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How to prep stretched cotton duck canvases for airbrushing

Discussion in 'Tips & Tricks!' started by CanvasAirbrushing, Oct 13, 2013.


  1. CanvasAirbrushing

    CanvasAirbrushing Young Tutorling

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    Here it is if you haven't seen it.

    Always prep canvases with a smile :), clean and dry hands and work on a flat clean surface.

    NOTE: You will need a good breathing mask for this as the binder will insure gesso will stick to the skin up your nose and sinus for weeks. I haven’t heard of anyone crying tears of gesso yet but anything’s possible. You should already have a good mask for airbrushing anyway which will be fine for this!!

    NOTE2: Most canvases today come “pre primed”. I highly recommend you still gesso them yourself. They use very little to prime and the quality of their primer is questionable. You will find the colours pop much more if you take the following steps.



    Step 1 Canvas assembly
    To assemble the canvas we must first complete the stretching process.

    Apply PVA (wood glue) to each of the wedges provided with the canvas.

    If you’re not confident enough to use glue, that’s ok. Follow the same procedures listed until you get more comfortable with assessing canvas tension.


    Image3299.jpg


    Insert each wedge as shown in the instructions that comes with the canvas. This requires a gentle tap with a hammer being carful not to allow the hammer to run along the back of the canvas as this will create push marks. Placing something flat and solid on the back of the canvas will help prevent this (like a clip board).

    Image3301.jpg


    Start at one corner then work your way around the canvas in cross/diagonal fashion rather than clock/anti-clock wise.

    Also, start with the bottom slits then when all the bottom ones are filled do the same with the top slits.

    Image3298.jpg


    Once all the wedges are in with glue and gently hammered you should be able to hold the canvas by the frame at the back and gently tap the front part of the canvas in the middle with your hand (Like one would with a drum skin) and feel/hear some slight tension.

    Image3296.jpg


    Now, with the PVA glue fill in any gaps that may appear at the corners where the wedges are. (This shouldn’t really happen; if it does you may have inserted the wedges with too much force.) Also, if the canvas has a single brace or cross brace, inspect them and if there is a gap fill them in with more glue.

    I use the cardboard label that comes with the canvas to apply, and smooth off the glue for a neat finish.

    Image3291.jpg Image3294.jpg


    NOTE: do not get any glue on the canvas itself. Not on the front. Not on the back. As some paints will not be able to paint over it and you might end up with white spots that cant be painted over!!

    NOTE2: Be careful not to make the tension too tight as this will lead to the frame warping. Once you coat the canvas in gesso it will shrink a little more. You’ll have to find through your own experience what the correct tension should be.



    Step 1.1 Do this if the canvas is warped (otherwise move to step 2)

    Once all wedges are glued in place and all hols are filled, before the glue dries, keep the canvas face down and put some weights on each corner. I use water bottles for this, but anything heavy and clean will do.

    Image3288.jpg



    Step 2 Gesso preparation

    Get your hands on your favourite brand of gesso. The more liquefied it is when you buy it the better in my experience. But it may differ depending on the brand. Trial and error is the only way to be sure here. The main thing here is to use a water based gesso, otherwise you’ll have to use other cutting liquids to think the mix out…. I don’t have any experience with that… maybe someone who does can make a little tute about it?

    Next, get a clean (sealable) bottle and, to save potential confusion in the future, label it “Pre Mixed Gesso – Ready to spray!!”

    In it pour the following ratios, 70% gesso 15% water 15% binder medium. These percentages may vary according to brand but this is a good mix to start if you’re not sure. Some thinker gesso's might require as much as 30% gesso, 30% water and 30% binder, if it’s too thick or too thin adjust ratios accordingly and make a note of it for next time.

    NOTE: always put the same percentage of binder medium as you do water. So if you change it to 60%gesso it would then be 20% water and 20% binder. Easy.



    Step 3 Spraying

    Before spraying gesso insure the glue has fully dried, this may take a day or two depending on the climate. After you have applied the gesso it is also a good Idea to leave the canvas flat and for a week or two. This will allow the canvas frame to settle in to it’s new tension and allow you to notice if there are any issues.

    Shake your “ready to spray” bottle very well.

    Then put it into a HVLP spray gun. Personally I have a cheap ($30) gravity feed HVLP with a 1.4mm setup which I use specifically for gesso base coats and final clear top coats.

    Image2193.jpg Image2209.jpg


    NOTE:
    Make sure the gun is well cleaned before going from gesso to clear tops coats…. Otherwise you’ll reach a new high score for cursing combinations.
    NOTE2: Most spray guns come with a little internal filter. Make sure this is in the gun!!

    Spray a dust coat. This is also known as a dry coat because it is a very light application. This is done to “bridge” between the canvas and the next coast you will apply. If you skip this dust coat (not recommended) you may find adhesion issues.

    Image3295.jpg


    Next put the canvas in front of a fan to dry (any clean fan will do). This first dry coat will take about 1-2 min to dry. How will you know if it’s dry?? When the gesso is still wet it will have a gloss shine to it when viewed at an angle with lights. Once it’s matted out again it’s ready for the next coat.

    Image3290111.JPG


    Then spray more coats, wetter and wetter (thinker) until you’re happy with the surface coverage. This takes a little time but as you may know applying too many think coats from the start may cause cracking and other undesirable effects so apply lightly and build it up as you go.

    Make sure each coat has dried completely before you apply the next one!

    NOTE: It has to be said here that you may or may not want to sand the final few coats. It’s personal preference really. However and here’s the exception to the rule, if you intend to finalise the image with a think clear coat (like a cat’s cornea) for a solid finish sanding the gesso is essential. Otherwise you may find little pits in the clear coat or the clear may take on the texture of the underlying canvas textile. These issues can be fixed but will take time, so sanding the gesso will save you the time and effort later.
    Personally I don’t always find it necessary to sand but sometimes i do. Again it’s personal preference.



    Step 3.1 Save time, effort and gesso by prepping multiple canvases

    You can do canvases quickly this way.

    Personally I get 2 to 4 canvases ready for their base coats so when one, two or three are drying under the fan I can take another outside and keep spraying then swap and carry on spraying.




    And there you have it.
    If I can think of anything else I’ll edit this and add it.
    Feel free to ask questions too.


    Happy Prepping!!!!!!!!!!!!

    Canvas storage
    To help prevent warping (if you intend to keep them for while before painting), store canvases vertical or lying down on a flat surface. Also, if possible, don’t expose them to high or low degrees of humidity.

    What to do if the gun splatters big splotches of gesso on your canvas
    Get a paper towel and gently pat the affected area. This does not require pressure. I fold the towel or scrunch it up a little and use the bit that freely sticks out. (see image below) pat pat pat pat pat pat pat. Do not rub. use the weight of the towel not your hand.

    Correct (using towel weight) Image33022.JPG


    Incorrect (using hand pressure)[​IMG]

    Last edited: Dec 5, 2013
    MeeshellMP, frowan and Vladimir like this.
  2. Melbee

    Melbee Detail Decepticon!

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    Thanks a lot, great tutorial.
    Cheers Mel
  3. Diegojavbau

    Diegojavbau Air-Valve Autobot!

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    Thanks for share !!!
  4. WhiteKnight

    WhiteKnight Code Dragon Slayer Admin

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    Thanks for the tutorial :)
  5. shadow2462

    shadow2462 Elite Member! Elite Member!

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    You always learn something new....I used to dabble in oils on canvas and always used as is from the store except for the extra gesso. I always assumed the canvases were prepped properly and ready to go. Good clear information, thanks!
  6. kchopp

    kchopp Young Tutorling

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    Thank you so much for the info! I tried to gesso some with a brush, what a mess! I like the idea of spraying it on.

    Kathy
  7. kchopp

    kchopp Young Tutorling

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    What is the binder medium?
  8. CanvasAirbrushing

    CanvasAirbrushing Young Tutorling

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  9. Talla

    Talla Needle-chuck Ninja

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    Really good tutorial. I am going to have a go on canvas and will gesso it and try and get a flat smooth finish (I have always been put off by the rough finish of pre-prep canvas ecpesially when masking tape and film is involved). Whats is a gessoed surface like for masking off?
  10. CanvasAirbrushing

    CanvasAirbrushing Young Tutorling

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    It’s magic to mask on!! But I can give a few tips about this.

    Firstly, if you want a smooth finish with gesso it’ll require heavy cots and sanding. The only disadvantage to a very smooth surface is tooth (paint adhesion). You may or may not get spider type runs when you first start spraying on it, however, even if this is the case I find once you put the first layer of paint down (like a dust coat) the rest of the passes go over the top quite well. Also depends on what paints you’re using.

    I still recommend a light clear coat before masking (inter clear coat). Also, just to be doubly sure, I lessen the tack of the tape by sticking it to my pants, then peal it off, stick it back on again over and over until I get just the right amount of stickiness. Again this will all depend on the paints you use, the clear you use etc. trial and error is the best way to figure out what works for you here.

    Lastly, unless you have an extremely think gesso coat i.e. to the point where it’s like an automotive panel, I’d advise against cutting tape on the canvas.

    Rather than cutting on the canvas I put the tape over the areas needing masking, use a good pencil to mark out where it needs cutting, then take it off, put it on a cutting board and cut it on there. Then I use that to mask the canvas. It takes a bit to get the hang of it but it give great results.

    Hope this helps :)

    If there’s anything else feel free to ask :)
    Chris g likes this.
  11. Talla

    Talla Needle-chuck Ninja

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    I'm use to Dibond and other extremely hard and unflexible surfaces (like helmets, body panels etc) so I'm used to spidering! Working with something even remotely flexible is going to be a challenge for me. What I may do after I have gessoed the canvas and got it smooth is give it a light misty coat of 2k clear (I have another project that will need clearing soon!). A dusting of 2k should give it a nice key!

    I intend to cut out the masks needed from paper and use some repositionable spray glue to hold them in place.

    Cant wait!!!
  12. Chris g

    Chris g Young Tutorling

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    Very useful guide.

    Thanks,
  13. Vladimir

    Vladimir Needle-chuck Ninja

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    Thanx for the tips!:)
    I've tried to do it myself almost the same way. Tried gossoed board last year. It works great for scratching and erasing. Just any blades and erasers work well without making any damages. This year I've gessoed boards and canvases.

    But there are some things I've done in other way.

    One thing is I'm not agree with applying glue. Wedges are there to have a possibility to adjust tension of the canvas when conditions like temperature and humidity are changed, also the wood that frame is made with can have some humidity in it when being produced so after total dehumidifying it can change its size. For example even work done in humid summer time is placed in a house heated in the winter time, the tension of the canvas will be different an anyone can make proper tension. Without the wedges it would be impossible.

    5.JPG

    Another thing I'm not agree is applying the first dust coat of gesso. I know it's done while clearcoating and done because of the reason for the clear not to bleed.
    The canvas is gossoed in horizontal position, so any bleeds can not be possible. I was applying wet coats with drying time between coats as the topicstarter says.
    I sand the canvases from a shop and after clean them with water with further complete drying before applying gesso so issues with loosing adhesive properties can't arise.

    I was applying gesso with inexpensive HP system spray gun with 2,5mm nozzle. Nozzle of less diameter requires more reduction of gesso thus more layers are required to get desired thickness of gesso layer.

    6.JPG 7.JPG


    Besides the canvases, I've treated MDF in the same manner and can say it's at least five time faster to treat than the canvas as sanding of the canvas MUST be done very carefully. One can apply the biggest pressure on the sanding block thus getting desired quality very fast.
    I'd advise to make gessoed MDF as they're cheap and great result in the end. It's even more convenient to paint on MDF as on canvas, as again it can bare any pressure on it, while the canvas can not and we should be careful while working with it. Concerning scratching and erasing, no matter if it is canvas of MDF, as gesso is just the same.
    Interesting thing that the colour of my gesso had warmer tone than one applyed by the producer of the canvases, but it's not an issue.
    Here are my results.

    1.JPG 2.JPG 3.JPG 4.JPG
  14. AndreZA

    AndreZA Elite Member! Elite Member! Artist of the Month!

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    Those MDF panels look perfect.
  15. Vladimir

    Vladimir Needle-chuck Ninja

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    Thanx Andre!:) I'd agree that painting surface looks and feels perfect and it actually is, but I disagree about the edges;) I was a bit lazy to make them perfect as no perfection is required in this case. These panels are for my training but if they were for a client, they would be perfect certainly. Some more time of edge sanding and you got it!
    I even think, maybe it would be good to glue let's say 6mm MDF panel to the wooden frame, apply gesso and paint on it. I like the hardness of MDF it's just great for applying pressure when erasing.
    One thing I forgotten to say. Prior to applying gesso I've applied that milky looking acrylic based liquid, that is used before painting walls etc. I don't know the translation:) I think everyone knows what I'm talking about. I've used one from Ceresit.

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