Epoxy HELP

[Riotvan88]

Hello

I've been building a smit rotterdam kit. I've gone and used west systems 650 gflex epoxy with 410 microlight fairing additive to seal the Hull and provide a base for painting. 

 

The problem is the epoxy just does not sand at all. I've spent over 12 hours sanding with everything from coarse grit, fine grit, wet sanding, tried everything. The microlight additive was supposed to make this easily sandable and give a smooth finish. It's like sanding solid rock. 

 

I mixed the epoxy exactly as instructed. It has fully cured. After 12 hours of sanding I'm now left with a horrible lumpy model and several threadbare sanding pads. Picture is after 12 hours of sanding and multiple pads worn through. Any ideas? 

[glbarlow]

This won’t br helpful at this point, it was unnecessary to seal the hull for painting and if you did it would be sanding sealer or something like wipe on Poly. I’m not sure anything will change with that much epoxy. Sorry. 

[Charles Green]

Try using garnet paper with various backers shaped to the hulls contours. Balsa would be easy to shape.  The garnet pieces are sharper and harder than what is used on run-of-the-mill sand paper.

 

Another type of sanding medium would be pieces cut from a belt for belt-sanders.  It's stiffer than sheet paper but it holds up a lot longer. 

[druxey]

Another time try wood filler (if needed!) and sanding sealer before priming. Less nasty, too.

[Riotvan88]

45 minutes ago, Riotvan88 said:

Hello

I've been building a smit rotterdam kit. I've gone and used west systems 650 gflex epoxy with 410 microlight fairing additive to seal the Hull and provide a base for painting. 

 

The problem is the epoxy just does not sand at all. I've spent over 12 hours sanding with everything from coarse grit, fine grit, wet sanding, tried everything. The microlight additive was supposed to make this easily sandable and give a smooth finish. It's like sanding solid rock. 

 

I mixed the epoxy exactly as instructed. It has fully cured. After 12 hours of sanding I'm now left with a horrible lumpy model and several threadbare sanding pads. Picture is after 12 hours of sanding and multiple pads worn through. Any ideas? 

 

30 minutes ago, glbarlow said:

This won’t br helpful at this point, it was unnecessary to seal the hull for painting and if you did it would be sanding sealer or something like wipe on Poly. I’m not sure anything will change with that much epoxy. Sorry. 

So just throw away then? Must be some way to sand this smooth 

[Roger Pellett]

I’ve used a lot of West System Epoxy for boat repair projects.  Here’s what I know:

 

If mixed in the correct proportions it cures. Otherwise, you have a sticky mess.  For example, adding too much hardener does not make the end result harder, it just keeps the mix from fully curing.

 

Cured epoxy resin itself is not especially hard and the fairing compound that you used is intended to be sanded.

 

I am therefore of the opinion that you mixed and applied the epoxy correctly, so your problem is with the abrasive that you are using, not the epoxy/ fairing compound system.  And if you are just sanding with the paper held in your hand, it’s just skidding over the high spots, not fairing.  It needs to be backed up with something solid.

 

Make sure that that you are using high quality abrasive.  I’ve had good luck with 3M abrasives.  Back your sandpaper up with a sanding block. A block of wood works fine, as does a large diameter dowel for concave areas.  As soon as your paper “loads up” get a new piece. Ditto when it stops cutting, otherwise it’s just polishing the surface.  Use coarse files for major shaping.  When they load up clean them with a wire brush or better yet a file brush.  

 

Roger

[vaddoc]

Trade products like West system are usually not appropriate for modelling as they are very hard when cured. I run into a similar issue years ago when I used a large amount of trade filler that dried rock hard. It took a very long time of difficult sanding to rectify things.

 

I use Zpoxy and when needed thicken with gypsum, much easier to sand. I used to use talk powder but I have concerns it may contain asbestos. As Druxey said, for your purposes filler/sealer might have been a better option.

 

Cured epoxy can only be removed by sanding or chiselling away the excess material. 

 

3M silica carbide sand paper are indeed amazing

Edited December 24, 2021 by vaddoc

[Riotvan88]

29 minutes ago, Roger Pellett said:

I’ve used a lot of West System Epoxy for boat repair projects.  Here’s what I know:

 

If mixed in the correct proportions it cures. Otherwise, you have a sticky mess.  For example, adding too much hardener does not make the end result harder, it just keeps the mix from fully curing.

 

Cured epoxy resin itself is not especially hard and the fairing compound that you used is intended to be sanded.

 

I am therefore of the opinion that you mixed and applied the epoxy correctly, so your problem is with the abrasive that you are using, not the epoxy/ fairing compound system.  And if you are just sanding with the paper held in your hand, it’s just skidding over the high spots, not fairing.  It needs to be backed up with something solid.

 

Make sure that that you are using high quality abrasive.  I’ve had good luck with 3M abrasives.  Back your sandpaper up with a sanding block. A block of wood works fine, as does a large diameter dowel for concave areas.  As soon as your paper “loads up” get a new piece. Ditto when it stops cutting, otherwise it’s just polishing the surface.  Use coarse files for major shaping.  When they load up clean them with a wire brush or better yet a file brush.  

 

Roger

Thanks for the advice, I'm using sanding block by infi model. The model is getting smoother but at this rate it will take weeks of sanding. I'm going to try with some m3 sanding blocks. See if that madrs a difference. 

[Roger Pellett]

My definition of the term “sanding block” is different from yours.  I was suggesting wrapping high quality abrasive paper around a block of wood, not using a proprietary block of material impregnated with abrasive material.  I have not found these proprietary sanding blocks to my liking.

[Riotvan88]

10 minutes ago, Roger Pellett said:

My definition of the term “sanding block” is different from yours.  I was suggesting wrapping high quality abrasive paper around a block of wood, not using a proprietary block of material impregnated with abrasive material.  I have not found these proprietary sanding blocks to my liking.

I'm going to try your suggestion with some 3m sandpaper. The blocks have been ok for balsa,milliput and the like but don't seem to touch this epoxy 

[Roger Pellett]

For what you need to remove start with 120 grit or even coarser; 80 grit.  Once you have a nice fair hull, sand with finer grades to remove scratches. 

[Dr PR]

A good way to remove the higher "lumps" would be to use a coarse file or rasp. Hardened epoxy actually machines something like a soft aluminum, although it is more prone to cracking and flaking. You can also carve some hardened epoxies.

 

However, these tools are much more aggressive than sand paper, so start out gently until you get a feel for how much material you are removing.

 

A rasp will leave relatively deep gouge marks. A file will leave a smooth surface. A rat tail file or rounded file will not leave sharp cut edges, but they also do not leave smooth surfaces.

 

After you reduce the lumps and have approximately the correct faired surface, use hard grit sandpaper, as suggested above, to finish the job. For an even smoother surface finish it with fine (#0000) steel wool. Afterward you will need to clean the surface thoroughly to remove any remaining sandpaper grit or steel wool filings.

[Jaager]

Just some thoughts complicate this situation.

Two of the divide point categories with sanding media are open coat and closed coat.   When sanding wood, relatively large particles are being removed at the beginning and often these particles have sticky or gummy molecules as part of the mix.  Open coat has spaces for these particles to be carried away and the 3D zone of the abrasives knife-like edges works better on wood.

When working metal, the particles are of a different nature and close coat does a better job. 

Your epoxy is probably closer to a metal than wood as for what is needed to pare down your surface, so perhaps closed coat should be where you start your choice.

You need a quality backing, but a cloth backing may be too stiff - heavy wet-dry paper may work better.

 

It may be useful to view this from more of a broader perspective.

You have made what seems to be an ill advised choice in finishing materials.  Rather than continue spending unproductive time on a frustrating attempt to recover from this poor choice, punt.

If this was a scratch project, the choice would be simple:  place the hull on a shelf and start over and make a new one. 

A kit presents a major fork in the redo road.

Fork one:  buy a new kit -  the potential cost and re-plowing the same furrow sorta means that you should really love the vessel.

Fork two:  use the kit plans and gather the materials (and tools) to scratch build a new hull.  Better wood than the kit supplied stock is one possibility here.   The danger here is that the additional skills and perspective gained from jumping from the kit world to the scratch one, could take hold and the much wider world of choice of subject, size of the model, and quality of materials would keep you there.

[Riotvan88]

6 minutes ago, Jaager said:

Just some thoughts complicate this situation.

Two of the divide point categories with sanding media are open coat and closed coat.   When sanding wood, relatively large particles are being removed at the beginning and often these particles have sticky or gummy molecules as part of the mix.  Open coat has spaces for these particles to be carried away and the 3D zone of the abrasives knife-like edges works better on wood.

When working metal, the particles are of a different nature and close coat does a better job. 

Your epoxy is probably closer to a metal than wood as for what is needed to pare down your surface, so perhaps closed coat should be where you start your choice.

You need a quality backing, but a cloth backing may be too stiff - heavy wet-dry paper may work better.

 

It may be useful to view this from more of a broader perspective.

You have made what seems to be an ill advised choice in finishing materials.  Rather than continue spending unproductive time on a frustrating attempt to recover from this poor choice, punt.

If this was a scratch project, the choice would be simple:  place the hull on a shelf and start over and make a new one. 

A kit presents a major fork in the redo road.

Fork one:  buy a new kit -  the potential cost and re-plowing the same furrow sorta means that you should really love the vessel.

Fork two:  use the kit plans and gather the materials (and tools) to scratch build a new hull.  Better wood than the kit supplied stock is one possibility here.   The danger here is that the additional skills and perspective gained from jumping from the kit world to the scratch one, could take hold and the much wider world of choice of subject, size of the model, and quality of materials would keep you there.

 

Thanks for the advice, I'll try to sand this with different abrasives as has been suggested. The epoxy is actually designed to be sanded so I do not believe this is beyond salvage with a better choice of abrasives. This is a kit and a re purchase is simply not an option. The choice of epoxy was actually a recomendation from this site. 

[glbarlow]

I can’t imagine recommending epoxy used in the way you have or why anyone on this site would recommend doing so for a wood model hub, it is an adhesive not a sealant at least for modeling purposes.  If you ever sort out a means to sand it I wouldn’t think the finished result would be very appealing. You really should be able to remake the hull without sacrificing the rest of the kit provided there are decent plans. Modelers Sawmill can likely provide the wood you’d need, if you don’t have a scroll saw for the bulkheads you’d spend less time with hand tools cutting new bulkheads than you will with sanding your rock hard mistake. Sometimes you just have to accept the error and start over. 

[No Idea]

There's nothing wrong with using epoxy on a hull.  The Smit Rotterdam is a kit that is also designed with radio control conversion in mind.  These boats do get battered a bit whilst being used so epoxy is a favourite with RC builders.  I usually use epoxy in combination with fibreglass cloth and it gives a beautifully smooth surface ready for paint.  It does need to be applied correctly though as its not a filler its a sealant and gives very good protection.  Here's a ship I made a few years ago with one side being epoxied with cloth.  

 

 

[No Idea]

Sorry I should have said to Riotvan88 - In my opinion all is not lost.  You have applied way too much epoxy and have tried using it as a filler and I'm sure that you are aware of this now.

 

So moving forward I would use aluminium oxide paper starting with 120 grit working my way down to 320 grit.  This stuff will tear through hardened epoxy so give it a try.  I reckon that you have a good 2 or 3 days solid sanding ahead of you so wear a mask.  Sanding blocks for this sort of job are not the way to go.  You will use lots of paper but so be it.

 

Good luck and the effort will be well worth it - just learn and move on 

[Roger Pellett]

The West System Epoxies, widely used here in the USA are “modular.”  One formulation of resin can be used with several different hardeners to vary working time.  West System also sells a variety of compatible fillers.  Viscosity of the resulting mix can vary from a light syrup to peanut butter.  What Riotvan88 did is exactly what West System recommends for fairing full sized boat hulls.

 

I suspect that as you point out, a more aggressive abrasive will solve his problem.

 

Roger

[Riotvan88]

Update*

Thanks for all the advice in the end 

I used 3M sandpaper as someone else suggested previously. This sandpaper on a wooden block has knocked back the lumps and high spots in about 2 minutes of sanding. 

 

I didn't apply the epoxy thick, I used a credit card to try to squeegee it thinly onto the Hull rather than slather it on with a brush. I intend this to be a radio control model which is why I used epoxy. 

 

Now that the 3m paper is sanding it very easily I think the issue is exactly what someone suggested poor abrasive products.  The surface is already smooth after a few minutes with 80 grit so I'll keep going with it.

 

Perhaps worth mentioning is the sanding blocks I used previously were infi model sponge pads as pictured (I used 220g not 800g) 

[Nirvana]

Simple question without any critics: Are you building 

Smith Rotterdam to be a R/C ship? If yes, epoxy and cloth is the way to go.

Building for display - forget epoxy! It's too much work.
When I built my T37 R/C yacht I applied one thin single layer coat epoxy of West Marine product. 
The auto primer was applied twice along with 10 layers of paint before 2 coats of clear coats. 
The surface should be clear. If white -  the ratio is off. 

[Riotvan88]

*UPDATE*

 

Managed to sand the epoxy smooth and is now in primer. 3M aluminium oxide sanding paper 80 grit and then 120 followed by 400 did the trick. Ready for paint now

[Roger Pellett]

Looks great!!!

[vaddoc]

Good job!

[Charles Green]

I'm glad you stayed with it.  That's a beautiful hull.

[druxey]

Well done. That looks soo much better!

[robert952]

This is the reason I like this forum.  Watching people stick with the issue to get it resolved.  Lots of advise from people who have used the various methods.  

 

Nice looking hull.

[Jim Rogers]

Great recovery! Beautiful hull.