Lack of Pore Fill

[kiwinoz62]

Hi everyone,

My problem is lack of pore fill (epoxy) on the EIR b/s once I have scraped and sanded.
I progress through the grits 150, 180, 220, 320, 360 & got a fantastic finish but now notice I have maybe a 60% pore fill coverage.

Who has experienced this or similar and what has been the remedy to fix this problem?

I know, I could pore fill again but hopefully that will be my last resort.

Thanks for any help in advance.

[kiwigeo]

Hi everyone,

My problem is lack of pore fill (epoxy) on the EIR b/s once I have scraped and sanded.
I progress through the grits 150, 180, 220, 320, 360 & got a fantastic finish but now notice I have maybe a 60% pore fill coverage.

Can you clarify.....you've scraped and sanded before or after applying the epoxy? Could you give us a run down on the procedure you went through with surface preparation and pore filling.

[kiwinoz62]

Hi,
Sorry for any confusion.

I have prepared b&s going from 150 - 360 grit sandpaper for pore filling, pore filled then scraped and sanded going through the grits once again to be left at my present stage.
Approx. 60% pore fill coverage, a scattering of open pores over b&s.

I guess my main concern is, if I apply the lacquer to b&s in it's present state how un-sightly will the finish look?

[kiwigeo]

I go through following procedure when I pore fill using Z-poxy:

1. sand back to 320 grit. Wet to raise grain and light sand with 320 grit again. I then clean the surface using a tack cloth (non silicone!)
2. apply full strength Zpoxy using an old credit card.
3. sand back to level surface with 220 grit. In places Ill be back to bare wood.
4. apply half strength Zpoxy using a paper towel.
5. Once hardened I level the surface using 220 grit. I go back to bare wood so finished surface will have Zpoxy only in the pores.
6. if the result is unsatisfactory I repeat from step 4 again.

I think your scraper is going to pull epoxy out of the pores.....it may be part of your problem.

[Allen]

If all you've done is one pore fill session, then that is the biggest part of the problem. Even on fine grain wood you would need at a bare minimum 2 sessions, and most times with wood like EIR which has pretty big pores it will take 3 sessions even if you know what you are doing.

As well, you don't need to go through all those grits between sessions. You're just waisting time and material. In fact, I absolutely never sand finer than 220 before any pore filling, as the scraping and sanding with 180 later simply negates using anything finer. That's the type of thing that gets you an ass kicking by the boss in a production environment. Also why everyone seems to struggle so much getting a nice finish in a reasonable amount of time and effort.

[kiwinoz62]

Martin & Allen,

Thank you both for your concise & informative explanations.
Back to the shed for a couple more pore fill sessions & then should be ready to lacquer.

OBTW the boss said he won't kick my butt this time but if it happens again. . .

[Allen]

We'll let this one slide by then.

[joolstacho]

Here's what's happening. Zpoxy is a fairly viscous (thick) fluid. As you drag it on with the credit card it's actually trapping air bubbles in the pores. These get 'opened up' when you sand back.
I don't like to thin 2 pack resins because you can easily compromise the correct curing (hardening). Incorrect curing temps are also a big issue.
I use 2k Auto clearcoat. It's thinner, and unlike epoxies, is formulated to be thinned a little. I rub it in with a cloth (you need to work fast-ish). Because it's thinner it soaks in better, and rubbing it in fills the pores better. If it's cured at around 35C it hardens nicely. Most often I find one 'rubbed' coat and 1 or 2 brushed on coats will do the trick, then spraycoats... (although the Alpine ash I used recently took a lot more than that!)
Don't sand between rubbed coats. What happens here is that sanding dust gets into the pores, which traps air, and subsequent coats won't fill the pores properly.
Cure at between 35-40C. More would be better for hardness but we're dealing with fine wood structures eh?
Curing oven? An old wardrobe - some foam insulation-, with a small dimplex heater and thermometer is dead easy to rig up.

[kiwigeo]

Here's what's happening. Zpoxy is a fairly viscous (thick) fluid. As you drag it on with the credit card it's actually trapping air bubbles in the pores. These get 'opened up' when you sand back.

The Zpoxy I use is not that thick neat out of the bottle and after the first session I cut it by 50% with alcohol for subsequent sessions.

As Allen notes you'll never get a 100% satisfactory fill job with just one application of z-poxy.

Note there are two approaches to epoxy filling:

1. aim for a smooth coat of epoxy filling the pores and wood.
2. sand back so the epoxy remains only in the pores. This is the method I use.

[joolstacho]

At the risk of getting anal about this!...
Link below has some useful info. If you want to read through it you'll see that thinning epoxies with a solvent always compromises the performance (that basically means hardness). You can use heat to lower the viscosity without causing probs, but it does mean you've got to work quickly/differently.
(I've seen a few sad cases in the aviation industry where people have produced structurally piss-weak components because they thought they knew better than the formulating chemists).

http://www.seqair.com/skunkworks/Glues/ ... nning.html

Jools

[jeffhigh]

I'm no chemist, but perhaps in this pore filling application, we are having very little degradation by thinning, because the thinned material is applied so thinly, that the solvent is able to flash off well before the end of the epoxy working time, leaving undiluted epoxy on the surface and in the pores.
Very different to a closed joint or a high build coat.

[kiwigeo]

At the risk of getting anal about this!...
Link below has some useful info. If you want to read through it you'll see that thinning epoxies with a solvent always compromises the performance (that basically means hardness). You can use heat to lower the viscosity without causing probs, but it does mean you've got to work quickly/differently.
(I've seen a few sad cases in the aviation industry where people have produced structurally piss-weak components because they thought they knew better than the formulating chemists).

http://www.seqair.com/skunkworks/Glues/ ... nning.html

Jools

All taken on board Jools and thanks for the info. Your link refers to West systems epoxy which is designed to higher specs than Z poxy. Z poxy is a finishing resin.....I believe its main use is in the fields of theatre (eg masks) and modelling.

Cutting the Zpoxy with alcohol works for me and since I'm pore filling a guitar not building a 747 a degradation in the hardness of the epoxy isn't a big issue. I also pore fill with shellac and pumice and the material filling the pores is going to be far softer than thinned Z-poxy.

Cheers Martin

[Kim]

Just another point on degradation of epoxy from thinning...what would be the issue with that in this particular application?

It is not like it is structural or bonding anything to anything else. Its only filling small holes in wood and in doing that, if it did not harden as much as it could, why is this such a bad thing? I would think that as long as the MOE remains such that the product still sands well, being a little more flexible to move with the wood as it reacts to ambience is probably a good thing.

Just keep a fan blowing to keep the fumes from being absorbed by your skin while you use the stuff and don't try to make things more complicated than they need to be is my advice.

Cheers

Kim

[kiwinoz62]

Hi everyone,

Just an up date, today I scraped and sanded back 2nd pore fill session.
It's worked a treat, 100% pore fill & I'm happily impressed.
There seems to be a fine line in just removing enough epoxy before cutting through the barrier and into timber.

Thanks for the advice guys. . .