About Sanding Finishes

[kpcrash]

How to sand a finish - by kpcrash

First, it is important to understand a few basic things. This is not the all-knowing, end all of sanding techniques - merely what I feel is a good place for beginners to read about what's necessary (tools) to be able to make your finish look incredible using the minimum in expense. There are several ways to do this with more advanced techniques and equipment, but if you're just starting out - follow along below and you should have more than adequate results.

1. The tools needed?

Your hands - they are very important for this

Sandpaper of the following description: Regular 400 Grit Dry, Wet/Dry sandpaper in 400,600,800,1000,1200,1500,2000 grits. (More about this below)

Water

A little soap

A damp rag

A clean dry lint free cloth

A small spray (spritz) bottle that has never been used for anything else - especially a household cleaner.

A sanding block

2. About Sandpaper:

Sandpaper works by making tiny cuts in the material it is rubbed against to remove minor amounts at a time - otherwise you could do this with a knife

All sandpaper has an abrasive glued to a paper material. Wet/Dry sandpaper uses a paper and adhesive that keeps the abrasive attached and the paper solid even when completely soaked in water.

The higher the grit number, the finer the sanding - hence starting this process at 400 grit. Anything rougher would gouge the finish too deeply and there are times when 400 is too much it depends on the level of "orange peel" you have.

3. Setting up

At this point, you should already have any color coats on your guitar and depending on clear coat type, several coats. For this specific example, I'm using Rustoleum Painter's Touch Clear Gloss (Acrylic Lacquer) out of a rattlecan.

So I've taken a small container and filled about 2/3 of the way with warm water and a few drops of dish soap (Ivory). Next, I put 2 1/4 sheet pieces of each grade of wet/dry into the container to soak overnight. Why? IMHO, it holds water better that way. The paper absorbs just a bit and becomes very easy to work with. Also make sure you have a clean work area. A small speck of grit, dog hair, etc. can cause a deep scratch you just don't want to deal with. Hence the lint free towel, as you'll be wiping this down frequently to make sure no grit gets left behind.

4. What does sanding until all the clear spots are gone mean?

When you spray with a rattlecan, or other sometimes, the finish is not perfectly flat. It has little pits and groves or is just generally "bumpy" in a way that can resemble "orange peel". Sanding until all the clear or shiny spots are gone means sanding down the finish until you can't see them anymore such as shown below.

When sanding your finish - make sure you go with the grain and use a block. Sure this can be done with a machine, but often leaves swirls or "fish scales" that make it not worth it. Also if you're new to finishing, using a machine makes it too easy to sand through the finish. Using a machine also makes it impossible for to "feel" the finish as you're sanding.

5. So, enough talk, what does it look like?

This has been the hardest part to learn. Here is what the various stages may look like as you sand from 400-2000 and final "buffing" (discussed later)

First, use dry regular 400 grit to get the finish as level as possible (meaning, no shiny spots). DON'T USE HEAVY PRESSURE - let the sandpaper work. Then hit it with 400 wet/dry... guess where we're going from here...

Sanding is again, always done with the grain and in as long a stroke as possible. If you have problems with the horns, a little piece of PVC pipe can be quite a help. The reason for each of these grits that what we're doing is making the groves (or sanding marks) smaller and smaller. Your goal is to make the finish look like a nice satin finish with lines so small you can barely (if at all) see them.

Use the spray bottle to make sure things stay lubed up.

After giving the guitar a good once over with the sandpaper, make sure to use the damp cloth to wipe it down, then use the dry towel to wipe it down again.

6. How do I know that I've sanded enough with one grit?

You will come to know the feel associated with when the sandpaper isn't really doing anything anymore - until then...

You'll sand an area a few times, wipe it down, dry it off and look. It should look very smooth. Any lines should be quite light, but visible. Again, the lines should be fading more and more as you increase grit. As you get close to done, you'll start to notice a definite sheen, see below:

You should have a nice "flat" finish with no real noticeable lines or what looks like a satin finish with an extremely fine brushed look.

7. Ok, I'm there - what next?

This is an area of personal preference as well. Some like to hand rub various creams/polishes - I like my buffer . For this step, I use the following:

A 9" buffer (regular electric car buffer), Maguier's #9 and ScratchX, and 3 different pads - an applicator (thin gauze like), an applicator/remover (terrycloth) and a finishing buffer pad.

Starting with Mag. #9 on the applicator, give the entire unit a good once over. You'll quickly start to see the shine come through. Make sure to keep the spritz bottle close by here as well to keep extra water going as these products use self-reducing grit (it breaks down while being used).

Wipe down with clean damp rag, then wipe off with lint-free dry towel and move to ScratchX on applicator/remover, then final buff.

As for horns, I do them by hand, sometimes using a flannel buffing wheel to expedite for something that looks similar to the below:

For this, held up to the television to get a good shot of how reflective the image is. The clearer the finish, the better the reflectivity (we can discuss physics later).

Hope this helps out - one more thing -

What if I sand through? You need to finish sanding to get a level surface and refinish. Keep in mind that edges are damn easy to sand through and correcting this has just as much to do with painting technique as sanding technique. Personally, I do edges by hand, with no block.

[bluesy]

This comes at a good time for me, as I am just putting on my colour coats today. I will be polishing the clear finish soon then. How long do you let the acrylic clear wait before sanding and polishing?

I had planned to start at 400 and work through to 2000 grit, so all is OK to follow your tutorial for that. Great pictures btw - they will give me confidence it is all working correctly.

I wanted to ask about how to use the 9" buffer. I bought one while they were cheap the other day. I have never used one of these things before . I found the buffer pads very hard to stretch over the foam disk that spins. Even so, when I turn it on, as it gains speed, the cover will spin off. I noticed that if I keep it in contact with a surface that needs polishing, it never spins nearly that fast, and the cover stays on, so would I be correct in assuming you never let the machine spin free? <is that laughing I hear in the background? >

How do you go about using the applicator pad? How much polish/cutter compound do you put on it? Do you cover it or just add a few drops, or do you put the polish on the guitar then just use the applicator to spread it?

Do you let the polishing compound dry to a white film before putting on the polishing pad?

Excuse all the questions, but you might save me from a silly mistake

[kpcrash]

Thanks bluesy!

How long do you let the acrylic clear wait before sanding and polishing?

For the one I'm using the manufacturer specifies a 24-hour cure time. I'm paranoid, so I wait 72 (or until it doesn't smell so strong).

is that laughing I hear in the background?

Only my laughing at myself stretching these things on the pad . They are supposed to be hard to get on and hard to get off. If yours is spinning off, you may need to keep contact when starting, but make sure you do it with the center of the pad, flat against the surface.

The applicator should be kept quite flat so that the center of the pad is doing the work. The edges can be unpredictable until you get the hang of it. I usually keep my applicators damp because I use very little pressure - if fact, sometimes I am not even letting the weight of the buffer on the body. Usually I have a few drops (maybe between nickel and quarter size or 1 euro size) in the middle of the pad. It's always easier to add pressure Be careful as this stuff will wear through your finish if you use too much or press too hard (don't ask me how I know).

Do you let the polishing compound dry to a white film before putting on the polishing pad?

Nope. I try to keep it wet the whole time. The only thing I'll let dry is if I do a thin coat of yellow (carnuba) wax on top. Then I hit that with the finishing pad.

Also - another reason I keep it damp is heat. Friction=heat, so since you don't you want sags or burns in the finish, it's easier to let it spin a few more times that refinish because you made a "silly mistake" - of which, I am quite an expert in making

[Sami Ghouri]

since we're already bombarding poor ol' kpcrash with n00b questions... i wanna have my share!

i'm using minwax polycryllic clear...... and i made the shtoopid mistake of not waiting for it long enough to dry (eventhough it said 3 days on the can and i waited for 5) so some parts ended up peeling like very dry old plastic.... i waited for it to dry again and tried sanding those thin flakes and it seems fine now! should i be concerned???

and apart from this, how many coats do you usually apply? coz it seems that the recommendations on general tutorials are made for ppl who use proper equipment and don't need a lot of level sanding coz when i worked with the number mentioned i mostly ended up sanding through the clear at least!

and are all acryllic clears so f'in hard to apply? when i was working with polyu life was beautiful! however not so beautiful for white guitars! hence the reason for using polycryllic... it even foams sometimes and NO i'm not applying it too heavily... the nozzle sprays like you wanna wash a car with lacquer not get it to stick on the surface!!!!

/rant

[kpcrash]

hmmm.... polycrylic? I've not used it on a guitar, but have on floors/furniture Honestly, it seems to take it about a week (or two) to fully dry. I wouldn't be concerned if you were able to send the flakes out without sanding through. When I use the rattlecan, I'm applying between 7-10 coats - BUT - it goes something like this - dusting coat X 3 (20 min in between), wet coat (wait 45), dusting coat x 3 (see previous), wet coat, touch up edges to prevent sandthrough. I have no problems (other than the occasional dog hair) with this finish. I've tried most of them and use this one when I use a can because it's stable and not enamel.

I've never had one "foam", but then, polycrylic takes so long to dry, it's pretty safe to brush.

[bluesy]

I want to say thank you. My guitar's finish has turned out very nicely. The help on the use of the electric buffer was good for my confidence.

For the benefit of any other Aussies reading this, I used K & H primer and clear top coat, and Powerplus white in between for the colour coat. I got them from 'Autobarn' . This stuff is amazingly simple to use and fast. You only need to wait 20 minutes between coats for the colour, and only FIVE minutes between each clear coat. I applied a large can of primer, a large can of colour, and two large cans of clearcoat (overkill? maybe) in the space of 3 days.

Then after only 4 hours ( I left it overnight) before you can sand and polish it. Bunnings were a bit limited in their sandpaper range, so I only had 400, 800, and 1200 grit. However, the K&H can had instructions that implied that sanding may not be necessary, and recommended their K&H "Buff and Shine". The guy in the store said it depended on how good the finish already looked. I had a mild amount of orange peel, so I hit it with 1200 grit only, until the shiny spots were gone, then used the "Buff and Shine" with the electric buffer, and it came up nice and glossy. Very happy !

[kpcrash]

Awesome bluesy! Pics?? Glad it worked out for you.

[bluesy]

OK, pics. (if you're wondering what that line across the middle, especially in the second photo, so was I. Turns out to be a reflection of an overhead cable :-) )

[kpcrash]

Nice job!!! Make sure you tape up before drilling. Would be a shame to scratch that.

(Hey just noticed this will be post #300 for me ha!)