I had the hull glassed with 2 fill coats, should have done 3. I then put the deck on, glassed it, scored the first layer at the tape line and pulled the tape/fiberglass off. Everything was going great. Next, I let the epoxy cure for about 3hours. I then wiped the hull down (denatured alcohol)avoiding the fresh layer. The hull was sanded but looked like it could use some more fill coats so I thought when I was filling the weave on the deck I would add another coat or two on the hull at the same time. After the first fill coat I noticed that the epoxy where the tape was was not flowing right. I tried rolling it more thoroughly but to no avail. It appears the denatured alcohol did not remove the adhesive residue. I’ll add photos. Apparently I should have used something else to wipe the tape residue off, maybe lacquer thinner or something else? I’ve sanded it all back down and certainly don’t want this to happen again.
Yeah, tape residue is nasty and the longer it stays the nastier it gets. Denatured alcohol does nothing about it. The only way I’ve been able to wash it off is with some kind of petroleum distillate, which itself doesn’t play well with epoxy. So sanding is your best bet.
If you must put tape on bare wood keep in mind that:
- You shouldn’t press hard; that works the adhesive residue into the pores.
- A fine line masking tape leaves less residue than most other types.
- You need to get the tape off the bare wood as soon as possible.
Laszlo
Ouch!
tell us more about the tape. i use tape in a lot of steps…and as laszlo says, you need to be careful of residue.
that said, depending on the particular part of the construction, i have, through the school of hard knocks, developed some approaches that have minimized those knocks…that i would be happy to share. i just can’t figure out from your description, what was the tape application step that created the residue problem (e.g., were you using tape to mask an area, were you using tape to hold something in position? some other step?). And to the extent you can clearly identify the substrate (wood, epoxy, a painted surface) and what you expected to do on the surface after the tape removal (more epoxy, paint or varnish), that would be helpful.
without the specifics, some general conclusions i have from a lot of builds are:
-
pay for good, “fresh” tape from reputable brands like 3m. …which generally, relative to their use, leave little residue
-
do not leave tape in place any longer than needed (the longer its in place, the more likely to leave residue than not and
-
inspect after tape is pulled to ensure that you have a clean surface prior to the next application (could be paint, or more epoxy, or varnish) and to use the right cleaner in anticipation of that step.
i hope, absent more details, that this is helpful.
h
Thanks Laszlo and Howard,
The application that I was using the tape for was to protect the epoxy/glass surface on the hull from the raw fiberglass that I was applying to the deck. This makes for cutting a clean line after coating the deck. I was using blue painters tape. I will use 3M tape whenever possible, I’m a big believer in 3M products. The tape had been on for maybe a week. I have since sanded everything back down including the deck and hull. The instructions call for wiping the cured epoxy surface down with lacquer thinner but not specifically for removing tape residue. I’ve been using denatured alcohol which I believe was a mistake. I will try this for the next 2 fill coats keeping a close eye out for “alligator skin” is best description of it. You can see the blue tape under the raw cloth in the first photo.
One suggestion of last resort when an epoxy coating is going bad… I’ve never had as bad an event as your pictures show, but over the years have hit a contaminated (non-stick) patch or two that became evident during coating, or more frequently pushed a little too long in trying to use epoxy that was setting up, and thus got stringy and milky in the final spreading process. I’ve found it better to grab a well-wet alcohol rag and scrub the bad stuff off right away. The result can be that less effort is required to sand out the more minor “washed off” area blemishes prior to the next recoating. For me this seems to save time on sanding, and limits the chance of creating sand-thru’s or a wavy surface as you try to sand off aligator skin/orange peel, or milky-stringy epoxy patches that you’ve let harden in place.
Doug,
All is clear now. I use that same technique, just with different tape - 2" wide clear plastic packing tape.
I also typically leave the tape on the boat for less than a day. If it’s a hot day build, it can be only a few hours. That’s not enough time for residue to become a problem with that particular tape.
I think that you’ve also got something else going on there - the type of tape. That blue painter’s tape is more textured so that epoxy sticks to it somewhat. I don’t know if that interacts with the adhesive in forming residue. I do know, however, that I’ve never had an issue with the packing tape over multiple boats. I’d recommend that you switch to that in the future.
Laszlo
I am a little skeptical that this degree of “fish eyes” is an artifact of tape residue. What kind of epoxy was used? Is there any chance that the alcohol or rag that was used for the wipe had been contaminated.
Pretty sure it was tape related because the only area affected by the “fish eyes” was the area directly under where the tape was. If you look at the picture that shows the “fish eyes” you will see a white scratch that was from the razor knife cutting the cloth at the top of the tape. The area above it is not affected only 2” down from the white scratch and then it stops. I wiped the area from the scratch down to the bottom (bilge) chine. Both sides of the kayak were wiped down and coated with a “fill the weave” coat. The only areas affected were the ones directly underneath the tape. The rag was new in a plastic bag free from dust.
Doug
This is approximately the same area after sanding. I plan on a thorough lacquer thinner wipe down on the deck and hull and will add two thin epoxy fill coats. As bad as everything looked I only spent around 3 hours sanding it back down. The silver lining is the next two coats are going to go on a very smooth surface that takes less epoxy. Just trying to put a happy face on it
I recommend against using lacquer thinner for pre-epoxy cleanup. Thinners are just a cocktail of various chemicals that may or may not interfere with the epoxy. Use denatured alcohol instead. Pasted from the MAS website: “All surfaces must be clean, dry and free of contamination. Contaminates include, but are not limited to dust, oil, moisture, sap, lint, and sanding debris. Do not use paper towels, dirty rags, contaminated sandpaper, or touch surface with oily fingers. Sand as needed and clean off sanding debris. Wipe surface down with a clean cotton t-shirt rag soaked in an oil free solvent like denatured alcohol prior to applying epoxy seal coat. Do not use tack cloth.”
Hi Doug,
thanks for more details. based on further detail, the main issue i see is how long the blue tape was left in place.
i routinely use blue tape for the purpose you describe but have never left it on beyond a day after learning some tough lessons…i consider now ‘masking and unmasking’ part of the ‘unit of work’ for putting down a coat of epoxy.
since its more there for a visual cue for a cut line vs real masking, i don’t really push it hard onto the surface either…because it has to be removed as part of the cut…so you are only waiting until the epoxy becomes just ‘plasticy’ enough to cut and remove. i once waited a bit too long…and it was quite a problem.
i have on occasion used packing tape as well..but for cut lines like this have a strong bias for blue tape given my eyesight is not as good as it used to be …but again, on, semi cure, and then right off.
my personal view is you are more likely to get residue from packing tape.. once bought some inexpensive stuff to save some money …and it created quite a mess.
but it strikes me that the killer is how long the tape was in place…just a lot of stuff that can happen when tape is there - even blue tape is not meant to peel off residue free if on for a while…
tape removal for stuff that’s been there a while is its own kettle of fish…what does it take to get the ‘glue off’ may be one treatment, and then what does it take to ensure the surface is clean and ready for epoxy is not necessarily the same solvent. have occassionally resorted to acetone (need to be very quick…but when used properly can do some amazing things).
in the end, it looks like you cleaned it up really nice…so glad you are back on track.
h
I left the tape on for maybe a week which sounds bad after reading your comment. It’s also made me reevaluate contaminants that can end up on the surface. I plan on wiping the surface down one or two more times probably with either lacquer thinner or acetone. I’ve used acetone in the past but switched to denatured alcohol per CLC recommendations. I’ve never had problems with acetone in the past. CLC does recommend using a lacquer thinner wipe down prior to varnishing though. Personally I’ve had more experience with acetone and plan on going that direction to remove tape residue or other stubborn contaminants. Once the surface is decontaminated I will be extra careful and not touch any surfaces with my bare hand. I will still use denatured alcohol mainly for dust removal. Thanks for your advice this episode made me rethink how important it is to have a “sterile” surface when applying any type of coatings
Thinks, Doug
Success,
at least for today! One more fill coat and the epoxy work is done. I have to admit I was getting sloppy on my cleanliness of the boat surfaces. Sometimes one just needs a kick in the butt to get back on track. Thanks to everyone for their input
Doug
Howard,
When I use the packing tape it’s not for a visual cue. It actually does the work of giving me a clean, loose-thread-free interface at the glass boundaries. The wetted glass does not bond to the tape, so when it cures to the green stage, it can be lifted up off the tape. Since it’s bonded to the untaped area, you can make a cut right at the fold which starts a tear. By gently pulling on the glass the tear will propagate the length of the joint, leaving a clean straight line that needs only a quick hit with sandpaper to become an invisible interface.. Since this process depends only on the mechanical properties of the tape (too smooth for epoxy to adhere), the tape can be completely invisible.
Also, this process doesn’t leave any scratches in the epoxy from the cutting tools since the only cut is the nick that starts a new tear. The picture I previously posted show this process in action. Where the tear departs the boundary, you just need to nick it again in the proper spot to restart the tear.
This picture shows the result after the tearing, removal of tape and a quick hit with a sanding block. The boundary is still barely visible because the weave has not been filled. Once the weave is filled, sanded and varnished, the line is invisible.
Laszlo
Hi Laszlo,
thanks for the additional color. i am a bit curious how you describe it though we appear to be doing the same thing.
in looking at your picture, i am assuming you are making a cut/scoring the ‘plasticy’ glass along the top of the tape which i am assuming is the ‘blue line’ that i marked in your picture:
merely the point i was trying to make, is with clear tape, seeing where you want to score the plasticy glass that you wetted out a couple hour prior can be difficult to see (or at least difficult for me to see).
the pictures below are, what i think, is the equivelent process using blue tape. in this picture, i am applying handmade glass tape (regular 4 oz cloth i cut into 5 inch wide strips vs standard 3 inch fibreglass tape) that i use to attach a hull to a deck in a strip build. (i cut 5 inches wide even though i am looking for only 3 inches at the end becuase i am going to lose ~ 1 inch on each side after I trim it back):
so when i want my clean lines, what i was saying is its easier for me to see where i am scoring the plasticy glass when i use blue tape underneath the glass…
like yours, this sands out very easy and is invisble with little effort.
as discussed, the taping, glass placement, wet out and cut/cleanup is all typically happening in less than an 8 hour session (one hour of set up, 4-6 hours expoxy application/plasticy cure, one hour cut/remove the blue tape/scrap glass).
let me know if there is something i missed…your lines are exceptionally clean.
howard
I think I did something of a hybrid of both of those techniques. From what I remember I did Laszlo’s technique on my first build. If I remember correctly I used packing tape and cut and unzipped the cloth from the boat. The tricky part is the timing. To early and the cloth separates from the surface and to late well we all know what happens then. It seemed like a fairly tight window when it was “just right “. It worked well and for some reason I did the blue tape and scored it for this build. I’m still new to boat building so I don’t do anything the same twice. This time I scored it lightly and when the glass got rubbery I pulled it off. I think I should have waited a little longer because as you can see in the photo it pulled strands of glass out maybe even lifting them off the surface slightly. See the top of the tape in the photo. This left more of the little white little dots than I would like and more sanding.
Doug
Howard,
I don’t score the glass. I only nick it at one edge enough to start a tear, then pull the glass off the boat. The tear propagates along the edge of the tape where the glass has bonded to the surface underneath and naturally forms a clean line with no chance of scoring the wood below.
The mechanism is that the nick is a stress concentrator, the glass fibers try to resist the stress but fail and break. The stress is greatest where the nick meets the edge of the bonded glass. On the unbonded side the fibers flex and dissipate the force. On the bonded side the substrate supports the glass and joins in resisting the force. Right at the boundary the force is at a maximum. The glass fibers break and the epoxy matrix ruptures causing the epoxied glass to tear along the boundary line (my apologies to professional mechanical engineers who are no doubt cringing at this amateur explanation).
Doug is correct that timing matters. The glass has to be cured enough so that the fibers have become slightly brittle but before the layup develops its full strength. If you pull it too soon, before it has sufficient adhesion to the previous layer, it will peel off the boat instead of tearing. Too late and the tear won’t propagate and you have to revert to the scoring method.
That said, it’s pretty easy to judge. When the glass is no longer tacky but is still flexible enough to bend, lift it off the packing tape (second picture) and make the nick. You can start pulling. If it tears cleanly at the nick, keep going, otherwise, push the glass back down and wait a bit longer (since it’s not fully cured, it will adhere - apply a dollop of unthickened epoxy underneath if you’re nervous).
The only issue I’ve ever had is that sometimes the tear departs from the ideal line (third picture). The fix is to stop pulling, find the point of departure, make a new nick there and continue. No big deal.
The packing tape defines the boundary along which the tear propagates. There’s no scoring of the glass, so visibility of the tape to guide the blade is not an issue. There is no blade to guide.
And to bring it all back to the actual subject of this thread, the tape goes on just before the layup and is removed as soon as the glass is torn off to avoid a chance of contaminating residue.
Laszlo
Doug,
Looking at your latest picture I’m struck by the fact that you’re pulling the blue tape off at the same time that you’re pulling the glass. That may have actually caused the lifted threads more than your timing. By providing support under the glass on both sides of the tear you may have changed the stress distribution such that there wasn’t enough force to cleanly break all the threads, sort of the equivalent of trying to cut with dull scissors. Visually, the result sort of looks the same as dull scissors.
Mind you, this may be too much extrapolation from one photo, but I’ve never had that result with the technique of pulling the glass and leaving the tape. My glitches have been the tear departing from the boundary, which is analogous to a blade steering error as opposed to a dull blade. Food for thought.
Laszlo
Thanks Laszlo for your detailed response. I should have done it like you suggested. I remember doing it with my first build and it worked great. I’m always trying to tweak my techniques which can create some confusion when trying to replicate the process a couple of years later. Sometimes I look a my first build and wonder “how did I do that”? Seems like when I’m building every day is a new day but problem solving is good for the brain. I can’t say that about sanding though.
Doug
cool laszlo…
definitely different than the approach i am using. i am basically cutting the glass…you are breaking it…or so that’s my understanding. will have to give that a try. with the technique you are describing, i would not try with blue tape…it does not resist epoxy bonding enough in my view to work with the approach you described. fine for what i was doing 