as for washing the muslin---those who believe in pre-washing everything will tell you (YES---SHOULD HAVE) Those i who don't bother pre-washing anything will tell you---no need-
i have done both- and to tell the truth- when using the muslin for a foundation i have never had any ill effects from the foundation not being pre-washed- so--- i really don't think it matters.
i have a friend who maked 3 or 4 string quilts (large queens/kings) every year- she brings them to me to quilt for her---and they are HEAVY! she generally sends an inexpensive poly batt from joannes (like fairfield-or mountain mist) that is fairly thin & lightweight-
for my foundation pieced quilts i tend to use a dream batt of some sort-i used Dream Green in the last one.
cotton batts are heavier than poly batts so they will add more weight to an already quite heavy quilt---if you want a really heavy- warm- durable winter quilt a string quilt with warm & natural & a flannel back would be amazing.
i have used just a layer of flannel instead of batting in a couple string quilts too---its' totally up to you- anything is ok, just remember that it will be heavy
as for your sashing...that too is a personal choice- sometimes the blocks are put together with no sashings- sometimes they are put together into (4-squares) with those surrounded with sashings; sometimes they are put together with a particular pattern/number of blocks making up a center, then bordered, then surrounded by more string blocks---there are lots of design layouts---after you get a dozen or so blocks made start laying them out- playing with them- turning them this way & that--sometimes with strips between- other times without---playing with the layout is where the true fun comes in- you could put 4 together- add setting triangles to make the new block on point---you can make them into stars...oh--now you've made me want to go start a new string quilt!
