I've had dings like that from first session on a new board - maybe not so noticeable on white foam vs black surfboard...
"Everybody is ignorant only on different subjects." - Will Rogers
Just my 2c….. It’s a common misconception that 6 oz cloth takes the same amount of resin as 4 oz, making a stronger board.* Testing done in labs (as posted here on Sway’s) has shown this. In my experience with lay-ups by myself or various glass shops, 2 x 4oz or 2 x 4oz + patch is the strongest for long surfboard life. Now to your issue; what it looks like to me is that you have too much resin on the deck, either in the lay-up, hot coat or gloss. That creates the ring cracks seen in your pic. All standard construction will dent over time, including epoxy lay-ups on foam or eps. It’s the nature of the beast. I don’t sweat the dents, I but try to reduce the amount of resin to limit the cracking which can wick water over time. Epoxy is more flexible, but in my experience with using it for non-comp boards, the costs don’t outweigh the benefits. Just my 2c….
*A note on cloth for those who are starting out: 4 oz cloth threads are smaller in diameter but a slightly tighter weave in standard cloth than 6 oz. The weight difference per square inch comes from the diameter of the threads, not the weave. This makes it easier to wet out and take less resin than 6 oz. You can see this by using a 10x loupe on 4 oz & 6 oz scraps.
Excellent info, thanks for your 2c.
I tend to use very little resin on my lay ups, I scrape pretty hard with squeegee (something I thought I was doing wrong in the past but when I stopped doing it I had more problems so I tghink my layups are good, and only JUST enough resin to fill the weave and bond). However I think I may be putting hot/gloss coats on too thick, I think it's my way of trying to cheat and get a glass like finish which requires less sanding (I still do plenty of sanding, hours of it!). I will try using thinner hot coat next time. I am a bit paranoid about the slightest weave showing through on the finished product, and I think that game caused me to chase thicker and thicker top coats. Will try correct that next time. Also, in light of what you said (and others have told me similar) I am going to try using 4oz only. 3 or 4 x 4oz rather than 2 x 6oz. I have read all the stuff showing how 6oz is "stronger" than 4oz, but I have to say even in my limited experience (10 or so boards), the ones where 4oz was used instead of 6oz do seem at least every bit AS strong as the heavier boards, and seem to dent equally but less cracks.
Pressure dents are virtually unavoidable if a person is heavy footed or a bit 'rough' on their boards. It doesn't make a lot of difference whether you use epoxy, poly, or alternative style fabrics. The main reason decks get dented is the density of the foam.
“That which can be asserted without evidence, can be dismissed without evidence.”
for me it’s skin flexural stiffness / foam compressive stiffness ratio. for windsurf we use very light foam, 10 to 16 kg/m3 and really stiff sandwich skins with carbon = zero dents even more boards take far more loads. strangely at same stiff skins higher density eps like 30kg/m3 keep dents more than lighter more elastic eps which have more « foam memory ».
There is no fix based on experience with my 2 sons who are adults now. The only real way to prevent this is to laminate veneer or thin ply as Lemat said. But whatever fix is used they still complain that it's now too heavy and doesn't ride "right". The good news is it will change when they have to supply their own boards or at least buy the materials (then wait forever). A bonus is that you'll become a very good builder up to then. When you get my age you'll look back on this and say "damn kids".
Ha ha, I am looking back and saying that already!! I have just repaired another dent!!!!!!
Looks to me like the reason for the circle cracks is that the lamination and subsequent coats were too resin ritch. With a tight glass job you shouldn't be getting those.
Thanks Mako, that was my first worry but I don't have enough experience to know. All I can say is my lamination coats are scraped too hard (from what most people have told me, and compared to videos I have watched of others doing it). For example I often struggle to get rich deep tints when using color, and I realised I am scraping too much resin off. I still do scrape it well though, probably still too dry. BUT my hot coats colud be too thick, thats definitely a possibility as I started making them thicker to try and get a better glassy finish. That may be my mistake, or perhaps he is just a very heavy footed surfer, posibly combined with not very dense foam. Interestingly, my other son who is lighter (skinny instead of stocky) has been using his board for 2 years around 2-4 times a week (they surf right thru winter too) and not one single dent like that on his board. I think I need to make myself one next, then I have a bit more to compare to.
I use Iso 10X resin from seabase and I know the Silmar stuff cures much faster so I might try that too, it could set harder/sooner
iso 10x is a far better resin than ortho 249 silmar. for ding resistance silmar 2880 ortho poly with acrylique in is better than 249.