Repainting non-skid ......
I find that if painting with a 2 part Urethane, etc. such as Interlux "Perfection" etc., there is NO need to sand the non-skid nor apply a primer. Especially for 'sanded' nonskid, just scrub very well with coarse cleanser, remove the residual 'grit' with a water hose. Thin the paint to it 'maximum' (usually 5-10%); then, directly roll on the paint and work-out all the bubbles with a 'tipping' brush; the tipping brush is used to remove the excess paint that fills-in the 'valleys' of the non-skid. Obviously, for FLAT or non non-skid surfaces you need to apply primer, etc. but sanded non-skid has enough 'tooth' to hold the paint without primer, etc. Sanded non-skid and most 'tight basket-weave' patterns will hold such paint without primer .... just apply 'thin' or work out the excess with a brush so not to 'fill-in' whats already there. Dont do this with "BrightSides' or other relatively 'thick' paints ... just Interlux "Perfection" or similar 'thin' paints. You can also discuss/verify this 'technique' for non-skid with the application engineers / customer service at Interlux or from the manufacture of your specific chosen paint.