Glueing plenum down

[meatbal80]

I just finished installing the plywood base and i am debating glue to install my mdf plenum. I am a flooring contractor and have urathane hardwood flooring glue avaliable. The main perk is that it is moisture cure allowing me to cut my plenum 6-8 hours later. The thing i am not sure about is that the glue has some flex to it. It gives a great hold i am just not sure about using it for this appliacation. The other option will be titebond 3 which is very rigid and full of moisture. if i use the wood glue i will be waiting 2-3 days before cutting the plenum, since i am in phoenix az which is normally dry but we have had rain for the past few days with more to come. I dont want the dry hot summer to come and have things warp.

Any comments or suggestions would be greatly appreciated.

[knight_toolworks]

flex may be good. no glue holds mdf really well since the surface will just pull off.

[billp]

Joel,
As Steve points out MDF is tough to glue using most"standard"glues, so if you are familiar with the hardwood flooring glue, try it! The entire vacuum table "issue"is really still a "work of art in progress"and it's through "experiments" such as this that we might ALL learn a better way.
When you say "flex"the real issue will be how well it holds over the entire 32 sq. ft "field"of your plenum. I'm guessing if it holds at all you should have enough structural integrity to keep it in place. In the worst case scenario you can use your machine and plane off the MDF, and then try it again with another bonding product...
Please let us know how it works !

[meatbal80]

I dont think it will be any problem for the glue to grab, if you use it on subpar concrete it will hold as the wood movement pulls the concrete apart (crunchy floor). I do worry about the same thing with the mdf that the glue will be so strong and throw in the flex that the mdf will get torn apart. I guess the mdf being very stable will help that but i guess we will see. BTW the glue i will be using is Bostiks EFA

[knight_toolworks]

I wish I could use a floating spoilboard but I don't aways use vacuum and that becomes a problem. one method I want to try is to seal the spoilboard where it gets glued then glue it down and see if it holds better.

[meatbal80]

I got my plenum board glued down last thursday and to say the least i am very happy. I ended up using the hardwood floor glue i spoke of and it seems to have worked great. I cut out the holes for the vacume and could then see a cross section of the joint. It was very uniform and i could not take the pieces apart just banging the piece around will do a little more testing later. To sumarize i have come up with a list of pros and cons






Pros-
Great holding power
flexible (dont know if this will help or not but the glue bond wont break with expansion and contraction)
uniform glue transfer
good open time
moisture cure (unlike wood glue which has alot of moisture in it this glue is a urathane which as it drys actually sucks moisture out of the air and the materials you are using. I didn't have to worry about the mdf swelling or warping and could mill directly after the glue was dry)
relativly quick dry/cure time (i got the top glued on about 2pm and was flattening the top by 9pm)
Cons
expensive (for the non flooring pro, most of bostiks products come in 5gal pails and i only used about a gallon. And at about $110-$135 a pail at my cost retail is from $135 - $175, the remainder is a very expensive door stop)
Messy ( for the average person who does not have any experience trawing full spred glue it can be. I add about 30-60 min a day when i have a green worker spredding glue just to clean up the extra mess.)
availability (most flooring supply houses dont generally sell to the public and those who do charge a pretty pennie in mark up)
For any one who may want to use this method at least one of the bostiks moisture cure urrathane glues come in tubes for a large caulking gun. I dont know the cost since i just buy by the pail, but it could save some by not having all of the extra.

Joel

[Gary Campbell]

Joel...
Thanks for the post. I already wish I had used it!

[meatbal80]

i read your statement about moisture and figured even though i am in a arid climate it couldn't hurt