Block Sanding Primer Dos and Don ts Transcript

Block Sanding Primer Dos and Don ts Transcript Hey, this is Donnie Smith. And welcome to this lesson on block sanding primer. In this lesson, we're going to give you some of the do's and some of the don ts when it comes to block sanding your primer. Now, I'm sure the goal that any of us have when it comes to the end result, the finished product, once it's been painted, is for it to have that flawless look, that show-quality paint job look. A lot of it comes from your body work. How well did you block your body work out and how smooth and level did you get it? But block sanding your primer also plays a big role in how straight of a finished product you're going to have. Now, in the last video in this series, we left off-- we had sprayed some epoxy primer. And then we applied some primer surfacer. And now, it's ready to block. Now, let me give you a little tip. We've already got the car all masked off. So let's leave it masked. Now, I know in some production shops or in your certain situation, you may not always be able to leave the car where it's at until you're done priming. But if possible, leave it masked off. Even leave the plastic over it, if possible. Remove just what plastic you can to move the car. Maybe take the plastic off and move it out of the spray booth or the prep station, because the goal here is to do everything with the least amount of effort. We want to do things right, but why work harder if you don't have to? Now, at this point, we may have a good idea-- especially if you're experienced, you may have a good idea that this is going to take one block and you're done. And that may be a different story. But let's assume that we're not sure. We're going to block it out to see if we're going to have to prime and block again. If you should have to prime again, it's ready to go. You clean it up and you can spray more primer. So leaving it masked off during your primer stages is going to save you time. Now, when you go to paint, obviously, you re going to have to take all that off, wash it, and clean it so you don't get a lot of dirt in your paint job. But for now, leave it masked off. And the second tip I want to give you is using guide coat. Don't be afraid to use guide coat or think that you're too good to use guide coat. I still use guide coat, and I know there's a lot of people that have been doing this for years and years that use it. However, I know there's some people out there that don't think that they need it anymore. And maybe some don't. But I would recommend going ahead and using it. It's a tool to help you to make your job easier. Remember, to do this with the least effort and using what tools you have available is going to make your job much easier. Now, what guide coat is--that's a spray or dry powder form that goes on the surface. And it's a contrasting color. Usually, your primers are light, so your guide coat's going to be

dark, usually black. And you put that on there. So if there's any pin holes, scratches, or minor lows, that guide code is going to stay in that area, and that way, you know there's a problem there. There's a small low. You see a line of guide coat, you know that's a scratch that you're going to have to do something with. I recommend using guide coat during the priming and even some of the body filler stages. Now, let me give you a tip of not to do-- a don't. And I've seen this a lot. You see an area that has guide code and in your mind, you think the objective is to remove all the guide coat, sand all the guide coat off, which it is. But if there's some guide coat left and it's not sanding out don't sit there and dig the block into it. I've seen that time after time, where you're sanding on a fender or something like that and you tip the block on the edge just to get that guide coat out. Well, that defeats the whole purpose. You might as well not even guide coat, because it's not doing you any good. Now, when given the block level, it may sand out before you sand through the primer. Or it may require that you have to prime and block again. Now, guide coat comes in two forms. They have the spray that you can use. It comes in an aerosol can. And they also have a dry form. And if I'm doing a hell damaged job or a real big area, I've even mixed some in a paint gun and sprayed the entire area. But there is a trick if you're going to mix it up in the spray gun to spray. You don't really want to use any type of enamel or base coat or anything like that, because it stays tacky. And it's just going to clog up your sandpaper. If you're using a spray gun on a large area, I recommend some type of-- if you can find-- old lacquer primer. That works really good, because it dries and it doesn't really gum up your sandpaper like paints do. I know they make black lacquer primers. That would work good. I would over thin it and guide coat the whole area. You just want to mist it on there. You don't want it on too heavy. Now, with that said, I know there's some of us out there that tries to save money. The guide coat's a little bit expensive, so we go to Walmart and get that $0.99 spray can paint thinking we're saving money. And I used to do the same thing. I'm guilty of it myself. But if you'll notice, whenever you go to sanding that, it just gums your paper up. You sand twice as long, go through twice as much sandpaper. But when you have a big area, really, you don't want to spend all that money on sandpaper and all at time blocking that area. So I really don't recommend using that cheap spray paint as a guide coat. It does the job. It definitely will identify the lows. It works like a guide coat. But it sure does gum up your paper, cost you more sandpaper and a lot of extra effort and time. Now, let's talk about what grit of sandpaper you use. Now, this is going to kind of depend--are you going to have to prime it again or not? Sometimes, you may not know. If you do it often, you kind of know.

My body work is kind of a little bit rough. I think I'm going to have to prime and block it two times. And sometimes, it may even take three. And with time, as you get better, more experience, it gets to the point where usually, you're going to prime and block it one time. If you know your body work's just going to need prime and blocked one time, I would start out sanding with 320 grit paper. You can do that dry or wet. But I do recommend blocking your primer by hand. Now, you can use a DA, and there are systems out there for that. And your production shops may use DAs for blocking primer. But I'm still a little old fashioned in that sense, and I like to hand block the primer, especially if you're a restoration person out there wanting that show quality job. You're definitely going to have to block that out by hand. Now, if I'm not sure or I think it's probably going to take another prime and block, I won't spend my time blocking it with 320. I'll go ahead and drop down to 220, which is a little bit coarser. It's going to block it a little bit faster. Then you can block it out. And once you're done blocking, you're ready to prime again. And then you can block again with 320. Now, what if we block it out with 220 and it blocks out perfect? Do I have to prime it again? Not necessarily. If it blocks out perfect with 220, go ahead and go over the surface with 320 to remove those 220 grit scratches. And then to final sand it, you need to go over that area again with 500 grit to remove the 320 grit scratches. So if you're a beginner, this is what I'd recommend. I would block it out with 220. If it blocks out fine no problems, you hadn't sanded through the primer anywhere, go ahead and switch to 320. Then block it out with 320. And then final sand it with the 500. That's what I'd do. That's somewhere to start. As you become more familiar with this, you'll learn your body work and know if it's going to need one or two times of priming and blocking. If you know it's just going to need one time, you can eliminate or skip the 220 grit stage. Now, let's talk about selecting the right block to block sand. We know what grit to use, but what kind of block do we use? We were at the lake the other day, and it was a little windy. Jake, my son, he was dying to ski. So he wanted to get out there and ski one afternoon. So we went out there, but it was a little bit rough. As my boat hit those waves - and it kind of bounces around a little bit. He was able to ski, but it sure did wear him out. So when it comes to blocking, think of a boat in water. The reason for this story is to explain how a small boat is going to follow the wave patterns. And that's kind of like blocking whenever you're blocking. If you've got a low area, your block's gong to dip down with it. It'll sand the guide put out because it's following that shape. Now, if you've got a bigger boat, you've got little waves, it's not going to affect it as bad. And just like with blocking, if you've got a small low area

right here, that block's not going to dip down in there. It's going to go straight over that low area. And that will help to identify that low area and not just block the guide coat out. So when blocking, use as long block as possible. Now, this is a little bit exaggerated, but use a longer block whenever selecting the block. You may be thinking, I've already done my body work. I did a good job on that. Why am I worried about lows at this point? Well, there are still going to be some imperfections, no matter how well you do your body work. Even a feather edge area-- that's one of those real gradual dips. You see the rings. You may not be able to fill it too good, but if your block follow that pattern where it goes down--you look at the side of the car. You have that finished product, looks great. But you can look down the side of it. You can just see that little wave in there. And that's really something none of us want. We want that perfect, smooth, straight look-- that show quality job that we've talked about. So to do that, use a long block. Now, talking about selecting blocks in boats in the water, it wouldn't make any sense-- obviously, we're not going to go get a cruise ship and put it in a lake like we have here. It wouldn't fit. So a long block is not going to fit every area that you're sanding. So you're going to have to select the right block. So if you're setting on curved areas, by body lines, small areas that you can't get a big block to, obviously, it's going to take different blocks. So it's good to have an assortment of blocks that fit the shape that you're working on. But with that mind, whatever area it is, use the biggest block that you can that will fit-- fits the contour, fits the shape, and fits the surface that you're blocking out. Now, the purpose of blocking is to sand down all imperfections. So if you just try hand sanding it, again, your hand is going to follow all those waves and patterns. So try to eliminate using your hand. There may be a few areas you have to, or they make some flexible blocks that will get those areas. But in general, use a hard block that's not going to follow any of the patterns or contours that's in the surface. Another question I've been asked when blocking-- how do I know when to stop? Well, that's a good question. But if you use your guide coat, you know when to stop, because the point is to sand all the guide coat off, without dipping your block in it, of course. But if all the guide coat sand's off, you're good to go. You're good to switch to 320 if you're using 220, or you're ready to final sand that area with 500. Now, if you still have some high areas, if you sand through your primer and you start hitting your body filler or your metal that is another indication that you need to stop. Once you get your metal, it's not going to sand down any further. You're just going to start sanding the surrounding areas lower, and that's going to cause more damage than good. So once you sand through your primer, stop. So if I'm block sanding a fender, continue blocking until all the guide coat's sanded off.

Let's say there's a little spot left there. Well, you can go ahead and block that area until you either sand the guide coat out, until it's removed, or you sand through the primer. That's two indications when it's time to stop and you're going to have to prime and block again. Now, let's talk about blocking techniques. You don't want sit there with real short strokes like that. It's going to make it look choppy. You're going to see that in the finished product. If possible, use longer strokes-- nice, smooth, longer strokes. And sand at 30 degree angles. And you can continue your cross sanding like we talked about in body filler. So sand it in one direction about 30 degrees, and then come sand in the other. So cross sanding at 30 degree angle that is what's going to produce that show quality level surface that we're looking for. And another thing when blocking-- we've already talked about this, about not tipping on the edge to sand your guide coat out. Keep the block surface flat on there. Don't take tip it on its edges or on the ends to get guide coat out or for any other reason. Keep that block straight and level and flat on the surface when you're sanding. OK. In this video series, we got the fender. We have it epoxy primed, primer surfacer. Now, we've blocked it out, with 220 if necessary, and then come back with 320 to remove the 220 grit scratches. And now, we're going to sand that area with 500 grit. And if you remember, the rest of the fender is already sanded, because we did that before we primed. We've got the area that's going to be painted sanded with 500, and then the area that's going to be blended and clear coated only with 800. So now, when we have that sanded with 500 grit, that fender should be ready to paint. Now, we can prep it and get it ready to put in the paint shop. Well, I hope you found this video useful. If you did, be sure and go down below, give us a thumbs up, give us a like. And subscribe to this channel if you're not already subscribed. If you have any questions or comments, go down below in the comments section and leave your comment there. Thanks for watching. And be a resource for someone else. Share these video with someone else that may want to learn the basics in auto body and paint. And remember, if something's worth doing, do your best and have a blast doing it. Hey, before you go anywhere, be sure and check out some of my other videos and playlists.