(Note: all degrees are Fahrenheit) Many things have been said about how long a board needs to cure before it is ridden. For the first 48 hours resin is very soft. Severe dents will occur wherever pressure is applied to the surface. Most boards are laminated one day, hot coated the next day, and sanded the following day. Severe denting is generally not a problem with glossed and polished boards. The gloss and polish process usually takes an additional several days, making about 5 to 6 days from the day it was laminated. The lamination process is the application that most needs to resist denting. If you wait an additional week after polishing the board will be reasonably cured. This time estimate is based on a typical 70-degree ambient temperature. If it is the dead of winter, and days and nights are very chilly, the waiting period can double or triple. Conversely, heat can greatly accelerate the curing process. Your board, exposed to about 115 degrees heat for several hours, will be adequately cured. Reliable sources tell me that this rapid cure actually increases the strength. Surfboards that are already cured cannot be made stronger by this process. Be very careful not to let the board get over 125 degrees. Polyester resin actually begins to soften at about 150 degrees. Foam begins to get unstable at 130 degrees.
DEFLECTION AND BREAKING
- Surfboards are a foam sandwich. The deflection rate of this sandwich is a mathematical formula. Thickness cubed delivers a relative number. For example: a 2″ thick board has a deflection rate of 8 while a 3″ thick board has a deflection rate of 27. The 3″ board is 1/3 thicker but more than three times stronger! The closer your feet are to the actual bottom surface, the more sensitivity and leverage you have. Thinner is better to surf on, but more subject to breaking.
- The surfaces of this bending foam sandwich are one side tensile and one side compression, much as a deck of cards. Most fiberglass that covers surfboards is split – 50% going lengthwise (warp) and 50% crosswise (weft). The fibers that cross the board do little to reduce deflection. Their main function is to reduce denting.
- The width of a stringer has the expected proportional effect; 1/4″ is twice as strong as 1/8″. However, increase the length by one-quarter and you double the deflection. Surfboards need to get thicker as they get longer.
- The combination of the stringer and fiberglass surfaces form an “I” beam. Increasing stringer size or fiberglass weight will decrease the breakage potential of the surfboard.
- Stress fractures are the hairline cracks that are the result of a surfboard going into an extremely stressful flex. The films of resin above and beneath the glass cloth are usually both cracked. This is a difficult repair job, as most of the cloth must be ground away but not removed. A batch of resin that has been diluted at least 50% is forced through the remaining cloth. When dry, several layers of very light cloth are applied over the damaged area making sure to cut the ends in a wedge. This disperses the load if the board again gets too much bend.
- Salt water weighs 64.3 lbs. per square foot. An unsupported section of surfboard will be at risk when exposed to the force of a wave.
- Dents are a natural Bi-product of surfboards. The old balsa boards, when whacked really hard, will dent. I have been in this business since 1959 and have seen no production foam boards with more than a total of 20oz of glass per side. When using contemporary polyester resins, the real problem in denting is the substrate or foam. Even with the early 60’s when foam weighed about 3.9 lbs. per cubic foot, surfboards still dented. Think of this: put one layer of 4oz glass on concrete and you will not dent it. To make a surfboard of reasonable weight, we cannot apply enough layers of glass to make it ridged enough to be dent resistant. Today’s longboard typically is made of foam that weighs somewhere between 2.5 and 3 lbs. per cubic foot.
- Heat is probably not the cause of most deck delaminations. The main cause is that fiberglass just does not stretch. The shortest distance between two points is a straight line. A dent makes the distance between the edges of that dent greater. As the dent increases in depth so does the distance between the edges of that dent. Repetitive pounding in the dent causes slippage in the bond with the foam. This movement deteriorates that bond and accelerates the separation. The fiberglass, which has little or no elasticity, has no choice but to release from the foam. Deck dents delaminate primarily because of the constant pounding in one spot, and the lack of elasticity of the fiberglass. Failure to reinforce deep dents may result in delaminations.
- To reinforce a dent:
- Before the dent delaminates, remove the wax and sand the area thoroughly with 60 grit sandpaper, leaving absolutely no shine. Sand about 1 ½” onto the flats. Using a catalyzed batch of resin, apply 2 layers of 6 oz. glass to the dent. The key to this is to cut the glass so that it just overlaps onto the flats, making sure that the weave direction matches the same direction as the glass when the board was constructed. This technique will make the glass disappear. The object here is not to fill the dent, but to create more strength in the dented area, and to have a new layer of fiberglass that forces the old glass to hold the new shape. Hot coat all of the way to the edges of the sanded area. Do not use any masking tape. Free stroke your brush strokes, feathering at the edges and get out of it quick. Resin has a wonderful way of self leveling if you give it a chance. Sand the area when the resin has kicked off with 60 grit paper. Just blend the edges onto the flats so there is no lump. I finish the sanding with 120 grit paper, wax it and surf. Unless you are going to remove the wax when you eventually sell the board, the only person that will know that it hasn’t been glossed and polished is you. This is absolutely the simplest repair, and every surfboard owner should know how to do it.
- The delamination of glass from foam can have several different causes:
- Fiberglass does not stretch. The shortest distance between two points is a straight line. A dent makes the distance between the edges of that dent greater. As the dent increases in depth so does the distance between the edges of that dent. The repetitive pounding in the dent causes slippage in the bond with the foam. The fiberglass, which has little or no elasticity, has no choice but to release from the foam. Now there is an air pocket and the heat of the sun will cause this to swell.
- Glass weight can contribute to denting. High performance boards typically have a lighter glassed deck than their cruiser counterparts. A lighter glass job and lighter foam is necessary to get the performance that performance driven surfers demand. High performance boards are going to be more prone to denting.
- Foam weight can also be a source of denting. The less dense foam that is found in higher performance boards is more prone to denting.
- Heat can cause a board to bubble. Fiberglass begins to soften at around 150 degrees. Its’ bond to the foam begins to deteriorate and is then subject to delamination.
- Foam spray: Acrylic paint sprayed on foam does not have as good a bond as resin directly to the foam. The difference between the two applications is minimal, but if a laboratory were to conduct a test a clear board will win the bond contest. Color in the lamination cannot be as strong as a clear because the pigment has displaced some of the resin. Pigment has no strength so the amount of strength lost will be the percent of pigment added. However in laminations with color the hot coats are thicker, so there may be no measurable difference in the final product.
- Some surfers just seem to be harder on their boards than others. If you are one of these, extra caution must be exercised, both at the time of your purchase, and after use.The real problem with delamination is the uneducated public. A customer purchasing a high performance board should not expect it to be as strong as a classic nose rider. Surfers should strip the wax from their boards – at the minimum – with every change of season, if only to keep up with the proper temperature of wax. During this cleaning, a thorough study of the condition of the dents is in order.
- Surfboards are very sensitive to heat. Most polyester resin begins to noticeably soften at only 150 degrees. Foam begins to become unstable at about 130 degrees. A dark colored board can reach these temperatures in just minutes. I have seen surfboards get amazing twists from improper storage or exposure to heat. More than one customer has brought back a fin that is severely warped. I have to inform him that the fin and surfboard have been exposed to excessive heat; usually in a car while it is resting on the fin. This fin is not ruined! Heat a large pot of water to 160 degrees. Using tongs, immerse it for about 30 seconds. Pull it out and using pot holders, bend it straight (it should be as soft as salt-water taffy). After it cools it is as good as new.A heat twisted board can be fixed with offset weights clamped outside the rail on the two high ends of the surfboard. I made a set of clamps from a pair of one by one pieces of wood about 24″ long with 4″ screws and wing nuts at each end. On a warm day, put the board inside of a car. Add the weights to the appropriate ends and clamp with the screws. Close the car and wait till it gets about 160 degrees inside. Take the board out with clamps and weights still in place. Put it on a set of level saw horses and lower the temperature with cool water. Check the twist. You may have to repeat this process or, if luck is with you, that is it.
- Fix any ding that exposes the foam to water. A ding on the rail will make the board susceptible to breaking. If it gets into a stressful situation, the stress will focus on the weakest point – the ding and may cause the board to break. Don’t let a split in the glass on the bottom go unchecked. I have seen the entire bottom glass ripped off because water was forced into a small split in the glass. Dents in the deck, which are commonplace with today’s surfboard construction, should have a couple of layers of glass put in the dent before it delaminates. Delaminated glass is far more expensive to repair than reinforcing the existing glass. Delaminated glass also exposes the board to breakage, as the foam sandwich construction has been compromised.All shatters will take in a minute amount of moisture. Large shatters may need some maintenance. While working with the clear silane glass, a really good repair person can virtually make a shatter disappear. Volan cloth will always show a little bit where the repair has been made.