Preventing Rotten Balsa Wood Core
Balsa wood is a common construction material used in the manufacturing of fiberglass boats. Used as a core material, balsa wood is placed between two layers of fiberglass to add strength and rigidity to structures that require it, usually the deck, many times the hull, and sometimes the other areas that require strength.
Using this wood in a marine environment where the boats are constantly exposed to water is dangerous because of the ability for the balsa wood to rot. Once water enters the cored areas of boats using balsa wood, it is a complicated repair job. The balsa wood is between two layers of fiberglass, and to remove and replace it requires removing a layer of fiberglass. This usually involves grinding and sawing as seen here:
As you can see, there is a lot of dust created from removing the fiberglass to get to the rotten balsa. The balsa must then be replaced before the removed fiberglass layer is restored. Care must be taken to ensure that this is completed correctly in order to maintain structural integrity of the area that is being repaired.
To prevent balsa rot in the first place, care must be taken when doing activities that have the potential to expose it to water. Adding fittings and features to structures that contain balsa wood require careful craftsmanship to prevent water infiltration.
Installing fixtures and fittings through balsa wood is possible, but careful work upfront will be very valuable in the long run. There are several ways to do this, one of them is here:
This method of making holes through your balsa wood-cored structure will provide a wall of epoxy resin around the hole and keep the balsa wood back away from any water that may pass through the hole. Good marine-grade sealants applied to the hardware will add another layer of protection.
Underwater Pipe Repair
An epoxy and fiberglass wrap can repair steel pipes while submerged underwater. Repairing small holes in pipes by wrapping them is sure to be much less expensive and disruptive than replacing bad sections of pipe. Divers must have access to the whole circumference of the pipe and the pipe must be free of its contents to prevent contamination and allow for the wrap to seal the leak.
As always, surface preparation is very important, and is demonstrated in the video with the grinder. The epoxy must form a good bond with the substrate material, not the rust and scale that is on the outside of the pipe.
Jeff Longmoore of TFT demonstrates how this repair is performed in a Youtube video, but does so in a dry environment rather than the actual underwater one. Very interesting.
Vacuum Bagging Video
Vacuum bagging is a process that requires unique materials and processes, but can be simple to operation in an ongoing basis.
There are many advantages to vacuum bag molding, a few of which include:
- Improved resin/glass ratio
- More consistency across the laminate and part -to -part as compared to open layup
- Containment of air emissions from the resins
As compared to hand layup and chop layup, there are a few disadvantages, including
- Higher consumable material cost
- Higher capital equipment cost
- Difficulty with superior surface finish
Some parts are more suitable for vacuum bag molding than others. It also depends upon which process it is being compared with.
Vacuum bag molding requires an extremely tight seal between the mold and the bag. Molds with multiple pieces or holes for inserts can be difficult to complete a seal.
Parts that are overly large and complex can present challenges with placing resin and reinforcement before the cure cycle starts. The bag must be completely sealed and under full vacuum before the curing cycle of the resin begins.
The basic premise of vacuum bag molding is that the air is removed from the bag, allowing the atmosphere (air on the outside of the bag) to push the bag onto the part on the mold, compressing the layers of resin and reinforcement. Many misinterpret the process as “sucking the extra resin out.” We are merely allowing the laminate to be compressed by the weight of the air above us in the atmosphere to consolidate it before cure. The excess resin is usually absorbed by extra layers of sacrificial material inside the bag.
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