Scratches in finish after micro mesh

[Steve.Toscano]

Hi all.
On my latest build i thought i would try a full body rubbed on shellac finish for the first time. Note im not calling this French Polish - no oil or spiriting off.
Started on the back, many sessions of a very diluted Hard Shellac. Not rushed, a day drying between sessions. Waited 2 weeks for it to harden.

Anyway after attempting to polish up the back by working my way up the grits in micro mesh pads all the way up to the finest (12000). Im left with the below scratches on the finish.
I've attacked this twice now, after the first attempt i went back to the course pad and all the way up again. Spending roughly 5minutes with each grit. 10 - 15 with the finer grits.
Any thoughts on what to do next to remove these? Do i need to spend longer with each grit of the pads? Do i need to go to a buff/polishing compound? Or should i have aimed for a finish straight off the fad and therfore go back to it to blend the scratches?

I was of the understanding the finest micro mesh pad would get it pretty close to a gloss without needing to buff and use polishing compound.


They're definitely on the top of the finish not in it.

Thanks in advance, im fairly new to finishing my own instruments. I now know why I always paid someone else to finish them for me.

Close up, scratches on either side of the light reflection.

[simso]

Hard to get a nice finish simply shellacking and sanding without using oil.

That being said it looks okay,

If you suspect that the issue is with your sanding. Then work up in grit sizes working the surface in different directions, example one grit go left to right at an angle and then next grit go right to left at an angle, this will show any points not sanded well enough.

I have never left an instrument finished in shellac unless I used olive oil and spiriting during the process, so others may have better advice on what I have said.

Nitro finish process of mine, ignore everything pre the bottom buffed pictures

Buffing makes a huge difference

http://www.mirwa.com.au/HTS_Paint.html


Steve

[demonx]

Hard to tell from photos but it looks like sanding scratches, ie: not going through the grits properly.

Maybe post your sanding process, in grits from start to finish and something may jump out.

[kiwigeo]

Which hard shecllac are you using? I use Robert Rae's hard shellac rather than Ubeaut on most of my builds. My comments:

1. 2 weeks isnt really long enough for hard shellac to properly harden and cross link. I wait at least 4 weeks after french polishing with HS and then finish off with Mcguiars No 10 and No 7 products.
2. The source of the scratches - possibly shellac build up on the micromesh....most likely the coarser grades?
3. Solution - Treat the finish youve applied so far as your spit coat and do a few bodying sessions with a pad and oil (walnut my preference). Wait 4 weeks and then hand rub out with Mcguiars car polish products.

[kiwigeo]

Hard to tell from photos but it looks like sanding scratches, ie: not going through the grits properly.

Maybe post your sanding process, in grits from start to finish and something may jump out.

After a bit of thought I think I agree with Steve..the scratches seem to be in the wood not the finish. To double check sand of a small area of finish and check the wood with a jewellers lens. I find that a sanded surface can look great but after a few bodying sessions the scratches stand out like dog's balls.

[Steve.Toscano]

Thanks guys.

Hard to tell from photos but it looks like sanding scratches, ie: not going through the grits properly.

Maybe post your sanding process, in grits from start to finish and something may jump out.

I agree, it certainly is sanding scratches, as i said in the first post it is ON the finish (eg sanding scratches) not in it. Problem is that isnt the micro mesh supposed to leave a finish with scratches the naked eye cant see?

Wood surface was sanded to 800 wet/dry.
Shellac'd surface:
Started with the course micro mesh pad and worked up to the finest. 5mins with each grit, 10-15mins on the finer grits.



The scratches are definitely on the finish, as they follow the sanding pattern from the micro mesh. If i go at an angle with the finest pad the scratches follow that angle.

The shellac is Ubeut premixed hard shellac, I mixed it 4 parts alc to 1 part shellac for the bodying coats. Which i understand makes it a pretty weak mixture.

Martin - I thought about doing a few more bodying sessions but then I dont want to cover the existing scratches with more shellac. As that would just create more work down the track right? Or even after 2 weeks would the new coats/sessions blend these scratches.

This morning I went and got some Meguiars Clear Coat Safe Polishing Compound. (they dont seem to call them by the numbers anymore). Tried a small amount of it on a corner of the back and found it too created fine scratches on the surface.

As Martin alluded to, im thinking the finish might be still too soft.

If it's any help I did notice that there was small 'grains' of shellac coming off the surface while working with the micro mesh pads - the finer the pad the finer the 'grains'. Is that normal?

I guess this is why i should have practised on a piece of scrap first right....

[Steve.Toscano]

This is the Meguiars stuff i just tryed.
http://www.meguiars.com/en/automotive/p ... XIO3Mds.97

[kiwigeo]

Steve, if the scratches are only in the finish then subsequent bodying sessions should fill in same. There have always been questions asked about further bodying sessions or repairs to hard shellac after its been left for a while and cross linking has started. I've touched up a hard shellac finish after having left it for a few weeks and I haven't had any issues.

[kiwigeo]

This is the Meguiars stuff i just tryed.
http://www.meguiars.com/en/automotive/p ... XIO3Mds.97

I bought mine (at inflated price) from LMI: http://www.lmii.com/products/finishing/ ... -compounds

I had a search but couldn't find any online auto product suppliers stocking these products.

[Steve.Toscano]

Thanks heaps Martin, I guess im spending my arvo doing more bodying sessions then.
This time with oil / spiriting off.

[kiwigeo]

Thanks heaps Martin, I guess im spending my arvo doing more bodying sessions then.
This time with oil / spiriting off.

I find using walnut oil I don't need to remove excess oil....walnut oil tends to blend with the shellac. If any leveling off needs doing I tend to use wet and dry with oil as a lubricant rather than spiriting off. Spiriting off is something Ive never got down pat and alot of other people have the same experience...the secret is in having a pad that's done some miles during bodying sessions and still has a bit of shellac in the wadding. Pete Coombe is probably the expert in this field.

[simso]

I have never tried walnut oil, where do you get that from, I would not mind giving it a go.

I am no expert on this subject, just know the basics and what works for me.

typically I use olive oil as it's readily available

For spiriting, I find the opposite a fresh clean pad, two drops of shellac and then 4-6 drops metho. Repeat as required. I use an eye dropper bottle.


Steve

[kiwigeo]

Steve,

I was buying my walnut oil direct from an online walnut product farmer but I've found that most supermarkets stock walnut oil. Just make sure it's one without preservatives or other additives.