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LukeSGee
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Hi all,
I am new to composites and I am currently trying to skin some parts for my car.
To begin, I had issues with bonding the fabric to the parts but I have seemed to solved my issue by not folding the excess behind the part for a clean edge. My main issue at the moment is sanding. I am struggling to get a nice flat surface and I am reluctant to use 120 to begin flatting as I always end up with scratches I struggle to sand out. What is the most efficient way to get a smooth finish without sanding forever. Also, what is the best way to remove drips that have cured and also a bulging edge where the resin has collected on a vertical edge on a part? I worry when I’m sanding I will hit the fabric.
My last issue seemed to be on the weave when I finished sanding, it looks like a void between the resin and the weave as well as moisture under the resin when damp outside.
I am using XCR resin and have been told it is self levelling and does not have air bubbles but I keep getting bubbles!
Thank you
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MarkMK
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The XCR resin is very good but, as it is quite thick, it will retain a lot of air after mixing. Gently warming it will speed-up the de-gassing and make it go on quite well, but be careful as it does cure quite quickly. It's also a good idea to cover your just-brushed parts to limit the amount of dust particles that will invariably fall onto it, leaving small nibs and eventual holes when sanding. You can get a small scraper tool that holds a razor blade in places like Wilko (if you're in the UK?) and this is really good for shaving-off small lumps of resin and drips which will save a bit of sanding time with the coarser grits. Despite the resin being quite good on vertical sides, I've always found it best to coat parts in stages so that surfaces can cure horizontally, so leaving a 'flatter' starting point. You can also think about using 240 grit as a start point if your cured part is not too bumpy to begin with but, with even the most careful blok sanding, you'll usually find your self needing to re-coat at some point if visual perfection is required. Of course, the amount of sanding might be reduced if you're only going to a stage required as a key for final spray clear-coating with an automotive-grade product, but getting an excellent finish on anything but smallish bits will always be quite a labour-intensive process if progressing all the way to 1500 or 200 grit for a gloss finish.
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Warren (Staff)
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Another tip with drips is when the resin is just firming up (like firm cheese), use a scalpel blade to slice off most of the drips. They cut through easily at this point leaving just the smallest base to sand and shape when the resin has hardened up fully.
Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant
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LukeSGee
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Group: Forum Members
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+xAnother tip with drips is when the resin is just firming up (like firm cheese), use a scalpel blade to slice off most of the drips. They cut through easily at this point leaving just the smallest base to sand and shape when the resin has hardened up fully. I massively appreciate the advise! It should hopefully solve my issues. What would be the best way to heat the resin up? Use a hairdryer on the underside of the cup? I am aiming to have very high quality aesthetically finished parts. What would be the best procedure to finish with a very flat/smooth and glossy surface? Are spray clear coats required? Thank you again for your help,
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MarkMK
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A hair dryer will work okay or just leave tge pot on a radiator for a few minutes
You just need good patient wet sanding, using a block where appropriate. Change the water at each grit chage also.
Aim to get the resin flat to the touch using the coarsest grits and use the finer ones only to remove the marks left by the previous one.
Be prepared to re-coat if necessary during the coarse flatting stage. A new brush used for each coat will also limit the possibility of 'fish-eyeing' which, I've found, can happen when using brushes previously cleaned with acetone.
Finishing with a sprayed clear coat will likely give you the best cosmetics and most resilient finish but excellent gloss can be achieved without. It's just a bit more labour-intensive.
However, if your parts are likely to be exposed to the sun or other heat sources, it's likely that you'll experience shrinkage of the resin that can leave a bumpy surface, given the relatively high resin thickness. In this case, it's a good idea to give the coated parts an elevated temperature post-curw after fully coating and deal with any shrinkage impact during the subsequent flatting. This should help make them a bit more resilient to temperature afterwards but probably not quite as UV-resistant as a clear coat finished part.
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Warren (Staff)
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Also watch the temperature you are working at. Much above 20C and the XCR viscosity drops a fair bit and that can cause issues with fisheying and getting uneven coats etc.
Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant
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LukeSGee
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Group: Forum Members
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Thank you again for your replies!
I have taken your advice into consideration and have achieved a lot better results!
The panels have I made have come out to a very high standard with high gloss levels, potentially not as glossy as It could be so I am going to look into applying an automotive spray clear coat. Please could you advise the best method to apply spray clear coat? Which grit to sand to before applying ect.
Also on one of my panels, I realised when flatting with 120 git on a block to achieve a flat surface I ended up sanding into my fabric, the fabric looks closer to the surface in places on the corner edges on the panel so I think by adding another layer of resin should solve this issue, am I correct?
What is the best way to achieve a flat surface without hitting the fabric? Sanding between fully cured layers?
My current technique
1. Prep surface + Black basecoat, wait till tacky and apply fabric then alloy to cure
2.Apply a coat of resin, wait till tacky then apply a second, alloy to fully cure
3.lightly sand with 120grit
4. Apply 3 layers of resin ensuring the surface is tacky in between
5. Block sand with 120-240-400-800-1200-machine polish.
Do I need to allow full curing on my layers then flat with 120 before another coat of XCR or do I just need to assess the low spots when finish sanding to decide if I need to add another layer of resin?
Thank you again for all the advise it is greatly appreciated
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Warren (Staff)
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You should always take care when sanding at 120 grit as you do take off a fair bit of material. There is no harm in taking off the high spots to level it out, keying the rest at 120, then re-coating to avoid going through the fabric.
Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant
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MarkMK
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If a better gloss finish is desired also, it's worth going up to 1500 grit, at least, as 1200 grit can take quite a bit of machine polish work to get to a good shine, especially with a relatively hard epoxy. If I'm doing any repair jobs using epoxy, I usually go up to 2000 grit, which usually results in only needing a couple of passes with the polisher to get a good gloss. If you're parts are large, though, this might feel a bit too laborious, but going to 1500 will likely make getting a good shine a lot easier
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