Replies

1. 
   DanH | Apr 08, 2012 02:48pm | #1

   The only thing I've found to glue redwood long-term is resorcinol glue.  But it's a PITA to use -- you have to mix it, and then it must be clamped somehow for at least 4 hours (longer in cool weather) for the glue to set.

   But you'd pretty much have to "clamp" any glue, and the only reasonably efficient way to do that is with screws, so why not just skip the glue?  Use one of the hidden fastener systems if you don't like exposed screws.

2. 
   DanH | Apr 08, 2012 02:50pm | #2

   (But you asked this same question 3 weeks ago.  Are you expecting a different answer this time?)

3. 
   KDESIGN | Apr 08, 2012 04:04pm | #3

   GLUING DOWN DECK BOARDS

   I think I would try polyurethane construction adhesive such as PL Premium by Locktite, in the tubes that you dispense with a gun.   It is rated for outdoors, seems to produce a very tenacious bond.  However proper glue bonding requires some technique.  The wood should be dry and clean.  Are you gluing 2 x 4s flat to 1.5"-thick framing?  I would make sure that the entire area of the joint is filled with the adesive, and apply just enough to accomplish that plus produce a small amount of squeeze-out. 

   The boards will want to slide around when you press them down, so you might want to use spacers to control positioning.  This adhesive tends to foam up as it cures, so it will tend to add to the intitial squeeze-out.  The company says that the foaming will not push the joint open, and my experience indicates that to be the case.  But I would experiment with that for your application because just laying down deck boards onto the framing would be pretty easy for force open.  If it proves that the adhesive will not force the joints open, I don't believe you would need to clamp the joint if the pieces fit together flat.  Sometimes clamping is needed to force pieces to flatten out as they make the glue joint.  But clamping is a big hassle because it will really make the board squirm around and tend to drift out of position.  Clamping requires very specific shims, bracing, etc. to hold the position of the board as the clamp pressure is applied.   For deck boards, clamping would mean gluing one board at a time and waiting for a couple hours between boards. 

   It would pay to go about the glue process quite methodically, applying the adesive carefully to exactly where you need it.  Don't just run a zigzag line of adhesive on the framing and plop down the board.   Dispense the adhesive in parallel lines over the whole area of the joint contact as if you were mowing the lawn.  If I use this adhesive on larger joints, I apply it to both surfaces and then rake it out with a notch trowel.  That way full area bond contact is assured.  For small joints, just applying heavy to one surface and contact transfer to the other surface is adequate. 

   Don't get the adhesive on your hands because it stains into the skin, and even though mineral spirits will wash the uncured adhesive, it won't get it out of the skin.  So you will be wearing a polyurethane skin for about a week or more until it wears off.    

4. 
   IdahoDon | Apr 08, 2012 04:23pm | #4

   Glue without other fasteners on an exterior deck is a bad idea - discussing the best method of doing something that is a bad idea doesn't make it any less so.  Why not use some hidden fasteners?  Hidden fasteners and glue seems to be the ideal, while glue by itself is the worst option.

1. 
   KDESIGN | Apr 08, 2012 06:53pm | #5

   I would not glue it because it seems like it would be more work.  But I don't really see a serious problem with using glue if it is done right.  A lot of it depends on the glue and the wood, and even how it is finished.  I have a cedar bench that has the seat boards glued down with some kine of middle-of-the-road mastic adhesive.  It has been sitting outside for over thirty years, and one board has popped loose.  The others are still tight, and the cedar has rotted so much in places, that the bench is not worth trying to protect or repair.  And that mastic was not as high permormance as today's polyurethane. 

   For decks, I would use headed screws and not try to hide them.  But I lay them out so they look very even and lined up.  On one deck, I used 5/16" GRK stainless steel screws with the big torx button head with flat washer as part of the head.  And I just left the heads standing proud of the deck surface.  I like the effect of the way they are so possitive in holding the boards down.  When you contersink into the boards for flatheads, it seems like, over time, the board just rises up as though the screw were pulling down through it.  Then those pockets get water standing in them and cause more swelling up around the screw head.  I like to be able to draw the boards down tight to the framing and have it stay that way.   So that requires clamping force from the head.

1. 
   IdahoDon | Apr 08, 2012 07:06pm | #6

   There is day and night difference between glued up exterior furniture and 2x framing material - furniture is designed to shed water and the wood exerts much less pressure on any of the joints - both because it's almost always a higher grade of wood as well as much shorter and thinner boards.  How much pressure do you think a 2x creates as it cups, twists, or bows?  Add in freeze thaw cycles, seasonal humidity swings, and getting water soaked during rains and bone dry during the hot summer months and you honestly think a glue bond to deck framing is going to hold? 

   We build decks with the least amount of fasteners possible to hold the boards in position over the life of the deck, that's based on real life conditions and countless deck failures that show what works and what doesn't.  I have yet to see glue of any kind hold up to the conditions decks are put through.

   I think it's poor judgement.

1. 
   KDESIGN | Apr 08, 2012 07:28pm | #7

   Well, my preference for decks and any outdoor exposed wood structure is to use plenty of screws plus adhesive where it can contribute.  But the bench I mentioned is a piece that I built, and it is built of construction grade cedar framing lumber consisting of 4 x 4s and 2 x 4s.  And it is built like decks are framed. 

   The 4 x 4 joints are glued and nailed with pole barn spikes, but the seat boards are just laid down in mastic.  And they do pocket water.  That water pocketing was actually a rather bad aspect of the design.   But it is an example of glued construction and the effect of 30 years of weather. 

   I am not sure what the original poster is trying to achieve by using glue, but he seems determined to try it.  He even wants to experiment with different types of glue to see what works best.  But I do agree that using glue as the only means of fastening outdoor wood is perilous.  But then again, I have rarely seen glue properly used, so that might be part of the problem in many of the common cases of failure.   

5. 
   Piffin | Apr 10, 2012 08:56pm | #8

   Idaho Don explained the details.

   You are wasting your time on this one