pvc exterior window trim sealant/adhesive

Mudball

We are going to install some pvc window trim around the exterior of our newly installed windows. The pvc trim will be cut to length and countersunk to attach with wood screws directly to the window frame buck (pressure treated) board. We planned on sanding the back side of the pvc trim for the silicone to better adhere to. Question is there any reason 100% silicone wouldnt work just fine on the back side of the pvc trim just before installing to help seal and secure or would you use something else ?

Tom Struble

silicone sticks best to non porous materials so it's great on the pvc not so good on raw wood,i'd use a polyurethane,not really necessary to sand the pvc

hopefully this caulking is not your primary water seal and you have a metal drip cap that will be going on top of the trim

Mudball

Thanks tomstruble sounds great. We thought about polyurethane adhesive but it doesnt hold up to expansion/contraction as well as silicone. Some instructions I found for polyurethane applications suggest to rough the surface to be adhered and I thought it would only help for the silicone. This is not the main seal but we rather just want to keep as much water and other things out from behind it and help hold it in place.

Tom Struble

good luck with your project

Mudball

Ive done a lot of reading since my last post. Ive decided (99.9%) sure to go with a hybrid (silicone/polyurethane) sealant/adhesive. We have to hold on to our wallet though because a tube is anywhere from 9.00 to 13.00
I dont think we will regret spending the extra money on a higher quality product that is known to give excellent results
http://www.boatus.com/boattech/casey/35.htm
Some more information I found on another site...
Finding a solution to some of the shortcomings of field-applied liquid sealants (principally those related to workmanship and dependence for performance on resistance to tensile stresses) was the cornerstone of hybrid sealant research that began in the early 1980’s. The product that resulted from this research combines ultra-low-modulus silicone and impregnated open-cell foam. The combination is a preformed sealant with movement and sealant performance exceeding that of either component used alone. Unanticipated additional benefits of the hybrid resulted from its thermal-insulating and non-invasive anchoring properties.
More than two decades of successful performance, evaluation and refinement have proved the hybrid sealant’s increasing versatility in addressing larger and also dynamic-movement joints. Evolution in materials and manufacturing technique show the promise of new hybrids for use in still broader and more demanding applications. Additionally, hybrids as alternatives to conventional field-applied liquid sealant use in low-movement or non-moving applications are likely to become available in the near future.
Keywords: liquid sealant, impregnated-foam sealant, hybrid sealant, tensile stresses

Tom Struble

your just trying to seal and glue pvc to wood,its not going to the moon or nothing like that
standard construction adhesive will do what you need it to do

Mudball

Thanks for reminding me that I was just being overly concerned. All that reading for nothing.