Sanding problems with epoxy?

[ear3]

I'm using the cut-offs from my spalted maple slab conference table project (http://festoolownersgroup.com/member-projects/bookmatched-spalted-maple-conference-table-build/) to make a smaller coffee/end table, and I ran into some issues with sanding that I've never encountered before.  I noticed these issues when doing the conference table as well, but didn't think much about it at the time -- but now that it's happened again I know it was not just my imagination.

With the size panel created by the offcuts, I should normally be able to do both sides with a single sheet of Granat abrasive.  But I found as I stepped up the grits that the life span of the sheets became progressively shorter (mounted on ETS-EC 150/5 with DC).  At 180 it was only one sheet per side, and by the time I topped out at 400 it was almost 3 sheets per side.  The abrasive would quickly stop cutting the surface and instead just burnish it.  I feel like the abrasive life span might have improved slightly after I started vacuuming and wiping with a cloth between grits, which I normally don't do at the lower grits, but that might have just been my wishful thinking.

The only thing I can think of is that there's something about the epoxy resin I used to fill the cracks and holes (West System 105 + 205 and 207) that takes a toll on the abrasive.  The epoxy is certainly fully cured, as I did it last weekend.  I examined the paper and there was no visible loading up or clogging.  I didn't do any experiments with changing speed of the sander.  I would note though that when sanding with the RS2 (which has a smaller/finer orbit), which I used up to 150 to keep the plank flat, I did not seem to have any problems.

Any thoughts?

 

[Vondawg]

Edward, first thanks for all the posts/projects, I don’t think I’ve missed one and have enjoyed them very much. I’ve been using west system for close to 30 yrs and I never grind/sand...the excess down...I use a carbide scraper and a heat gun, heating/softening enough so it peaks away, much like curls of wood off a hand plane...the gun aids in keeping the area clear by blowing away the scrapings as well...when flush with surrounding wood I then begin sanding. So I think yes the epoxy’s hardness could be part of your experience...just my thoughts

 

[Michael Kellough]

Some Interesting reading.

 

[Cheese]

I've used West 105/205 and 105/207 combinations before without any issues. Here's a 32" x 25" slab of white oak that I poured a 2 mm thick coat of 105/207 on.

Here's a close up of a test piece I did and you can clearly see the edge build up and the amine blush that needed to be removed from the entire surface.

[attachimg=1]

I started with a RO 125 with 80 grit then went to 150 grit. I then changed to an ETS EC 125 with a 150 mm pad and worked through the grits up to 2000.

Here's a photo of the papers I used. Some don't even match the size or shape of the sanding pad. However, they all worked well and I'd have to say most are probably still serviceable. I never went through more than 1 of each different grit paper.

[attachimg=2]

In this photo you can see the reflection of the LED light bar from the upper cabinet along with the reflection of the back splash. So there was quite a bit of sanding that I had to do.

[attachimg=3]

I wish I had an answer for your problem.  [sad]  I did check out Jamestown Distributors as they're heavily into epoxy for boats. If you open this link and scroll down to Epoxy, there may be an article of interest there.
https://www.jamestowndistributors.com/userportal/how_tos.do

 

[deepcreek]

Saphir 50 grit makes short work of excess epoxy and doesn't load up.

When it's flush, I switch to Granat 80 and move up to 100 grit. 

After that I use Rubin 2 through the rest of the grits.

 

[ear3]

Thanks for the replies.  Just to clarify -- the problems I encountered occurred not during the initial removal/flattening of the epoxy, which was easily achieved with a combination of the RAS and the RO150, but rather when I moved into finish sanding after everything was flat.  Looks from the link given by [member=297]Michael Kellough[/member] that I might be encountering "amine blush" which I did not know about before.  Will adjust accordingly on my next epoxy-involved projects.

Really nice work BTW  [member=44099]Cheese[/member]

 

[peter halle]

Many years ago I had a disaster with a gelcoat job.  An old-timer kept me from doing that again when he told me about poly vinyl alcohol.  It is used as a mold release agent when laying up fiberglass but it also can be sprayed on an epoxy or fiberglass project to ensure full curing by sealing it from the atmosphere.  I have applied it using a spray bottle or a cheap finishing gun.  I wonder if that might help you in the future.  Jamestown Distributers could certainly chime in on that.

It is water soluble and has a nice smell - well at least to me.

Peter

 

[leakyroof]

Some Interesting reading.

. Very interesting reading..... [thanks] [thanks]