How to Install Polystick MTS Plus Underlayment

Types of Underlayments on the Market

In this video, I’m gonna show you how to install a self-adhered underlayment under your tile roof.

Underlayment is an extremely important part of a tile roof system. It actually keeps out a lot of the water as tile roofs tend to actually let water in. Tile both absorbs water and can get in through the cracks and crevices. So a good quality tile roof means the best of all underlayments on the market. What we like to use is a material by Polyglass, it’s called Polystick MTS Plus. There are similar products on the market. We’ve tested a few and looked into the warranties, we believe the MTS Plus is a great system. And you can do this by installing either one layer or two, that’s up to you. The one layer of MTS Plus provides a 20-year warranty, when two layers actually provides you a 30-year warranty and double the protection. The nice thing about self-adhered underlayment, that it adheres to flashing and it also self-seals around nails, so even if water gets in under your tiles, your roof is not gonna leak.

The general concept of any tile roof underlayment is, you wanna make sure that the underlayment itself is waterproof and done in such a way where even if water were to get on the underlayment without any tiles, you would have zero leaks. Let’s get into it and let me show you how to properly install the MTS Plus.

Install Drip Edge First

The first thing we wanna do prior to installing our underlayment is install our drip edge at the eaves. Now, if you’re installing two layers of MTS Plus, if you’re installing two layers of self-adhered underlayment, what I’d like to do is first install the first layer prior to installing any flashings, then install the second layer with flashings. Now, in this case, we’re just gonna be installing one layer of the self-adhered underlayment, so we’re gonna install our drip edge first. I’m not gonna show you how to install a full piece, you can watch our other videos how to do that. It’s standard installation processes, nailing every 10-12 inches on center and calling it a day. I also like to use a wider drip edge, so a 2 X 4 is what I like. 2 inches looks nice and slick on the front side, 4 inches gives you nice wide area so we can have our self-adhered and then you get a nice bond to it. As always we’re gonna be installing this again 12 inches, on the center using the 3/8-inch diameter hot dip galvanized nails.

Now, prior to installing our underlayment, what we wanna do is actually prime our drip edge with an asphalt primer so we get good adhesion. You can do without it really, but giving it a nice light coat of asphalt primer is gonna make sure you have great bondage and it’s really gonna protect your eaves. And on tile it’s extremely important ’cause once we install our bird stop or a tile riser, that’s gonna block water from coming all the way down the roof. So you wanna make sure that this gets a good bond.

Install Layer of Underlayment Around Chimneys, Skylights and Penetrations

Now, prior to installing your entire field of underlayment, another thing we wanna do is go through all our penetrations whether that’s a chimney, a skylight, or a dormer, a roof-to-wall joint, and install one layer of the self-adhered underlayment on it and we’re gonna cut it at a diagonal at an angle prior to installing our primary field. This is gonna make sure that these corners are protected and that we’re overlapping properly. I think once we install it, it’ll make a lot more sense.

On this first layer, what we wanna do is cut up at a 45-degree angle up towards this top slope of the roof. That’s gonna allow us to bend this over. Then our second layer then we come, we’re gonna cut it at an angle going down to make sure that this corner is protected here. And now that we’ve got this cut and aligned, you wanna hold it in place and just remove your adhesive backing, then slowly slide this in place. It’s easier done with two people to make sure that you get a nice tight seam and it’s properly aligned. And in the corners, you can fold them in. Then once you’ve got the top in place, it’s super easy, just lift the bottom half, remove your film and let it drop. You kinda wanna smooth it out with your hands to make sure that you don’t have any wrinkles.

So we’ve got this in place, again, this could be a skylight, it can be a chimney, it can be a dormer, whatever it is, as long as it’s a wall, that’s what we wanna do. Cut it at a corner, coming up. Then our next piece, we’re gonna come and overlap it and we’re gonna have a super tight seal right here.

Install the First Row of Self-Adhered Underlayment

Alright, once your asphalt primer is dry, you can install your first row of underlayment. The way we we like to do it throw it on there, align it. Do not remove any of the self-adhered lining right here. You first wanna align it in place. And what we wanna do is bring it about a 1/4 to 1/2 inch up from your drip edge. You don’t want it coming out ’cause it’s gonna look ugly from the bottom and with 4 inches, you’ve got plenty of room to grab onto, so do it a 1/2 inch, I would recommend up from your drip edge, align it. And what we like to do is just install one or two nails to help keep it aligned while we remove the film from behind it.

Now that we’ve got our piece tacked, relatively aligned and our corner installed already, what we wanna do is make the cuts for this area. Now, we call these our end-laps, anytime two ends of a roll are meeting. On our end-laps, we want to have a minimum of 10-12 inches overlap, more is always better. So right here, we’ve got 24 inches, that’s definitely okay, it’s preferred, but just don’t go any less than 10-12 inches.

Now you can see what we’ve done here. The first layer we’re cutting up at a 45 degree angle, and the second layer we’re cutting down at a 45 degree angle so that this corner is fully protected and there’s no way water can get in here. What we’re gonna do is just remove our adhesive backing. Now you can see what Marco’s doing, is keeping it in place and just tucking it underneath it. That way it stays aligned and all you do then is just remove that film and you have a nice tight bond right there. So we’ve got our bottom pulled out already. At this point, you can really just pop this nail off and get going on your top half. You remove it and you can always just roll it in to place and do the same thing. Just pull the film out from underneath it.

When to Use Asphalt Primer for Your Underlayment

Now, one last thing I wanna show you on these details, on these corners. Anytime you have an overlap that is crucial and critical, we always recommend installing and priming it with an asphalt primer. That’s just always gonna help with adhesion. Even though without it, this stuff is super tacky. You can see it’s sticking out my fingers right here, look at that. But even with the fact that it’s so tacky, installing an asphalt primer is just gonna make it really grip and especially on corners like this it’s super important, it’s one quick step that’ll make this job nice and tight. Now again, you can do this on all your end-laps, but I really recommend doing it on your vulnerable corners.

Now once the asphalt primer is dry, you can just roll this on. You wanna be super careful to lay this down properly ’cause it is extremely tacky. Now, another thing you can do using a silicone roller or a rubber roller is work these details in. This really helps, especially if it’s on a colder day, to get a nice tight bond here. Generally on hotter days and warmer days, you don’t need this, but on days that are colder, definitely, it doesn’t hurt.

Layering the Next Row of Underlayment

I wanna show you how to install this side-lap. So, an end-lap is where two ends meet. Now, this lap right here is gonna be continuous along the length of this underlayment, and you can see here, what this underlayment has is a two, three-inch strip of black film, and this is essentially what you’re gonna use as your line. You can go a little bit past this, and this is really gonna provide a great adhesion. No need to prime this, this is already made to just really bond real tight and real fast, regardless of the weather.

You just really wanna make sure that you’re holding the your line because if it gets tacked and adhered in the wrong position, it’s gonna be very difficult to later shift. So once that’s off, we just kind of just slightly push it in place. And I wanna show you right here, you can see in just a matter of like 10 seconds, how difficult it is to pull off. You can imagine, once the sun heats this up a little bit more and it gets really melted in and heated up, it’s not gonna come apart regardless of what you do.

How to Install Self Adhered Underlayment And Flashings Around Pipes

Now that we’ve got our base layer installed, what we actually wanna do is install a piece of pipe flashing around these pipes. We wanna do that around all our penetrations and we’ll show that in further videos, whether it’s a T-top, a dormer vent, or any other type of penetration in our field. Essentially, the idea is that our underlayment needs to be a 100% waterproof, so if we were not to install tile on our underlayment, we would still not have any leaks regardless of how strong of a rain we had. So, the way we wanna do it is first off, just install this pipe flashing. Now we wanna nail it, we’re gonna be nailing it just like any other flashing, using 3/8-inch galvanized nails. We don’t wanna put any nails on the bottom side here. Now, we’re still not done with this process. What we wanna do is actually install a piece of underlayment on top of this in order to make sure that there’s no water that comes in on this top edge right here. You can see, if water were to come and roll down here, it would get underneath here and cause a leak. So we wanna install a piece right here before installing our top layer, to make sure that this is a 100% waterproof. So Marco has already cut this out for us and the width of it is not as crucial.

Now, before we actually install this, what we wanna do is prime our metal. I’m not gonna fully prime it but you’re pretty much using an asphalt primer both on your flashing and on your underlayment. You can also do it on your wood deck. What this does is really provides a very solid bond between your self-adhered underlayment and your flashing. Alright, now that the primer is dried, we are ready to install the second piece of flashing, we just wanna align it on top and now start cutting out the opening.

Alright, you can see how Marco cut it, he made it wider than the actual pipe flashing itself. There’s two reasons for this. Number one, is to allow water to properly flow and give a path for the water to come down. Second of all, once we install our tile, our tile is not gonna be butted up tight against this. It’s gonna be set back a little bit so that once we have our tile, it’s not gonna be visible from an exterior. So, we have this cut already, we just have to remove our adhesive backing. Here we go. With just a few seconds, I’m already having a hard time pulling this off. So, again, once the sun heats this up, this is gonna be solid, definitely not gonna leak. And with this piece of underlayment installed there’s no way this pipe is gonna leak, even if you don’t have tiles installed, this is gonna be completely waterproof.