Oil Stain may have affected glue joints

S

suspend6

Joined
Dec 26, 2023
Messages
63
Points
58

Location
Geelong, Australia
I used an oil-based stain to stain some parts before gluing. The instructions encouraged staining before assembly. I emailed the PVA glue manufacturer (Gorilla) to clarify if the stain would affect the glue joints. They responded with an assurance it should be fine. The joints in question were those fixing the bulkheads/frames to the false keel. Needless to say, about five of the 14 joints came loose easily. However, there could possibly have been two other contributing factors - laser ash and lack of glue.

The joints first need to be sanded to remove the ash created when the parts were initially cut with a laser, and being stingy with the glue is false economy.
Given this is my first build, I thought it wise to make these observations known, to hopefully avoid others falling into the same traps.

However, I am not convinced gluing parts stained with an oil-based stain is completely trouble-free and will result in a full-strength bond. I used oil to avoid the wood swelling.
 
I pre stain and avoid CA Glue when possible. I have always used Titebond products, prefer Titebond II. Haven't had any issues. I did try Gorilla Glue but found it more difficult to use. I recall some requirement to dampen the wood prior to gluing, apparently the glue is moisture activated and takes longer to cure.
 
Almost any adhesive for wood will always work better on clean dry wood with well-fitting joints. This is because wood glues work by penetrating into the fibers of the wood. If wood contains even moisture, that means it can't absorb the glue as well, because the wood can only hold so much moisture. The one possible exception, as @Quint mentioned, is Original Gorilla, which is a polyurethane glue. However, and that is a BIG however, PU glues require a tight, well-fitting joint and moderate to high clamping pressure. PU glues expand as they cure, which helps them to penetrate into moist wood, but if your joint has voids and/or you don't clamp it well, the PU will turn into a brittle frothy foam inside the joint with no strength at all.

Oil stains will also displace moisture as well as seal the wood fibers, also contributing to a lack of glue penetration. If at all possible, you should mask off any areas that will receive glue when pre-staining or pre-painting parts.

The other contributing factor to a failed glue joint is how well the parts fit together. For all but one of the typical adhesives we use (the exception being epoxy), a glue joint made up mostly of glue will be inherently weak. PVA, CA, Hide and PU glues are not gap-filling. Only epoxy will do that, but you must take steps to make sure the glue doesn't run out of the joint before it cures.

As far as sanding the char off as @suspend6 mentioned, I'm not so much convinced that it's the char that prevents a good joint (removing it certainly doesn't hurt), but I think that the inherent bevel created by laser-cutting is more of a contributing factor. As a laser burns through a sheet of wood, it burns a wider gap at the top surface than at the bottom, creating a beveled part. The thicker the wood, the more pronounced the bevel. It's really this bevel that needs to be squared up to create a well fitting joint. I think most established kit manufacturers have taken this into account and cut their parts slightly oversized to allow squaring up. You must be careful, however, and go at it with a light touch. Use files or sanding sticks/blocks. Never clean it up with bare sandpaper and your fingers. That will only round the edge off.

Most keel to bulkhead joints are of the interlocking slot-on-slot type. If, when you dry-fit the bulkhead and then hold the keel upside down, the bulkhead falls off under its own weight, your joint is too sloppy and the only way to get a good joint is to reinforce it with pieces of wood veneer IN the joint, cleats or blocks on the outside of the joint, or thick epoxy adhesive.
 
Last edited:
the manufacture of your glue probably meant the oil stain wouldnt effect an already cured joint. im not sure any glue would take to an oil stained wood.

but a water based stain would have no problem.
 
You must log in or register to reply here.
Back
Top