I am fabricating a salad bar countertop out of “granite” which is relatively weak/prone to fissures.
The waterjet shop that will cut the twenty or so 6.5″ circles and one 14″ circle in it has recommended I bond a piece of 3/4 ply to the backside to minimize the risk of it breaking apart while he is handling it.
The stone slab has been reinforced at the quarry with fiberglass mesh and and some kind of resin (probably polyester) on the unpolished side. It is an irregular surface with ridges and folds in the resin. I think the resin was covered with a sheet of plastic while it cured and that created the surface irregularites.
My objective is to permanently bond a layer of 3/4″ marine ply to the backside of the slab. I usually use epoxy for most of my gluing but I have had poor luck in the past bonding epoxy resin to polyester. Also I could easily use a gallon of epoxy at a cost of $100 for this 9′ X 30″ slab.
Does anyone have any ideas on an effective adhesive for an application such as this?
If I haven’t adequately described the resin coated side of the slab, it reminds me of the rough side of a fiberglass boat hull.
I am thinking polyurethane glue but don’t have adequate experience with it to make a well informed decision. I am intrigued by the fact that it tends to expand as it cures so that might help ensure 100% contact between the irregular surface of the resined slab and the plywood.
I do worry about providing adequate pressure between the slab and the plywood as it cures. I could put another slab or two on top as a weight but it would be tough to get much more than 25 lbs/sq/ft of pressure using that method.
FWIW I am aware that stone slabs that require resin and fiberglass to stay in one piece are not the strongest material to choose. I am merely the fabricator and the client wants me to do what I can to make his material choice work.
Thanks in advance for any insight and suggestions.
Karl
I do have 4 gallons of flowing polyester resin I would like to use up. I have just gotten wary of polyesters performance after getting acquinted with epoxies.
Anybody think I should use the polyester to glue to a wood slab that will be submerged in water for an hour or two while the waterjet shop works on it?
Edited 5/9/2003 1:53:41 AM ET by karl
Replies
Try this site to see if any of these products help.
At work here we use the 3m scotch-weld 3549B/A adhesive. We refer to it as structural adhesive. Used on the airplanes. it is a semi rigid glue that would give as much as the wood will let it.
I worry about using a brittle epoxy for a glue as the bond would break with any movement.
Just a thought.
If at first you don't succeed...try again! After that quit! No sense being a dam fool about it! W.C.Fields
why not use polyesther resin?
It is about as expensive as epoxy but if the custome5r can afford a granite salad bar, they need to be able to afford to do it right.
Excellence is its own reward!
karl,
Piffin says (don't think He's recommending it)
"why not use polyester resin? "
It shrinks over time BIG time. In thin layers, that's not a big deal, (That's also why a car that's had bad body work gets wavy over time. Bondo that's been laid on too thick, it's polyester) I'm new to masonry work, but why not just use thinset to adhere it. It's dirt cheap. Through in a layer of fiberglass mesh between for added strength. If you started off with white you could even dye the thinset to match if there would be any visible.
Jon
Piffin -
Poly resin is actually not a particularly good bonding agent between FG cloth and plywood. The resin is rather rigid when cured, and plywood, though stable for wood, tends to creep enough to break the bond. I imagine this case would be worsened by having something as unyielding as granite as one part of the sandwich.
I'd be more inclined to stick the thing down with silicone or construction adhesive.Formerly BEMW at The High Desert Group LLC
I knew it was used to bond to wood in boat construction sometimes but when you contrast the granite to the wood in immediate conflict, I see your point.
I'm curious what kind of granite is so flaky as to need this back up work..
Excellence is its own reward!
Most granite seems to be naturally flakey or fractured. Also very pourous. This is a resut of lower geo thermal forming temps. After a time it is refered to as decomposing granite.
White, because of mineral content / impregnation, (quartz) is soft and brittle.
Red seems to be made up mostly of tiny little cubesand pieces held together by surface tension. Contains some quartz.
Gray going into black is the densest. (higher temps) Polishes well and has some unique visual character.
Salt and pepper... Nice to look at. Large usable pieces a little tough to come by unless quarried.
Thinned polyurathane will "tighten" granite's grain and make it more manageable. Cements like or similar to vynal base or vynal sheet seem to work just fine. Henry brand is at the top of the preferred list. They seem to have an elasticity that holds to granite, substrate, compensate for creep or movement and not "bleed"..
"I knew it was used to bond to wood in boat construction "
Still is, typically to bond a plywood floor to the 'glass hull in a fiberglass hull boat, and often to form a 'glass covered structural rib (sometimes plywood but often balsacore) Also, 'glass molds that are made of polyester resin and fiberglass often incorporate lots of plywood. Problems arise later on, as the slow but continuous shrinkage of the resin causes warping of the mold. FYI, when you need to bond something to 'glass, the method of choice is methacrylate adhesive. Like white glued wood, the mtrl. will break before the adhesive. The reson it isn't used in every instance is cost.
Jon
If you see poly resin used to bond to wood in boat construction, it's from a builder who is still thinking in 1960's terms. It's not a good application.Formerly BEMW at The High Desert Group LLC
Piffin,
You mentioned curiousity about what kind of granite is so flaky as to require reinforcement.
I am very wary of virtually all yellow/gold granites that have an irregular distribution of color. Some people use word "movement" to describe the way the color varies.
One of the worst that I have worked with goes by "kashmir gold" or "madura gold". The stone seems more like sandstone or even yellow dirt. These slabs typically don't have fibermesh bonded to the back but have the entire slab impregnated with resin.
Without the resin the stone would be way to porous and weak to use in a high traffic area such as kitchen countertops. If you rub a piece of wood, steel, etc on a sharp corner of this stone you can easily abrade granules off the edge. I wouldn't recommend anything other than a bullnose on edges as it would be too prone to chipping.
That said, I have done a few kitchens in Kashmir gold with which the owners are thrilled and have no problems two years down the road.
Karl
Thanks for the comments. I had thought of granites as fairly stable. I'm familiar with some marbles that need the whole slab impregnated for stability. flakes, chips, and kernels..
Excellence is its own reward!
I dealt with a similar situation about 8 months ago. Was applying 3/4" ply to a large sheet of marble that had the factory applied fibermesh reinforcment on back. Like you, didn't really know what to do. Had the same thoughts - need something to fill void. Tried a couple different things on some small scraps, and found the polyurethane glue to work best. Moistened the plywood and the slab (for what that was worth) and liberally applied a layer of the glue.
I would think putting another slab on top, or any other weights you can find would work for clamping. The piece I was working with was on the A frame yet and needed to be reinforeced before we could tip it off to a horizontal plane - as it had a hairline crack running through it already. I ended up sandwiching the piece between 2x4s and clamping them where possible - not many spots. The rest of the face I clamped by using Third Hand (basically long spreader) clamps against the plywood and the wall I had moved the A frame against. Also just spring fit lengths of 1x4 between the wall and the piece on the A frame.
Anyway, the polyurethane glue held - we just had to cut and place - no water - but, it worked fine.
I also just used polyurethane glue to attach wood trim around tiled area on concrete floor. Maple trim boards to frame tile and transition to carpeted area. Moisted concrete and wood, applied glue, set in place, and topped with weights from weight bench in next room. Also put a bead of clear caulk between the tile and the wood that was rabbited out to go over it. Seems to hold well.
Good luck,
Shoe
Shoeman and the rest of you,
Thank you for the quick responses!
I like the polyurethane idea as it has already proven itself.
I appreciate the warning about polyesters and epoxy having shrinkage or being brittle. In bulk I pay about 25 bucks a gallon for polyester (K bond flowing) and 75 for epoxy (touchstone/bonstone). I rarely use polyester anymore as I have found it is much more brittle than epoxy and I have seen several failures with it and zero epoxy failures.
I considered thinset (latex modified) and my only real objection a desire to limit the thickness of the glue layer and my lack of experience in thinsets viscosity, grip strength, flexibility.
I can't get more material in this color ("yellow river") so if I don't get it right on the first try I need to scrap the rest of the project and start over with 2 replacement slabs.
If I had more time to research I would try the 3m product mentioned for use in the aircraft industry.
If I go with the polyurethane can anyone offer guidelines on what sort of quantity/sq ft would be appropriate? Given its tendency to expand and foam up I dont want to apply too much and have it blow up an me. My local lumberyard carries PL polyurethane so that is the most likely mfg I would use.
Thanks again, Karl
good epoxy doesnt shrink. Cheap epoxy with lots of solvents do shrink.
Epoxies id recommend are West and System 3.
However you must allow for movement. consider the poly. However id advise that you coat the underside of the ply with a finish so you can control the movement for the long term. Dont leave it bare or down the road you could have problems.
If I remember correctly polyester resis (or maybe it is epoxy) end up with a waxy surface (amines or something like that) that needs to be removed before getting something else to bond to it.
That's partly why I thought it the natural choice since it was already in place - the materials compatability issue.
Excellence is its own reward!
Piffin
It has been a long time since I read about this and don't remember any of it, but I think that even a new application of polyesters won't bond without some pre work.
30568.15 in reply to 30568.14
"Piffin
It has been a long time since I read about this and don't remember any of it, but I think that even a new application of polyesters won't bond without some pre work."
Piffen is correct. Polyesters bond mechanically. You have to scuff the surface (36 grit works well) for them to "bite." Polyesters have a somewhat shiny surface on their own after catalizing that that results in their not rebonding well with without scuffing.
Jon
It was somebody else who said that, adressed to me. I thought there might be a chemical compatability issue with other products and that it was best to avoid that by using same product regarless whether it had mechanical or chemical adhesion. .
Excellence is its own reward!
I used the liquid polyurethane glue in the bottle not the thick stuff in the tube. Brand I used was Pro Bond - Elmers brand that I beleive is called Ultimate Glue now - think it is similar to Gorrilla Glue. I used a spreader to get a coating over the whole surface. If I remember right, I used a little better than a quart to do a piece 32" wide and 8 feet long
As I stated in my first post - I really don't know much about this - just tried a few things on small pieces and went with what held best.
Good luck,
Shoe
Shoe, Thanks for the follow up. I am doing only a few more sq. feet than you did but I will buy two quarts just to be safe.
My only experience with polyurethane has been that it is incredibly sticky and very difficult to clean up if it gets on surfaces you don't want glued. So I am wondering, did you just spread the glue with a plastic spatula or did you use a roller? Did you figure 24 hrs was adequate cure time before handling?
Karl
Incredibly sticky it is. Use acetone if you have to clean anything up before it hardens. Letting it harden and then scraping, chiseling or sanding is the best strategy. Epoxy resins leave a "bloom" on their surfaces when cured that is waxy and hard to adhere to. It is water soluble and thus easily washed away. It can be very troublesome if not cleaned off though. I am not sure that polyester resins do the same but I'd clean it ... just in case. The polyurethane glues (gorilla glue is the best known ... and I think, the best) cure from moisture. They are basically polyurethane foams of very high density. They have decent flexibility and great adherence. They are VERY waterproof. Your cure time will depend upon humidity, temperature, and other variables. I'd suggest allowing a couple of days curing time if possible, because for this project you will have difficulty getting moisture in the center areas of the slab.
Thank you Clay and Shoe for the additional info.
The nice thing about this particular application is that the slab is being cut with a water jet saw so there will be adequate moisture introduced to the center of the slab as the h20 jet cuts out all the salad bar holes.
Before gluing the plywood I will scuff the resin coating with a sander or grinder and pressure wash it.
I truly appreciate all the suggestions. This has made the glue choice and technique a well informed decision rather than seat of the pants guess.
Karl
I kind of got called into the whole thing late in the game. Client called me to rush over, as he had someone coming to cut the stone that afternoon and wanted some advise on the frame we were setting it on, and a couple other things. When I got there and saw the stone - I decided it should be re-enforced ran out right away and bought glues and plywood and started testing. Cut guy was coming soon and couldn't be called off.
I did scrub the back of the stone real good with plain hot water, and as I said, I wiped the plywood down with a damp rag also to get the moisture in there to help things cure. It has been a while, but, if memory serves me, we tipped the stone off the frame about 4 or 5 hours after we glued it up. I would have liked to wait a day or better, but as I said - everyone else was in a hurry. Seemed to be bonded well. We were very careful though and only had to pivot the slab down from the A frame to a bunch of sleepers we had laid on the floor, to get it horizontal so it could be cut. I had another hour or so to cure while we cut it, and I belive we let it cure a couple more hours after that before moving it to the frame.
As for glue application, yes I just spread it around with a rubber scraper - I would think a roller would work fine - I was simply making it happen with what I had available. I have heard many other people echo a previous poster's position on Gorilla Glue - Strongest out there. Costs about twice what the Elmers Product does, but in a case like this you might want to go with it. I always use the Elmers Ultimate Glue/Pro Bond for everything else because it has all the strength I need at about half the price.
Hope this helps,
Shoe