Caulking by combining butyl tape and Sikaflex 291

[Julsburd]

We have a deck seam on our fly bridge that requires maintenance caulking. It isn’t a wide seam but it can vary in depth. I caulked it with 4200 in November and I don’t like the way it looks already. It seems to be receding away from the fiberglass edges and I’m worried it may create seepage spots. I am thinking the 4200 sunk into the deeper areas of the channel or didn’t really adhere well to the deeper areas. Anyway I’d like to apply a layer of butyl tape to penetrate deeply, and leave it ¼ to ½ below the surface and then apply Sikaflex 291 to this top layer. What do you guys think? Will the Sikaflex bond to the butyl tape or at least cure on top of it without a problem? Also any tips on applying Sikaflex 291? I did not like working with the 4200 at all which also may explain the crummy job I did!

 

[Comodave]

I don’t see any reason that you couldn’t do it. The problem may be that the butyl will stick to the edges as it goes in and you may not be able to get it off and then the 291 would be sticking to the butyl and not to the fiberglass. I use butyl quite a bit. We replaced 11 portholes with new S/S ones and used butyl to bed them. I used spatulas to push the butyl in but used the opposite end from the spatula, in other words the handle end. Had to use the paper that was in between the butyl to cover the end of the spatula handle so the butyl would not stick to the handle, one side of the paper had a coating that would not stick to the butyl. I like the butyl from Compass Marine. It would be like caulking a wood boat planks and the butyl would be like the oakum or cotton that goes in before the caulk. As to Sika, I like it much better than 4200. It is easy to use and tools nicely.

 

[Bacchus]

Julie
I don't know the compatibility of butyl & Sikaflex but would offer a suggestion based on conventional caulking best practices.
With deep joints caulking presents problems either in getting the joint filled (caulk sags into the joint) and/or the caulked joint fails (pulls away)
The recommended practice is to use a "backer rod" in addition to the caulk. The backer rod comes in various sizes and is simply a flexible foam rod. The backer is inserted into the joint and pushed down leaving a controlled depth to be filled with the caulk (see diagram). I believe the science behind this method is the caulk adheres to the edges of the joint and a thin section of caulk stretches with movement. Being a relatively thin cross section it stretches before pulling away from the edges. Without backer the caulk is much thicker in deep areas and instead of stretching it pulls away from an edge.
What you suggested is similar but what I don't know is 1) chemical compatibility (your question) 2) whether the Sikaflex will adhere to the butyl and still pull away from an edge. I would give the backer a try (available in different sizes in many home improvement centers or masonry supply houses) and just use the Sikaflex (or your favorite caulk)
Hope that helps -

 

[firehoser75]

Julsburd,
I asked Rod at Compass Marine (sells Butyl Tape and advocates it's use) and he stated "there are no compatibility issues between Butyl tape and Sika). Just an FYI. If you do go that route, let us know how it went for you.

 

[C lectric]

Bachuss's explanation is essentially what I learned many years ago .
If the joint is totally filled, a three sided fill, the caulk will tear away over time from one or both sides.

THe idea is to get a two sided, opposite sides, join. On a 90o joint it is needed to put something in the very corner as a bead breaker.

You may also need to lightly sand the are you want the caulk to bond to. FIRST dewax, then sand lightly , then dewax again. A trick I have read about from boat hull painters. If you just sand first you may drive any wax into the surface and then when you solvent clean the roughness will hold some of the wax/dirt.

The final join is very dependent upon how clean you got the surfaces. Any wax, any dirt, will interfere with a good bond.

I have not had to fill a join like yours is described but I think I would first try the foam backing rods available at the local building supply. THey can be purchased in several different diameters.

I'll add that I use butyl tape but have not for anything like described here. However for working it I use scissors to cut strips where needed, narrowing the pices and shortening as needed. It will bond to itself thoroughly when the final press is done.
Several strips could be worked into place without too much fighting where one bigger one may be a fight. Use a tool, several, made of polyethylene. The butyl will stick less tenaciously to that than to other materials. If the butyl can be kept cool it will be easier to work into place. Ice box to cool it. Once it warms it can get a final pressing into place.

Cleanliness of the area will also be important even with the butyl.

For that final pressing use some of what Commodave suggested, the backing tape., Maybe waxed paper .

 

[koliver]

The backer rod comes in various sizes and is simply a flexible foam rod. The backer is inserted into the joint and pushed down leaving a controlled depth to be filled with the caulk (see diagram). I believe the science behind this method is the caulk adheres to the edges of the joint and a thin section of caulk stretches with movement. Being a relatively thin cross section it stretches before pulling away from the edges. Without backer the caulk is much thicker in deep areas and instead of stretching it pulls away from an edge.
What you suggested is similar but what I don't know is 1) chemical compatibility (your question) 2) whether the Sikaflex will adhere to the butyl and still pull away from an edge. I would give the backer a try (available in different sizes in many home improvement centers or masonry supply houses) and just use the Sikaflex (or your favorite caulk)
Hope that helps -

When I made a replacement hatch, the instructions and supplies from Lifecaulk were similar to the above.
The bond breaker tape I used looks a lot like a wide shoelace, in the case of teak decking the seams were about 1/4 in, so that is the width "shoelace" material I used. Still working after more than 20 yrs.

 

[bayview]

If 4200 is failing it is because of surface contamination ( silicone?) unless the two parts are moving independently for some structural reason. No mater what you use that must be fixed first. Even the good technique Bacchus posted will fail if you dont have clean surfaces.

 

[Julsburd]

Thank you so much! All good suggestions. I can say the seam does not connect 2 independent parts so movement is not the problem. After reading your suggestions I am thinking its failure is a combination of not cleaning the edges enough and not filling the depth of the seam enough. I should say though, the seam itself is only around ⅛ " wide. I am going to experiment with a couple of methods and I'll report back.

 

[Julsburd]

I just looked at backer rod products in Home depot's website and they are not going to work in my case because they are too wide for the gap. The smallest diameter I found was ⅜ and that would be double the width I have. I suppose I could try to cram it down the seam with a putty knife but I am going to try the butyl tape first and use it as my "backer rod" underneath the sikaflex...

 

[Comodave]

A1/8” wide gap is going to be very difficult to get butyl into. It will stick to the sides as it goes in and you will have a hard time getting it to bottom out. When we put our new portholes in we needed about 5/16” gap to get it down in the seam.

 

[Julsburd]

Thanks Comodave. You're probably right. Maybe I'll try to just put the Sikaflex in and try to do a better job of pressing it down into the seam. Hopefully it will be easier to work with than the 4200. I just found that product to be so sticky, and it skinned over so quickly. I have done a lot of household caulking projects because my husband and I have renovated 6 old homes so I am comparing it to household caulks. This is my first experience with marine caulks. I understand they need to be very waterproof and flexible for the overall movement on a boat but do they have to be so quick to skin over and so difficult to smooth out for a nice finished surface? Can I use a bit of mineral spirits or acetone to smooth out the surface on the sikaflex?

 

[Comodave]

I used to use 3M products but the last few years have gone to Sika products and like them much better. I have not had a problem with 291 skinning over too quickly. I use a plastic mixing stick to tool the caulk and it seems to work for me. I have not tried any chemicals on it. You might try flattening the open end of the nozzle with a set of pliers to get it down into the seam further so the caulk gets to the bottom. How deep is the seem?

 

[Lou_tribal]

I used to use 3M products but the last few years have gone to Sika products and like them much better. I have not had a problem with 291 skinning over too quickly. I use a plastic mixing stick to tool the caulk and it seems to work for me. I have not tried any chemicals on it. You might try flattening the open end of the nozzle with a set of pliers to get it down into the seam further so the caulk gets to the bottom. How deep is the seem?

I did caulking if some windows on my boat using Sika 291 LOT and I am very happy with it.
Just plan enough rag to clean any extra. I found out that WD40 degreaser/cleaner is very good to clean any mess.

L

 

[Bacchus]

Any chance somewhere in the past it was caulked with the "S" word (sillycone)?
If so you need to do a very intense job of cleaning. I have tried acetone alone and found I needed to sand to get to clean surface.

 

[Julsburd]

The depth is 1" or so. Can't really measure it but based on the depth of the old caulk I removed I would say it was around that.

 

[BruceK]

Can I use a bit of mineral spirits or acetone to smooth out the surface on the sikaflex?

I`ve used paper towel wetted with mineral turpentine("turps") as a smoothing or cleaning up solvent for excess Sika. A finger wrapped in plastic wrap works too. You need a helper to handle/dispose of/replace these things so you get done before the Sika goes off.

 

[Julsburd]

I doubt that but I'll be sure to do that. The previous owner of our boat was meticulous and I am sure he would have known not to use silicone. He was the one who told me to use 4200 in the first place.

 

[Bacchus]

How about a strip of think foam wrap like parts wrapped for shipping? Cut a 1/2" or so width and slide it in before caulking. Make your own backer that fits. Even RIP saw a piece of polly lumber, etc

 

[Comodave]

How about a strip of think foam wrap like parts wrapped for shipping? Cut a 1/2" or so width and slide it in before caulking. Make your own backer that fits. Even RIP saw a piece of polly lumber, etc

I like this idea.

 

[BruceK]

I seem to remember someone in a previous discussion using pinstripe auto detailing tape as a bond breaker tape.

 

[CMS]

Julsburd,
I asked Rod at Compass Marine (sells Butyl Tape and advocates it's use) and he stated "there are no compatibility issues between Butyl tape and Sika). Just an FYI. If you do go that route, let us know how it went for you.

Actually, I said there are no compatibility issues with Bed-It Tape and Sika. Bed-It Tape is not a butyl tape but a butyl hybrid product.