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What size and type backer rod can I use for Movement joints?
QUESTION
New garage floor. Contractor cut break lines 1/8 wide by 1 in deep. 350 lineal feet to fill. I bought Sikaflex 1C SL. I cannot find where 1/8 in backer rod is available. Sika says max depth is 1/2 in. Do I need backer rod or can I just fill the 1 in? It's really slow and tedious to squeeze into a 1/8 cut. Please advise. Thank you.ANSWER
ANSWER - The closed-cell foam backer rod is suppose to be wider than the movement joint. You can compress a 1/4" foam backer rod into a 1/8" wide movement joint.The backer rod serves two main purposes, one that it fills the void so moisture doesn't fill it, and it acts as a bond-breaker so the sealant doesn't bond to it that would limit its performance in stretching and compressing when subjected to various stresses.
I have seen sand used to fill the joint that will act as a bond breaker, but it does absorb moisture.
3 thoughts on “What size and type backer rod can I use for Movement joints?”
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I’m in a pickle. My tub/tile shower combo with a glass slider door was leaking. Builder put grout between tub/tile and used grout in vertical corners. I have removed all the grout from those areas and the old silicone from around the slider to redo everything. The gap between the tub/tile varies from 1/2″ along the front end of tub and continues to eventually decrease to 1/4″ by the time you get to the back end of the tub. The vertical corners joints are even worse. The seams in the corners vary from 1/8″ or almost touching to a 1/2″ gap in other areas along the joint. These vertical seams vary in that some are right in the corner to a hole more on one side where the tile is cut too big and the tile on the other corner wall goes all the way back to flush with the backer board. I am a first time DIY at this task. This same problem is in another bath and has leaked and degraded so much that will be totally ripped out to fix it. This shower has not been used as much so I’m trying to fix it to put off ripping it out until we have saved the money to do it as well. Here are my questions.
Do I apply clear silicone around the slider first? Or do I caulk around the tub first? I have researched that I apply the silicone around the slider on the outside both vertical passes and the horizontal pass, but inside the slider the silicone is installed only to vertical passes to allow the bottom of slider to allow water to weep back into tub.
I am going to install backer rods in all the gaps around tub and vertical corners. I will need to use varying sizes due to the issues. I plan to use a backer rod that is 1/8″ larger than the width of the joint. Is this correct?
I am using the proper sealant that you specify in all the answers I have read about in your blogs. I plan to tape the joint before caulking. How do I tape when these joints are so uneven? I fear the caulk will look terrible. One vertical corner is the worst. Very uneven with each tile and the joint shifts from directly in the corner to a little on the back wall of shower to a little on the front wall of shower. A nightmare. How do I approach this?
This is an additional question from “I’m in a pickle” posted earlier. In regard to my tub/tile shower with slider that has been leaking. Usually around the slider bottom corners. My earlier post will tell you all the details, but after further thought and countless videos I have a new question. After removing all the grout from above the tub to flush with the slider rail, there is still grout below the tile where it goes behind the slider and then the grout continues on past the slider. Do I need to remove slider and remove grout, put in backer rod (joint will be 1/2″) , caulk , and then reinstall the slider to fix this issue? Or can I just leave the slider up and try to just put backer rod in only to where the slider starts (and leave that grout in that’s behind the slider? I fear I know the answer, but I’m hoping for good news. Sorry I did not post everything together at once.
There is no way that we can determine exactly what are the underlying conditions of what you are describing. We can only provide some key information to consider when caulking transition joints in a shower.
Based on your descriptions with the kind of extreme variation in the various transition joint widths it sounds like the shower was not properly constructed.
Keep in mind that fixing a symptom of a problem doesn’t fix the underlying problem. There is no guarantee or assurance what will or will not work.
You must follow the installation directions of the manufacture of the ASTM C920 silicone sealant. Most manufactures say the thickness of the sealant has to be at least 1/4″ thick and can’t be more than 1/2″ thick. The closed cell polyethylene backer rod serves two main purchases. You can control the thickness of the sealant and it acts as a bond breaker to the sealant to achieve the intended performance. The manufacturer will require the joint to be properly cleaned per their directions.
Clear silicone sealant can tend to discolor from microbial activity. A color that blends in more with the adjacent surfaces will not accentuated the joint.