Thread: How to repair surface damage in plywood?

There are three basic types of thickened epoxy mixtures, cosmetic, light and heavy structural. Cosmetic is just as it sounds and imparts little strength or stiffness to the area. These mixtures contain light materials, like talc, balloons and spheres. Structural mixes have heavier, fibrous materials in them, like milled fibers, cotton flock, metals, minerals and stone. The difference between a light and heavy mix usually just involves some fabric. A light structural fillet can stand by itself, adding strength and stiffness, while a heavy structural fillet will have biax tape or cloth over it, increasing "purchase" on the surrounding areas.

Simply put, look at what you have and decide if it needs a cosmetic or structural repair. Cosmetic is just lipstick under paint typically. If the area needs local reinforcement, you'll want the heavy structural mix with sufficient fabric to insure it stays put. If you just need to beef up an area, you can skip the fabric. A common structural mix would be milled fibers and/or wood flour and/or cotton flock and/or some sort of mineral (like calcium carbonate or metasilicate), with finally a bit of silica (cab-o-sil) added to control viscosity. How much of each depends on several factors, but a usual mix for me is cotton flock (West 403) or calcium metasilicate (West 404), some talc to smooth it out and enough silica (West 406 or cab-o-sil) to stiffen it up for the application (vertical, overhead, non-sagging, etc.).

Your attachments didn't come through (at least for me), so I can only guess at your needs, but if you have case damage, error on the way too much reinforcement side of things, as cases can be put under a lot of strain.

Thanks for the great info, I have uploaded the photos again so hopefully they are viewable now.

I am guessing that a light structural mix maybe the way to go as I dont think the damage is to deep in most areas so sounds like I need to get somthing other than microballons to mix up with, is there any preferance from the list you suggested, and if you can see the pics now do you think that will be enough?

Many thanks for advice

Anthony

The damage near the board slot should be reinforced with biax, but the other areas are light structural, only because you're into a few layers of plywood, which weakens the area locally.

Wood flour (40%), milled fibers or cotton flock (40%) and silica to a non-sagging consistency will do. Naturally these areas will need to be well wetted out prior to filler. I'd also go to the trouble of feathering out the damage with a grinder, to make a smooth transition from damage to surrounding areas. This last step prevents stress risers within the damaged areas, from commuting through the filler.

fantastic, thanks for all your help, very much appreciated! )

I should add that each time you mix up some filler, the material combinations will be different. A glue might be runnier than a bonding mix or a fillet or if working on a vertical surface. Temperature can affect the mix too, with higher temperatures requiring more silica. The materials you're gluing, bonding (yes, these are different) or filleting can also affect the mix. On 'glass surfaces or previously epoxied substrates, I like a higher percentage of milled fibers, than cotton flock and usually only wood flour on wood, for example.

To keep things consistent, I've mixed up specific combinations of filler materials and placed them in 1 gallon pretzel jars (she thinks I really like pretzels, but I really just want the jars). I have 3 different fairing compound mixes, one super light, used as a thin surface treatment, another for deeper areas and the last for filling screw holes and the like. Each uses a different combination of fillers, to suit the need of the job. For example the screw hole filler has wood flour and a bit of milled fibers, but the other two have neither. The screw hole mix needs to restore the strength of the missing wood, in the screw hole, so I added some "stuff" specific for the job.

The same is true for a fillet blend, a fastener bonding mix, etc., etc., etc. These premixed batches help me have consistent results, which is especially important with fairing fillers, which need to be light and easy to sand, plus consistent from batch to batch around the hull.

If you are using Botecote Anthony, they have 3 standard fillers similar to what PAR has described. Sanding, filleting/glueing and high strength. Plenty of info on their website.