Sanding Sealer Vs Grain Filler Vs Prime-n-paint

[Bryan316]

Just got done searching, can't really find explanations as to WHY you would use these phases of finishing.

I want to learn perhaps by comparison, why you would use sanding sealer, as opposed to just priming and painting? Or why you'd use grain filler instead of sanding sealer? Or what you really should or shouldn't use when doing a clear or stained finish?

It's just one of those choices, that never really seems to get a thorough explanation from the ground up. More like, "I had X wood, so I used grain filler first..."

Bring forth your n00bian insults and belittle me with belittlement!

[mattharris75]

Bring forth your n00bian insults and belittle me with belittlement!

Well, the first n00bian insult I can think of is.....This thread belongs in the finishing section, not in progress and finished work.

[avengers63]

DISCLAIMER: I'm only repeating information from Bob Flexner's book "Understanding Wood Finishing". I may not be repeating 100% of the info, but I will do my best. You are highly encouraged to drop the $30 on the book if you have any serious desire to get into wood finishing. The info in the book and the finishing voodoo that is debunked is invaluable.

These are all answered with the understanding that you'lll be finishing a guitar. If it's being done on other pieces, some of this can change. With a guitar, it's generally desirable to have a flat, uniform, glass-smooth finish. If that's not what you want, a lot of this goes right out the window.

For discussion purposes, let's use the premsie that you're going for a traditionally smooth guitar finish.

First, let's make sure that you understand the reason you finish the wood: protection. A hard barrier finish protects the wood from damage and signifigantly slows the exchange of water vapor. Water is the enemy of wood.

SANDING SEALER: You don't need to use sanding sealer. You can use it without hurting anything, but it isn't needed. Each and every type of wood finish that offers a protective barrier against moisture and damage will effectively seal the wood. Therefore, an extra layer of sealer is not necessary.

In many cases, products labled as "Sanding Sealer" are thinned finish with a soap added to aid in the sanding. This soap makes the finish turn into a powder when sanded, making the process easier. Unfortunately, this soap can prevent the top finish from sticking. (Bob doesn't tell us which combos are bad.) If you're going to seal the wood anyway, Bob suggests using a thinned down coat of whichever finish will be used. This is also called a washcoat.

GRAIN FILLER: The purpose of filling the grain is purely asthetic. I repeat: there is NO structural benefit to filling the grain. For guitars, however, it's sometimes necessary so the finish will be smooth. It all depends on the wood. If it's open-grained, you need to fill it. If not, you don't. End of story. This applies regardless of if you're painting, staining, or going clear.

Some people say Sanding Sealer can be used as a grain filler. Others swear that wetsanding with Tru-Oil does the trick. I haven't done either of these, so I can't testify to these methods.

PAINTING: Consider painting like an extra layer of finish for a second. If the wood isn't smooth to begin with, the finish won't be smooth. Paint won't be either. Once the grain is filled, if it needs to be at all, you can go right to primer. You don't need to seal the wood at all. You'll end up with primer, paint, then the clear coat. Whatever moisture that can get through all of that deserves to.

[kpcrash]

avengers nailed it. As far as what can be used for sanding sealer.... I'll not start a flame war - but spackling compound is generally not a good idea.

[avengers63]

I used some watered down wood putty once. I scraped it into the pores with a plactic putty knife, then sanded it smooth when it dried. It may not have been the ideal solution, but it worked. Of course, I wouldn't suggest this, especially if you're going for a clear finish, but it worked in a pinch.

[Bryan316]

Well... let's take my current ideas. The quilted top is getting a red and yellow staining scheme, and the rest of the body is getting burned with a propane torch to scorch the surface and blacken it with ash. Then I'll rub away the loose ash, and tung-oil or Tru-Oil the entire body.

Two things. First, I've not tested Tru-Oil over my stains. Second, I actually love how I can "feel" the grain after burning wood. It pops physically as well as visually, and once it's jet black, the tung oil over it looks absolutely awesome. Like a centuries-old castle's wooden pillars... aged, ancient, and worn by weather and time.

So... if my stained areas can't accept the oil finish without bad discoloration, I need options to keep the stained effect protected. Will sanding sealer affect a stain's penetration and performance? Will a sanding sealer over a stain work?

I really need to stain some wood and put the tung oil over it, to see if my ideas are compatible. If anyone's oiled over a stained finish, let me know how it turned out.

[kpcrash]

If I can find it in the shop I've got some stained cedar with Tung Oil, looked really good - did it as a sample piece for someone. Stain on sanding sealer should work fine, stain on grain filler will only look right if the grain filler is clear.