It seems to me that if it is done properly that it would be stronger than just a conventional glass job with the same weight or less even…
as a general rule , a standard hand layup with and adequate filler coat for finshing , will give at least a 6 to 1 resin to glass ratio…
100 grams of glass , 600 grams of resin …total 700 grams …
one layer of 4oz is usually about .25 mm thick …
with a decent vacumn procedure you can get resin to glass ratios down to 1 to 1 …
200 grams of glass 200 grams of resin …but put a sandwich inbetween the layers and check the numbers …if you work with a density of sandwich core that is roughly the same weight as one wet layer this is what you get …
100 grams resin , 100 grams glass , balsa sandwich say 2mm thick 200 grams , 100 grams glass , 100 grams resin … total 600 grams …
but its 2.5 mm thick ,
it weighs less but is 10 times the thickness…
because your glass job is 10 times thicker , you can use a way lighter core and still have better durability…
In the process at the above website it looks like the skin is created by laying down a patch-work of thin balsa veneers custom to each blank itself. It looks as if the patchwork of balsa is held together by just taping it together on the blank. If so, is it just taped in place as you are doing this and what keeps it in place while applying the bag and during the bagging process itself?
thats it , just tape the sheets together , in the outline of your board get a razor blade and get your outline close , then glass the sheet on a flat table , you can then lift up the whole sheet and lay it on your board , then tape it down so it doesnt move while your sliding it in the bag , once you apply vacumn , its not going anywhere …
How perfect can you get the seams like this especially where the top and bottom laminates join at the rail?
the whole job sticks down so well , that even if your woodwork is messy , you just sand a clean join line …
What are the best uses of bagging materials like Peelply, Release Film, Breather, Sealant Tape, and other bagging materials? How are these other materials used, or not? I’d assume that you can get bagging film as a “bag” that goes completely around the blank where you only have to close the ends of the “bag” at the nose and tail of the board and not the sides. What material used in the process is consumable or reusable?
you can buy continuous plastic tubing on a roll…just seal the ends …
i used to get about 10 vacs out of a bag before it started getting punctured with little pinholes from sharp splinters of dry glass and resin …from memeory i used to get about a kilometer of the stuff for about 280.00 … its quite cheap …
the down side is the time involved in preparing a new bag each time …looking for pinholes in your last few vacs , befor you decide you need a new bag …
all the other products you mentioned are a hoax and a waste of money …
just 2" tape and a bag is all you need …o ’ and some bubble wrap … youll soon figure out what that is for …
these days i just use a more durable permanent bag , 1 bag costs me about 120.00 , ive been using one bag now for six years , once i established it was the way to go i just converted the whole system to permanent bags …
less hassle preparing new bags , and looking for holes when they start getting worn …
Do most builders using this process always put a fiberglass layer under and on top of the balsa as to make a composite core of the skin itself? Can a complete composite; glass-balsa-glass be done in the same bagging session effectively for either the top or bottom or both? What thicknesses of balsa are best and what might determine your thickness choice? It seems from the website above that glass is put under the balsa while bagging on both the top and bottom balsa, then after both sides have the glass-balsa it is sanded and then probably glassed again as a convention board would be only lighter cloth. If the balsa is bagged with a layer of fiberglass under it at the same time, how do you keep the balsa skin from moving about on the wetted out glass while setting up the bag and during bagging? Does the balsa absorb much resin in the process?
yes you have to have glass either side of the balsa , if not glass at least a fabric of some kind …
a complete composite can be achieved , but first you gota learn the basics…
balsa thickness ,1mm to 9mm depends on the flex or lack of it , small wave to big wave , flex return speed , overall stiffness and impact resistence …
thinner is more impact resistent, thicker can with stand a heavier lip hitting it …
apply your wood , sand it clean , then glass it like a normal board …
glass the wooden skin you made from taping the bits together …it will actually help hold it together , even if tape should fall off …tape it in place so it doesnt move while your manhandling it into the bag …
of all the woods ive used , balsa sucks the least ammount of resin ??? figure that one out…???
Do you need a rocker table so that the blank is not twisted or warped in the bagging process? Is there a possibility of twist even if stringers are used? What are the best ways to avoid using a rocker table to keep the board from warping?
rocker tables are handy …
your hotwired offcut can help there …there is a possibility of twist even with stringers , stringers help enormously … especially perimeter stringers …
if you dont want the board to warp , stretch your bag evenly …watch for pinholes …a pinhole will leave a region of bag with less pressure creating uneven force , thats where the bubble wrap comes in as well …
What are the best vacuum levels to use? At the above website it says 15mm for that particular EPS board to attach the balsa. I’ll assume he means 15mm of mercury (Hg), which is equivalent to 15,000 microns or 29.30 inches of mercury. Getting into the 29”Hg range seems like it would be rather high for a Styrofoam blank since most typical vacuum bagging is done at less. How much vacuum can a Styrofoam blank handle before it starts to collapse?
i use kpa -100 kpa = 14 psi =29inches of mercury …
that will pretty much give you a prune , if left over night at that pressure , you gonna have something resembling a wrinkled wet towel bent into the shape of a banana…
urethane can handle higher loads …
the density of eps will determine how much pressure you can use …
- 20 kpa , 3 psi or 6 " is a safe load for super light eps …
high density eps can handle -60 or about 10 psi …
One aspect of this process that concerns me is the affect that a balsa skin might have on the preciseness of a surfboards rail. Were Bert Burger has shown that he uses a solid balsa rail which I see as probably being able to be dialed-in a bit if needed later, once you do your thin balsa skin around the rail that would seem to be the end of it except for the final glass that you could only add more to the rail if wanted, not take away. I guess you could plan for this though in your initial shape.
just plan ahead …
shape it in your mind first … calculate what goes where on the final shape …
it does take some getting used to …because you dont get the final shape till the last bit of wood goes on …
Do all boards of this construction need a vent? And what is the purpose of a vent anyway?
if you allow your core to be completly impregnated with resin , you dont need a vent …
the vent is so the core can breath , the more air you leave in the board , the more it will need a vent …
to get it light you want as much air as possible , then you need a vent ,
ive been spoilt by lightness …
And what happens to the balsa skin itself if water gets to it?
not good …that depends on how well insulated your skin is from the core …the epoxy bonds real well … it takes alot of effort to ding … small dings and cracks will go grey with time if left ,if its an open wound , thats suicide , itll soak in water and weaken you whole laminate …
leaving dings untreated is the achiles heal of this construction …
you wouldnt drive your car without water or oil …you cant leave a ding untreated with an eps core , balsa skin…
if you dont get a seal between your eps and balsa , you can then get a situation where water will suck through a crack ,travel along the wood and then into your boards core 3 feet away from where your ding was , keeping the core sealed from the skin means you can crack and damge the outer layer of glass and your core is still water proof , then the crack in the outside wont draw water in itll just seep into the ding locally , and cause the grey stain …
What is the water absorbing rate of the current Styrofoam blanks?
by law its 3% of the foams volume …
but that really depends on who your dealing with , lower densities suck more water , but also drain and blow out easier … voids and bad bead bonding can cause a foam to hold more water …
Also what if you get a break in the very outside glass job, what happens to the balsa when it gets wet, and how much water or how fast can the balsa itself absorb water?
depending on your seal to the core and pressure difference , if your wood has good resin impregnation , there is no room for water …
if you do get you balsa real wet , by leaving dings untreated , thats probably as bad as snapping a normal board , they lose there spring , and strength …
if someone does bring in a board that is logged with water in both the core and skin , then the core can be blown out with air pressure …
the outer layer of glass needs to be stripped off , if the wood is wet it will come easily … allowed to air dry for a week or 2 then about 100 to 150 grams of resin painted on then the outer layer vacumned back on , even if you lift some wood when peeling the glass up , it all fits back into place …
letting a board get really logged ends being a major repair to get it new again …
thats why i say its as bad as snapping a normal board … similar costs …
just fix your dings and you have no problems …
So many questions……………
so many answers …
regards
BERT
