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One of the more common questions about garage floors is how to fill contraction and expansion joints. In particular, many want to know if you can fill the joints in the garage floor before applying an epoxy coating. Others want to know if you can fill the joints before or after a sealer is applied. What about sealing the expansion joint between the garage floor and the driveway?
We will answer all these questions and more, as well as discuss how to fill expansion and contraction joints in your garage floor. But first, you need to understand the difference between these two joints because it can determine which type of joint filling materials you use and why.
Difference between expansion and contraction joints
In a typical 2-car garage, contraction joints usually look like a big plus sign that divides your garage floor into what appears to be four separate slabs. These joints (sometimes called control joints) are the deep V shaped grooves that run from one end of your garage floor to the other. Some concrete floors may have saw cuts as a contraction joint instead. Saw cuts are usually a minimum of 3/16” wide and 1” deep.
Because concrete slabs will crack with expansion and contraction, these joints create a weakened line in the concrete that encourage cracks to follow the line within the joint. This helps to discourage cracks from following a more resistant line across the surface of your garage floor.
Expansion joints (sometimes called isolation joints) are joints that separate one slab of concrete from another and can be at a minimum of 1/2” in width.
They are commonly filled with a compressible fiber board material. The joint between your garage floor and driveway is a good example of this.
Many times the garage floor is poured independent of the home foundation. When this is done, there is an expansion joint that will run at the perimeter of where the garage floor meets the house foundation.
In simple terms, expansion joints help prevent adjoining slabs from damaging each other when they expand and contract.
Filling contraction joints before epoxy coatings
When the time comes to paint or epoxy coat the garage floor, many people want to fill their contraction joints in order to have a seamless looking floor. So, is this advisable to do? Well the answer depends on what material you use.
When your garage floor expands and contracts with temperature changes, it can create movement (very slight) within the contraction joint. This is why there are cracks within the joint in the first place. If the joint is filled with a solid material that does not flex and then is covered with epoxy or paint, you have just created the potential for the crack to telegraph up through the coating.
The reason for this is because you have a solid seamless coating which does not flex (epoxy) that is bonded to both sides of a jointed surface (concrete) that can move. As a result, you can create a break in the surface of the epoxy right above these joints if they are filled.
Though the chance of this happening is not great, many professional contractors will not warranty an epoxy coating for cracks where the owner has asked to have the joints filled. Most contractors will fill the joints if asked, but they will warn you about the possible problems.
If you want to fill your contraction joints, the key is to use the proper joint filler.
The best material to use is a 100% solids epoxy filler or polyurea filler with an elongation rate (flex %) much higher than that of the coating you are using. It will cure to a hard solid that is sandable and will flex slightly (relative to the concrete) underneath your epoxy coating if the joint moves in order to prevent cracking.
This flexibility also prevents the filler from pulling away from the concrete as the floor expands and contracts. These qualities help tremendously to keep the paint or epoxy coating in one piece and not crack.
Contraction joints filled with Legacy 2-Part epoxy gel and ground flush with floor
product recommendations
Most of these special joint filling compounds can be found online from your favorite concrete floor coating vendors. They are not cheap and home improvement centers do not carry them.
There a few different products we can recommend. The first is a 2-Part 100% solids epoxy gel by Legacy Industrial. You mix the two components together and then fill in the joints. They also have a 2-part polyurea crack filler that works extremely well. It works great as a crack filler also. We did an article on it here.
Another great source is Garage Flooring LLC. They have a few different types of joint fillers depending on what the job is. You can find them here. We recommend that you talk with them first to learn which is best for your project.
ElastiPoxy is yet another product that works very well for filling joints. You can find it here at Amazon
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Application of these joint fillers is not hard and requires little preparation of the joint other than making sure it is clean.
If you have saw cut contraction joints, we recommend that you fill them first with a foam backer rod or silica sand so you don’t use as much filler.
You want to leave approximately 3/8″-1/2″ from the surface. If you have “V” shaped contraction joints, the foam backer rod will not work well. Silica sand is a better choice. Both the silica sand and foam backer rod can be purchased from your local home improvement center.
When using foam backer rod, make sure it’s approximately 1/8” wider than the joint. If your joints have cracks in the bottom of them, the backer rod or silica sand will also prevent the filler from slowly sinking into the cracks and creating low spots as it cures.
Once the joint is prepped, follow the instructions of your product of choice and fill the joints up. Make sure you don’t have any low spots or you will have to go over them again. It helps to use a putty knife to force out air pockets and to remove excess material.
Once the joint filler has cured, you will need to grind the joint flush to create a seamless surface to paint or epoxy over.
The grinding of the joint is important because some garage floors with the deep V groove can be lifted at the edges of the joint. This happens when the surface of the slab cures and contracts quicker than the rest of the concrete and pulls up the edges. If you apply the filler but don’t grind it smooth, your joints will telegraph right through to the surface of your coating and become visible.
Contrary to what some people recommend, do not use latex caulk or water based crack fillers.
Latex caulk and water based crack fillers are too soft and will slowly shrink. As a result, you will end up with slight depressions that outline where your contraction joints are. Additionally, the coating will crack if you have rolling toolboxes, jacks, creepers, or other heavy objects that move across the joint. This happens because these fillers are too soft.
Filling contraction and expansion joints after epoxy coatings or sealers
Sometimes the contraction joints in a garage floor and the expansion joints around the perimeter of the floor can be very wide and collect a lot of dirt and debris. This can create an eyesore for some people plus make it more difficult to clean them out. The same can be said for the expansion joint between the driveway and garage floor.
You can always fill these joints in your garage floor after an epoxy coating is applied. It can also be done after clear sealers, stains, or other floor treatments are applied as well. Not before.
The easiest solution is to fill these joints with a self-leveling polyurethane joint sealer/filler. These are a 100% solids polyurethane which means that it will not shrink as it cures. They are gray in color and applied with a calking gun.
These type of joint fillers are inexpensive and can last for years. They also do an excellent job at sealing the joint from moisture. The material is flexible and somewhat spongy feeling after it cures, yet strong enough to drive vehicles over. Most are not paintable.
We personally like SikaFlex SL for these type of projects. You can find it at your local home improvement centers for less than $10 for a 10 oz. tube. The best deal is the 29 oz. tube, but you will need to purchase the larger caulking gun to use it. If a home improvement center isn’t nearby, you can also find SikaFlex here from Amazon.
This is a good example of how to fill and expansion joint when using foam backer rod
Prep of the joint is the same as before, however, do not use sand to fill up an expansion joint. Expansion joints need the material withing the joint to be compressible and sand is not. It can be used though if you are just applying a thin layer over old fiber board to prevent sealant from leaking through.
It is also extremely important that the concrete is bone dry before application or it will not adhere well. For expansion joints it’s important to remove any old filler using a utility knife or grinding wheel. If the joint is filled with fiber board or felt, be sure to remove any of the material in the joint that is protruding past the surface of the concrete.
If the fiber board in an expansion joint is missing or deteriorated, you will want to clean out the joint and use backer rod within the joint before you apply the joint sealer. Do not place it more than than 1/2″ deep.
Because these joint fillers are self-leveling, the viscosity is similar to honey. As a result, they will seek out any low spots along the joint. So be prepared ahead of time for any areas where the sealer/filler may want to run out of the joint.
Once applied, it skins over in an hour or two and completely cures within 3 to 5 days. You need to wait at least 24 hours before driving over a freshly filled joint.
Final points
Sealing and filling your contraction and expansion joints for a garage floor is not difficult. The key is to use the proper sealer or filler depending on the intended purpose and what type of joint it is.
Just remember that expansion joints should always be sealed and filled with a flexible joint sealer and never be epoxied or coated over. Contraction joints can be filled in the same manner after a coating or sealer is applied.
Nevertheless, if you want a seamless looking epoxy coating, contraction joints must be filled with a specialized epoxy or polyurea joint filler that cures hard, but has a high elongation rate for flexibility in order to prevent the garage floor coating from cracking at the joints.
Hi. Thank you for this great article. I do have a quick question. Any product available at home depot or lowes that can be used for “V” shaped contraction joints in my 2 garage car before I apply Rust-Oleum RockSolid Polycuramine? I would like to work on this project next weekend instead of waiting weeks for shipment on the products you recommended.
Also “V” shaped contractions have a crack right in the center. Will the product you mention take care of that as well when applied?
Hi Daniel. If you can find PC-Xtreme at Home Depot, then that will work. It has the right elongation numbers to work for a contraction joint. If you have a crack at the bottom of joint, then the joint is doing exactly as it should – encourage cracks in the joint and not across the slab. The joint filler will cover the crack without issue.
Is it safe to use degreaser cleaner or etch after PC-Xtreme has cured? Thank You!
Yes, it is Daniel. Degreasers and acid etch solutions have no impact. Make sure you grind the joints flush after application though. If you don’t, the filler will telegraph right through the coating. If you don’t grind it, you need to rough up the surface of the joint real good with 120 grit sandpaper or the coating will not stick to it.
So I am planning to use PC-Extreme before epoxy. Do I need to use a backer rod or sand below or just the PC-Extreme? I have a V shape expansion crack and filling before doing Rustoleum epoxy. Planning to do single coat of color epoxy and got 2 boxes of the clear coat. Was thinking of doing 1 single clear coat and then the 2nd with the rubberized texture. I also didn’t want to wait for the stuff to come in and though it was a lot more expensive. Hoping to get the same look with the PC Xxtreme and durability. Please let me know. Thanks
Hi Salman. PC-Xtreme is not recommended to fill contraction joints. If you intend to use it anyways, use the polyurea and not the epoxy. The epoxy will not flex and will crack if the bottom of the joint cracks. The polyurea, relative the to the epoxy, has a little bit of flex and may not crack. We recommend adding some clean silicone sand in the bottom half of the joint first. This will help to reduce the amount of PC-Xtreme that is used. Once it cures, grind the joint flush. Also, Rust-Oleum EpoxyShield epoxy is thin. One color coat is not going to be sufficient to keep such repairs from showing through the coating. You would be better with two color coats. What is the rubberized coating you are referring to?
Oh! I read in the above comments to Daniel that the PC Xtreme Polyurea was ok to use in the contraction joint. That was my plan but let me know if it’s not a good idea. With that I wanted to know if I do use it then is it smart to do silica sand or backer rod? If I use sand now much should it fill the joint? Also if I epoxy over it you believe it will show through? I have the tinted dark charcoal version of the epoxy from Rustoleum and plan to put that down and then a clear coat from rustoleum. I also used their patch and garage repair will that show through as well? For the additive it is the rustoleum rubber additive. Let me know if you suggest that or not on. My final coat. Lastly I used the floor maintainer and have degreased and tried everything under the sun to get a few spots out. Any suggestions as they are quite stubborn and have been delaying just bc I’m like maybe there is a way. Thinking my last resort may be the epoxy oil stop primer. Thanks for your help
Hi Salman. We don’t recommend PC-Xtreme at all. It’s the wrong product for the reasons we state in the article. There is not enough flex. We told Daniel that if he insists on using it anyway, then use the polyurea version. Backer rod does not work well in “V” joints, but can be used in saw cut joints. Clean silica sand can be used in either. You can fill the joint about 3/4 full unless you use a product that requires filling the joint all the way like this one here. It’s very important to grind the joints flush with the surrounding concrete if you want a seamless look. Thin coatings such as Rust-Oleum do not do a very good job at hiding the joint. You would need a minimum of two coats. If the grinding was not flush, it will still telegraph through. Sealing joints works best with higher solids commercial quality coatings.
Sprinkle some water drops on the spots you are having trouble with. If the concrete immediately turns darker and begins to absorb the water then you are good to go. However, if the water just sits there for a while or beads up, then you have more work to do.
Can you provide a link for the rubber additive or an exact description so that we can look it up? You are not referring to an anti-slip additive are you? If so, then you can mix that in with the final clear coat. FYI, it’s not rubber 🙂
Hi, I filled half of the the contraction joint with concrete (joint already had a crack) and now plan to level it up with DAP Flex concrete. Will this cause major issues in future? It is my Garage floor. I plan to paint the floor when it is all done.
Hi Andy. Contraction joints are supposed to have cracks in them. That is their purpose. They encourage cracking in the joint instead of across the floor. Did you use actual cement in the joint? If so, it will delaminate at some point and come loose. Regular cement does not adhere well and makes a poor repair product. If it was a polymer-modified cement patching compound, then that is OK.
Most of the DAP Flex products are an acrylic latex of some type. The problem with this is that latex shrinks over time. If your goal is to prevent water intrusion, then it is OK to use. However, if you are looking for a structural repair or something that can be ground smooth to provide a seamless surface, then it will not work. Paint can be applied to DAP, but not a true concrete coating such as epoxy, polyurea, and etc.
I have aggregate slab flooring with a 2×4 trench separating the slabs. We have dug out all the rotted wood separators and need to fill the trenches. What do you recommend?
What are you planning to do with the floor, Niki?
It is a floor under a screen porch.
We are going to lay down some carpet over ir
OK, if you are just going to install carpet over it then you can use a self-leveling floor underlayment. Your local home improvement stores carry it. There are many videos available on how it works. It’s actually very easy. You mix up the product and pour it into the joint. Just make sure that the ends of the joint are properly dammed up so the material does not flow out.
Hi. Should I use the same product to fill in cracks and the expansion joint? Or a separate product? I plan on grinding after the repairs? Thank you, Shawn
Hi Shawn. Do you want to fill expansion joints or contraction joints? There is a difference in the type of material to use. Also, are your intentions to apply a coating or something else?
I’m sealing the concrete around my pool and it has several expansion joints. Should I tape off the joints before applying the Concrete sealant. This seems to be what your Saying but I want to be sure before my “do it yourselfer” endeavor. Thanks for your advice.
Hi Sandra. If the joints have filler in them then we recommend taping them off so that you don’t take the chance of the sealer discoloring the filler. However, if you need to refill those joints after application of the sealer, then there is no need to tape them off.
The expansion joints are in good shape so I’ll do tape off before I begin. Thank you for sharing your expertise v
Great article. Plan on filling the contraction joints, grinding, then epoxy sealer.
Questions: Do you recommend using a small amount of sand at the bottom of the contraction/expansion joints to minimize bleed through of filler at the bottom of the joint?
What product do you recommend to complete a nice coving at the right angles of the garage floor?
Hi Greg. Yes, a little bit of sand at the bottom of the joint is OK to use. It will also help to reduce the amount of material used. For the perimeter expansion joints around the slab, we recommend using a self-leveling polyurethane sealer such as SikaFlex or similar. You want to apply that after the coating is applied and cured.
Is it ok to leave the contraction joints unfilled and then use the polyurea coating right over it? Im assuming i’ll need to use a paint brush to get into the joints, but is there any other tips when leaving the contraction joints unfilled?
Hello Ryan. You have the right idea. It’s actually more common not to fill them. Run the roller just over the joints and use a chip brush to run the excess across the bottom of the joints. You will get the hang of it real quick. As long as they get coated like the rest of the floor, they will be fine.
Hello, it says in the Rock Solid instructions not to go over the joints. Do they just mean not to fill them flush or with the excess product? If you use a chip brush to remove the excess, cracking shouldn’t be an issue, correct? Thanks for your time and great advice.
Hi Andrew. What they mean is that you can’t fill the joints full/flush with RockSolid. You would need to fill the joints with the proper filler first if you wanted to create a seamless look. You can run RockSolid down into the joints though and it’s recommended. Using a chip brush works great. If they are the troweled “V” shaped joints, random color flakes will fall in them as well. The cracks that typically run down the center of contraction joints are not an issue.
Very informative article, thanks for the share. I plan on filling my expansion joint at the entrance of my driveway, I’ve got my backer rods on hand, along w/ the polyur caulk. I’ve seen a few videos of people applying sand over the caulking while it’s wet and sticky to hide any imperfections and to leave a more attractive finish. If only applied on top for cosmetics, will this prevent the expansion of the slabs? What type of sand should be used for this: fine sand, joint sand, or a playground sand? Also, should you caulk the joint all the way to the top or leave some space?
Hi Deniz. No, the sand sprinkled on top will not affect the expansion or contraction of the joints. You should use clean silica sand or play sand. You always want to fill the joint to the top if your goal is to prevent it from being a dirt trap.
I appreciate the quick feedback. Ok, so I’ll use the play sand as it comes a lot cheaper than silica. Should I wait to apply the sand or do it immediately after caulking? Not sure how long the caulk will be wet and sticky. Also, how should it be applied? Should I pour on a nice layer and have it sit there for a few hours before blowing away the extras?
I also have a question about the v joints on my driveway. They have some cracks in them as they should. I’m noticing ants traveling back and forth in them and I’d like to seal those cracks. Will just a thin layer of a polyurethane caulk do the trick on this one? I wouldn’t want to fill all the way to the top. And what are your thoughts on Trim-a-slab for filling joints? I’ve heard mixed reviews.
As soon as you fill the joint, go back and apply the sand before the surface of the sealer can skin over. Let the sand sit on for a day before sweeping it off and don’t drive over it for 48 hours. I wouldn’t worry about ants. A sealer won’t stop them and they will still use the bottom of the joint or some other path to travel. Not the biggest fan of Trim-A-Slab, but it can work fairly well for some expansion joints. It won’t well for troweled “V” joints though. That type of joint is a contraction joint and not and expansion joint which separates two slabs or concrete structures.
What product would be used to fill the cracks but will stand up to welding slag?
Hi Richard. There isn’t a product that will not get burned if hot slag settles on it. It won’t affect the integrity of the material, just the cosmetics.
I have a local builder concreting me a very large and very smooth floor fo my garage in 2 weeks time. I don’t think he is planning on have any expansion joints as this will make getting such a large slab really smooth(with a helicopter) really difficult.
Could we cut expansion joints in the next day and fill them after a couple of weeks or so with an appropriate rubber fill? The floor will be 14m by 8m (45’11” x 26’2″) and another with underfloor heating pipes done the same day will be 8m by 8m ( 26’x26′). Both will have steel mesh reinforcement and be 15cm (6″) thick.
Hi Steven. Ideally you want to get the cuts done as soon as you can get the saw cutter on the slab. Many times the next day is too late and you will already have cracks starting to develop. Once the cuts are done, you can fill them with the appropriate material after the slab has cured.
Would a cut of 1/4″ wide be sufficient? How often should I put cuts?
Hello Steven. Saw cuts should be 1/8″ wide and 25% the depth of the slab. Joint spacing can range from 10-18 feet. Cuts are typically started at the center of column lines, but not always. This is when it is important to get with your concrete contractor to discuss beforehand. Inside corners typically have cuts that run to the corners as these areas are more prone to surface cracking during the cure. This link here has excellent information on new slabs. It’s from a professional with decades of concrete contracting experience. Scroll down to the section on “Crack Control” and you can get some additional information.
Fab, thanks mate,
I just want to fill the joint that goes under the garage door to keep bugs and water out what should I use for that? Would a Self-Leveling Concrete Sealant work, it would only be about 6-8 inches long
Hello Jay. Are you referring to the expansion joint that is between the garage slab and driveway? If so, you can use a self-leveling polyurethane sealant such as SikaFlex to fill the joint.
just the part of the joint in two areas that come from the garage floor goes under the garage door out to driveway. It leaves a small dap under the door, have seen bugs and water come under it at times
Those sound like contraction joints, Jay. You can use the same product for those. You should be able to easily find it at your local home improvement center or hardware store.
Thanks so much
Best article I have read So far and answered all my Questions. Thank You! I spent hours until i found you.
We are glad you found us as well, James. Good luck!
Great site Shea, what a wealth of information. Thank you!
I am in the process of prepping my unsealed 6 year old triple garage. Will be applying 4 x 21/2 car Rocksolid Polycuramine gray kits and then Rocksolid clear coat. I have degreased, washed, filled a few hairline cracks and ground (diamabrush) the floor, applied Drylok to the stemp wall. I am currently filling the contraction (+) joints with PC Xtreme joint filler that I filled with a touch of silica sand prior. Unfortunately, I used up my 4 -9oz tubes and have 2 more on order to finish up (lesson learned). I have noticed that the filler in a few spots sagged ‘slightly below the concrete level line and I am wondering if I can re-fill more on top of the pc xtreme product on a second pass or should I leave it? I still have to lightly sand with 120grit before I apply the rocksolid over top of it all. After all this is done, I will be filling the Expantion joints with Sikaflex sl.
Hi John. Yes, you can apply more PC Xtreme if it’s been less than 24 hours since applied. If it’s been longer than that, just sand the top with some 120 grit sandpaper first. It’s not uncommon for settling as the filler finds nooks, crannies, and small cracks to fill in. Sometimes it take longer for the sand to absorb it. Just keep in mind that if you don’t grind those joints flush with the concrete, their location will telegraph through the coating because the surface is not flush like the rest of the floor.
It sounds like you have enough RockSolid for two color coats. This is good because the first coat is going to get absorbed by the concrete due to the grinding and it will not look good. It will act like the primer coat. The second coat will bring nice even color and gloss. I suggest you read this tip about ensuring even color when using more than one kit for one coat. It won’t be necessary for the first coat, but we recommend it for the second.
Thanks Shea! I have to wait for the last 2 tubes to arrive on Friday so I will sand it down and do the 2nd coat all at once at the end. I used a good 4″ scraping knife to trim excess but maybe I will sand w/120grit instead to a smooth flush to concrete. Then do a good sweep/rinse again, let dry for 2 days and then epoxy the 3 coats over a couple days.
Yes, I planned on mixing part A & B’s for the 2nd flake coat.
Is it okay if I plan to use 2 kits Rocksolid clear coat ( over total 900 sq ft) and is it okay to add 1 more kit spread over entire floor for a 2nd
and final skim clear coat?
The two kits of clear for one coat is fine, John. However, you can’t do 1 kit for that many square feet. Coatings should never be stretched. It’s imperative to stay withing the coverage rates.
Great article. I have a slightly different scenario I’m hoping you can help me with. The floor I’m dealing with is in my basement. I had previously used it Rust-Oleum 203007 Epoxy Shield to paint the floor including the contraction joints. I’m now looking to convet the room to a family room and plan to lay down laminate flooring, so I need to fill in those contraction joints. Is there something you’d recommend in this scenario that would work over the previously applied epoxy? (Wish I had read this article years ago and flattened the contraction joints before the epoxy
Hello Kyle. If you are applying a firm, free-floating laminate flooring, then you don’t need to fill the contraction joints at all. However, if it’s a flexible laminate that is glued down, then you will want to fill the joints. Purchase some 60 grit foam sanding blocks from you local home improvement center to degloss the finish in the joints. You can then use one of the fillers we recommend in the article.
Thanks for all the great information! When my basement was originally pored, a 15″x15″x2″ deep recession was molded in the floor for supports. The supports are standard 4″ metal supports in the middle of the recession. I’d like the floor to be level all the way to the metal support. Can I fill in these molded recessions with concrete (or some other material?) so that the floor is level right up to the metal support?
The rest of the concrete is sealed and my eventual plan is to grind, stain, and clear coat the floor.
Hi Eric. Yes, you can do that. You will want to use a polymer-modified cement/repair product. Not standard cement. Do not use an overlay or self-leveling underlayment. RapidSet Cement All is a good example. It can be used for applications up to 4″ thick.
Shea-you have a great site here! I want to fill my floor saw cuts prior to coating with epoxy. Looking at Garage Flooring TL829. I have already ground my floor and was wanting to go with a polyurea you can shave off flush with a razor. Have you heard anything on this product? Much thanks.
Dave
Hi Dave. Yes, Garage Flooring LLC has been using TL829 with great success for their customers. The one issue with filling joints and then shaving off the excess though is that the joint outline/shape can still telegraph through the coating somewhat depending on the joint. If they are saw cut joints, then generally you will be fine. However, if they are “V” shaped troweled joints, then those tend to still show. The reason is that the edge of the “V” shaped joints tend to curl up ever so slightly during the concrete curing process. Even though the joint is filled, the shape can still be seen or recognized through the coating. We recommend grinding these type of joints flush with the rest of the surface. Just double check with them that TL829 can be ground flush once it cures if you want a truly seamless look with “V” shaped joints.
Luckily I have 3/16” wide saw cut joints. Planning to put silica sand in them up to about 1/4” from the top.
Don’t know exactly what the consistency will be but maybe I can use grout bags or squeeze bottles to get product in the joints. Thanks
I have used a product from Lowes called SLAB for my V control joints. Can I Rocksolid over those then apply an after coat of that product. I wasn’t looking for a complete smooth top finish.
Hi Robin. No, you don’t want to coat over that product. Though it is paintable, it’s a latex acrylic caulk. This means that it is soft and it will shrink over time. “V” shaped joints are wide and deep. If you were to coat over this product, any heavy object that rolls over or presses down on the “V” joint will cause the caulk to flex and the coating will crack. In addition, if the caulk eventually shrinks, it can create voids under the coating that can create cracking issues as well. Since you already filled the joints, we recommend taping them off when applying the coating. Either that or dig it all out and apply the proper joint filler.
I have a sub coming over in a day to do the profiling on really great shape 20 yr old concrete. Not sure what I should do about these V joints. There pretty good size 3/8 to 1/2 at the bottom V bullnosed troweled. Would like to get something in them before they profile but am limited to Lowes and HD by location for good product without ordering. Any suggestions.
Unfortunately, neither stores carry the type of product you need. Home improvement centers are not the best place to get all the products you need for quality coatings. You can check if they have a polyurea or polyurethane crack repair product – not epoxy. They need to be the 2-part repair products with the special tip that mixes from the tube. Don’t use epoxy since it does not flex at all. The other two may provide just enough flex, but it’s a gamble. Plus, it’s going to require a few tubes or more to fill the joints. You may just want to consider leaving the joints as is. FYI, if you are profiling via grinding, you will definitely need the second RockSolid kit.
Hello I applied a sealer on my outside concrete driveway before I caulked the joints. Before I caulk do I need to sand the joints before applying the self leveling caulk and if so how do I do that without buying expensive equipment.
Hi Christine. No sanding or additional prep is necessary. Just make sure that the surface is clean and dry.
Hi
I am planning a large shop with a 16 foot door opening. The floor will be radiant heat. so i want to thermally break the outside concrete under the door to the inside concrete. if i place a 2″ foam insolation panel into the concrete in between the outside concrete and inside concrete (across the door threshold) will this product fill that large of a gap (2″)? Also will it hold up to tracked vehicles or heavy machines driving over it?
Hi Kevin. Which product exactly are you asking about?
SikaFlex
Standard SikaFlex can only be used on joints up to 1.5″ wide, Kevin. We recommend that you give their Customer Service line a call. They should have a procedure and product recommendation for a joint that wide. You can find their info here.
Very informative article and links. I have follow up DIY application questions and would appreciate your recommendations based on brutal AZ heat conditions.
Project 1
I removed rotted out expansion joint board from driveway (1/2” thick near garage door and length of driveway and about 3/4” along the base) but I am conflicted on whether I should replace it with the same material (I cant find any info on this, is there a reason why) or follow your backer rod method to seal EJ? Would you recommend Tremco Dymonic FC?
Project 2
Extended our back porch this summer with a 600sqft concrete slab that has troweled CJ’s. Want to paint our slab to match our pool decking (troweled “V” joints but doesnt look like they were ever filled with sealant, just painted over) and don’t even know where to start with this project. Can we just paint the slab with pool decking as is or should we seal it first? Would you recommend us opening up the CJs with a diamond blade crack chaser or can we leave it as a thin troweled joint? Pros/cons? Why use v? Do i need to round out the check edges to avoid chipping? Do I fill the control joint with a little sand, fill with Tremco Dymonic FC and then paint over it? If so, should it be flush with the concrete or should we leave the appearance of a joint? Why/why not?
Thanks!
Hi Linda. Tremco Dymonic FC would work fine for Project 1. Just pay close attention to the instructions in regards to how deep the backer rod needs to be compared to the width of the joint.
For Project 2, do not apply a sealer. Pool decking paint will not adhere if a sealer is applied. In addition, the pool decking paint should seal the concrete anyway. Just check with the product you plan too use. Leave the contraction joints as is. Contractions joints are either troweled in place during the finishing process (V shape) or they are saw cut as soon as you can walk on the slab. “V” shaped joints for patios and walkways are visually more appealing than saw cut joints. If you want to fill the joints, do so after the concrete is painted and then fill the joint with a colored joint sealer to match or to add contrast. Not all joint sealers will accept paint and the one that do sometimes have issues will peeling when applied to wear surfaces.
I have contraction joints in my garage floor (cut with a saw) – with cracks in the bottom (like they should). I am just painting the floor with a 1-part epoxy (to make it look better), but was interested in filling the cracks at the bottom of my contraction joints – just to keep bugs and moisture out. I have a product called *Rapid Set Self-Leveling Sealant (Hybrid Silane Polyether)* Should I apply the 1-part epoxy paint first, and then run a small bead over the cracks, or do it before I apply the epoxy?
Hi Matt. The Rapid Set is paintable so you can do it either way. Something to consider is that sometimes the color of the filler can bleed through and be noticeable if you paint over it. If your joints are an inch deep we recommend filling them about 2/3 of the way with clean silica sand first. This will reduce the amount of filler required as well as the possibility of bubbles forming as it sinks down into the joint.
Thanks Shea.
And I assume your recommendation would be the same if I used Sikaflex SL instead of RapidSet?
That’s correct, Matt. However, we do know that Sika will discolor paint and coatings if painted over. Not sure about Rapid Set though.
Thank you very much for your informative article on finishes. Just wanted to suggest a correction to your background information on the cracks. Concrete slabs on grade do not crack due to changes in temperature. At least not with any significance. Rather they crack due to the concrete shrinking as it cures. These cracks are called shrinkage cracks and that is why control joints are used. Typically once the concrete is fully cured and there is no more hydration occurring, the slab will no longer move. You can even design a slab to use no control joints, but that typically takes special concrete and reinforcing details. Now heavy loads (such as fork lift traffic) can cause slabs to curl, but that is a result of the design of the slab.
Thanks for the info CJ. Everything you have stated is on point. We can probably word it a bit better since we know that temperature swings will not cause a cured slab to crack across the surface. However, the reason we mention further cracking within contraction joints is because we have been witness to and spoken with many coating contractors that have witnessed coatings that have cracked over filled contraction joints when the wrong material has been used. There obviously is some type of stress or movement going on after the fact to create the new cracks within these joints that telegraph through to the coating.
I will be completing an epoxy floor in my garage and would like the seamless finish. I plan on filling the contraction joints with one of the products you mention above. I would also like to fill the contraction joints on the sides before epoxy, but I thought I read some conflicting information above that said you shouldn’t fill expansion joints and the epoxy of them. Did I read that incorrectly? Based on your experience, what is the very best products to use to 1) Fill V shaped contraction joints before epoxying over them, 2) Beat product to use to fill expansion joints on the sides before epoxying. On one side of the garage I have a 2ft stem wall and wanted to do a solid transition from the floor to wall over the expansion joint (Almost likes a mini U shape cover from floor to wall). Any suggestions? Your information is very helpful and much appreciated. Thanks.
Hi Evan. That is correct. You should not fill an expansion joint and then epoxy over it. There is too much movement in that joint and the coating will crack. Unlike contraction joints, expansion joints separate two different concrete structures. The joint is required to allow for the expansion and contraction of those adjacent concrete structures so that contact cannot occur and cause cosmetic or possible structural damage. However, you can fill the joint with a flexible concrete sealant. Some are available in colors other than gray. When coating a stem wall like the floor (particularly with heavy color flakes) and you run the coating over the edge of the joint, the joint has a tendency to disappear or be less noticeable. We would recommend doing that first and then decide if you want to fill it. Sometimes a contrasting joint color is a nice accent.
Our favorite product for filling contraction joints as well as cracks and small pits is a product called Xtreme Set 100 by Legacy Industrial. You can read about it here. It has just enough flex to work in contraction joints.
I’m not painting or epoxying but am putting a floor tile system (Swisstrax) over my garage floor. Live in Denver and was told that because of expansive soils here, I should not let water seep down into the v-grooves segmenting the garage floor. The floor tile systems let water through to the floor when you’ve got snow under the wheel wells that melts in the garage. The garage floor is sloped to the garage door so water flows towards down the v-grooves towards the garage door and collects in the v-grooves nearest the door.
What product(s) would I use to “seal” the V-groove tracks to lessen the water seeping down through the cracks at the bottom?
Thanks for such great advice!
Hi Ed. Use a self-leveling polyurethane sealant such as SikaFlex. You can easily find it or similar at your local home improvement center. The only prep necessary is to make sure the joint is clean.
Thank you, Shea! Much appreciated!