I got around to doing my deck soft spot with this technique this past weekend. I am not an expert with glass / epoxy work, so I thought I would share how it went for me and some of the issues I ran across. First off, I taped the entire soft area, then marked the holes on about 4" centers:
I drilled 82 holes. I poked all the way thru on only three of them. (circled in sharpie).
A couple of observations on the drilling- if you use a new, sharp drill bit, once you break the top skin, the bit will take off in a hurry thru the wood underneath. When you pop thru the top skin, ease off and reduce bit speed. By going slowly, you really can feel the bit work thru the different layers of material. I drilled 1/4" holes.
Next, I mixed up resin and hardener (west system) per the instructions. I intended to inject some of this resin mixture with no cabosil into the holes as described to get some type of saturation before going with the thick stuff.
I found that the holes I drilled in the areas of "transition" (where the soft spot got better and eventually became sloid) would take little or none of the resin. The result was that the pressured material in the caulk gun came storming out of the hole when I removed the gun tip. I had a pint + of resin all over the place on a number of holes. What a mess. I basically took the spilled material and squeegeed it into nearby holes and let it drain in. This part of the procedure did not go well and frankly made me a bit nervous. Other holes- specifically the ones furthest outboard, where the core was in the worst shape, took almost a whole caulk tube full of resin. If I had to do it over again, I would probably go back to the syringe method and samller holes to start out with when doing the thin resin mixture.
Next, I switched off to the thicker mixture with the cabosil This was quite a bit easier to control in the caulk gun, but certain holes would take little or none of the material. It was far less messy as well. The problem I had in this stage was that by the time I got done mixing the epoxy ( I believe I did around 12 or 15 12 oz batches), the stuff I had initially injected was already starting to kick. I had to move fast to get all the holes injected. The heat generated was incredible- almost to the point of scaring me.
Looking back, I would probably do the project in two sections of about 40 holes each. I would drill holes only where the soft spot is clearly defined and stay away from injecting near the edges or transition areas. I would consider forgoing the injection of pure resin and maybe start right off with the thickened mixture. The caulk gun method seems to force the material in with enough force to fill all the voids and bleed out of several neighboring holes.
Anyway, the final result was pretty awesome. Floor is solid now like someone poured concrete. It's not pretty to look at, but I feel a lot better about the stability of the area. The floor was so soft that the area of the floor where it curves up to form the gunwale was cracking and getting ready to fail catastrophically. I filled in the cracks and now it should last a good long while.
Here's what it looked like when finished:
