curing interval for shellac before nitrocelluolse

[fanlee]

Hi.

I'm about to pad on my last coat of hard shellac. All is going well so far.

How long should I allow before spraying on nitrolcellulose lacquer?

1 WEEK? 48 HRS?

Riobbo.

[ozwinner]

Why do you want to put NC over shellac?

Al :confused:

[durwood]

It depends on how many coats you have applied and how long between them you left as to how long too wait. the more you pile on and the shorter the time the longer it takes to dry out. You have to let the metho evaporate the longer you leave it the better but it should normally be OK after 24 hours. Leaving it longer will only help but if you are too quick you will slow everything down.

Question: why did you use shellac instead of the correct sealer (lacquer sanding sealer?

The reason I ask is you have just made your surface prone to heat, any hot cups,plates, etc will blister the shellac and so will sunlight if its left in the line of sunlight , especially now its summer. If thats not applicable then it doesn't matter as much but sanding sealer make the end result far better.

When applying the lacquer, one coat at a time, leave at least 15 minutes between coats. thin the lacquer 50% or more to start off with 50-50 and if you have the right gun it should spray Ok if not add more thinner and after about 3 coats give it a dry rub with about 800 paper dry. Then thin the mixture down to about 80 -20 and apply 2-3 more. This will make it flow out a lot flatter.

After the 5-6 coats let it dry for at least 12 hours This is the normal amount required for best results.

You can work faster than those times but if you arn't use to the material its better to play safe. Also if you need to you can add extra coats just keep in mind that the underneath coats will be stopped from leaching their solvent if you apply more too quickly. If a lot more are needed you havn't prepared the surface enough in the first place.

[fanlee]

Thanks guys.

To answer some questions.

I'm making a solid bodied electric guitar. Now initially I wasn't sure whether to stain it or clear coat it, so I put on a coat of shellac to get some idea of how it would come up.

I decided I'd like it red and the Feast Watson prooftint in shellac gave me a red I really liked, so I used the hard shellac as a vehicle for the stain.

I well know staining the timber clear coating then lacquering is simpler, but I've gone this way this time and I have to say the colour is just what I want. In future I will probably take the other approach.

I figured finishing it all of with Nitro cellulose lacquer would give me more durability and lessen the odds of the dreaded 'sand through'...although I could still manage it!!

Hopefully I will keep it away from direct sunlight, water, alcohol ( ) ...probably might have to use it for hand to hand combat at times...

The answers provided give me the info.

Thanks again

.

[Auld Bassoon]

Echo to Al (Ozwinner),

Why on earth would you want to apply N/C over shellac? This doesn't make any sense to me at all...

[kiwigeo]

I dont use nitro on my guitars but quite a few people use shellac as a wash coat under nitro.

Heres one guy who does it:

http://wellsguitars.com/Articles/Lacquer_Finishing.htm

[durwood]

What you are doing will work but its an ass up way to go about it.

The industry way is to stain (and fill the timber if needed) then sanding sealer then lacquer then use a pad to work the lacquer into a flat smooth finish. That way you don't rub though anywhere and you won't damage the finish.

I certainly wouldn't be using a buffing wheel to produce a shine as per the article kiwigeo posted. I can just see the neck of the instrument getting ripped off or the lacquer being burnt.

[Phil Mailloux]

It's pretty common in the guitar building industry to use shellac as a sealer coat between the stain and the lacquer coats.
ALL pro builders use a buffing wheel to get a shine on a guitar. You obviously need to know what you're doing not to burn through the lacquer.

[fanlee]

Could you expand on or give me a reference/s for rubbing the lacquer with a pad please?

I was planning to use wet n dry with paraffin from about 600 -> 1200 grit & then Meguair's Mirror Glaze 2, 9 & 7 for gloss.

I presume using a pad to fuse the lacquer is a differnt technique to the polishing moves described in the Handbook on p91.

TIA

[Phil Mailloux]

Here's a quote from "finishing 101" a document you can find on www.reranch.com a great source of guitar finishing information:

'After the final grade of sanding is completed, the final polishing can begin. Use a soft cotton rag either folded or shaped into a ball and held between the fingers. Either way try to prevent individual fingers from causing furrows. Polish in random circles. The polishing can be done in steps starting with a white polishing compound. If the surface was prepared as noted in the last section, red (more abrasive than white) compound should not be necessary. In fact white can probably be skipped and the finish can be polished with a swirl remover type polish. We use the 3M product, "Finesse It II" going directly from #2000 to final finish. Skipping the white and red steps may take longer to polish but on a relatively new surface the final polish seems more reflective.'

I've met a few guys that finish exactly as you mentioned with wet n dry up to 1200 and with meguiar's 2-9-7, that's fine. (i've never heard about the paraffin though)

I personally use the stewmac foam pads that you chuck in your drill to polish it up to a gloss with a local Dutch car polish I had bought when I lived in Holland and finished it with 3M imperial hand glaze.

There's nothing really complicated in rubbing out a guitar by hand. Just try it, you'll see how simple it is. Which handbook p91 are you talking about?

[fanlee]

Thanks Phil.

I meant the Polishers' Handbook.

Yes...the ReRanch site...I remember reading their sunburst tutorial, but they can't ship the products OS

There's so much info out there it's impossible for me to 'assemble' it all coherently....

and then you get those 'healthy disagreements between experts'

.

[durwood]

The forum update seems to have introduced a few bugs as It won't let me copy a post to here. So the info on using a pad can be found by going to the finishing thread then to page 12 and scrolling down to 6th Feb and the entry spraying lacquer page two about half way down.

The method described is similar to french polishing except you have changed solvents.

What Phil describes is compounding which uses a paste to rub away the scratches put in by the abrasive paper. A spray painter uses this method to produce the final finish on car paint. It works but is inherently messy especially if you use amachine buff , it leaves behind compound residue which then needs to be cleaned. Phil is actually using 2 types of compound the white and red are normal lacquer ones the "Finness it" is made for 2 pack urethane paint.

A french polisher avoids this process by using the pad, he only rubs the material and moves it around and brings up the gloss. It also allows him to easily get gloss on shapes like turned legs on tables where their are lots of hill and hollows.

Compounding wears away the coat of paint as it has to remove the scratches from the abrasive paper. The finer the paper the smaller the scratches and they come out quicker but you are still removing material and risking rubbing through an edge or worse still making an area bald.

[fanlee]

...that's a mighty thread...:eek:

Just so I know I've understood...

You would use French Polishing moves, with a pad, but the pad contains lacquer & thinners, not shellac.

Is that right?:confused:

TIA

Rob.

[durwood]

thinners and metho (Not lacquer) start with circles then figure 8's then straight lines. What you are doing is scooping the lacquer off the high spots and pushing them into the low spots (grain holes)

Once you get the feel of the lacquer you can work pretty fast.

This time of year is a transition period, the paint manufacturers change the formula of the thinner from winter to summer so depending on which one you have will govern your times as to when it softens and drys out but if it starts to get sticky move on or let it dry out before continuing.

Do it on a warm normal day, avoid wet, humid days.

[fanlee]

Just a couple more questions ...they're relevant

I'm planning to use spray can nitrocellulose.

Will the lacquer/metho rubout work with this? and

What sort of thinners do I buy? Do I ask for "thinner for nitrocellulose lacquer"?

TIA
Rob.