screws for clamping expoxy glue-up

[tnert]

I'm glueing together the centerboard trunk using West System and drywall screws to clamp. Phase 1 was glueing the spacers to one side (spacers are white oak, sides are ply). I glued up and let it sit for four days. When I went to back the screws out, most broke. Luckily I have one of those miracle "unscrew-ums". What did I do wrong? Cheap screws or did I let it sit too long. I did a search and someone suggested backing the screws out a quarter turn after an hour. Is this the practice? By the way, I predrilled first.

[NormMessinger]

Cheap screws. Drywall screws won't take much torque and the epoxy probably had a little grip on them as well. If you have more screws to remove hold a soldering iron on each to warm it a bit. They wont have to be over about 130 degrees F. or so.

[John N]

Like Norm said and I coated every screw with wax and had no problems. A good cheap source is the wax ring used for toilet bowls. I never left them in for longer than 24 hours though.

[JeffH]

A can of Butcher's wax is a good addition to any shop working with epoxy. We probably used close to 50 pounds of drywall screws over the course of one project, and managed to not leave any in the boat, even ones left in place for weeks. We did use a Makita impact driver for driving and extracting almost every screw, which may or may not have made a difference.

JEff

[tnert]

So, just wax the screws I have? I'm overly cautious and want to leave the screws in for a week unless otherwise advised. I'm still new to this exopy gunk. Temps in W. Michigan 80's and humid during the day, 50's and 100% humidity at night. 206 Hardener. Cheap drywall screws are cheap drywall screws right?

[paul oman]

regular grease or petroleum jelly will work with the epoxies, although I don't know if the process of 'screwing them in' would wipe off the grease....

paul oman
www.epoxyproducts.com/marine.html (http://www.epoxyproducts.com/marine.html)

[NormMessinger]

And what effect does the wax and grease have on the adhesion of the epoxy when you go back and fill the screw holes?

[On Vacation]

If you are using Cotton fibers as a thickening agent, Very few screws will come out upon curing of the glue.

[tnert]

So how soon should I pull the screws (realizing a wide range of conditions?) What do you make of the quarter turn back after an hour suggestion?

[Mike Vogdes]

Nix the wax its more trouble than its worth, the amine blush is enough trouble by it self.

Use the black drywall screws not the cheapy galvinized, the galvinized screws give up alot easier than the black ones. Waiting a week to back out your screws is a waste of time as well, after the epoxy kicks its all over, next morning is fine..

[Paul Scheuer]

A good reason for more C clamps - A man can never have too many. If I need allignment, I use nails in predrilled holes, left high enough to get them with vice grips if necessary.

[Ross Faneuf]

And letting it sit for four days, that is, letting the epoxy cure thoroughly. When I use screws for clamping, I try to get those screw out when the epoxy is green or just past green. Way easier then.

[Hughman]

Wax the screws, and remove before four +/- hours go by. If you have a glued screw, heat with a soldering gun, it melts the epoxy.

Heat (gun, for example) will help with stray glop cleanup, too. Just don't breathe the fumes.

[Aramas]

I tend to 'try' to remove the screws as soon as the epoxy goes to a hard gel stage, but in reality I found that sometimes the last bit went in late in the evening and I couldn't be stuffed hanging around for hours. Next day, of course, the screw heads shear off neatly smile.gif
I just used hardware store brass woodscrews, since I figure any left behind won't be fatal. I'm a bit reluctant to use wax around stuff that my life might depend on, but then I tend to get crap *everywhere*. If you take a more surgical approach, then it might work for you.
The boat I rebuilt last summer had a *lot* of broken drywall screws in it - it got really ugly gouging them out in areas that I had to saw. They seem to have a deep thread and narrow cross section, and break off if you look at them funny. I hate them with a vengeance.

[widsith]

Use square drive floor screws,cheap in bulk and stronger in the shank then drywall screws.Remove screws within 24 hours max. Don't waste time with waxes,jellies or heating guns.Did a 300 square foot triple ply lam with screws on a 6" grid pattern(can you say hundreds of screws?) did not break a single screw next morning when it was time to remove screws.Finally,drive the screws with power but remove by hand,gently to break the bond with the epoxy.
Good Luck!!

[Boatsmith]

what widsith says is the ticket we use screws from home depot (not lowes they dont have)they are sold as deck screws and have a head that is a combo square/#3 phillips drive head you can use either bit but they come with a dedicated combo bit in the box buy an extra pack of bits and you can reuse the screws until the slot starts to wear too much then trash very stong screw they just dont break if you have epoxy inthe slot then heating an awl or old screwdriver with a torch will help clean said slot drywall screws are only good for drywall regards david

[MiddleAgesMan]

My practice has been to give the epoxy 8 or 10 hours to cure then back out the screws just a little to break the bond then drive them back in. Once you break their bond with the epoxy you can leave them indefinitely and they will come right out.

I would not do this after only an hour. The epoxy needs longer than that to develop most of its strength.

[Ian McColgin]

What do the screws do when backed out after a reasonable cure (4 - 24 hours) and then reset. If you were going to ruin the bond, it would happen when you back and resetting the screw does not help that. I'd pull the screws the next day but not worry too much.

Twisting the screw against bar soap also helps. No one in life has ever had a problem with the epoxy you put in the hole to seal it up then dribbling out due to residual wax or oil . . . but

. . . screws are pennies wise and pounds foolish for anyone doing more than one job per life. Lots of clamps - a worthy life investment. Jobs that don't lend themselves to clamps, like laminating big sheets, may benefit from sandbags laid out. The labor saved not extracting hundreds of screws and filling holes is worth it.

That said, there are still jobs where the drywall and flooring screws really are the great advanced of the last part of the last century.

[Thorne]

What boat, design and materials?

A lot depends on what you are doing, but I'll second the recommendation for deck screws (of nearly any type) over drywall screws. And since cost seems to be an object, unless you strip 'em, they'd be reusable.

But as above, why not use bar and/or C clamps? If you must use screws along with epoxy, why not use bronze and bung 'em, or Stainless Steel and leave 'em exposed?

I built my CB case from white oak sideboards and posts, used epoxy and silicon bronze screws with bungs to put it together.

http://www.luckhardt.com/cb-case5.jpg

[willmarsh3]

I tried the soldering iron approach that Hughman mentioned. It worked great. I was putting the cabin top on the Elver. I bent 1/4" plywood and held it in place with drywall screws. After cure, I put a 25 watt soldering iron on the screw for about 2 minutes then it backed out easily.
One thing not to do is to heat the screwdriver. I heated a screwdriver with a propane torch and set it against the screw. The steel lost its temper and bent all out of shape when I tried to use it. I had to throw the ruined screwdriver out.

[redbopeep]

Clamps. You'll always use them on another project. Raptor plastic nails (can be left in place) for some things.

We did our laminated frames (2-7/8 x 2-7/8 ranging from 10' to 15' in length lam in place) entirely with clamps. Worked great. Did the backing ribs for the chain plates (lam in place) with thru-bolts where the bolts through the hull were going to be. Had to get the bolts out within 18 hrs or they required major heating up (found that out when we left a few in over a weekend, oops). Did plywood subdeck (glue to overhead and glued together 2 layers of 9 mm 1088 to make subdeck) with combo of permanent si bronze screws and Raptor (plastic) nails that could be left in place.

Clamps...You can make some kinds of clamps, you can get them cheap at swap meets. You can buy them from folks finishing their "only" boat project. You can go to Harbor Freight and buy cheap ones (but be selective on design) that will last a project. We did all of the above. We have lots of clamps.

good luck!

[MiddleAgesMan]

If the joint is not highly stressed there really is no good reason to leave screws in past 8 or 10 hours. Where I have backed them out and then reset them is in highly stressed joints such as where the sides meet the transom on my GIS. I back them out and reset them one at a time so the mostly cured epoxy is not stressed during the process.

BTW--Boatmik (Michael Storer, the designer of my GIS) tells how to remove screws that might have been left a little too long. He uses a soldering iron to heat the screw (via the head). The heat weakens the epoxy-screw bond and you can back them out even when the epoxy has been allowed to fully cure. So far I have not needed to give this method a try.

[RodB]

I too think using wax or soap is not a good idea if you want to fill the holes later with epoxy and have good adhesion and a perfect seal. I have removed hundreds of sheetrock screws within a few hours...longer in cooler temps.... and never had a screw head break off. I have even left screws in for a couple of days in 100 degree weather... and never had a head break off. I have used galvanized and black dry wall screws... no problems with either breaking off. When the epoxy is dry to the touch and not even tacky anymore... take em out. I may wait a little longer on stressed joints... but still not longer than overnight in warm weather. In general, once the epoxy is cured, it is a waste of time to leave the screws in any longer.

RodB

[Boatsmith]

we have literaly hundreds of clamps we also have almost a hundred 25 lb bags of lead shot for weights deck screws are just one more arrow in our quiver and lots of times are just the ticket things get pretty slippery with epoxy and it sucks to have a part shear out of place from clamps that are ever so slightly misalighnedregards david

[Boatmik]

Removing the temporary fasteners - don't wait toooooo long.
Remove the temporary fasteners (which can be re-used) within a couple of days so the glue doesn't bond them in place as well.

It is no problem if a fastening is accidently glued in - heat it with a soldering iron for about 30 seconds and it will screw out OK - it just takes some extra time - so best to pull them out when the 'pox is hard.

http://www.storerboatplans.com/Faq/fasteningsolderingiron.jpg

[Boatsmith]

another clamp trick is to slice pvc pipe int rings and slit the side very cheregards davidap and sometimes just the ticket you can cut your own or buy them from a solid surface tool supplier cheaper than you can cut and deburr them if you count your time and material we have a range from 6"diam to 18" diam they are suprisingly effective but one must wath against clamp sheer

[JimConlin]

I use drywall screws a lot for temporary clamping. The difficulty of removal seems to be a function of the number of laminations and the strength of the material being bonded. The soldering iron trick works well.

we have literaly hundreds of clamps we also have almost a hundred 25 lb bags of lead shot for weights ...
Where might I buy lead shot?

[Boatsmith]

there are numerous locations on the web or you can check with a local gun shop which caters to reloaders i bought several bags from a local store and then bought 1oo bags from an armory in nc dont remember exactly who but it was 1/2 the price picking it up freight on lead adds up regards david

[JimD]

Out of curiosity I just googled 'lead shot' and the first link I opened advertised 25 pound bags for about $45. Does that price sound about right?

[Boatsmith]

bought mine in 03 were 25$ retail only 13$ wholesale but i picked them up in nc on way to canada for a 1200ft2 deck installation

[John Meachen]

If I want to be sure of getting screws out of epoxy I dip them in wax.