact and I had some trouble. I swithced from 15% extender in my sandig sealer to 0% and sealed the contamination. All anecdotal but I am a fan of using sanding sealer, at least for refinishing. I also use it after stripping and staining.

    If I was doing only new construction I may change my ways but it is a habit now. The sanding sealer is less expensinve and I think it is a great prep for the finish coats.
    Gary

  3. #18
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    Gary, what shellac did you use under the GF Pre-Cat lacquer? I've used SealCoat shellac with the their Pre-Cat lacquer (the one with the red label) w/o problems. GF will always tell you to use their sealer; pretty much just like every other finish manufacturer.

    John

  4. #19
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    There are many variation on what is considered a sanding sealer not to be confused with grain filler. Getting a glass smooth finish should have been part of the original questions and is dependent on wood type. You won't get a glass smooth finish on Red Oak unless you use a grain filler. Not true on maple. In your post you didn't mention whether you were using WB or solvent. There are specific sanding sealers, shellacs of various formulations and diluted topcoats used as sanding sealers and its typically at the users discretion/experience. Broad based, non definitive questions like you asked will always get you a smash smash of answers like above.

  5. #20
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    Quote Originally Posted by John Kee View Post
    There are many variation on what is considered a sanding sealer not to be confused with grain filler. Getting a glass smooth finish should have been part of the original questions and is dependent on wood type. You won't get a glass smooth finish on Red Oak unless you use a grain filler. Not true on maple. In your post you didn't mention whether you were using WB or solvent. There are specific sanding sealers, shellacs of various formulations and diluted topcoats used as sanding sealers and its typically at the users discretion/experience. Broad based, non definitive questions like you asked will always get you a smash smash of answers like above.

    I am simply practicing and learning for now using oak. I have a fireplace mantle I want to paint in the future and don’t want the grain to show through and am hoping to achieve a smooth glass like finish I understand I need to use a grain filler and have a can of Old masters grain filler in my arsenal. The slick salesman sold me some oil based sanding sealer Ultimately I want to topcoat with the old masters Armour Clear

    I am learning... slowly..... thanks for all the great info so far
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  6. #21
    David,

    Just so I am clear what you are asking for...

    Is it this:
    You want a mantle clear coated - but you don't want the grain texture printing through the finish?

    Or this:
    You want the mantle painted some color (such as White) with paint and you don't want the wood grain or texture showing through?

    If you want #1 - Mantle clear coated so you can see the wood but no grain texture printing through the finish..
    Consider either some sort of dark paste pore filler or a clear pore filler product. Fill all the pores and sand back carefully. Red oak literally has bottomless pores - so you will have to do multiple rounds of pore filling and sanding back to get them all.. Then stain as per whatever makes you happy. At that point - you only need a "sealer" if your finish dissolves your stain or pore filler..

    Next is the tricky part - as most every high build varnish, urethane, or epoxy sort of product will leave witness lines where you sand through one coat into the next... Power buffing helps this a lot. The general procedure is to apply multiple coats to a total finish build of 0.020"+ and then level and sand going through grits up to 2,000 or so, then machine polish with a buffer.... Interestingly enough - Ace interior varnish has a reputation of being well behaved when spraying (for a varnish. )... That's an option since you already have spray background...

    If you just want to paint it white or some such... Well - paint the wood with a good high quality PVA primer. Skim coat it with drywall compound. Sand back smooth... Repeat skim coating and sanding back as necessary to get all the pores filled. Then prime with a quality interior primer and paint.
    Last edited by John C Cox; 03-13-2018 at 12:33 PM.

  7. #22
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    Quote Originally Posted by Gary Muto View Post
    I may be a bit different from the rest in opinion and usage. I bought a Furniture Medic Franchise about 3 years ago and started refinishing items where I had no reference as to how they had been used.

    For my own past projects I rarely used sanding sealer and/or shellac and was using mostly solvent based stains and finish.

    One of my first paying jobs was to refinish a table top. I was only sanding and refinishing the top. I decided to use shellac as a barrier and a waterborne finish (General Finishes pre-Cat urethane) as a top coat. I had contamination problems which caused crazing. In retrospect, I think I had sanded through the shellac in spots which casused or aggravated the issue. General Finishes told me that I had to use GF sanding sealer not shellac since teh Pre-Cat shrinks as it cures. I swithcehd to that and was able to seal in the contaminants. it took multiple coats but it worked. i suspect the shellac would have worked too.

    Anyway, as a result, I now always apply stain (GF water based), GF sanding sealer and then finish (GF waterborne). I almost never have trouble. The sanding sealer also seems to have more solids so it fills faster and sands very easily. I had trouble once (on a table). I use a lot of extender since it is so dry in CO and last spring i did a table and it was a litle more humid. I noticed my finish coat took a while to dry. or at least skin over. I think the extended drying time allowed some contamintates to interact and I had some trouble. I swithced from 15% extender in my sandig sealer to 0% and sealed the contamination. All anecdotal but I am a fan of using sanding sealer, at least for refinishing. I also use it after stripping and staining.


    Gary if you do a little research you will find that products like Zinnser Sealcoat and other other shellacs combos sometimes do not play well with urethanes, especially if you use a heavy coat. Just a little heads up to add to your knowledge base.
    Last edited by Jim Becker; 03-13-2018 at 2:37 PM. Reason: fixed quote tagging

  8. #23
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    Quote Originally Posted by John Kee View Post
    Gary if you do a little research you will find that products like Zinnser Sealcoat and other other shellacs combos sometimes do not play well with urethanes, especially if you use a heavy coat. Just a little heads up to add to your knowledge base.
    I've never had a problem with Sealcoat under WB polyurethane, or any other finish. I'd be very interested to see any of the references you found. Thanks.

    John

  9. #24
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    I used the Zinzer dewaxed shellac. I don't think it was the shellac. I think OI may have sanded through it though. I also used a 1-/2 lb cut so maybe it was too thin to begin with
    Gary

  10. #25
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    Previous reply was to John T.
    John K.,
    Thanks for the info. Genereal Finishes position on it was that Shellac was not compatible with their Pre-Cat Urethane. I recall having the impression that Tom was implying not to use it under any catalyzed finish but i don't recall him specifically saying that.

    He also told me that the General Finishes sanding sealer is a Pre-Cat formulation. I found that surprising since i didn't think it would be compatible over a variety of finishes. In my limited experience it does work well but on 2 occasions I had to apply multiple coats to seal in some contamination
    Gary

  11. #26
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    Quote Originally Posted by John TenEyck View Post
    I've never had a problem with Sealcoat under WB polyurethane, or any other finish. I'd be very interested to see any of the references you found. Thanks.

    John
    John Kee did indicate "especially if you use a heavy coat" which as been mentioned as sometimes causing issues with water borne finishes both here and elsewhere. I'm guessing that would be the case when the person applying the shellac isn't knowledgable or experienced with applying shellac.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  12. #27
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    Thanx for the clarification Jim, I have a really hard time doing peoples research for them. Here's one reference: https://www.targetcoatings.com/faq/ Also if you read the TDS from General Finishes they don't recommend anything but their sealers and when you want to vary from their recommendations to contact them. People often view that if they don't have a problem no will have a problem, unfortunately the finishing world and the finishers themselves vary too much to state something like that as gospel. I've applied Zinsser Sealcoat under a lot of different clear coats, sometime you win sometime you lose.

  13. #28
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    Quote Originally Posted by John Kee View Post
    Thanx for the clarification Jim, I have a really hard time doing peoples research for them. Here's one reference: https://www.targetcoatings.com/faq/ Also if you read the TDS from General Finishes they don't recommend anything but their sealers and when you want to vary from their recommendations to contact them. People often view that if they don't have a problem no will have a problem, unfortunately the finishing world and the finishers themselves vary too much to state something like that as gospel. I've applied Zinsser Sealcoat under a lot of different clear coats, sometime you win sometime you lose.
    Thanks for the reference, John. I'm actually surprised TC's said you can use shellac in any form. Kudos to them. Most manufacturers, as in your GF reference, only recommend their own sealer.

    If you look at a can of SealCoat it says something like "Safe under all finishes". With the finishes I use, including several from GF, I've found that to be true. Everyone should test any new finish recipe for themselves prior to using it on a project.

    John

  14. #29
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    About 12 years ago I starting researching Zinsser Sealcoat and polyurethane problems 0n Woodweb, back then I actually think Zinsser warned about possible issues with some urethanes. The common consensus was it was something in the solvent mix. 10 years has been a long time in finishing industry, it sounds like a few ingredients might have changed in the Zinsser mix. You are right John T always do tests to avoid surprises. Target also make a WB Shellac, I experimented with and it works but doesn't come close to the pop in wood grain that an alcohol base shellac brings.


    For others the actual quote from Target Coatings.

    "Yes. You can use Zinsser SealCoat underneath any EMTECH™ water based sealers or topcoats. However, we stress that you reduce the SealCoat with denatured alcohol at a ratio of 1:1 before applying SealCoat as a bed coat or intermediate seal coat. Full strength Zinsser SealCoat may create a fine craze or crackle effect underneath high pH water based finishes. To prevent this effect we h3ly recommend that you, 1) Reduce the SealCoat, 2) Apply thin coats, averaging 1-2mils in wet film thickness, 3) Do not exceed two coats of reduced SealCoat prior to applying EMTECH™ finishes."



  15. #30
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    The Sealcoat Web page is interesting reading:

    About SealCoat™ Universal Sanding Sealer


    Save time when finishing porous woods by starting with Rust-Oleum® Zinsser® Bulls Eye® Sealcoat Universal Sanding Sealer. This high-building solution seals the wood to create a surface that can be easily sanded. Contributes to an ultra-smooth final finish.

    • Compatible with ALL clear wood finishes
    • Great for sealing ALL interior wood, including floors
    • Dries lightning fast - can be sanded & recoated in minutes
    • Does not darken or yellow with age
    • Easy clean up with alcohol or ammonia and water
    • Gives extra beauty & warmth to water-base polyurethanes
    • Can be used as a pre-stain conditioner for pine and softwoods
    • Can be used as a bond coat under new finishes – adheres to any existing finish


    For Best Results

    Apply two coats to improve film build and give added depth to the final finish.
    Available Sizes

    • Quart
    • Gallon
    • 5 Gallon

    That's a pretty bold statement to say it is "compatible with ALL clear wood finishes". It has been true for the finishes I use, but could easily imagine there being exceptions. Test.

    The primary reason I like Sealcoat is because it doesn't raise the grain like waterborne sealers tend to, and because it really highlights the grain. I've tried MinWax's and GF's WB sealers. I can't remember which one, but one of them was terrible for grain raising. I think that's what caused me to look at Sealcoat in the first place. I love waterborne products, but there is real need for improvement in the sealers. If someone has used one that doesn't raise the grain, please post it. Thanks.

    Another way I use Sealcoat is to create a bond coat over an oil based stain so that I can use a WB finish. GF and others say you can apply their WB topcoats over a well cured OB stain. I haven't found that to always be the case. A light sprayed coat of Sealcoat (or rattle can shellac) has always worked. As always, test.

    John

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