Newbie questions Fiberglass and Stringer repair

The weather is nice and it is time to repair my stingers. What has happened is my rams were leaking hydraulic fluid; the fluid ran down into the motor mounts and penetrated the fiberglass that the stingers are encased in. These caps popped right off (see pic). They had a piece of wood attached to the side of the stringer for one lag bolt, the other two were in the stringer. this was then glassed to the stringer. I have since cleaned up the area with acetone and now is the time for more prep. I plan on more cleaning with acetone and then roughing up the area with a Dremel tool. The stingers seem ok but a few lags just spun, few were rusted (threads about gone). I plan on filling the holes with epoxy, then hammer oak dowels in and redrilling. I bought galvanized lags. Here are my main questions?

1.) What would you suggest with regard to epoxy? Can I use poly or is that a bad idea?
2.) What type of mat or cloth should be used for the best strength? We are talking stringers so I imagine using the right fiberglass is key. Do I use
cloth or mat? Woven, biaxial or what? Sorry I am this is all new to me.
3.) How much build up, how many layers?
4.) Prep between layers

Thanks for your help.

Re: Newbie questions Fiberglass and Stringer repair

No takers? I guess this question comes up quite a bit. I searched the site and can't really find the info I'm looking for. I guess my main question is the type of fiberglass mat or cloth to use. I appreciate any help provided.

Re: Newbie questions Fiberglass and Stringer repair

Hello,

I am not an expert, but will give you my opinion. From the pictures, it is hard to tell the condition of the wood. Are there any signs of rot or is the wood soft? If the fasteners rotted out, to me it suggests that the mount may be wet. Also for any resin to stick, all traces of oil must be removed. If the wood was that saturated, I would think removing all the oil may be a very difficult or impossible task. My motor mounts looked very similiar to yours. The block which the mount sits on was installed after the stringer was glassed in, and if there was an oil leak that saturated the mount, it would have not reached the stringer. If yours is the same, it may be better to remove the entire mount and install a new one, glassing it to the stringer and hull. This way you have eliminated any oil contamination, and have new solid wood. As for what type of resin to use, I am using an ISO poly resin and seems to be working great. If you buy good quality poly resin it should be OK. Just don't get it from an auto supply store. However many who visit this site only use epoxy. Yes epoxy may be better, but poly is cheaper, I have no experience with epoxy. You must do proper prep work for any resin to stick, grind, I use a 24 grit disc, and then clean with acetone. With regards to what fabrics to use, I would look at what was originally there and maybe add a bit. Mine had only matt, but I added a layer of WR in between. As for fasteners, I do not use galvanized, only use stainless.

Hope this helps

Have a great day,

Rob.

Re: Newbie questions Fiberglass and Stringer repair

For some reason I can not view the pix.. From the description here are a few thoughts:

1. Resins have a hard time sticking to wood/anything that has been soaked with petroleum based oils. Epoxy would be the most likely to adhere, its great stuff and easy to work with but more expensive than poly or vinyl resins. BUT get all the oil out.
2. There are multitudes of cloth.. For thickness building @low cost, chopped strand/matt is fine but does not provide any real tensile strength. Woven cloth, Bi Directional and E glass all provide varying improvements on tensile strength but tend to be more expensive.
3. If you go the epoxy plug route, the oak dowel is not necessary. Assuming the plug is an epoxy mix of your choice of Cabisil, glass micro balloons or wood flour, you can drill then tap for BIG machine screws. The oversize ratio of the plug for machining seems to be from 1.5 to 3:1 depending on your nerve. If the hole is through the stern, the epoxy plug works well if it is keyed (dished inside and out) then through drilled for stainless bolts. The idea is to over size the plug enough that the transom core will not ever be exposed to water.. DO Not mount an outboard with lag screws.
4. If the picture was of an engine bed for an inboard, then the job is different. The stringers should have the oil penetrated wood removed back to clean wood then a new piece laminated in placed and glassed. The mount bolts can be tapped into the epoxy plugs that you plan to put in the stringers for the engine mounts. There are also installations that have aluminum or stainless ?saddles? made to go over the stringers that are epoxied into place and the engine mount then fastened to that. (A viewable picture= 10k bad ideas..)
5. Galvanized lag fasteners and engine mounts although very popular at one time, are a bad idea.. Corrosion/electrolysis, iron sickness (especially in oak) and moisture penetration will get you in the end. Stainless or silicone bronze seem to outlast the others when used in conjunction with a plug or saddle.
6. Replace stringers with preformed FRP I beams (Google it) glassed in place then mount the engine to that..

My apologies for the shotgun answer, I can?t figure out why the pix will not display..

Re: Newbie questions Fiberglass and Stringer repair

Thanks for your help. These aluminum things you were talking about, that fit over the stringer, where do I find these?