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Thread: Filling knot holes and checks without access to the back.

  1. #1
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    Filling knot holes and checks without access to the back.

    Hello all,

    I’m in the middle of installing a house full of unfinished live sawn white oak planks and I could use a little advice.

    I ordered “character grade” and was even shown a complete bundle before ordering. I was assured it was around 80% #1 common and 20% #2 common. I just planned to cull the non-structurally sound defects out prior to install.

    However, what showed up at my house was mostly #2 common with a bit of #1 thrown in. 1/3 to 1/2 of the boards have structural defects.

    I would be upset but, honestly, my wife and I love the look of the flooring with the included defects. For the price we paid, I’m not even sure I would feel right complaining.

    I’ve been creative about cutting out defects where possible to maximize the yield, but I am going ahead and installing pieces with knot holes up to a dime size and some checks that are completely encompassed by the board (no checks extending to any of the board edges).

    I’ve researched filling defects in wood, including on this site, and almost all suggest pouring epoxy in the void after backing up the hole with tape of some sort. However, I have 1/2 the floor installed and I didn’t tape any of the voids on the backside. I’m not even sure it would be efficient to do so, as I would probably be taping every piece “just in case”.

    Does anyone know a product or method that I can use to fill these defects from the topside without backing up the void?

    I’ve considered:
    1) Troweling epoxy putty in the larger voids with an artists pallet knife, using just enough putty to dam the voids. Then pouring black epoxy in from the top to finish it off.

    2) Using a slightly thickened epoxy in a cartridge (System 3 Quick 5 or West Systems Six 10) to begin filling the voids and finish off pouring black epoxy for subsequent layers.

    3) Thickening epoxy myself with wood flour and/or colloidal silica and apply with a piping bag, ziplock bag, or even a caulking gun first and then topping off with tinted epoxy.

    4) Just packing 1/4” of wood flour and/or colloidal silica in the voids and pouring the black epoxy right on top of the filler. I figure with this method that I may have to repeat the process a time or to to really dam the voids up.

    Does anyone have experience doing any of the above or have another preferred method of doing the same?

    Thanks in advance for any comments or suggestions,

    -Andrew
    Last edited by Andrew Nemeth; 10-22-2018 at 6:14 PM. Reason: Typo

  2. #2
    We do a ton of this at work, it's very en vogue right now. We usually just pour in 5min epoxy a couple of times until the void gets sealed up. West system is a little trickier. Any thing bigger than a check seems to bubble up and burn. It's also very runny and tends to seep right through like water. I personally like to do the saw dust paste thing. It will then take oil and have a little more of the wood's tone.

  3. #3
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    Just stuff something deep down in the hole to keep "whatever" from flowing under the board(s) and do the epoxy thing if that's acceptable to you for looks. (I would dye the filler brown/black, personally, and also use something dark under the filler to stuff the holes)
    --

    The most expensive tool is the one you buy "cheaply" and often...

  4. #4
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    Thank you both for your responses.

    Johnny- Do you have a preferred epoxy brand? I was planning on West Systems 105 resin, 207 hardner, Transtint Black/Brown (and/or coffee grounds and/or artist charcoal), and filler of wood flour or colloidal silica. Then I stumbled on System 3 general purpose epoxy and #3 (slow) hardener.

    Jim- Whatever method or product I use, I plan on heavily tinting the mix black/brown for the larger voids. Fortunately, I’ve always installed solid wood flooring with roofing felt so the bottom of all of my voids are already black, and the planks are isolated from the subfloor should (when) the epoxy runs through the voids. Now I just need to find something dark to stuff in the holes...

    Thanks again!

  5. #5
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    Have you considered backer rod? Comes in different diameters. I realize it’s grey, but the dark epoxy should hide it.
    Last edited by Phil Mueller; 10-23-2018 at 7:52 AM.

  6. #6
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    The last time I did this in a friend's house I used a rotozip tool to clean out the knot hole then cut and glued in a knot from another board. The repair was undetectable.

    JKJ

  7. #7
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    Thanks for your replies Phil and John, much appreciated!

    Phil- I had not considered the backer rod but that may be extremely useful for sealing off the bottoms of the through voids. Thanks for bringing it to my attention. It’s pretty inexpensive in the size I would need and I could pretty easily pack it around the bottom edge of the voids with a pick or two....

    John- Filling the knots with another knot or the cross section of a tree limb was one of the first ideas that popped into my head. I certainly have enough knots in some of the culled pieces to use. However, I dismissed the idea as too time consuming given the number of defects I have to fill and the time I have to reasonably complete the floor. However, I may revisit this idea in some of the more noticeable areas of the floor. If I was prepping a board for a piece of furniture, this would likely be my approach. Thank you for your input.

    -Andrew

  8. #8
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    There are some products that you can trowel on: http://www.woodwise.com/wood-patch-full-trowel-filler/ I used that on mine.

    Another quick option I have used for non-flooring areas is the Rangate knot filler. It is basically tinted hot glue. It works very fast and comes in many colors. https://rangate.com/products/knot-filler You would need to ask someone from Rangate if any of their customers have used it in this application. I have used it for drawers, exterior projects and all sorts of things.

    If epoxy, I would look at the west 610 system. The viscosity of the 105/207 would not be great where it could flow under the planks.

  9. #9
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    Thanks for the links Brad! I was already planning on using a water-based trowel fill color matched to the white oak after filling the major defects. It may actually be the brand you linked too. Have you used the woodwise filler to fill larger holes, say 3/4” diameter by 3/4” deep? I’ve been told most water-based fillers will take a long time to dry at that thickness and will likely shrink significantly and be brittle in a floor.

    The Rangate knot filler looks very interesting. It comes in different hardnesses and flooring is mentioned as a recommended use for the harder (higher temp) sticks. It’s cirtainly a tempting option as I doubt it would flow too far under the voids before solidifying.

    Thanks again!

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