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strengthening cracked planks5/22
I looked through the other forums for answers to this question, and didn't find anything exactly, but admittedly did not look in depth, so if this has already been covered, my apologies. I am in the southwest and am resawing reclaimed, 70 year old Douglas Fir timbers to make planks to be used to make box beams. The customer loves the old bolt holes and rusted washer marks on the material. The problem is that this material is so dry and fragile, that it if you even look at it wrong, it cracks and splinters. While the customer doesn't mind the age cracks, those that go all the way through the material make them very unstable and difficult to work with . I actually tried some mesh drywall tape and fiberglass resin along the backside of the cracks. That actually worked ok, but just wondering if someone had a better, faster way. The resin dries faster in the sun, but it has been rain and clouds for several weeks. Inside, the resin has been taking 6 hours, and I have tried many different amounts of activator. Thanks for your help.
Use an epoxy with the fibreglass tape, it should set up faster.
How about resaw the faces off and glue them onto something that is strong and stable?
Drywall tape would be the least structural fiberglass product made. It's like putting a handfull of rebar in a bridge. The concrete does almost nothing structurally. The ideal fibre/resin ratio is 70% fiber:30% resin. You have got a 10% fiber:90% resin layup at best.
Polyester resin does not work well on ply or wood. There is a relatively narrow range of catalyst. Read the directions. Epoxy is the proper resin for wood.
I would glue the old wood to a brand new stick of lumber. You can use DG fir or fir or pine. We do this all the time with recycled chestnut & oak. We have done thousands of feet of recycled chestnut crown utilizing that technique.
Also you can use typical wood glue.
Thanks all. These are going to be beam and post wraps, so just need to hold together long enough to get to the jobsite and installed on the posts and beams. Once installed, there is sufficient solid backing to relieve the problem. Sun finally came out and resin is drying quick. I'd love to try epoxy though, especially if this would be the correct and acceptable way to do it. I used to shape surfboards and just like the smell of the resin. That resin seemed to stick solid to everything and anything back in the day, so I tried it. Adam, do you have a brand that you use and location to purchase (chain store) or just a local woodworking store like Woodcraft? On bad cracks, I was routing out a zipper shape with an 1/8" spiral cutting bit and pouring the resin into the zipper. This worked pretty well too. I know you are all rolling your eyes and shaking your heads...hahaha. Related subject: When you laminate the reclaimed onto a newer solid piece, how to you clamp it? I don't have a press or vaccum bag system. I have a ton of c clamps, but some of these pieces are 21" wide. How to you put pressure evenly across material to clamp it?
The best and most cost effective epoxy in the US is MAS epoxy. 2:1 ratio(easy to mix without pumps) less expensive, you can mix the slow and fast hardeners together, no amine blush(waxy contaminate that oil based finishes will not adhere). 2 different resins(thick & thin) which you can mix together. FLAG resin is great for woodworking. Regular is designed for glass/carbon fiber.
It is used by composite professionals to build carbon masts for huge yachts, Olympic grade rowing shells & oars.
West System epoxy hasn't changed since the 1970's. It is expensive and does not do any of the above.
Professional composite boat builders use a different Gougon Brothers(West System) that is high tech like MAS. Super expensive.
System3 is similar to MAS, but more expensive and less products. One thin resin.
I am not a salesman. I switched to MAS 12 years ago when my best friend built a 42' hi-tech racing sailboat. Mast was built of MAS, hull was the Gougon Brothers Pro stuff.
That said, get the local variety, so you can easily get more. I had a dist. 1/2hr away they could regular UPS me it and it came the next day.
Adequate clamping can be achieved on wide boards by using pipe or case clamps(Bessey or Jorgonson). Clamp the board every 16" as if you were gluing up a regular panel. Then take shims(2" cedar shakes work well. Drive a few under the clamp. This will provide adequate down ward pressure, and is adjustable.
The other option with your C CLamps is to essentially do the same thing except you just need a bunch of stout sticks of wood. I would use 3/4" x 2" hardwood or rip a 2 x4 stud in half. Place 3 or 4 shims at each location under the caul(the stick). Clamp the ends with the c-clamps. Then hammer the shims until you like the pressure.
The old school method was to take the stick of wood and cut it on the bandsaw so that it was a curve. Then clamp it down. I prefer the shim method so you have accurate, adjustable pressure.
Good luck and be safe, Adam
To develop a good epoxy joint, it is necessary to avoid too much pressure as all epoxy adhesives need to be fairly thick to be strong. Too much pressure squeezes out too much adhesive.
For exterior exposure, make sure that the epoxy is uv stabilized.
A good epoxy joint will be stronger than the wood, so various manufacturers will supply adequate products...I am not hung up on just one manufacturer. This is based on my own use for my sail boat and also the experience of a lot of others I have worked with and heard from.