The Mushy Vermiculite Problem

By John T. Custer, Customer Service / J Boats, Tillotson-Pearson, Inc.


With the weight requirements for the J/24 Class, there has been interest In the process of replacing the vermiculite material in the sumps of early boats. The focus of this attention has been not on the possibility of strengthening the keel joint of the boat or on improving the hull's stiffness and longevity but rather upon the effect this operation can have in relation to the boat's total weight.


The purpose of the vermiculite mixture found In the keel sump was to support the keel bolts both vertically and laterally In some boats, (hull numbers undocumented) this same material was spread throughout the area under the main cabin sole and aft. As this was done in a relatively small number of boats, I think we can assume that the hull stiffening properties of a resin/vermiculite goo were found to be less than Ideal. Given the level of technology available at the time (1978-81) and the still experimental nature of fiberglass boat building, the use of this material was seen as a lightweight, simple way of providing a platform for the bedding of five keel nuts. Some, not all, of these early hulls have, over the course of time (let us not discuss the effects of hard sailing, groundings, poor maintenance, etc. etc.) developed the annoying tendency to retain water within the vermiculite mixture, and to ultimately become "mushy". The keel flex, this condition can allow is needless to say, slow and hard on both the boat and the owner's nerves.


There are many steps one can take to assess the existence or extent of a vermiculite problem. All will provide good clues, but short of removing the original material there is little that can be done to prove the lack of a problem or to locate the beginnings of such a problem. With the boat in the water it is possible to check the Integrity of the sump material by trying to drive screwdriver or similar object into the surface of the vermiculite. If it is easily possible to penetrate the outer layer, obviously there is a problem in the upper parts of the sump it may extend throughout the sump or be just a problem at the surface. Further Investigation can be completed by drilling small (1/8" - 3/16") pilot holes Into the vermiculite. If wet, mushy material is removed, it is probably past time to consider a complete removal and replacement of the existing vermiculite mixture ‑otherwise known as doing a 'verm job'. Again, remember that by drilling into the sump, one only determines the condition of the vermiculite in that particular area. Regardless of the result of the above tests, any opening through the gelcoat coating of the vermiculite should be resealed with gelcoat or an epoxy based resin or paint. Cracks In the existing gelcoat should always be treated in the same manner, with the boat out of the water, check the lead/keel sump joint (about 9" below the hull itself) for signs of hairline cracking. This may be an indication that the keel is not adequately supported. It may also be simple stress fractures, or a result of past impacts. If the boat is suspended with the base of the keel free, assess the integrity or the keel joint by "shaking" the keel. Is it firmly attached to the boat, or is there some play? Mushy vermiculite is only one possible explanation for such play. A loose keel may be just that a result of loose keel nuts, a broken seal between lead and fiberglass, or a break in the band of glass around the keel joint.


While not too technically demanding, a verm job is rather labor intensive. When done by Tillotson-Pearson, it takes 17-20 hours. Someone without the experience or facilities found at the factory can expect to spend much longer on the effort. Keep In mind that experience in working with fiberglass and resin is critical to doing a proper job.


The effect a verm job may have upon boat weight is difficult to predict except on a case-by-case basis. By doing a verm job as suggested, one will add some weight as compared to the original weight of the vermiculite installation. If a boat is carrying considerable water weight within its sump material, one can then reasonably expect the job to reduce total weight. Also, removal of the vermiculite spread throughout surrounding areas on some boats will reduce weight significantly.



Vermiculite Replacement


1. Stage boat securely on boat stands, trailer or cradle making sure that the keel is supported.


2. Mask off interior of boat (this is going to eliminate quite a bit of clean up time later).


3. Cut out cabin sole along nonskid back to the cooler location leaving 1 1/2" lip all around the edge.


4. Remove the nuts from the keel bolts and protect the threads with two or three layers of duct tape. Remove vermiculite filler from sump and bilge area as far as possible up under remaining sole. Use of an air chisel or rotary hammer (available at most tool rental shops) will save a lot of time and effort. Great care should be used when nearing the bottom and sides of the sump so as not to damage the hull laminate.


5. Sand away any remaining filler left in the sump and bilge area to expose fresh, clean laminate. Be careful not to remove any good laminate. It is critical to the rest of the process that the area be clean and free from any residual filler, water, oil or other contaminants.


6. Install the floor supports (8) at the following locations measuring back from the main bulkhead: 12 1/2", 26", 40". Tack them in place with polyester filler so that the tops are flush with the top of the lip left from the original sole. This ensures that the replacement sole will be supported evenly with minimal shimming. Using the polyester filler, form a small radius where the floor supports meet the hull (the supports will not contact the hull directly), glass these in place with two layers of 1708 biaxial cloth or three layers of 1.5 oz. mat alternating with two layers of 10 oz woven roving.


7. The sump must now be filled to the threads on the keel bolts using a mixture of resin (70-80%), chopped or milled fibers (10-15%), and cabosil or aerosil (10-15%). The mixture should be just pourable but not so stiff that it will not fill into the corners. The curing process of this mixture will produce a great deal of heat making it necessary to fill the individual areas in several stages to prevent excess heat buildup and shrinkage that will cause crystallization and cracking in the resin. A catalyst ratio of 1 to 1.5% by volume should be used (10cc/qt) of resin=1%) depending on the ambient temperature. The warmer it is, the less catalyst you will need. Do not use less than 1% catalyst. Catalize no more than two quarts of filler mixture at one time. Allow the previous batch to cool before proceeding with the next layer. Repeat the process until the sump is filled to the original level. Remember to leave an indent between the aft two keel bolts to allow installation of the lifting shackle or hook.


8. Coat all exposed bilge areas with air dry gelcoat or epoxy barrier coat after lightly sanding all areas to be coated.


9. Install keel nuts and tighten to 100-120 ft/lbs.


10. Install cabin sole and shim as needed. Screw sole to floor supports and seal around the edge with RTV silicone sealer.