Glue Line Splitting

Glue up jointed pieces quickly after jointing, to avoid problems caused by edge and end drying of the wood. September 19, 2009

I've been having trouble with my glue joints holding. I'm gluing oak and cherry hardwoods using Tightbond II extended. They seem to glue up fine at the time then a couple of days later they start to split. The pieces are about 4 inches wide by 16 inches long. I'm wasting a lot of time having to redo the pieces. Any ideas will help.

Forum Responses
(Adhesive Forum)
From contributor G:
How cold is it in your shop? Those glues don't work well below 55*F, they will chaulk up and be brittle.

From contributor J:
How fresh your jointed edges? I try not to let the wood set more than a day before I glue them up.

From the original questioner:
The shop is 60-65 degrees and I usually join them the same day, sometimes up to two days later. I didn't have this problem over the spring or summer so I wonder if the heat could be the problem. I've also wondered if the shop is too dry. Any and all ideas and tips are welcome.

From contributor G:
60-65* is at the lower edge of the temp rating of TiteBond. Itís still well within range though. How cold are the boards you are gluing? Are they below 55*? If you get into your shop in the morning and the shop is 45* and you start to glue up, even though the air is 65* the boards still may be too cold for proper drying. Are you letting them sit in the clamps at least 45 minutes at these temps? 1-1:15 would be best.

From contributor K:
I have two thoughts for you. First I use normal TB II (not the extend) and get by in pretty cold temps in the shop. Second make sure your jointer blades are sharp and the edges are not glazed over. That would keep it from making a good bond also.

From contributor V:
I agree with what contributor K said about the jointer blade. You can also do what we have started doing and that is to take a sanding block and lightly scuff the joint directly prior to glue up with 100 grit or coarser. I finally quit using TB2 and went back to the original because of glue creep. I have not had the problem since.

From contributor A:
Sounds like the glue may have been frozen, or the MC of the wood is too high. Is your shop warm all the time? What's the moisture content of the wood? I stock-up on glue for the winter, because most things are frozen in transport around here.

From Gene Wengert, forum technical advisor:
Try and glue the joints within 15 minutes after jointing. That will give you 100% success. The problem is not the adhesive, which is more than you really need already. The problem is that the individual pieces are too wet for the environment and so they dry, especially the ends, in the hours between jointing and gluing. Drying means shrinkage, especially at the ends which dry faster than the rest of the piece. This gives you a larger opening at the ends than the glue can successful bridge. The maximum is 0.006".

Remember that wood does not change size or shape unless it is changing moisture. The fact that you see the open joints in four days is a positive indicator that you have wood that is too wet for your environment. Check the wood MC and also measure the shop's RH. For 30% RH, you need 6.0% MC. For 50% RH, you need 9.0% MC. Apply species and temperature corrections, as needed, for the moisture meter.