Here's a picture of the pits ......

https://www.flickr.com/photos/156245622@N05/shares/J34W06

Is the resin thinner on the end with the dips?? 

Might be localised contamination or the resin has just cast a bit too thin in that area.  Some pictures would help here.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Thanks again Warren
I sanded (random orbital sander) to 120 grit. I washed the whole board down with soapy water, that was about a week ago and I rubbed it down with acetone yesterday and dried well and blew with canned air before the pour.
I would say 95% of the finish is perfect but it's just these couple of small pits but nonetheless it has to be perfect finish. That's my aim.
So if it was a sanding problem (too smooth) why would only 5% of the area pit ?
Regards.

What sort of grit are you sanding to?  It sounds like the resin is properly fisheyeing off the surface to open up like that. That is usually a sign of some contamination or too smooth a surface (or a bit of both).

We would normally key to a minimum of 240 grit - although  120 is typically the norm - and then clean the resin surface afterwards to remove dust and dirt from sanding.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

Thanks for your reply Warren

The pits go down to previous coat surface - that's about 1.5 mm

I don't think it was too thin. You (previously) suggested around 300ml for 800 x 400 mm, that was at 1mm (I think) I mixed 350ml for this pour

I did make a cardboard box / cover for the piece and covered as soon as I had poured which was 15 mins after mixing. I checked on the pour after a couple of hours and it looked great but that changed overnight.

So, what is the best way going forward now. Can I pour into the pit areas only , wait to cure and do final coat ? Or do I sand and do another cover coat ?

Also - do you suggest to clean / prep with isopropyl alcohol before next pour ?

How deep are the pits? you can get pits from dust settling on the surface.

Also, if you coat the resin too thin, the surface will not be very smooth, it tends to pull and get dips and lumps  when too thin. 

Try and keep the room dust free as much as possible  (or cover the part) and pour it so it is a minimum of around 1..5mm thick which is about 1.5kg per metre square.


Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant

I did a third coat Glass Craft 3 on my first resin piece (800 x 400) last night and I checked it two hours later and was looking good - this morning it has several pits.

I did lots of preparation , I sanded it down to a flat smooth surface with a random orbital sander. I cleaned the surface many times , dried and blew it over with canned air. I washed it with acetone and made sure it was very dry. It was levelled out and pre heated before I did the pour. All the temps looked good and I made a cardboard box to cover it after the pour and I get this result. I am thinking that I have to change my brand of resin.

Simply can't carry on getting these results.