Bubbles in Epoxy Thru-Hull Fix

[geoffr]

We have found that while filling in a thru hull we are getting bubble forming between the layers of glass. ( photo below).

We have been laying out the layers of glass on a sheet of plastic one a time and wetting them out. Once all the layers are wetted out we wet out the hull, then apply and duct tape the plastic in place.

Any ideas on the cause of the bubbles and how to stop them from forming?

[Don1500]

No photo

[Pete7]

Use a stiff 2" paint brush to stipple the epoxy to drive out the bubbles but one layer at a time until the bubbles are gone. I presume you are using cloth not mat.

Pete

[rognvald]

Geoffr, epoxy bubbles are caused by an underlying void in the substrata. The only way to prevent them is to assure an airtight bond between layers of glass by rolling. Once the glass is set, the only way to prevent a reoccurence is to use a drill bit to hopefully open up access to the void and refill. I spent 2 hours on a helm seat I was repairing that had a persistent bubble. Without creating a larger mess by multiple exploratory drilling, I filled the void with thickened epoxy, waited until the epoxy kicked(but not completely) and reworked the epoxy into the void with my finger until it sealed. Not very scientific or professionaly sounding but it worked. After it was hard, I rewet the area with epoxy resin and applied a thin layer of fairing compound to the area for a final seal. No bubble. P.S. Epoxy bubbles are a nightmare! Good luck and good sailing, Ron

[Artif]

You might want to try vacuum bagging it, as long as the through hole has been blanked first.

[geoffr]

[geoffr]

Don - photo should be fixed (link only worked for me when logged int ;()

Pete - that is what we did - there were no bubbles when applied to the boat, they came out as it cured. I think there was a little bit of mat as well as cloth.

Artif - I don't understand what you mean by "blanked first"

thanks,

Geoff.

[thinwater]

Most likely lay up errors, as others have well described.

However, there is another possibility. If the hull has some porosity (I can't tell if you are into the core or the density of the existing hull laminate) it will sometimes out-gas as the temperature rises during the day, creating big bubbles. This is VERY common when applying epoxy linings over concrete.

The cure? Either vacuum bagging, or more simply, not applying resin while the temperature is rising. Generally it is as simple as keeping the sun off the work area. Was the sun hitting the backside?

[Artif]

Originally Posted by geoffr

Don - photo should be fixed (link only worked for me when logged int ;()

Pete - that is what we did - there were no bubbles when applied to the boat, they came out as it cured. I think there was a little bit of mat as well as cloth.

Artif - I don't understand what you mean by "blanked first"

thanks,

Geoff.

The hole for the through hull should be filled with something, either permanent or temporary to support the back of the mat when laying up. If you try vac bagging with nothing behind the through hole, it will just push the mat/cloth through the hole.

Actually the lack of a blanking plug might the reason for your problem, if your trying to lay up on fresh air.

[Pete7]

Also, I don't think you can use chopped stand matt (CSM) with epoxy. It has a binding agent to hold it together so it can be worked. This reacts with epoxy so you need to use GRP cloth.

So what to do now? well if it was my boat, I would be reaching for the angle grinder to get rid of those bubbles, then have another go.

Pete

[swagman]

I'm with the others. Use a small steel roller over each layer of cloth, then borrow a vacuum pump from someone and tape it over to suck it down. You'll pull out any remaining bubbles plus get a much stronger repair.
Enjoy
JOHN

[pressuredrop]

pete is correct about CSM, however there are some mats that are compatible with epoxy. the ones that are not are the one held together with binders that the styerene in poly resin breaks down, however the matt in 1708 bi-ax is compatible with epoxy since it is stitched in not bound...

[Mark Johnson]

I would squeege the surface lean of excess air & resin, and the surface needs to be warm "before" application, but cooling "during" application. You want it to either not gas at all, or in gas rather than out gas. This is REALLY true with glassing a wood or porous substrate...

With this being under sheet plastic, it tends to heat up the resin, as it traps the heat being created by the curing process. Start in the sun, but create good shade just before application, and use a slower hardener. They create less curing heat.

Good luck,
Mark

[Whimsy]

I suspect your problem is from one or more of the factors already covered here, or some combination thereof.

To summarize the details in one place:

MOULD:
If you are closing a hole, it is usually unrealistic to laminate over air and expect a smooth job. A 'mold' is needed. Close the hole with whatever will assume the correct shape and provide a firm support for the first couple layer of glass. This might be a piece of cardboard, covered with plastic food wrap, then taped onto the back of the job, or for larger areas use thin ply covered with a thin plastic dropcloth taped or screwed in place. I've used both, and the point is to support the first laminates, and to use a smooth release layer that will peel off the hard epoxy cleanly and easily.

SEAL PORES:
Its very important to seal whatever existing core, filler or other substrate you are laminating to: Seal with a coat of epoxy resin brushed on, allow to cure, then sand the 'bumps'/'zits' off the surface. Recoat (& sand) if needed to seal pores or whatever.

FAIR LAMINATING SURFACE:
If there are rough areas or voids that will keep the glass from laying fairly in the repair and being supported 100%, these should be faired with bog (medium density, filled/sanded) until first layer of glass can lay smoothly and tightly to all of the area covered. When you have a smooth, unbroken surface for your laminates, proceed to begin laminating.

MIND THE TEMP CHANGES:
If this sealing/fairing step is done while the job is cooling (usually afternoon/evening) rather than heating, so much the better, as cooling (contracting) air in voids will suck resin into the voids rather than heating (expanding) air causing small bubbles ('pores' or 'pinholes' after sanding) in the epoxy. The point is to close all pores prior to laminating.

INITIAL STRUCTURAL LAMINATES:
Usually I lay in one or more layers of glass and allow to cure. Whatever is needed for enough stiffness to allow the 'mold' to be pulled off to verify that all is good, and also to allow work to proceed on both sides of the repair during each epoxy 'session' (the 'back' of the repair, where the mold was pulled off, may need to be faired and painted if visible). That way both sides are done ASAP.

WETTING EACH LAYER IN PLACE IS LESS COMPLICATED:
Wetting each layer of glass, in place, on its final resting place is a good way to ensure no bubbles are present prior to adding the next layer. Pre-wetting an entire stack of layers, then expecting that mess to lie flat and have no bubbles (let alone a correct resin/glass ratio) without a vacuum bag/pump setup may be unrealistic. Pre-wetting is usually only done with vacuum bagging. Also, sanding off the bumps/zits prior to adding fresh layers to a cured surface is most often required. And sanding the entire surface to get a mechanical bond is required if fresh resin is not applied to the surface (laminating, fairing or coating) within the time window when an interlaminate chemical cross-linked bond can still be achieved due to partial cure. This is usually 48 hours for common boat epoxies.

WETTING TOOLS:
As mentioned, for a few dozen square inches, a chip brush can be used to add resin and poke at the bubbles of each layer until resin fills the voids in the cloth/mat. For larger surfaces, use a foam roller to wet out the fabric (I use a chop saw, circ saw, jig saw, hack saw, whatever, to make two 3.5" rollers from a 7" foam roller for ease of use and economy of both roller covers and resin), then use the chip brush to poke bubble spots if needed. Again, if the surface is properly sealed and faired, the glass should lie well and wet easily with few bubbles. For larger jobs of many square yards, or repeated production work, look into the grooved metal laminating rollers. Not really needed for small job or infrequent laminating as foam rollers and brushes work well.

SPEEDING THE JOB:
Several layers can be applied in one session, but one at a time - if each layer is wetted out singly, on the final site, in turn, no bubbles will be present (assuming abovementioned sealing/fairing). This helps speed the job by eliminating the waiting for cure and then sanding between laminations, and also by reducing the number of sessions (and consumable tools) required to complete the repair to a finished state.

GLASS MAT:
The type of CSM (chopped strand mat with the fibers in random orientation) that is used with polyester resin is held together with a styrene-soluble binder (styrene is the 'stinky' solvent part of polyester resin). As the styrene dissolves the binder it releases the strands from each other and the mat will then 'relax' in shape and conform to the surface, within the limits of the ultimate flexibility of the strands themselves. Epoxy will not dissolve this binder and the only result of trying will be a frustrating mess that never wets out much at all.

MAT FOR USE WITH EPOXY:
The type of glass fiber mat that can be used with epoxy is sewn to hold the fibers together (no added chemical binder), usually back-to-back with the same stitching holding together layers of non-woven fabric in a biaxial or triaxial configuration (IIRC, this product is sometimes called "Fabmat"). Biaxial and triaxial non-woven (sewn) fabrics are also available without the mat. This stuff (with or w/o mat) is much stiffer than standard cloth, but can achieve much higher glass/resin ratios (no 'pit' at each juncture of the kinked, woven yarn), especially with vacuum bagging, which is desirable where high stiffness/weight is important.

GLASS CLOTH W/O MAT IS STRONGER:
CSM in the laminate is a quick way to build thickness, but the ultimate strength is significantly compromised, compared to correctly-laid glass cloth, as the glass/resin ratio will be much lower in the mat. This is probably an insignificant factor in most small repairs, but is worth keeping in mind.

SILANE VS VOLAN:
Additionally, the surface of the individual glass fiber strands of most glass meant for laminating will have one of two primary treatments in manufacturing to allow maximum adhesion of the resin to the surface of the glass fiber strands. IIRC, its Silane for epoxy, and Volan for polyester and vinylester. I've heard that there is a combo of the two in some industrial applications that allow interchangeability of resin systems, but that is likely irrelevant here. The point is that glass and resin systems should be verified compatible in advance of purchase. Glass bought from an epoxy supplier like West, System Three or Raka will almost certainly be Silane treated.

REPAIR THE BUBBLE RATHER THAN REDO THE WHOLE JOB:
Finally, if you do have a patch in place with a significant bubble, and if you believe that bubble causes undesirable weakness of the repair, you can just do a repair of your existing repair - grind out the bubble forming a 'dished' area out onto the surrounding laminate (new or old...) and then lay in your glass patches one layer at a time as per above until the correct thickness dimensions are achieved.

I wish you good success.

[Mark Johnson]

I had assumed that you first filled the hole and had a concave surface to lay the glass over. If not... You can put duct tape on the inside hull surface as a back up, and fill the hole with West resin filled with silica. (Thickened till it wont sag) The hole must be well sanded first to NO caulk. Now you have to squeege the surface concave, and let cure. (Use super slow "tropical" hardner). Next you can lay on a couple of layers of fabric, sand fair after cure, and apply several topcoats so that after final sanding, NO glass fiber shows.

I have filled MANY through hull holes this way... It's a cinch! M.

This photo is a molded in recess, for next caulking in a flush through hull.