Coast Resorts Open Roads Forum: How to secure screws in plywood going with grain??

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Topic: How to secure screws in plywood going with grain??

Posted By: joebedford on 12/14/17 04:17pm

Some of you may recall that we thought we had a broken king pin mount this past summer when we went to Nashville for the eclipse. DW and I stripped off the plastic under the 5th wheel area, inspected and reinstalled. Most of the weight of this plastic is held by right angle brackets on the sides about 1/2" x 1/2". Screws go from below into the plywood behind the fibreglass outer wall - in other words into the layers of plywood not through the layers.

Well, when I got there to Mesa, I noticed that the bracket is pulling away. Obviously the screws didn't bite and hold in the plywood. Probably shouldn't have put them back in the same holes. Duh.

Anyway, is it worth pre-drilling new holes and coating the screws with epoxy before setting them. Or is there a better technique?

As a last resort, I could put SS screws into the side of the bracket and go into the wall cross-grain. That's only going to be 1/4" from the end of the plywood - can't imagine that will hold well.

Posted By: joebedford on 12/14/17 04:26pm

This is the bracket I want to secure.

If I have to, I'll put screws into the steel subframe.

* This post was edited 12/14/17 07:06pm by joebedford *

Posted By: Jim@HiTek on 12/14/17 04:30pm

What I'd do is head to a lumber store and get a length of hardwood dowel twice the diameter of the screw I intended to use. Drill a tight fit hole for the dowel(s) in the same holes that were used before, slather it with plenty of carpenters glue, tap the dowel(s) into the hole(s), cut them off flush. Give the glue 24 hours to dry. Then use a drill bit almost the same size as the new SS screws I was going to use to pre-drill the holes for use by the screws. Then use plastic washers maybe if the plastic sheet got damaged and the holes were torn a bit.

This all depends on how thick the plywood edge you're drilling into is. You do want some plywood on either side of the dowels of course. It's the glue that will do the work of holding things together in the wood.

Some measurements and a picture or three of your situation would really help get more answers. (The image above is blank).

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Posted By: gbopp on 12/14/17 04:42pm

Jim@HiTek wrote:

What I'd do is head to a lumber store and get a length of hardwood dowel twice the diameter of the screw I intended to use.
This all depends on how thick the plywood edge you're drilling into is.

This was my first thought. But the epoxy may be worth trying, especially if you can use longer screws.
(I can see the image, it's a cow standing in a field. [emoticon]

)

Posted By: Lwiddis on 12/14/17 05:18pm

Regarding the title to your post, by definition plywood has grains crossed ply by ply. How can one not go cross grain in plywood?

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Posted By: Jim@HiTek on 12/14/17 05:31pm

gbopp wrote:

Jim@HiTek wrote:

What I'd do is head to a lumber store and get a length of hardwood dowel twice the diameter of the screw I intended to use.
This all depends on how thick the plywood edge you're drilling into is.

This was my first thought. But the epoxy may be worth trying, especially if you can use longer screws.
(I can see the image, it's a cow standing in a field. [emoticon]

)

It's a white cow, standing in a field, in a snow storm.

Posted By: Yeti plus on 12/14/17 05:39pm

I would fill the existing holes with epoxy and let it setup and then reattach using existing holes in trim. Some of the dollar stores here in Canada have small syringe type epoxy dispenser with a mixing nozzle built into the syringe.I have used them to do just what you need to do. It is easy you just squeeze the syringe with the nozzle in the screw hole and go to the next one when the hole is full. Then scrape off the excess before it hardens.
Cost is $1.25 per syringe, so not very expensive and real handy.
I usually use the expensive stuff for a small job and it is no good a month later for the next project. These work great for small projects.
Second idea would be to get a box of toothpicks and glue them into the holes using epoxy or Gorilla glue.

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Posted By: Lwiddis on 12/14/17 06:36pm

“It's a white cow, standing in a field, in a snow storm.”

How big is the field? Wet snow or flakes?

* This post was edited 12/14/17 07:16pm by Lwiddis *

Posted By: joebedford on 12/14/17 07:08pm

I corrected the photo link. (I hope)

Posted By: pianotuna on 12/14/17 07:20pm

Drilling into a hardwood dowel is less than good.

Make plugs from laminated beech or maple. Talk to a local piano tuner to see if they have any left over pin block material.

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Posted By: joebedford on 12/14/17 07:21pm

This is the plywood I have to screw into.

Posted By: DrewE on 12/14/17 07:56pm

I personally would probably see about attaching the trim (or some different trim to hold the sheeting in place) to the metal frame. The end of that plywood looks a bit weather-worn and I think it would be difficult to get anything to hold in it very well.

Posted By: time2roll on 12/14/17 10:10pm

I would consider a stainless or outdoor rated drywall screw as they seem to bite really well. Use a pilot hole to avoid spreading the plywood. Go an inch longer than the existing screws.

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Posted By: Huntindog on 12/15/17 03:07am

I cannot think of a good way to attach anything going in to the edge of plywood. This is a poor way to put together ANYTHING with plywood. It should not have been made this way.

I would not try to put it back together the way it was.

Look into different trim, that can be attached in to a solid area, like the metal your pic shows. More work, but a permanent fix.

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Posted By: 04fxsts on 12/15/17 04:59am

Screws do not hold well if screwed into end grain compared to across the grain no matter if it is plywood or wood. That is a fact of life and it never should have been constructed that way. My fix is to use wooden dowels but in a different way. You can use the same screw holes so don't have to put more holes in the trim. get some 3/8ths or 1/2 inch diameter dowels and the same size drill. mark where the screws enter the plywood and drill your dowel holes into the side of the plywood. Cut the dowels to match the plywood thickness and glue into the holes; the dowel should have a snug fit into the holes. Now when you re-install the screws they will go into the side of the dowels where they will hold much better. Jim.

Posted By: DrewE on 12/15/17 07:31am

Another thought: it might not look pretty, but maybe you could attach the plastic/insulation piece to the sides with Eternabond tape, with maybe a couple of inches on the side and a couple on the plastic, and then screw the trim in over the tape if you wanted. The idea is that the tape might provide the majority of the structural support for the skin. I honestly don't know if that would be practical or not, but it sounds potentially workable at the moment.

Posted By: D.E.Bishop on 12/15/17 08:27am

There are a large number of edge molding profiles available and changing to a trim with a narrow edge that will show and a wide edge that will allow you to drill into the metal framing would probably be best.

The Teardrop Trailer Supply stores have a really good selections.

Personally, I would go to a trim that comes up the side at least 3/4" and preferably 1" and slightly curved to allow applying sealant to keep water from causing anymore rot to the plywood backing to the exterior skin.

There are some that have countersunk holes to allow the use of oval head screws and it is not too bad looking. To me function over form would be best.

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Posted By: Gdetrailer on 12/15/17 10:05am

joebedford wrote:

This is the plywood I have to screw into.

Nothing is going to stay put in that plywood, it IS shot!

Can you drill new holes in your trim to match up with the steel that is beside the plywood?

If so, you can drill out the steel and use self tapping sheet metal screws to reattach the trim.

Otherwise, the alternate to that would be to attach a piece of heavy gauge sheet metal to the steel frame in order to cover the edges of the plywood. That would give you something solid for sheet metal screws to catch and hold.

Be advised, the plywood rotted due to water that the TRIM held due to no sealant or sealant that was shot and in need of being replaced.

When you put it back together, you will want to ensure you use caulking on the wall side of the trim.. This prevents water coming down the side getting between the wall panel and trim.

Posted By: MEXICOWANDERER on 12/15/17 10:26am

Is the thought of replacing the panel with marine plywood, unrealistic?

With solid marine plywood

NUTSERTS bonded to the plywood with marine adhesive might be feasible.

Posted By: pianotuna on 12/15/17 02:30pm

Yikes. Try some wood restorer. It won't be easy to apply in this situation.

Posted By: John&Joey on 12/15/17 05:55pm

...post deleted...

On Edit:

Ok hears the scoop. I wrote I couldn't figure out what you were doing from the pictures, but I thought Molly Bolts could be an answer. Well when I posted it, it occurred to me what was going on. Molly Bolts would never work.

Here is my second shot at this. Thinking you might not have the clearance for it, but maybe with the right hammer and construction glue it might work.

Since the plywood edge is a FUBAR, you'll need to replace it with something structural. My thought would be maybe something like this. Pound and glued into place, then drilled and screwed.

Clicky

* This post was edited 12/15/17 06:43pm by John&Joey *

Posted By: joshuajim on 12/18/17 08:38am

These might work. Threaded wood inserts.

[image]

RVing since 1995.

Posted By: MEXICOWANDERER on 12/18/17 10:21am

Cut and Paste Discussion robbed from another site...

Whether used as a floor or a subfloor, marine plywood resists rotting, warping and shrinking. It resists humidity from steam and can stave off absorbing stagnant water. It even holds up well against boiling water! This makes it a superb option as an underlayment for your kitchen or bathroom floor. At lumberyards, it is usually stored indoors, and this also enhances its moisture-free nature.

Marine plywood is also stronger and more durable than regular plywood, which has only three layers. Marine plywood has five or more layers that are bound together with waterproof adhesive, which allows it to bear heavier loads and repel moisture from its core. As a result, you can use a thinner sheet that will have the strength of a thicker, regular sheet of plywood. In addition, it doesn't have as many voids as regular plywood, which makes it structurally stronger. While regular plywood has little spaces and air pockets in each layer, marine plywood has substantially fewer. The extra strength and durability makes marine plywood a good subfloor for heavy flooring materials, like ceramic tile.

Marine plywood is available in a variety of thicknesses just like regular plywood. However, it is easier to bend and cut. This makes it ideal as a subfloor, since you will doubtless be making many cuts to get it to fit around door jambs, cabinetry, awkward corners, and other tight spaces. Unlike regular plywood, it is usually rated higher, having fewer visual defects like knots. Its surface is smoother and less splintery. It takes paint well and could make a beautiful finish as a top floor—something that regular plywood could not do.

Posted By: joebedford on 12/18/17 12:28pm

Thanks Mexi - if I ever replace any floor I'll use marine plywood. However, this plywood is the exterior wall to which fiberglass is laminated.

Posted By: landyacht318 on 12/18/17 03:46pm

If I had to get a screw to grab into that black wavy rotted plywood I would dig out as much existng wood as possible where the screw needed to grab.

I'd then mix up some 2:1 surfboard epoxy I have on hand, which is thin enough to easily saturate fiberglass. I'd use a bristle brush with about half the bristle span taped to act somewhat as a resin cup, and get the properly mixed epoxy upinto the wood, twice. Then I would thicken the remaining epoxy with wood flour, or some other thicotropic agent nd use a putty knife to stuff it upinto the recess. If gravity was priving an enemy, use a Ziplock freezer bag and a flat edge and stick of the proper height to holt flat edge to plastic.

Once the thickened epoxy cures, I would drill it then slowly and carefully tap it for a machine screw. Stainless Coarse thread.

Wood flour can be made by collecting sanding dust. I use it from a belt sander. A lot more flour is required than one would think to thicken the epoxy to a peanut butter like consistency.

Epoxy left in a cup will exotherm and cure a lot faster. Spread it out for more working time.

There are other epoxies like system 3 rot fix which can be used then drilled and tapped. I would use what I already have but perhaps buying an epoxy designed for the task would be better for the OP.

Dry rotted wood can suck epoxy out of the thickened epoxy and lead to a poor bond, whch is why I would recommend painting epoxy upinto the cavity so it can wick up into the wood, then stuff the cavity with thickened epoxy while the painted epoxy is still uncured.

I would not use any of the store bought 2 part epoxies. Epoxy needs not only a very precise ratio of resin and hardener, or parts a and B if more familiar, but these parts also need to be mixed thoroughly for a proper cure to occur.

Improperly ratio mixed epoxy, or epoxy not mixed thoroughly, might harden, but it will NOT have the true strength properties as it would if it were both mixed in the proper ratio and mixed thoroughly, and the store bought epoxies allow for a lot of error on the thorough mixing part, and some of them can also leave a lot desires in the proper A to B ratios too.

5 minute epoxies are NOT waterproof either. I have some System 3 5 minute epoxy, and I have mixed it thoroughtly using a digital scale to the 0.01 gram, and the results in my application, had me sand it off and use the 30 minute potlife epoxy.

For a good Epoxy I would recommend System 3 General purpose epoxy with their medium hardener. It is fairly syrupy though. If maximum penetration of the wood was the desire, i would use the System 3 Clear coat resin which is very thin. Their CC resin is also very slow, and one can still thicken it with wood flour or fumed silica or one of the many other thickening agents available.

If one doubts my credentials with either woodworking or working with epoxy, this is my latest completed project.

[image]

It is strong and surfs very well and getting it both strong enough and accurate enough for both these requirements required huge amounts of labor and precision, and forethought as to design and method

Posted By: pianotuna on 12/18/17 05:32pm

Folks in the piano world recommend the West system epoxies and iirc there is one that is thick.

I've used wood restorer on my RV with fair success.

Beautiful work Landyacht318.

Posted By: landyacht318 on 12/18/17 06:15pm

Thanks

I've worked with west systems epoxy, By far my least favorite,

Way too much amine blush which makes secondry bonding troublesome, and the 4:1 mixing ratio leaves a lot of room for error. 2:1 is much better, but I prefer using to mix by weight. 100:45 or 44 or 43 depending on the epoxies I use.

West is kind of Ubiquitous, but few who work on boars choose it.

Posted By: time2roll on 12/18/17 06:50pm

How deep is the rot? Drywall screw goes to 6".

Posted By: John&Joey on 12/19/17 06:30pm

One more shot at this.

Buy the longest pop rivets you can and use them. As they suck down they will get fat sideways looking for a bite.

Posted By: Gdetrailer on 12/19/17 08:21pm

John&Joey wrote:

One more shot at this.

Buy the longest pop rivets you can and use them. As they suck down they will get fat sideways looking for a bite.

Did you bother to look at the OPs pix?

There is NOTHING for a pop rivet to grab, the wood has rotted and what is left is delaminated.

What the pix does not show is just how far up the sidewall the plywood has failed.. But from the pix I suspect it goes a good ways up the wall.

The OPs wooden part of the structure is pretty well weakened and really needs to consider ways to rebuild what is missing.. But sadly with fiberglass laminated to the now gone plywood it would mean having to strip back the fiberglass to make the repair properly.. Anything else short of that is simply a temporary at best "bandaid".

If the OP just wants to reattach the bottom trim, they can simply add a piece of sheet metal to cover the plywood edge to the steel frame. Then screw the trim into that additional sheet metal as I mentioned before.

Simple and effective without any need to resort to putties, epoxies, long screws or any other method which WILL eventually fail since the existing plywood left has no strength and the glue that held the plywood together is simply going to continue to degrade.

Posted By: MEXICOWANDERER on 12/19/17 09:02pm

Not exactly funny. The process is the same...

[image]

Posted By: time2roll on 12/19/17 09:56pm

Well you can always do more work. Sometimes good enough will get you through a few years and trade it in.

Is that your place MEX? Siding and a coat of paint and you will have a fine place there. [emoticon]

Posted By: Gdetrailer on 12/20/17 10:57am

MEXICOWANDERER wrote:

Not exactly funny. The process is the same...

[image]

Nothing that a little bit of bondo and a bunch of 6" long screws can't fix [emoticon]

Otherwise use some fluid film, 303, and eternabond tape and if feeling frisky splash some bedliner on for good measure..

But keep in mind, for what ever you decide to do, put some LT tires on it for goodness sake, the existing tires must be STs and blew out since I can't seem to see them..

[image]

Posted By: ol Bombero-JC on 12/20/17 12:41pm

Gdetrailer wrote:

John&Joey wrote:

One more shot at this.

Buy the longest pop rivets you can and use them. As they suck down they will get fat sideways looking for a bite.

"John&Joey" - you're shooting blanks!
Re-study the pic. Don't think you get it.. [emoticon]

Vote for - Your 3rd paragraph "If the OP wants to......etc."

Less grief than all the other solutions - and *way* more permanent.

[emoticon]

Posted By: Gdetrailer on 12/20/17 01:17pm

ol Bombero-JC wrote:

Gdetrailer wrote:

John&Joey wrote:

One more shot at this.

Buy the longest pop rivets you can and use them. As they suck down they will get fat sideways looking for a bite.

"John&Joey" - you're shooting blanks!
Re-study the pic. Don't think you get it.. [emoticon]

Vote for - Your 3rd paragraph "If the OP wants to......etc."

Less grief than all the other solutions - and *way* more permanent.

[emoticon]

Another "view" of the OPs pix that I straightened and cropped that might be helpful..

[image]

Notice that the trim that the OP needs to put back up will have screw holes centered on the plywood edge.

That plywood edge is shot, nothing is going to go into that edge and hold. Even screwing longer screws into that plywood will just result in ripping the weakened plywood further.

Learned back when I was 12 or 14 yrs old just how frustrating it can be to nail or screw into a plywood edge.. Nails and screws just splinter apart the plys of the plywood..

Screws sometimes can be used on a plywood edge but it REQUIRES one to PRE-DRILL the hole before attempting to drive a screw into the edge AND it requires solid plywood.

Another option would be to carefully remove some of the leftover rotted plywood, then glue and screw a piece of "one by" wood fitted between the steel and fiberglass.

Gluing the wood to the fiberglass and carefully predrill some holes at the lowest point of the fiberglass (the trim should go up the side of the trailer covering the screws) and use short drywall screws into the new wood.

This would give the OP a new surface to screw into and also provide solid backing for the sidewall which should stop the side wall from buckling inwards which would create gaps in the caulking.

OP would have to figure out what tools they have that could do this, grinder might work, small circular saw (battery powered might be a good idea for control), perhaps a non rotatory cutting tool (rotozip?).. Small router (battery powered might be best for control since routers do have a mind of their own).. Hammer and chisel (slow but better control)..

* This post was edited 12/20/17 01:28pm by Gdetrailer *

Posted By: Gjac on 12/20/17 04:14pm

Fasteners in tension are much weaker than fasteners in shear. I would get a steel T section and drive the center section into the rotted wood then drill from the FG outer skin into the T and install screws. This will provide a bearing surface and carry the bulk of the load. Use your existing holes in the section that fell down to transfer drill though the T section and then screw in place. Good luck on your project, and let us know how you make out.

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