Epoxy scratches - help?

[CC1]

Hi again

 

So I'm getting close to the end... but something off is happening in the finish that I didn't get when doing walnut tables...

 

So I have dry sanded the whole body to 5000 grit - because the epoxy needed to go there, so why not? Anyway - it was sickeningly smooth. Loved it.

 

Went for a wipe on poly - just 50/50 mix mineral spirits and poly.

 

The first 3-4 coats went on just fine (see image). The epoxy looks flawless (ignoring bubbles - point being there are no scratches). It was like new glass.

 

Then something happened. The 5th coat got too much dust in it. Not a problem I said - I got out the 400grit and did as I had done after coats 2 , 3 , and 4. Light sand, clean down with white spirit, let dry, then 5th coat of wipe-on....

 

(cont. in next post for image) 

[CC1]

After the 5th wipe on coat - it became clear that I had got grit/gunk or whatever in the sandpaper, and scratched the epoxy part, making it look like this after the poly was dry:

[CC1]

"Pain in the arse" I thought, but wanting to get it right, I thought bugger it, I'll sand that back down.

 

So I carefully wet-sanded the epoxy parts from 400 through 2000 grit by hand. Pretty sure I ended up taking off all 4 layers of poly, but at least it was back to looking cloudy (like it had been prior to first poly coat)

 

But, I then put on another fresh coat of 50/50 poly, of course while wet it looks fine, but now it's mostly dried (been 3 hours), it still looks like this:

[CC1]

What have I done wrong that means the scratches are now staying, and the poly isn't filling them in?

 

I am sometimes leaving an hour or so between coats, sometimes it's overnight (only so many you can get in a day)

 

If I need to keep the coats closer together, should I go do one now? (It's been 2 hours since a coat was done, at 4pm UK, it's now 6pm UK, and looks like the last photo)

 

Or is that normal and keep building layers until a final polish/buff?

 

The wood looks and feels great. The epoxy started brilliant, went to shit, seemed recoverable, but now seems cruddy and amateurish

[ScottR]

My guess is it has more to do with the poly and less with the epoxy. If that were lacquer I'd say you had a humidity problem. With poly, I think that could still be an issue. I'd say leave it till tomorrow and see what it looks like. Could be that it will clear up with more time.

SR

[CC1]

thanks. I can definitely see fine scratches though - and this is the first recoat after all that sanding

 

Will leave that until tomorrow

[ScottR]

41 minutes ago, CC1 said:

thanks. I can definitely see fine scratches though - and this is the first recoat after all that sanding

 

Will leave that until tomorrow

If you can still see scratches after only one coat it means you didn't them completely out during your re-sand. That being said, your poly needs a little bit to grip to, as there are no pores in epoxy to soak in to and create a mechanical bond. I'd say the fact that you are thinning your poly 50/50 means it's going to take a lot more coats for the remaining solids to fill those sanding scratches.

SR

[CC1]

18 minutes ago, ScottR said:

If you can still see scratches after only one coat it means you didn't them completely out during your re-sand. That being said, your poly needs a little bit to grip to, as there are no pores in epoxy to soak in to and create a mechanical bond. I'd say the fact that you are thinning your poly 50/50 means it's going to take a lot more coats for the remaining solids to fill those sanding scratches.

SR

What you thinking then... hard buff with brown paper between coats and keep applying?

 

Change the mix to 70/30 poly?

[ScottR]

Something along those lines. If you are going to run your poly that thin, you likely need nothing between coats or maybe a leveling light sand every 4th or 5th coat. You need to build enough to fill your scratches and then level it all and then put a very thin topcoat on. Leveling poly will show witness lines between layers Which is the reason for a very thin topcoat--that doesn't get leveled and therefore doesn't show the witness lines. If all your coats are very thin you will likely need less leveling at the end but it will require many more coats.

I'm hoping we can get @Andyjr1515 to chime in. Almost all of his finishes are poly or a poly mix and they are very nice. I'm mostly a lacquer guy and don't want to lead you astray.

 

SR

[CC1]

Fear was I'd start poly'ing over dust and nibs formed in the previous layer. I'm having to do this in a spare bedroom carpeted, too)

 

[Bizman62]

9 hours ago, CC1 said:

Fear was I'd start poly'ing over dust and nibs formed in the previous layer. I'm having to do this in a spare bedroom carpeted, too

One trick to prevent dust from flying is to hang wet bedlinen around your working space.

[Andyjr1515]

Hi

Another polyurethane varnish user

As @ScottR says, when I do gloss finishes I pretty much always use old-fashioned polyurethane varnish (specifically Ronseal Hardglaze).

I used to do that exclusively with wipe on techniques (there is a tutorial on the site about my methods) but since a formulation change by Ronseal (no criticism - it was to reduce the environmentally unfriendly volatiles) I have more recently started to use significantly less thinners and use an artist's watercolour fan brush to apply.

But that's by the by.  

Reading through your posts, I'm pretty certain I can see what's happened, I think it's relatively easily fixable and that you have a couple of ways of doing it.

Cause

- Remembering that a coat of thinned, wiped on poly is exceptionally thin** - it is more like a coat of glossness than an coat of finish - then using 400 grit will have cut straight through the poly and into the epoxy.  It will have been the same as if you had stopped at 400 when you did the epoxy sanding rather than going through the grits to 5000 grit as you described.  And epoxy is, on the other hand, pretty hard in comparison and so the only way to get back to that original finish (although you may not need to) is to repeat your original sanding regime through the grits to 5000 again.

Fixes

I think you could do this two ways.  Either:

- resand down the grits back to your original starting point and start the varnishing process again.  Once you've started varnishing, don't do an interim sand until you have put at least 10 coats on, and then use - at the very coarsest - 2500 grit, wet, to flatten before adding the final whisper thin couple of gloss coats

or

- put some thicker coats on the present finish (10% thinners max and at least 6 coats allowing it to cure in between each) to build up a polyurethane thickness (which actually will still  be pretty thin) and this will fully fill the present scratch marks.  Leave it a couple of days to harden more and then flatten gently - just to get rid of any dust buggies and slight ripples - with 2500 or finer used wet before the final two or three thinned gloss coats.

 

**With polyurethane varnish, I generally do a final flattening with 2500 wet and dry used wet before the final two of three final coats of thin wipe on.  Why 2 or 3 coats?  Because thinned wipe-on is SO thin, that it will actually still show the scratch marks off a 2500 wet-sanded finish after the first finish coat!!  The second coat usually finally fills it all and sometimes it needs a third.

 

Hope this helps! 

 

 

[CC1]

4 hours ago, Andyjr1515 said:

Hi

Another polyurethane varnish user

As @ScottR says, when I do gloss finishes I pretty much always use old-fashioned polyurethane varnish (specifically Ronseal Hardglaze).

I used to do that exclusively with wipe on techniques (there is a tutorial on the site about my methods) but since a formulation change by Ronseal (no criticism - it was to reduce the environmentally unfriendly volatiles) I have more recently started to use significantly less thinners and use an artist's watercolour fan brush to apply.

But that's by the by.  

Reading through your posts, I'm pretty certain I can see what's happened, I think it's relatively easily fixable and that you have a couple of ways of doing it.

Cause

- Remembering that a coat of thinned, wiped on poly is exceptionally thin** - it is more like a coat of glossness than an coat of finish - then using 400 grit will have cut straight through the poly and into the epoxy.  It will have been the same as if you had stopped at 400 when you did the epoxy sanding rather than going through the grits to 5000 grit as you described.  And epoxy is, on the other hand, pretty hard in comparison and so the only way to get back to that original finish (although you may not need to) is to repeat your original sanding regime through the grits to 5000 again.

Fixes

I think you could do this two ways.  Either:

- resand down the grits back to your original starting point and start the varnishing process again.  Once you've started varnishing, don't do an interim sand until you have put at least 10 coats on, and then use - at the very coarsest - 2500 grit, wet, to flatten before adding the final whisper thin couple of gloss coats

or

- put some thicker coats on the present finish (10% thinners max and at least 6 coats allowing it to cure in between each) to build up a polyurethane thickness (which actually will still  be pretty thin) and this will fully fill the present scratch marks.  Leave it a couple of days to harden more and then flatten gently - just to get rid of any dust buggies and slight ripples - with 2500 or finer used wet before the final two or three thinned gloss coats.

 

**With polyurethane varnish, I generally do a final flattening with 2500 wet and dry used wet before the final two of three final coats of thin wipe on.  Why 2 or 3 coats?  Because thinned wipe-on is SO thin, that it will actually still show the scratch marks off a 2500 wet-sanded finish after the first finish coat!!  The second coat usually finally fills it all and sometimes it needs a third.

 

Hope this helps! 

 

 

Thank you very much!

 

I had thought that what I might have done was go right through a very thin layer. This seemed more noticeable when the thin strip of red epoxy flowing through the body (same scratch problem), once wet sanded (I thought it was thicker...) slightly raised the grain on the surrounding wood. 

 

Now, it was all wet sanded to 2000 again, and that particular piece of the wood will be under the G String (It's a P Bass) so I'm not going to bother resanding the whole thing.

 

So, reading an above comment (before your reply), I decided to try one thing, assuming thickness was the problem.

 

I made a new batch of wipe on, this one much more like 70/30 to 75/25. It was noticeably gloopier. I wiped this on, a bit generously, but not enough to let it run/drip.

 

3 hours later, the scratches in the epoxy part are basically all gone. So it would seem that my first re-coat yesterday of 50/50, was as you say, so thin, it couldn't even fill in 2000grit scratches.

 

My concern, being that it's in a dusty room (no foot traffic, but it's in the air), is that I don't want to put on 3+ coats at any thickness without denibbing etc - because that's surely going to make fine dust stuck between the layers, no?

 

In any case, I will not be sanding between subsequent coats - but rather lightly buffing with brown paper between coats to de-nib and remove embedded dust, before a quick light mineral spirits wipe, followed immediately by another coat of the 70/30.

 

Where abouts should I stop do you think? I have 5 coats of 50/50 on the body for the most part, with 1 coat of 50/50 over the epoxy areas, and now have 1 coat of 70/30 over the whole thing.

 

I'm thinking, another 4 coats of 70/30 should be enough, at which point I'll do a quick 800 grit light sand, then apply the final 70/30 coat.

 

Then I'm down to the final bit - do I use my Briwax as a final seal, or go down the car polish route?

 

I know I need 2 different car polishes, one grittier and one very fine, and buff (I have lambswool RO-Sander pads) - if you've tried this, any exact brands I can use? They all name themselves differently

 

Sorry for the million questions  Every youtube video I watch does things slightly differently

[Andyjr1515]

19 minutes ago, CC1 said:

Where abouts should I stop do you think? I have 5 coats of 50/50 on the body for the most part, with 1 coat of 50/50 over the epoxy areas, and now have 1 coat of 70/30 over the whole thing.

 

I'm thinking, another 4 coats of 70/30 should be enough, at which point I'll do a quick 800 grit light sand, then apply the final 70/30 coat.

 

Then I'm down to the final bit - do I use my Briwax as a final seal, or go down the car polish route?

 

I know I need 2 different car polishes, one grittier and one very fine, and buff (I have lambswool RO-Sander pads) - if you've tried this, any exact brands I can use? They all name themselves differently

 

Sorry for the million questions  Every youtube video I watch does things slightly differently

Yes - once you have a modicum of thickness there, then you can start to do more regular de-nibbing and de-rippling flattenings.  At this stage, you are very unlikely to cut through as long as you are using 2500 grit and finer.  Certainly, brown paper will be no problem at all.  

Pre your final coats, I wouldn't go anywhere near as coarse as 800 grit.  Something like 1500 - 2000 gives you much more leeway - it won't take a lot off at any one time and as long as you use it wet and wash the slurry off regularly, you can 'creep up' on any small irregularities without leaving scratches and without the fear of cutting right through.  That said, be very careful with any sharp corners where (ask me how I know) the varnish layer will be much thinner than on the flatter areas...

The final gloss-gloss coats can be quite thin - as I said earlier, it provides the gloss without the thickness and therefore there is no possibility of reintroducing ripples or wipe marks.

Then leave for at least 2 weeks for it to fully harden and, personally for poly, I use Meguiers Ultimate Compound for a final polish - most other popular auto polishes are far too abrasive.  But - and this is important - applied and buffed off by hand.  Don't use any mechanical buffer - it will generate far too much heat and it will burn through the top layers.  Remember that a polyurethane finish is completely different to a finish such as nitro where each layer melts into the previous one.  Polyurethane varnish is more like slate, where each coat is essentially a separate layer and if you cut through the superfine top layer you will expose the layers you have previously sanded.  I  have a photo somewhere of one I did in the early days - it's like contour lines on an OS map!

Briwax is great for oil finishes, but isn't really the best thing for polyurethane.  Hand polishing with Ultimate Compound should be all it needs.

This is one I did wiped on and finished with the above method:

 

[Bizman62]

40 minutes ago, CC1 said:

I know I need 2 different car polishes, one grittier and one very fine, and buff

Not necessarily. I used the very fine (of three varietys of that brand) only after sanding the 2k finish through the grits 6000.

[Bizman62]

1 minute ago, Andyjr1515 said:

as long as you use it wet and wash the slurry off regularly, you can 'creep up' on any small irregularities without leaving scratches and without the fear of cutting right through

Another thing to remember is to avoid pressure when sanding. Pressure will roll the slurry into balls with loosened grit from the sandpaper and those will create deep grooves. You should leave space between the tips of the abrasive chips and the paper for the slurry. Think about a hand plane without a mouth, where would the shavings go? Sandpaper can be compared to millions of miniature mouthless planes.

[CC1]

7 minutes ago, Bizman62 said:

Another thing to remember is to avoid pressure when sanding. Pressure will roll the slurry into balls with loosened grit from the sandpaper and those will create deep grooves. You should leave space between the tips of the abrasive chips and the paper for the slurry. Think about a hand plane without a mouth, where would the shavings go? Sandpaper can be compared to millions of miniature mouthless planes.

qThat's a great way to think of it

 

I stalked your profile and found your write up on finishing at home without a workshop - will stick to that like glue

 

Cheers, will share back soon when it's all done!

 

C

[CC1]

@Bizman62 and @Andyjr1515

 

Sorry to bother you again - but just wanted to check something...

 

Should it, as I'm building the layers, look a bit... shoddy? There's the odd light streak, bump, slightly uneven texture, wipe mark, etc. Nothing major - but as I'm building the layers, is it ok to look a bit shabby? As long as major bits of dust etc are removed between layers with the brown paper and mineral wipe, is that professional glass-gloss achieved all in the final sand+50/50poly+cure+hand polish?

 

My experience with this is limited to say the least - all previous woodworking I've done, I used spray poly and then buffed. I just wonder if it's like the epoxy - where it doesn't matter how rough the first pour is (scratches etc) because it's the final pour that matters most.

 

I'm just getting flashbacks to a $50 strat I tried to refinish 15 years ago, where I painted on the poly in layers, and it ended up looking like I had dipped the thing in brown paint and freeze-dried it (actual full on lump runs and streaks etc)

[CC1]

... Reason I ask, is that with what must now be 4-5 coats @ 50/50 (with the odd light sand halfway), 3-4 coats at 70/30:

 

Knots look like this: 

[CC1]

... and majority of the grain looks like this: 

[Bizman62]

The pores are very deep and obviously the layers you're setting are thin. @Andyjr1515 knows that stuff better than I do, in my eyes it just looks like there's not enough stuff to fill the grain. I can't tell whether you just need another 30 coats with light sanding after every 5th layer or use less spirits for faster buildup.

[CC1]

and the back:

[Andyjr1515]

Ah - OK.  This is a slightly different issue.  In the previous posts we were talking more of the epoxy and the micro-scratches. 

This is about grain filling, which I had assumed (if required) had been done on the wood itself before your final sanding. 

Let's start by saying this is fixable, even when you have started your gloss finishing.  There are a couple of ways to tackle it. 

Cause

Basically, the polyurethane is a very thin finish.  Therefore to use the finish coats themselves to do the grain filling is a challenge.  Each finish coat will follow the contours, the hills and hollows, of the grain and knot-holes each time and so those features are still going to show:

Possible Solutions

If you want to 'lose the grain' at this stage, there are a couple of ways that come to mind.

- you could build up enough thickness (this might be a LOT of coats) to the point where the hollows are above the tops of the hills of the grain and then sand down to just above the wood line.  This can work OK for light grain but, to be honest it isn't going to fill a large void such as the knot hole.  Here you would be best to fill the hole with thin cyano or similar first (although this might react to very recently applied polyurethane)

or

- you could 'slurry and wipe' the polyurethane.  Have you seen the 'slurry and buff' method of applying Tru-oil?  Well I've realised that this technique can be adapted to act as a clear grain fill and also used with a number of different finish types.  I can't guarantee with your particular finish and wood, but I have used the technique with poly varnish.

      - basically repeat a 'flattening' sand, maybe slightly coarser (1000grit or similar) but this time the 'wet' of the 'wet and dry' is polyurethane varnish.  So you will create a slurry of wet varnish mixed with the 'sandings' of your previous dry polyurethane coats which, because it has already lost all the volatiles in the drying process, will contain much more bulk than fresh wet varnish.  Sand with a block along the grain, then wipe the slurry gently off with a lint free cloth across the grain, with the slurry thus filling the hollows. 

     - when it is fully dry, flatten in the normal way.  If the grain is still showing, repeat.  Once all of the grain is filled, carry on towards your final gloss coats.

This is basically how I 'slurry and buff' stained woods that most folks say can't be done without losing the stain... 

 

[CC1]

11 minutes ago, Andyjr1515 said:

Ah - OK.  This is a slightly different issue.  In the previous posts we were talking more of the epoxy and the micro-scratches. 

This is about grain filling, which I had assumed (if required) had been done on the wood itself before your final sanding. 

Let's start by saying this is fixable, even when you have started your gloss finishing.  There are a couple of ways to tackle it. 

Cause

Basically, the polyurethane is a very thin finish.  Therefore to use the finish coats themselves to do the grain filling is a challenge.  Each finish coat will follow the contours, the hills and hollows, of the grain and knot-holes each time and so those features are still going to show:

Possible Solutions

If you want to 'lose the grain' at this stage, there are a couple of ways that come to mind.

- you could build up enough thickness (this might be a LOT of coats) to the point where the hollows are above the tops of the hills of the grain and then sand down to just above the wood line.  This can work OK for light grain but, to be honest it isn't going to fill a large void such as the knot hole.  Here you would be best to fill the hole with thin cyano or similar first (although this might react to very recently applied polyurethane)

or

- you could 'slurry and wipe' the polyurethane.  Have you seen the 'slurry and buff' method of applying Tru-oil?  Well I've realised that this technique can be adapted to act as a clear grain fill and also used with a number of different finish types.  I can't guarantee with your particular finish and wood, but I have used the technique with poly varnish.

      - basically repeat a 'flattening' sand, maybe slightly coarser (1000grit or similar) but this time the 'wet' of the 'wet and dry' is polyurethane varnish.  So you will create a slurry of wet varnish mixed with the 'sandings' of your previous dry polyurethane coats which, because it has already lost all the volatiles in the drying process, will contain much more bulk than fresh wet varnish.  Sand with a block along the grain, then wipe the slurry gently off with a lint free cloth across the grain, with the slurry thus filling the hollows. 

     - when it is fully dry, flatten in the normal way.  If the grain is still showing, repeat.  Once all of the grain is filled, carry on towards your final gloss coats.

This is basically how I 'slurry and buff' stained woods that most folks say can't be done without losing the stain... 

 

God f***n damnit...

 

I didn't think I'd need to do any sort of sealing/conditioning before putting on an oil based poly - I thought they were supposed to sit on the top of everything?

 

The whole thing was smoother than glass before I started finishing... I should have just waxed it and left it there (sob)

 

Building up that many coats over the entire body sounds like weeks of work - and my wife would rather like the guest room back soon (I originally said 6 coats/applicatons, I've now done 10...)

 

I mean, it felt smoother a few coats back. I guess I just couldn't see it.

 

I feel like the slurry method is going to be a pain - I can see small areas being missed/the slurry being wiped or falling out.

 

It also sounds like the slurry method is going to rely on several more coats before it's a viable option - as I have to basically sand it twice.

 

I guess I put on 3+ more 70/30 coats, then slurry (I'm guessing I need to wait for a proper cure before attempting to slurry?), then let it cure again, then sand it, then add more poly back on...

 

This is going to take months!

[CC1]

If I do the slurry option - how fresh should the top layer of poly be - do I want it to be relatively fresh, barely dry, or completely cured? Will the slurry not be quite cloudy?